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AN-807 APPLICATION NOTE
Multicarrier WCDMA Feasibility
Brad Brannon Bill Schofield
ABSTRACT goal this application note determine feasibility implementing multicarrier transceiver what major subsystem performances must GENERALIZED BLOCK DIAGRAM block diagram Figure general block diagram used this document. While there many variations this design, focus this architecture. This architecture represents flexible radio platform that easily used implement wide variety standards including WCDMA, CDMA2000, TD-SCDMA.
Some possible variations this architecture include high sampling well direct conversion receive. Although latter feasible multicarrier today, acknowledged cost, high performance solution near future. transmit path, direct modulation feasible most applications long some amount balance provided. This represents lowest cost transmit path. applications requiring high performance without balance network, superheterodyne upconversion another excellent option.
MAIN RECEIVE SIGNAL PATH
FREQUENCY AD6654 AD9246 AD9445 AD8369 ADF4106/ ADF4360 SYNTHESIZER MIXER AD6654 AD9246 AD9445 DANUBE TigerSHARC® 14-BIT 4/6DDC 14-BIT 4/6DDC
ANTENNA
MIXER
Tx/Rx
DIVERSITY DRIVE SIGNAL PATH
AD9779 POWER DETECT CONTROL ADF4106/ ADF4360 SYNTHESIZER ATTEN AD9430 AD6636 BASEBAND PREDISTORTION W/PPR AD6633
MODULATOR MODEM
TRANSMIT SIGNAL PATH
PREAMP
ADL5330
MCPA
MONITOR PATH DIGITAL PREDISTORTION
Figure Wideband Multicarrier Common Platform CDMA2000/WCDMA/TD-SCDMA
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addition variations electrical schematic discussed, there many assembly options that have wide range implications. These options include system level partitioning form split boards well split radio baseband processing. Further options include chip partitioning. example availability MxFE functions that incorporate both functions single package. This option facilitate higher integration lower cost, offers excellent alternative capacity system options. Other possibilities include combining provide higher integration lower cost while avoiding import/export restrictions. These other options good sources discussion. WCDMA Specifications this report taken from requirements Wide Area defined 3GPP 25.104 V6.2.0, specifically, section specifications from this standard reference sensitivities, band deployment, blocking requirements. assumed that Node terminal required meet sensitivity blocking requirements different platforms same time. Meeting sensitivity wide area while also matching blocking requirements local area desirable, goal discussed here. should noted that requirements Node terminals medium local area have similar dynamic range requirements wide area version with exception that input levels shifted These accommodated within same design shifting level plans upward these systems also tolerate increased noise. RECEIVE DISCUSSION Receiver operating conditions: From standard, required minimum sensitivity -121 within 3.84 channel bandwidth. Hertz basis, this signal density -186.8 dBm/Hz. Where noted, WCDMA test conditions specify -115 dBm/3.84 (-180.8 dBm/Hz) also applies. second conditions determine inband blockers. From standard, there important subconditions blocking. first subcondition intermodulation between signals (-47 operating bands with GMSK blocker). tone other modulated WCDMA carrier (see Figure second subcondition adjacent first second alternate blockers. these, largest dBm/3.84 MHz. signal assumed modulated with single code therefore peak- to-rms value about From input conditions above, largest input power condition blocker dBm/3.84 MHz, giving peak power about dBm. assumed that out-of-band signals attenuated enter into dynamic range considerations ADC. Since signals adjacent bands same inband, some attenuation anticipated band filter. However, because they same level below after filtering inband blockers, little additional dynamic range should required, this depends characteristics band filter selected. requirement this wideband filtering that signal aliasing prevented. Therefore, analog filtering must provide sufficient rejection attenuate blockers into noise floor they alias back into useable spectrum ADC. This true either sampling direct conversion. Assumptions: Given this information, front- design information determined. largest peak signal antenna about converter full scale rms/7 peak into typical many ADCs), conversion gain used. gain causes driven with peak input about dBm, leaving that serve margin power from other nearby strong signals well component margin. Given current receiver trends LNAs, passive mixers filter elements, typical downconverter blocks possible with noise figures below (not including ADC). These numbers used following calculations. losses from cabling other hardware considered along with variations component tolerance, they must included well. final assumption that sample rate ADC. With base data rate 3.84 MHz, clock rates viable. Since converter data rates steadily increasing running, higher sample rate slight noise advantages. higher rates, such 92.16 MHz, should used. lower rates used actual implementation, requirement increases 76.8 MSPS 61.44 MSPS. addition noise advantage, higher sample rate allows more transition band filters, already discussed. complex baseband sampling used, dual 12-bit 14-bit converter family, such AD9228 AD9248, ideal. requirements: Given conversion gain above, calculated. antenna, noise spectral density assumed -174 dBm/Hz. Given conversion gain noise figure previously stated, noise spectral density (NSD) input -131 dBm/Hz (-174 This assumes that noise outside Nyquist band filtered using antialiasing filters prevent front-end thermal noise from aliasing when sampled ADC. noise floor below that front-end noise, contributes about overall receiver. Therefore, maximum noise floor -141 dBm/Hz expected. Higher noise floors used. noise begins contribute floor receiver, some nonlinearities described "DNL Some Effects Converter Performance"
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article found Wireless Design Development Online June 2001 online issue adversely impact receiver performance, especially when comes signal power estimation. Therefore, noise floor should small reasonable without over designing. sampling, total noise Nyquist band determined simple integration. Over 46.08 (the Nyquist band 92.16 MHz), total noise found -64.4 dBm. full scale dBm, this required minimum full-scale 68.4 When larger blockers considered, case band III, higher noise performance required from seen following sections. Although direct downconversion quite ready this market space, preferred architecture cost simplicity reasons. likely that this approach will available within scope multicarrier development therefore considered this application note. limitations currently quadrature demodulator data converters. multicarrier applications critical aspects balancing second-order intermodulation through demodulators data converters. Beyond this, data converters must still meet same general performance levels with sampling variations with advantage frequency input range. baseband sampling, frequency planning options exist direct conversion. first option balance active either side this number, this even number, exists this option selected, image rejection adjacent sideband must sufficient meet blocking requirements signal presence -121 (-115) discussed previously. reasonable assume that falls and, therefore, concern must exist noise form feedthrough, phase noise, offset. This concern addition second-order intermodulation distortion generated within demodulator. These primary impediments implementation multicarrier direct conversion receiver. Although unique multicarrier signal chains, restrictions great single carrier signal paths that easier implement. second option place signals side images fall other side unabated. This option wasteful spectrum, does allow less focus image rejection issues more specifications such intermodulation distortion.
FREQUENCY
ANTENNA GAIN 42dB DOWNCONVERTER BLOCK IN/IF OUT)
AD9444, AD9445, AD9446, AD9244, AD9245, AD6644 AD6645 AD6636 AD6654 14-BIT 4/6DDC DANUBE TigerSHARC
CABLES
ADF4106/ ADF4360 SYNTHESIZER
Figure
MAIN RECEIVE SIGNAL PATH
FREQUENCY
ANTENNA 14-BIT 14-BIT ADF4106/ ADF4360 SYNTHESIZER
DANUBE TigerSHARC
AD9248
4/6DDC
MODEM
AD6636
Figure
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possible address many quadrature balance issues digital domain; this discussed more detail later section. facilitate this, means addressing gain mismatch, offset, phase correction, complex baseband tuning required. order combat some these issues, AD6636 includes various features used compensate them. AD6636 equally suitable signal processing multicarrier signals multicarrier sampling. includes gain adjustment, automatic offset correction, phase correction, ability perform complex baseband tuning. direct conversion, there several other considerations that must made. First, lower sample rate likely. Since converters required, likely that lower sample rate used keep digital processing power possible. sample rate 61.44 MSPS likely, providing full 61.44 complex bandwidth. assumed that ADCs keep same input range, increase allowable since splitter also divides power between ADCs addition losses associated with typical frequency translation stage. Without this additional gain, (approximately) range will lost. digital processing, these signals again summed produce overall signal higher along with higher noise floor from noncorrelated noise floor both ADCs. same time, however, effective input range also higher noise floor effective contributions. This results first-order wash sensitivity signal levels noise each increase same amount. signal path includes extra gain, requirements increase proportionate amount. First order, each single must also meet same requirements sampling. Although sample rate lower than have otherwise been used sampling, noise bandwidth equal full sample rate. result that noise performance similar that sampling solution operating 122.88 MSPS with added advantages. First, because analog signals baseband, clock jitter longer problem. Second, because analog signals baseband, they subjected input slew rate limitations converter, which biggest causes poor harmonic distortion sampling systems. primary focus thus been provide fixed gain solution that meets dynamic range require ments. This requires delicate balance between placing noise sufficiently below receiver analog thermal noise without overdriving ADC. discussed earlier, converter with minimum 68.4 makes this possible. However, there times when desirable increase difference between noise thermal noise increase signal range end. This accomplished providing circuit. While this useful single carrier systems reduce dynamic range requirements ADC, desirable multicarrier application, albeit necessary many cases. such system, desirable trade gain control range converter resolution maintain similar dynamic ranges. Since individual WCDMA carrier likely reside about most time, significant additional gain could applied absence other blocking signals. However, this only desirable provided trade-off between gain intermodulation favorable, which often case nonblocking conditions. Signals this level significantly above noise floor and, therefore, this additional gain only provides marginal improvements. This indicates that fixed lower gain only desirable from performance point view, also desirable from logistical point view. Regardless implemented gain control, very important that power levels known. WCDMA's strict power measurement requirements require means estimating power levels. While this easily accomplished DSP, often more efficient implement digital hardware. Performing this hardware remove some processing burden from well minimize latency calculation, which also reduces chance front- overdrive analog required. Based requirements, good 12-bit could used preserve dynamic range between both minimum sensitivity largest inband blocker. However, this assumes deployment WCDMA band. When deployed MHz, MHz, 1800 MHz, 1900 band, conversion gain limited presence narrow-band blockers. These blockers higher than WCDMA band (20+ higher band) and, therefore, conversion gain must reduced, likely reducing sensitivity. This achieved either reducing overall fixed conversion gain maintaining higher gain, also adding that reduces gain during large signal conditions. this manner, reference sensitivity maintained sacrificed systematically total receiver input signal level increases. proposed solution convert conversion gain VGA. This then reduced under appropriate signal conditions prevent clipping limiting receive signal chain. Digital downconverter products such AD6636, configured control addition readjusting digital data stream such that absolute digital output data maintains correct power information.
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There ways implementing VGA. example, adjust signals bottom range, reducing gain soon signals large enough overcome noise limitations. Likewise, adjust signals range, reducing gain just prior clipping limiting within signal chain. Each advantages disadvantages with desirable goal being implement receiver without gain control. implemented, should include both voltage time hysteresis prevent remodulation signals. Table shows expected sensitivity gain rolled off. should remembered that gain reduced, contributes more total receiver therefore overall receiver impairments. example, high gain state, noise density front presented -131 dBm/Hz. gain state, noise dropped -137 dBm. noise density -145 dBm, implication increase percentage total noise that comes from ADC. Given this, long sufficient gain run, 14-bit converter more than adequate multicarrier implementation WCDMA. conversion gain begins low, noise dominates receiver performance suffers. required analog gain control implemented taking advantage power measurement within AD6636 through other calculations with loop completed through implementation. addition, AD6636 incorporates preclip function that allows peak signals that less than full scale detected sets gain digital gain amplifier diode attenuator before converter full scale reached, thereby preventing converter clipping. also incorporates digital compensation analog changes that final digital data relinearized with respect true analog input receiver. Similarly, latency analog gain path, including pipeline delay ADC, accounted this process. SFDR requirements: Spurious performance little less obvious from specifications. However, there several guidelines standard that provide SFDR requirements. These primarily found single two-tone blocking specifications. this test, narrow-band signal (CW) allowed intermodulate with Table Gain 125.88 122.64 Effective 6.25 9.48 Effective -121 dBm* 4.88 1.64 Clip Point either WCDMA signal GMSK signal depending band operation. WCDMA conditions, both signals posted whereas GMSK (bands III) dBm. Looking first band test with GMSK, intermodulation product falls outside channel interest, from channel center where channel bandwidth 1.92 MHz. Digital channel filtering provides adequate filtering intermodulation products before correlator and, therefore, direct impact anticipated with signal interest. assumed that fifth order products significantly better than anticipated third order products. Even though they fall inband, they should issue. they they must meet spurious requirements determined below. intermodulation between tone WCDMA carrier, resulting intermodulation product falls directly channel interest. effect this increase noise channel would AWGN. specification allows reduced sensitivity this test. Since receiver performance limited thermal noise, setting noise intermodulation spurious equal noise floor increases noise reduces sensitivity same amount. Since allowed, remaining allocated elsewhere (jitter, additional other). Assuming that conversion gain been reduced from (the point above two-tone levels) that providing SNR, total receiver Therefore, noise density (reflected back antenna) including -171 dBm/Hz. this integrated over channel (3.84 MHz), total noise -105 dBm. This power intermodulation term that isallowed intermodulation between WCDMA signals. This provides detailed information about spurious levels that have met. intermodulation product WCDMAtype product, energy already spread simply appears AWGN (and spread over convolution between different codes-assuming that aliasing does occur somewhere receiver chain). only exception this course, intermodulating signal orthogonal signal interest, this assumed case. Similarly, product tone (not specified standard, worst case), spreads sequence correlation process, again appearing AWGN. Since
This table assumes that during reduction gain that increased half gain reduction. *This number -115 blocking conditions. numbers this table represent this increase signal.
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energy tone within single frequency, this more stringent test. Therefore, input-referred spurious (the spurious) must (-105 plus dB), this sets absolute worst case spurious that tolerated cochannel interferer whether generated single tone, multitone, intermodulation. Since full scale (rms) worst case equivalent spur that tolerated dBm, this equivalent SFDR about dBFS minimum. While conditions that generate worst case vary, this represents worst case cumulative SFDR that tolerated.
-48dBm EACH
products must lower than -105 antenna port previously determined. With inputs dBm, required referenced antenna port dBm. Reflected input, this assuming conversion gain Realistically, there other more stringent tests. case wideband (multicarrier) receiver architecture proposed here, likely that signals large processed analog section receiver, only band edge. this case, numbers would need recomputed would need take into account reduction gain increase system noise. From perspective, equivalent performance excess factor; therefore, solely contributed from downconverter block. case where higher conversion gain used, requirements, well noise requirements, scale appropriately. Likewise, design specific margins increase required performance above minimums previously shown. Component selection: Based previous discussion, downconversion block must have conversion gain about noise figure output least dBm. Current receiver technology capable this level performance. Furthermore, room exists further enhance performance beyond minimum performance shown here with little effort. Synthesizer: number suitable synthesizers available this design. shown Figure these include ADF4106 ultralow noise PLLs ADF4360-xfamily integrated synthesizers VCOs. ADF4360 family synthesizers well suited WCDMA applications proposed here. ADC: discussed previous sections, converter needs about dBFS with dBFS input signal. Analog Devices number converters that meet this requirement well parts various stages development. sampling, products such AD9446, AD9445, AD9444, AD9246 some latest announced devices. Existing devices include AD9244, AD9245, AD9248, AD6645. baseband sampling, AD9238 AD9248 dual, converters available. These devices compatible allow assembly options platforms that common between single multicarrier applications where export/import restrictions exist. addition these pin-compatible devices, quad ADCs available, including AD9228 AD9229. These quad, 12-bit converters ideal diversity baseband sampling quad, sampling applications such phased array antennas.
-180.8dBm/Hz -115dBm 2f1-f2 -174dBm/Hz
Figure SFDR split: assumed that downconverter block equally share harmonic distortions correlated, each source should worse than dBFS (relative input) and, more appropriately, dBFS which allows only headroom case where contributions SFDR peak simultaneously. case where gain been reduced account larger blockers (band III), spurious requirements higher. Although details shown here, cumulative SFDR dBFS allowing headroom signal peaking, dBFS minimum. requirements: more stringent intermodulation tests band under GMSK test. this case, essentially narrow-band tones placed into receiver dBm. This would condition anticipated mixed band. band III, requirements easy predict. band where intermodulation tones tone another WCDMA signal, direct compute, less critical than specified band conditions. With narrow-band tones antenna port gain reduced, required intermodulation
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DDC: AD6636 offers 4-channel 6-channel option. Each these devices four inputs and, therefore, easily configured either diversity, diversity sectored, phased array. ADCs drive these devices form diversity two-(4 channel) three-(6 -channel) carrier receiver. interesting configuration shown Figure This application shows three-sector, four-carrier antenna downconverted digitized. digitized signal then passed different DDCs. Each then used select filter total four sector. addition four diversity sector, this configuration provides redundancy event failure. Since each antenna routed DDCs, failure does take entire channel. Likewise, diversity antenna routed different DDCs providing redundancy there well. addition, diversity signal path handled completely different signal path from main, providing much four-way redundancy signal processing. Therefore, event failure main path, diversity path totally redundant effected main path failure. Using this architecture, each sector 100% covered redundancy through channelization) receive path regardless loss. system reliant single component high degree ability reallocate channel capacity other DDCs, event failure even increased traffic volume. addition channelization capabilities, other functions provided DDCs. first power estimation. mean square power, peak power, number times signal crosses specified amplitude measured each input. Additionally, when used complex mode these measurements done complex signals well. This information used conjunction with attenuation front prevent overloading case strong signals detected. Additionally, each channel power measurement function with programmable integration flexibility. This function used receiver gain, determine loop loss, generate digital output function keep digital output bits narrow dynamic range with precision rake receivers. Other features include offset correction, gain adjustment, phase adjustment, complex digital tuning. these features required when implementing sampling multicarrier applications. Integrated functions: Currently, 14-bit ADCs under export restriction countries. AD6654 provides integration function combining AD6645 AD6636 cores single device. This device classified receiver function subject export control. addition this, combined functions available that integrate both transmit receive single package. Devices such AD9863 include dual, high speed ADCs DACs suitable
MAIN
DIVERSITY
MAIN
MAIN
DIVERSITY
DIVERSITY
Figure
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single carrier applications. This device excellent option capacity systems. Other devices, which offer variety precisions speeds many options available this family (AD986x). Validation: seen following simulator output, with minimum sensitivity signal -121 input, this receiver supports over with gain more than enough meet requirements wide area This sensitivity maintained total inband power level about antenna. Beyond this, input must attenuated prevent overdriving receiver chain. easiest meet specification insert attenuator reduce input signal level input receiver. While would ideal, additional attenuation used long sensitivity meets -115 specification. This case under alternate channel blocking test dBm. Table below shows resulting when conversion gain changed allowing modest increases seen, while changes slightly, should remembered that desired signal level increases thereby increasing above that shown table. Validation SFDR sensitivity little more difficult. However, clearly linear system, testing more stringent than testing with WCDMA signal. Therefore, signal input driven full scale (-24 antenna with conversion gain), worst case spurious should better than lower. WCDMA signals equivalent peak power produce much lower spurious results much lower spectral density level stimulus signal. Typical minimums 14-bit converters specified better depending frequency. minimum used above required), this SFDR power level dBm. After rake receiver, this produces spectral density -144.8 dBm/Hz antenna -172.8 dBm/Hz, about lower than thermal after accounting front thermal noise. Therefore, total noise channel interest increased less than reducing overall sensitivity during this condition better than -118 dBm, leaving margin meet specification -115 dBm. Since signal used approximate effects peak signal WCDMA waveform, expected that actual power realistic waveform much lower, thus achieving significant improvements SFDR performance receive channel over that expected tone.
Figure Table Gain 125.88 122.64 Effective 6.25 9.48 Effective -121 dBm* 4.88 1.64 Clip Point
This table assumes that during reduction gain that increased half gain reduction. *This number -115 blocking conditions. numbers this table represent this increase signal.
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Noise margin four carriers: Ideally, basestation should seek maintain relatively input level each frequency allocation. Typically, this would maintained somewhere between depending controller programmed. Under these conditions, each carrier should have around providing excellent without need engage gain reduction from loop. However, compliant with specification, adjacent first alternate channels must considered case where they outside control base station where they become large some unforeseen reason. this condition, desired sensitivity -115 dBm, indicating that gain reduced loop. impairing signals consist alternate signal (-52 dBm) first alternate (-40 dBm). Since these signals have only code modulation, peak about resulting peak power dBm, which upper limit highest gain setting. Given signal chain variations power from other inband signals, assumed that gain reduced setting, increasing 6.25 this condition, desired signal should processed with available channel about 10.88 resulting BER. discussed earlier, addition spurious energy from large first alternate signal should near thermal noise level have little impact signals this increased level. TRANSMIT DISCUSSION There several options architecture transmit signal path. factors that impact transmit signal elements discussed first, followed discussion different architectures. Figure shows direct conversion architecture initial point reference only. Section 3GPP 25.104 describes transmit signal requirements. Throughout architectures discussed, there assumption that there channel filter output power amplifier that sharp enough desensitize receive path ensure spurious emissions, when colocated, filtered sufficiently. Frequency error: specification mandates that same source used frequency data clock generation; this implies that with 3.84 Mbps data rate, frequency sources should have 3.84 integer divisor. consequence, converter sample rates 30.72 MSPS, 61.44 MSPS, 76.8 MSPS, 122.88 MSPS, 245.76 MSPS, which represent multiplication factors common WCDMA applications.
AD8349 MODULATOR PREAMP ANTENNA ADL5330 AD8362 POWER DETECT CONTROL SYNTHESIZER TUNING CONTROL LOOPS
AD9779 AD9786 AD6633 DUC, PPR, PREDISTORTION
CLUSTER
NETWORK INTERFACE
MCPA
AD9786
CLUSTER MODEM
DAC,
AD9510
AD9510 CLOCK DISTRIBUTION
SYSTEM CLOCK
AD9430/AD9235 AD6636
DDC, DUC, FPGA
PREDISTORTION MEASUREMENT PATH
TRANSMIT SIGNAL PATH
Figure
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Power control: maximum output power defined mean power level carrier measured antenna. wide area base station this should greater than with integration bandwidth 3.84 MHz. specification allows power control applied each carrier antenna output, code channel basis user quality service control. carrier power control needs have minimum dynamic range. system using single carrier DAC, dynamic power control best placed VGA, order optimize dynamic range requirements DAC. multicarrier system which there common power control setting carriers, this should adjusted VGA. possible that carrier multicarrier system below single carrier (see Figure spectral performance single carrier multiple carriers each maximum dynamic power achieved, this scenario would stress DAC's dynamic range requirements further. dynamic range incorporated into DAC's requirements, however, this would increase dynamic range requirements DAC. (This possibility with high dynamic range DACs such AD9786 AD9726, following analysis assumed that analog will present.) level code channel only small effect composite carrier's peak-to-average ratio (PAR), hence, marginally negligible effect dynamic range requirements analog downlink blocks. Peak-to-average ratio (crest factor): power amplifier that drives antenna opposing performance metrics when considering efficiency linearity. amplifier most efficient when driven into saturation, also worst linearity saturation, conversely amplifier driven linearity highly inefficient. Typically, compromise found between linearity efficiency. This results amplifiers that operated mode where average operating point such that signal crests just less than maximum saturated output power that amplifier deliver. Determining maintaining power amplifier linearity largest challenges WCDMA base station. Before channel combination, data control streams (not synchronization channels) mapped QPSK symbols spread with OVSF spreading code assigned that data stream channel, this provides orthogonality/separation between data streams. complex spread symbols then multiplied base station specific scrambling code, ensuring signal separation between base stations. primary secondary synchronization channels SCH, SCH) provide radio frame time slot synchronization combined with spread data control streams. This composite waveform usually pulse shaped nature form band-limited waveform. This waveform, depending upon number users type information being transferred cause very high waveforms component signals phase. Combining carrier with other carriers further increases probability phase alignment, increases PAR. increased lowers efficiency power amplifier certain level linearity maintained. heavily dependent upon traffic channel, representative test mode been established conformance tests, test model This test model have data streams, dedicated physical channels (DPCH), kSPS data rate with spreading factor 128, randomly distributed across code space random code domain power levels random timing offsets.
-18dB
-18dB
Figure When closed loop power control implemented base station keeps lowering code channel's power until user equipment (UE) detects increase error rate. closes loop with base station such maintains specified quality service. Inner loop power control base station's part closed loop code channel power control specification mandates step size with range extreme conditions normal conditions. This power control performed code channel level, before composite carrier formed. code channels required synchronization CPICH, SCH, S-SCH, PCCPCH) used, power
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Figure Figure shows DPCH distribution within code domain. help determine this single carrier, user look complementary cumulative distribution function (CCDF), which shows probability peak happening within this frame. common metric acceptability probability level; peaks with lower probability than contribute very little actual intermodulation performance amplifier usually handled either allowing amplifier into saturation clipping within digital processing. single carrier case, using Test Model peak average ratio approximately 10.5 results probability. previously mentioned, multiple carriers combined with little attention resulting PAR, resulting could very high. mitigate this, carriers encoded with different spreading codes time offsets, which helps reduce phase alignment carriers. Figure shows this effect four carriers, each with Test Model channelization, yielding reduction with appropriate choice scrambling code time offset. should noted that using different spreading codes time offset results four carrier PAR, which only higher than single carrier PAR. Peak-to-average power reduction: more reduced, higher average power made same efficiency. Peak-to-average power reduction techniques (PAPR) used that reduce peaking without introducing out-of-band distortion. typical method PAPR clipping followed filtering. Clipping negative impact significantly reducing performance creating spectral signals that must filtered. AD6633 provides PAPR without clipping baseband signals. uses technique that introduces inband distortion selectively reduce peaks without causing distortion adjacent bands. This allows directly traded with compression without adjacent channel distortion. Additionally, multichannel applications, amount allocated differently each carrier, facilitating quality service differentiation between carriers. example, voice carriers allocated higher favor high speed data carriers that need lower higher data rates. This cannot accomplished clip filter techniques. Figure demonstrates performance AD6633 with four equal power carriers; uncompressed exhibits peaks approximately greater than compressed displayed time slot. CCDF shows that probability, approximately improvement realized. Generally, more carriers used, greater reduction given probability.
SAME SPREADING CODE TIME OFFSET
DIFFERENT SPREADING CODE TIME OFFSET
Figure
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10-0 10-1
POWER RELATION LIMIT (dB)
POWER RELATION LIMIT (dB)
10-2 COMPRESSED UNCOMPRESSED
UNCOMPRESSED
10-3
10-4
COMPRESSED
10-5
TIME (WCDMA TIME SLOTS)
10-6
TIME (WCDMA TIME SLOTS)
Figure Power amplifier linearization: Another method increasing efficiency power amplifier allow amplifier move closer toward saturation, hence increasing efficiency, also compensating resulting distortion that results. There main approaches linearization. Analog feedforward uses linear feedforward compensation amplifiers around main power amplifier counter distortion problems provide sufficient linearity that spectral regrowth does pollute adjacent channels. This approach typically results efficiencies less than complicated, tractable, analog problem where feedforward amplifiers' linearity also need considered. second approach linearization comes form digital predistortion. This method uses simple concept that digital numerical representation very linear highly predictable, with effect from environmental operating conditions. Thereby, transfer function determined, summation with equal opposite transfer function (see Figure results highly linear system response which introduces noise distortion. Furthermore, manufacture analog feedforward amplifiers longer needed cheaper digital process used. impact converters system implementing digital predistortion should considered. forward path considered first, Figure signal passed through power amplifier disturbed ways; firstly, additive noise introduced signal, secondly, nonlinear transfer function leads odd- order intermodulation products. WCDMA signal these effects lead spectral regrowth adjacent alternate channels. Third- order intermodulation products cause spreading distortion over three times bandwidth carrier; fifth-order intermodulation gives fives times bandwidth, seventh-order intermodulation gives seven times bandwidth. single carrier, having wanted channel bandwidth 3.84 MHz, third-order distortion occupies band between 1.92 5.76 either side from center wanted channel (see Figure 14). This
PREDISTORTION RESPONSE
AMPLIFIER RESPONSE
SYSTEM RESPONSE
DIGITAL
Figure
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MCPA ANTENNA
PREDISTORTION FORWARD PATH DUC, PREDISTORTION
PREDISTORTION OBSERVATION PATH
Figure appears adjacent channel together with additive broadband noise. first alternate channel unaffected third-order intermodulation still affected broadband noise. Similar consideration fifth- seventh-order intermodulation products shows additional channel affected with increasing order intermodulation. With four carriers, distorted signal bandwidth 18.84 MHz. Consequently, third-order intermodulation affects band 9.42 28.26 from center signal bandwidth; third-order intermodulation affects significantly more alternate channels. Additionally, fixed performance, more carriers added there more energy alternate channel, which reduces ACLR factor 10log10 (#carriers) relative single carrier case. Recall that intent digital predistortion create antidistortion, system employing digital predistortion needs 10log10 (#carriers) more performance relative single carrier case maintain same ACLR single carrier case. Additionally, control over bandwidth signal bandwidth required completely null third-, fifth-, seventh-order intermodulation products. case four WCDMA carriers (signal bandwidth 18.84 MHz), control over bandwidth 131.88 required seventh-order products interest, with additional better performance compared single carrier case. observation path, sample output signal mixed down converted back digital baseband data where compared transmitted data. order remove fast moving power profiles downconverted signal averaged over many hundreds samples. algorithms used create corrected transfer function based either polynomial multiplication look-up table. function used implement algorithm which downconverted averaged result compared transmitted signal determine much distortion added forward path upconversion process. Once determined, inverse distortion computed then used modify future look-up table polynomial coefficients. coefficient update take seconds complete captures only distortion power profiles carriers also temperature aging effects.
FIRST WANTED ADJACENT ALTERNATE CHANNEL CHANNEL CHANNEL
IMD3
IMD3 BROADBAND NOISE 10.0 12.5 BROADBAND NOISE 10.0 12.5 15.0 17.5 20.0
Figure
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FIRST NYQUIST ZONE IMAGE SECOND NYQUIST ZONE IMAGE ALIASED
51.84
103.68
155.52
207.36
30.72
61.44
92.16
122.88
153.6
184.32
There number approaches capture distortion. approach mixes transmitted signal down close uses high speed sample bandwidth that equal order distortion times bandwidth spectrum. Nyquist band required three four carriers respectively. Common sample rates between used this function (see Figure 15a). alternate approach mixes down intermediate frequency (IF) undersamples transmitted signal. With this approach, samples signal third-order distortion components without aliasing; fifth- higher order distortion terms allowed alias over third-order terms compensated coefficient control (see Figure 15b). four carriers 153.6 MHz, 122.88 MSPS converter needed. limitation that must introduce less distortion than distortion being measured antenna have noise spectral density less than antenna wideband emission requirements. noise averaged over multiple samples, relaxing noise requirements oversample ratio typically ENOB ENOB. following discussion reveals required noise level offset level tenuated typically reduce maximum output that full scale; directional coupler typically about attenuation. Therefore, spectral density input -140 dBm/Hz; across Nyquist band, this corresponds about AD9430 provides SFDR 60s, meeting these requirements. ACLR: importance reducing composite signal been highlighted above. Current literature suggests that ACLR improvement realized using linearization. equation below links ACLR, IIP3; valid first adjacent channel single carrier only. previously mentioned, multiple carrier ACLR rationalized back single carrier requirements adding 10log10 (#carriers). ACLR -20.75 2(PIN IIP3) DAC, intercept point related output Equation reduces ACLR -20.75 IMD(dBc)
Figure What Equation does capture effect noise floor ACLR. Figure sweep channel power single WCDMA carrier with Test Model AD8349. With channel powers down about dBm, ACLR equation holds true with AD8349 exhibiting approximate IP3. channel power drops, ACLR begins become dominated noise, ACLR degrades.
1960 ACLR ACLR (dB) 2140 NOISE 1960 NOISE 2140 ACLR -149 -150 -151 -152 -153 -154 -155 -156 -157 -147 -148 30MHz NOISE FLOOR (dBm
CHANNEL POWER (dBm)
Figure case wide area base station with maximum output power, four carrier generic solution presented next. Figure simplified block diagram upconversion (mixer synthesizer), VGA, used.
SYNTHESIZER
ANTENNA MIXER
Figure Out-of-band emissions: Out-of-band emissions unwanted emissions immediately outside channel bandwidth resulting from modulation process nonlinearity transmitter excluding spurious emissions. Section 6.6.2.1 3GPP specification details emissions mask. Consider first single carrier case. Assume Test Model being used, having 10.5 PAPR being used recovers PAR; overhead
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(PREDISTORTION) +3dB 0dBFS (52.27dBm/3.84MHz) -62.43dBFS (-128.27dBFS/Hz) -6dB (PAPR) +10.5dB (PAR) AVERAGE OUTPUT POWER (44.77dBm/3.84MHz) (MARGIN) +3dB 3GPP SPEC (-13dBm/1MHz) (-7.16dBm/3.84MHz) (PREDISTORTION) +3dB 0dBFS (53.77dBm/3.84MHz) 74dBFS (139.84dBFS/Hz) -6dB (PAPR) +12dB (PAR) -6dB
AVERAGE OUTPUT POWER (44.77dBm/3.84MHz) CARRIER OUTPUT POWER, (38.77dBm/3.84MHz)
-56dB
SPURIOUS LEVEL (-10.16dBm/3.84MHz)
SPURIOUS LEVEL (-20.23dBm/3.84MHz) +3dB (MARGIN)
3GPP SPEC (P-56dB)
Figure assumed handle predistortion. This establishes peak power output also full scale dynamic range calculations. 3GPP specification spectral emissions requirements based output power carrier. single carrier case integration bandwidth specified. Allowing margin specification requires spurious content greater than -910.16 3.84 bandwidth. this case needs dynamic range 128.27 dBFS/Hz. Furthermore, frequency offset that this spurious specified covers adjacent channel, hence ACLR needed. consider four carrier case. same total average output power, carrier's output power lower. also little higher than single carrier case, pushing peak power 53.77 dBm. carrier power lower, there different emissions specification: below carrier. With same margin emission specification, spurious level established -20.23 dBm. This effectively increases dynamic range requirement 139.84 dBFS/Hz, more importantly, adjacent channel ACLR required Spurious emissions: This part specification broadly covers channel affects other radios, including this base station's receiver. There frequency separation between this base station's transmitter receiver; there also separation between this base station's transmitter potentially another base station colocated operating different frequency band. amount frequency separation greater than MHz, allowing duplexer's filter transition band. However, duplexer does have great deal attenuation away from band specification requirements away from transmit band. single carrier placed band edge, illustrated Figure 19a, there requirement dBm/1 away from carrier. This would represent second alternate channel, which usually dominated broadband noise single carrier. multiple carriers used, dBm/1 requirement still present (see Figure 19b), this case possible that thirdorder distortion could pollute this band.
Fc1-60MHz Fc1-50MHz
Fc1-50MHz
-15dBm -25dBm -30dBm BAND 2100 2110 2120 2130 2140 2150 2160 2170 2180
-15dBm -25dBm -30dBm BAND 2100 2110 2120 2130 2140 2150 2160 2170 2180
Figure
REV.
-15-
AN-807
(PREDISTORTION) +3dB 0dBFS (52.27dBm/3.84MHz) 79.43dBFS (145.27dBFS/Hz) -6dB (PAPR) +10.5dB (PAR) AVERAGE OUTPUT POWER (44.77dBm/3.84MHz) (MARGIN) -3dB 3GPP SPECIFICATION (-30dBm/1MHz) (-24.16dBm/3.84MHz)
0dBFS (53.77dBm/3.84MHz) 80.93dBFS/1MHz (146.77dBFS/Hz)
(PREDISTORTION) +3dB -6dB (PAPR) +12dB (PAR) -6dB
AVERAGE OUTPUT POWER (44.77dBm/3.84MHz) CARRIER OUTPUT POWER, (38.77dBm/3.84MHz)
SPURIOUS LEVEL (-27.16dBm/3.84MHz)
SPURIOUS LEVEL (-27.16dBm/3.84MHz) +3dB (MARGIN)
3GPP SPECIFICATION (-30dBm/1MHz) (-24.16dBm/3.84MHz)
Figure single carrier case (see Figure 20), same peak level previously discussed; there requirement dBm/1 MHz, which same margin used requires spurious greater than -27.16 dBm/3.84 MHz. this frequency offset close carrier filter transition band effective, this requirement sets minimum broadband noise requirement, ACLR requirement alternate channels almost four carrier case, peak level higher than single carrier case, which when coupled with spurious requirement sets minimum dynamic range requirement 146.77 dBFS/Hz. This requirement also increases four carrier alternate ACLR requirement almost minimum adjacent channel ACLR requirements out- of-band emissions requirements. four carrier requirement referred back single carrier requirement adding allowing summation broadband noise within adjacent channel yields requirement adjacent channel ACLR single carrier. alternate channel ACLR requirements derived from spurious emissions specifications. Here requirements single carrier case Assume that Test Model 10.5 that PAPR reduces around Also assume that linearization being used, giving improvement OIP3 mixer/modulator similar AD8349 used, likes have output channel power around dBm. single carrier power control done VGA, this requires minimum range; allocating gain requires gain deliver approximately from output DAC. Commercially available VGAs with these characteristics exhibit noise figure around Calculating cascaded OIP3 output gives +70.92 dBm; preceding stages assumed distortion free, cascaded OIP3 results adjacent channel ACLR, intermodulation 66.18 achieve alternate channel ACLR with noise gain, total noise output mixer needs around -156.8 dBm/Hz. possibly easier lower noise from than from mixer synthesizer, larger burden noise placed DAC, remainder split between mixer synthesizer. noise contribution adjacent channel needs adding order distortion adjacent channel, which these levels brings adjacent channel ACLR 66.04 above level plan places full-scale output dBm, requiring dynamic range -160 dBFS/Hz.
SYNTHESIZER
ANTENNA MIXER
OUTPUT POWER INPUT POWER GAIN IIP3 OIP3
OUTPUT POWER INPUT POWER GAIN IIP3 OIP3
MIXER
OUTPUT POWER INPUT POWER GAIN IIP3 OIP3 -158
OUTPUT POWER INPUT POWER GAIN IIP3 OIP3 IMD3 OVERHEAD 0dBFS (dBm) (dBFS/Hz) -163 -160
SYNTHESIZER
5MHz OFFSET
-159
OVERALL OIP3 ACLR ACLR NOISE
70.92 -66.18 -71.97
OVERALL ACLR (ADJ) OVERALL ACLR (ALT)
-66.04 -71.97
Figure
-16-
REV.
AN-807
AD9786 AD9726 AD9736 CLUSTER AD6633 PREDISTORTION CLUSTER MODEM AD8362 POWER DETECT CONTROL SYNTHESIZER DAC, NETWORK INTERFACE
PREAMP ANTENNA
ADL5330
MCPA
TUNING CONTROL LOOPS
CLOCK CLEANUP DISTRIBUTION
CLOCK GENERATION
AD9430
AD6636
DDC, DUC, FPGA
PREDISTORTION MEASUREMENT PATH
TRANSMIT SIGNAL PATH
Figure Transmit modulation: specification draws important metrics determining accuracy data. peak code domain error (PCDE) error vector magnitude (EVM) measures well code channels have been spread retained their orthogonality. following equations used link PCDE back ACLR, where spreading factor.
ACLR
PCDE log10
specification requires PCDE, with spreading factor 17.5% QPSK modulation being used, 12.5% with QAM. Normally, radio aspects specification met, code domain aspects usually also met. example, above radio design, single carrier ACLR having would result 2.5% PCDE Superheterodyne single upconversion: Superheterodyne single upconversion relies noise, high performance output technology, Figure linearization being used with correction fifthorder intermodulation products, five times signal bandwidth required, four adjacent carriers this would require approximately MHz. convenient output would decade away from final frequency, MHz. There many options synthesize carriers these frequencies;
REAL REAL
first (see Figure 23a) uses high sample rate Nyquist rate converter such AD9726 AD9736. update rate DAC, fDAC, same input data rate, sample rates above MSPS LVDS data inputs should considered. carriers first Nyquist zone increase frequency, second Nyquist zone images move lower, thus higher output carrier frequency same sample rate, more aggressive analog reconstruction filter needs alternative high speed LVDS inputs lower speed CMOS inputs interpolate output (see Figure 23b). This approach uses digital low-pass filter suppress second third input Nyquist zone image; interpolation image further suppressed analog reconstruction filter. same update rate Nyquist rate DAC, interpolating slightly less than half usable bandwidth produces image which needs consideration. image input sample rate needed, interpolation filters operated high-pass mode (see Figure 23c). analog reconstruction filter requirements between Nyquist interpolation approaches same sample rate comparable with interpolation approach suffering from added interpolation image. fixed input sample rate interpolation approach allows analog reconstruction filter relaxed unfiltered image pushed higher frequency. AD9772A good interpolation MSPS update rate.
SECOND NYQUIST ZONE POSITIVE FREQUENCY INTERPOLATION IMAGE DIGITAL LOW-PASS INTERPOLATION FILTER REAL
FIRST NYQUIST ZONE NEGATIVE FREQUENCY IMAGE
FIRST NYQUIST ZONE POSITIVE FREQUENCY IMAGE ANALOG RECONSTRUCTION FILTER
SECOND NYQUIST ZONE NEGATIVE FREQUENCY INTERPOLATION IMAGE
DIGITAL HIGH-PASS INTERPOLATION FILTER
-fDAC
-fDAC/2
fDAC/2
fDAC -fDAC -3fDAC/4 -fDAC/2 -fDAC/4 -2fs -3fs/2 -fs/2
fDAC/4 fs/2
fDAC/2 3fDAC/4 3fs/2
fDAC -fDAC -3fDAC/4 -fDAC/2 -fDAC/4 -2fs -3fs/2 -fs/2
fDAC/4 fDAC/2 fs/2
3fDAC/4 3fs/2
fDAC
Figure
REV.
-17-
AN-807
INTERPOLATION IMAGES FOLD PHASE
-fDAC -2fs
-3fDAC/4 -fDAC/2 -fDAC/4 -3fs/2 -fs/2
fDAC/4 fs/2
fDAC/2
3fDAC/4 3fs/2
fDAC
trum undergoes frequency shift, with aliasing. However, still only produce real signal, complex mix's output drives single DAC, asymmetric about spectrum potentially causes interpolation images fold desired signal phase with signal, causing distortion (see Figure 25c). AD9786 single accept either real complex input, complex mix, with ability reject interpolation images folding phase. AD9777 AD9779 dual devices with channels interpolation filtering ability either real complex mixing; single DAC's output used real output needed, device operated single transmit chains antenna diversity system. With exception AD9777 AD9772A, mentioned DACs have approximately -160 dBm/Hz noise power spectral density better than over desired frequency range; LVDS input DACs capable producing least Nyquist band. AD6633 still coupled AD9786, AD9777, AD9779 provide peak-toaverage power reduction fine frequency tuning. AD6633 also ability control interface DVGA power control.
COMPLEX REAL INTERPOLATION IMAGES FOLD PHASE
Figure Another approach generate signal digitally baseband signal single always outputs real signal, mirror symmetrical about multiples fDAC Consequently, when real signal subjected real digital (see Figure negative frequencies move into positive frequency interpolation images fold desired signal. Fortunately, interpolation images phase with desired signal does cause distortion. This approach creates congested spectrum requiring band-pass filter select desired signal. complex baseband available, complex interpolation possible (see Figure 25a); complex spectrum longer mirror symmetrical around still translationally symmetrical about With digital complex (see Figure 25b) entire complex spec(a)
COMPLEX
-fDAC -3fDAC/4 -fDAC/2 -fDAC/4 -2fs -3fs/2 -fs/2
fDAC/4 fDAC/2 fs/2
3fDAC/4 3fs/2
fDAC -fDAC -3fDAC/4 -fDAC/2 -fDAC/4 -2fs -3fs/2 -fs/2
fDAC/4 fDAC/2 fs/2
3fDAC/4 3fs/2
fDAC -fDAC -3fDAC/4 -fDAC/2 -fDAC/4 -2fs -3fs/2 -fs/2
fDAC/4 fDAC/2 fs/2
3fDAC/4 3fs/2
fDAC
Figure
-18-
REV.
AN-807
-0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5 -5.0 fDAC/2 fDAC 3fDAC/2 2fDAC 5fDAC/2 3fDAC 7fDAC/2 4fDAC
-3.92dB
-0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5 -5.0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
COMPENSATED
Figure produces high DAC's sin(x)/x response needs considering. zero order hold data, which produces frequency domain response with sin(x)/x characteristic (see Figure 26a). response deep nulls multiples sample frequency, fDAC, half sample rate there 3.92 loss. This important multicarrier signals high frequencies with respect sample rate, causes inband roll-off that affects PCDE; effect worst higher output frequencies. sin(x)/x response digitally compensated (see Figure 26b). inverse sin(x)/x transfer function superimposed data such that when synthesized response essentially flat. disadvantage this that final output signal attenuated approximately dBFS that inverse sin(x)/x filter only bound fraction Nyquist rate (0.42 fDAC Figure 26a). Consequently, using images higher Nyquist zones usually realizable with simple sin(x)/x filters. sin(x)/x compensation implemented almost stage transmit path digital predistortion being implemented, overhead sin(x)/x compensation trivial. desired sin(x)/x compensation DAC, AD9779 inverse sin(x)/x compensation filter.
AD8349 MODULATOR PREAMP ANTENNA ADL5330 AD8362 POWER DETECT CONTROL SYNTHESIZER TUNING CONTROL LOOPS
AD9779 AD9786 AD6633 DUC, PPR, PREDISTORTION
CLUSTER
NETWORK INTERFACE
MCPA
AD9786
CLUSTER MODEM
DAC,
AD9510
AD9510 CLOCK DISTRIBUTION
SYSTEM CLOCK
AD9430/AD9235 AD6636
DDC, DUC, FPGA
PREDISTORTION MEASUREMENT PATH
TRANSMIT SIGNAL PATH
Figure
REV.
-19-
AN-807
COMPLEX
FEEDTHROUGH UNSUPPRESSED SIDEBAND
-fDAC -2fs
-3fDAC/4 -fDAC/2 -fDAC/4 -3fs/2 -fs/2
fDAC/4 fs/2
fDAC/2
3fDAC/4 3fs/2
fDAC
-fLO
+fLO
Figure Direct conversion: This technique desirable simplicity, flexibility, relative cost imple mentation. carriers synthesized DACs complex pair then mixed quadrature modulator; action quadrature modulator complex frequency translation only output real component mix. baseband carriers, Figure 28a, either centered offset from outputs filtered remove images before upconversion quadrature modulator (see Figure 28b). ideal quadrature modulator perfect single sideband upconversion would result. Nonidealities complex real translation lead feedthrough unsuppressed sidebands frequency. using direct upconversion approach feedthrough unsuppressed images moved away from desired sideband, allowing them filtered. number permanently carriers, carriers placed thereby minimizing effect unsuppressed sidebands feedthrough. even number carriers, which permanently carriers placed symmetrically around which case feedthrough appear adjacent interferer that subject emissions limitations. number carriers that turned off, frequency allocation turned carrier filled with unsuppressed sideband, which would also subject emissions limitations. cause feedthrough unsuppressed sideband compensated for. digital predistortion loop being used, correction part that loop. Alternatively, output quadrature modulator mixed back down baseband corrected independently. There main error components that cause poor sideband rejection. Figure example effect quadrature gain error complex path's constellation. might expect, nonideal constellation causes poor PCDE. achieve sideband suppression range, quadrature gain error less than couple tenths percentage point (see Figure 29b).
SIDEBAND SUPPRESSION (dBc)
-0.5
-1.0
-1.5 -1.5
-1.0
-0.5
-100
QUADRATURE GAIN ERROR
Figure
-20-
REV.
AN-807
SIDEBAND SUPPRESSION (dBc)
-0.5
-1.0
-1.5 -1.5
-1.0
-0.5
-100 -2.0
-1.5
-1.0 -0.5 QUADRATURE ERROR (Degrees)
Figure second main error component quadrature phase errors. These errors tend twist constellation (see Figure 30a), degrading PCDE. achieve sideband suppression range, quadrature phase error needs less than couple tenths degree, Figure 30b. cause feedthrough predominantly quadrature offsets complex path. Offsets shift origin demodulated constellation, Figure 31a, degrading EVM. feedthrough also produced coupling, Figure 31b, shows degradation from ideally matched quadrature path. feedthrough subject emissions limitation typically needs below total mean output power base station.
FEEDTHROUGH (dBc) -1.0 -0.5 -1.5 -1.5 -100 -1.0 -0.8 -0.6 -0.4 -0.2 QUADRATURE OFFSET
-0.5
-1.0
Figure
REV.
-21-
AN-807
Since modulators only rated sideband rejection degrees phase accuracy, outputs only match important have ability adjust balance. This accomplished either adjusting baseband digital data adjusting gain offset output. done digital baseband, this part baseband predistortion through standalone routine. However, this consume peercentage total dynamic range modulator. Digital adjustment gain, offset, phase done using AD6633. most suitable partner AD6633 would pair AD9786s, which have sufficient dynamic range that percent degradation should affect system performance. Alternatively, select that includes gain offset adjustment functions found AD9777 AD9779. Using AD9777 AD9779 does reduce dynamic range requires dynamic interface between controller control port. Additionally, AD9779 ability couple outputs modulator still have offset adjustment modulator side coupling. proposed far, AD9777 AD9779 AD8349 recommended direct conversion architectures. addition features functions mentioned, these devices optimized work together providing smooth interface between devices, including matched common-mode input levels. Following modulator, typically used maintain output level operating conditions change. ADL5330 gain adjust range well suited this application. conjunction with VGA, power detector required. Devices such AD8362 matched power control range this with detection range
-22-
REV.
-23-
2006 Analog Devices, Inc. rights reserved. Trademarks registered trademarks property their respective owners.
-24-
AN05664-0-1/06(0)
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