LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Acces

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LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Acces

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AN-1374 LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Access Terminal AN-1374
LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Access Terminal
Since commercialization CDMA IS-95 cellular network started 1996, Code Division Multiple Access technology have been proven best wireless technology advancing cellular personal communications industry. prevailing standards, CDMA2000, W-CDMA TD_SCDMA, have adopted CDMA their access method. CDMA method based spread spectrum modulation techniques spread spectrum principle based Shannon information theory. Shannon capacity states that channel capacity Additive White Gaussian Noise SNR) Where: Channel Transmission Capacity Channel Bandwidth Signal Noise Ratio System with wider bandwidth, bigger BRF, requires lower comparing that narrowband system, smaller BRF, order achieve same capacity Csh. other hand, high will have higher transmission capacity channel given bandwidth BRF. This means have more users users transmit same amount data.
National Semiconductor Application Note 1374 Barry Yuen April 2005
summary, main benefits power control CDMA system are: Increase System Capacity Minimization Near-Far Effect Reduce battery power consumption
IS-95 CDMA2000 Power Control Mobile Station Access Terminal
power control feature controls interference level reverse link estimating best transmission power level reacting power control directions sent network base station. CDMA IS-95 CDMA2000 base station determines power control, whereas, CDMA2000 EV-DO, access terminal executes power control. Overall, power control schemes both standards very similar. employs power control methods, i.e. open-loop control closedloop control.
Open-Loop Power Control
open-loop method uses power level receiver estimate forward-link path loss then specifies initial transmit power such that forward reverse link powers kept constant user terminal's choice, i.e. Constant cellular calculated from Eb/Io, which measured MS's DSP. Eb/Io ratio Energy Bit, over Power Spectral Density Noise Interference, After initial obtained, both base station will start closed-loop control. base station transmits error signal instructing increase decrease power step depending which CDMA standard implemented.
Power Control Important CDMA Reverse Link?
Since Mobile Station considered interferer other users within same base station coverage area users neighbor cells, transmit power control becomes extremely important good performance higher system capacity CDMA operation. Therefore, greater number active higher interference level within system. Thus, lower transmission power, lower total interference, i.e. higher SNR, within carrier bandwidth higher system capacity Csh. main idea power control schemes transmission power minimum level that base station receives signals from with similar level. Under this condition, signal noise ratio base station input
Closed Loop Power Control
closed loop power control consists processes: outer loop (only base station) inner base station simultaneously), which achieve power control rates IS-95 CDMA closed-loop power control's main purpose minimize fast-fading effects caused signal multi-path propagation losses, based measurements made base station. both closed-loop power control processes, outer inner loop, combination lead fading compensations within msec frame-by-frame interval, within dynamic range
total number users this base station.
2005 National Semiconductor Corporation
AN201448
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Outer Closed-Loop Power Control
outer loop, base station specifies target Eb/Io (from base station) receiver each frame every msec. This Eb/Io automatically reduces steps rises frame error occurs. whole Outer Closed-Loop process only involves base station.
found that transmit radio architecture Figure reduce power consumption power amplifier thanks isolator, like Murata CE04
Inner Closed-Loop Power Control
inner loop, base station compares Eb/Io reverse traffic channel with target Eb/Io every 1.25 msec then instructs reduce increase transmit power that targeted Eb/Io would achieved. Power steps vary from 0.25 CDMA2000 CDMA IS-95. update rate bps.
Hardware Implementation Power Control CDMA Mobile Station
summary, CDMA IS-95 requires adjust transmit power level step every 1.25 msec while step size CDMA2000 could either 0.25 FIGURE Transmit Radio Architecture
20144804
20144803
FIGURE Output Power Control Linear Application Figure shows generic output power control linear power amplifier signal chain handheld device. Since high linearity required CDMA signal, output power amplifier usually biased fixed gain then output power level adjusted through gain control linear driver amplifier, usually called Automatic Gain Control Amplifier CDMA
CES30, accurate power detector LMV225. isolator provides close-to-perfect load PA's output while LMV225 detects accurate transmit power level then smartly output power just right level required base station. this application circuit, resistor used divert signal from main signal path input LMV225. about capacitor needed block enable control signal from entering main signal path. This blocking capacitor necessary since don't want voltage into output input isolator. Since isolator been place, very safe that most diverted energy from transmit Reflection energy from antenna will diverted built-in load inside isolator then seldom reach PA's output LMV225. Therefore, coupled power LMV225 estimated 20log[R1/(R1+50)].
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Hardware Implementation Power Control CDMA Mobile Station
(Continued)
20144801
FIGURE Output Impedance Smith Chart Figure briefly shows explains test results. PA's distortion performance with ACPR, Adjacent Channel Power Rejection, supply current improved ACPR supply current. current reduction this case distortion improvement about
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Hardware Implementation Power Control CDMA Mobile Station (Continued)
Figure shows typical test circuit boards used this kind experiment.
20144802
FIGURE LMV225 Eval Board CDMA PA's Module have shown that LMV225 together with CES30 isolator deliver better performance linear CDMA applications, term power consumption distortion, IS-95, W-CDMA, CDMA2000 TD-SCDMA interfaces. fact, necessary CDMA2000 mobile station access terminal have LMV225 transmit power detector order implement stringent inner closed-loop power control because variations uncertainties performance transmit signal path components, namely AGC, PA's gain, loss passive parts. going explain more detail next section. handheld devices. this transmitter architecture, output power antenna found RFOUT Where: RFOUT power antenna (assume matched) Output power from transmit chip Insertion loss filter Fixed gain CDMA Insertion loss isolator Insertion loss duplexer
PRFT LSAW LISOLATOR LDUPLEXER
Mobile Station Transmit Signal Path Radio
transmit radio architecture Figure used many different kinds CDMA chipset. very best popular solutions MSM6500TM/RFT6120from Qual Comm Inc. Diego, California, USA. Figure depicts recommended LMV225 application block diagram transmit power detection CDMA2000 EV-DO single band
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Mobile Station Transmit Signal Path Radio
(Continued)
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FIGURE Single-Band CDMA2000 Architecture Here insertion loss resistive power divider formed LMV225 negligible since both LMV225 have formed high impedance shunt load signal path. that LSAW, GPA, LISOLATOR, LDUPLEXER considered constant room temperature. then power antenna RFOUT will adjusted PRFT, which controlled transmit chip. fact, amplifier typically supports about dynamic range requirements from IS-95 CDMA2000. also discovered that CDMA work medium output power most time then power control accuracy more important from medium power level high output power. inaccurate high output power level will reduce talk time generate more interferences other network users.
Added-Values From Linear-In-dB Characteristic LMV225
from Figure Figure LMV225 linear-in-dB detection range. This characteristic reduced complexity production calibration process. calibration process critical part CDMA manufacturing process. Automatic test equipment used collect information regarding output power control code/signal from small signal strong signal. This information then stored memory field uses. Anytime output power level requested base station, will memory find what control code/signal should used order achieve requested output power level. Some market have exponential characteristic between control signal output gain. this kind used together with LMV225, linearin-dB characteristic will make original control curve more complicated original characteristic curve comparing other detection method, like diode detection, etc. However, linear control range, linear-in-dB characteristic will reduce calibration points from points points This two-point calibration process based principle that only different points needed represent order linear equation dimensional plane. equation, slope intercept could found test coordinates (x1, (x2, y2).
Highlight LMV225
LMV225 designed optimized provide best power detection range CDMA handheld device. detection range shown Figure Figure mentioned above, more crucial have accurate power control from medium output power level high output power level. coupling resistor should chosen that LMV225 signal representing that critical range. Suppose trying highest gain level that maximum output level from CDMA achieved, dBm. crest factor sent signal this time then instantaneous peak power level from CDMA will dBm. choose this maximum reference point which LMV225 should detect, i.e., RFIN/Enable LMV225 when PA's instantaneous output power dBm, coupling factor should used. fount that resistor could make coupling factor this circuit.
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Added-Values From Linear-In-dB Characteristic LMV225
(Continued)
20144806
FIGURE Typical Performance Cellular Bands
20144807
FIGURE Typical Performance DCS/PCS/W-DCMA Bands
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LMV225 Dual-Band CDMA2000 Mobile Station
Figure recommended block diagram CDMA2000 handheld devices. Although resistors same, possible users optimize
both bands performance that both have same value. other hand, isolation between band high band should acceptable because only power amplifiers real application resistor R1') will typically provide more than isolation.
20144808
FIGURE Dual-Band CDMA2000 Transmit Architecture
Conclusion
Finally, Logarithmic Amplifier Power Detector LMV225 been presented critical component CDMA2000 power control reverse link. found that LMV225 only delivers fundamental requirements specified
CDMA2000 interface standard, also save power consumption, improve distortion transmit path like ACPR, save production calibration efforts ease stage.
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AN-1374 LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Access Terminal
Notes
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications. most current product information visit www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products uses packing materials that meet provisions Customer Products Stewardship Specification (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) contain ``Banned Substances'' defined CSP-9-111S2.
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LMV225 Linear-In-dB Power Detector CDMA2000 EV_DO Mobile Station Acces

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