Make Precise Base-Station Power Measurements fiers, enabling meas

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Make Precise Base-Station Power Measurements fiers, enabling meas

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POWER MEASUREMENTS
Make Precise Base-Station Power Measurements
fiers, enabling measurechip integrated circuit (IC) that enables direct measure- ment alternating signals over wide dynamic range, ment comparison independent into continuously varying intermediate-frequency (IF) signals. low-frequency output voltage that corCircuits used measure power levresponds ratio magnitudes generally referred detectors. envelopes input signals. most common form detector More detailed information demodthe diode, which typically requires ulation logarithmic amplifiers availextensive calibration, linearization, able AD8307 datasheet (available RICK CORY temperature compensation accuat Applications Engineer, RF/IF rately measure power over nortion/pdf/AD8307_a.pdf). Wireless Products range temperature where radio need measure signal levels e-mail: richard.cory@analog.com must meet specifications. Discrete diode wireless infrastructure equipment PHILLIP HALFORD circuits replaced with sincritical adjust transceiver automatMarketing Engineer, RF/IF Wireless gle, highly integrated circuit which conic-gain-control (AGC) circuits, Products tains demodulating logarithmic amplireceiver (Rx) maximum sensitivity
infrastructure subassemblies through compact, singleAnalog Devices, Woburn MS-122, Wilmington, 01887; e-mail: phillip.halford@analog.com.
highly integrated device with pair logarithmic amplifier detectors operating approximately useful making amplitude phase measurements input signals.
easurements gain phase vital operation many radio systems. time, this capability required complex expensive instruments circuitry. Fortunately, this capability incorporated into wireless
Channel
detector
Phase mV/deg.)
Gain mV/dB) Channel detector
This functional block diagram AD8302 shows pair logarithmic detectors integrated single chip.
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AD8302 INPA INPB COMM INPA OFSA VPOS OFSB INPB MFLT Gain VMAG MSET VREF PSET VPHS PFLT Phase
COMM
measurement mode, AD8302's gain phase outputs vary function gain phase relationships between input signals.
varying inputs from mobile users transmitter (Tx) that output power maintained optimum level performance mask, power-amplifier (PA) efficiency linearity, government regulations. result many different logarithmic amplifier circuits have been developed, optimized specific applications. Within received-signal-strength indication (RSSI) used adjust gain extend dynamic range accurately controlling transmit signal power with transmitted-signalstrength indication (TSSI) frequencies higher power levels significantly eases implementation controls operating level maximum efficiency. sampling available power-detector/logamp circuits,
models AD8309 AD8310 from Analog Devices (Wilmington, operate with maximum input frequencies MHz, respectively dynamic ranges respectively, while company's models AD8313 8314 operate GHz, with dynamic ranges respectively. AD8309 AD8310 detectors designed RSSI applications, while AD8313 AD8314 suitable TSSI applications. these detectors provide output that proportional logarithm amplitude incoming signal. many applications, necessary detect compare power levels different points within circuit that adjustments optimal performance made. Temperature drift causes changes gain
mV/dB VMAG VPHS Gain
Relative phase, degrees
AD8302 provides linear transfer functions gain (left) phase (right).
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every decibel power must preserved maximum efficiency minimum power consumption. measure differences between input signals, circuit developed embodied company's model AD8302 Gain Phase Detector. This function allows users effectively calibrate their gain radio-transceiver chains computing gain attenuation between input output system subsystem. AD8302 integrates identical logarithmic detectors single chip, each having dynamic range digital phase detector, circuits used amplitude output scaling (Fig. With both logamps fabricated same die, their performance matched very accurately errors associated with each stage track each other, thereby effectively canceling each other. independent input signals, which might known reference signal, applied Channel Channel inputs. outputs from AD8302 voltages proportional relative amplitude (i.e., gain loss) relative phase input signals. AD8302 first integrated circuit (IC) enable direct ratio measurement between independent input signals. AD8302 enables designers build accurate, low-cost system diagnostics calibration into their final product. user measure amplitude difference range which corresponds input range from dBm. Measurements center point performed with exceptional accuracy. phase measurement simultaneously measured over 180-deg. range. full 360-deg. measurement range possible when known priori which channel leads lags other phase. amplitude-signal output scaled mV/dB phase output scaled mV/deg. through on-chip output amplifier circuits. possible adjust scaling that user may, reasonable extent, customize these slopes. These output voltages
analog-to-digital converter (ADC) they used drive analog circuits. performance accuracy AD8302 dependent multitude factors: relative difference between input signals amplitude phase frequency interest carrier frequency), signal bandwidth carrier frequencies, device operating temperature. characterizing AD8302, development team chose provide accuracy performance data over popular cellular radio frequencies: MHz, GHz, GHz. However, performs accurate amplitude measurement phase accuracy over somewhat reduced range GHz. addition, AD8302 operates exceptionally well frequencies, well-suited baseband applications. gain measurement, AD8302 offers excellent accuracy better than 0.2-dB error beyond 40-dB dynamic range better than over 60-dB dynamic range MHz. phase measurements, AD8302 offers better than 1-deg. error over full 0-to-180-deg. range. However, higher frequencies, accuracy reduced 180-deg. relative phase approached. AD8302 measure relative phase magnitude input signals operate modes: measurement controller. measurement mode, shown Fig. gain phase outputs continuously variable corresponding relationships between input signals varied. slope gain output linear decibels, rate mV/dB. slope phase output linear degrees, nominally mV/deg. These transfer functions shown Fig. measurement mode enabled connecting VMAG output MSET magnitude measurement function, connecting VPHS output PSET input phase-measurement function. gain-transfer function, avail-
AD8302 INPA INPB COMM INPA OFSA VPOS OFSB INPB MFLT VMAG MSET VREF PSET VPHS PFLT Phase Phase voltage Gain voltage Gain
COMM
open-loop controller mode, amplitude phase outputs AD8302 analogous comparators.
able VMAG pin, continuously measure gains from when input power reference channel, INPB, held dBm. phase-transfer function, available VPHS, unambiguously measure relative phase from deg. total relative phase excursion exceeds deg., then VPHS output less definitive, since sign slope transfer function changes from negative positive relative phase passes through deg. gain- phase-measurement functions, optimal accuracy obtained mid-scale output voltages, i.e., 0-dB gain 90-deg. relative phase, absolute signal amplitudes approximately dBm. controller mode, openloop operation VPHS VMAG outputs analogous comparators. This mode enabled breaking external connections between VMAG MSET, VPHS PSET, applying control voltages MSET PSET that correspond conditions which AD8302 testing. This configuration shown Fig. example, AD8302 indicate gain greater than less than reference voltage that corresponds +10-dB gain (nominally +1.2 VDC) applied MSET. Then, magnitude signal applied INPA more) larger than
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that signal applied INPB, voltage VMAG will most positive value, which approximately VDC. Otherwise, voltage VMAG will minimum value, which approximately VDC. controller mode phase-measurement output operates similar way. voltage that corresponds condition which AD8302 tests simply same voltage that would produced AD8302 measurement mode when that condition applied INPA INPB inputs. gain- phasemeasurement functions independent each other, possible operate these functions measurement mode while operating other controller mode. AD8302 offers ability continuously measure gain distribution variation across section circuitry. Within cellular base-station radio transceiver, ensuring that circuits signals adjusted meet needs cellsite capacity compensated drift over their operating temperature lifetime important considerations. AD8302 monitor circuit continuously measuring difference between signals, which then digitized, alarm indication when used controller mode. cell site thus dynamically
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adjusted over life base station. Another application AD8302 control gain across build simple linearization circuits (Fig. AD8302 used either mode feedback controller-based linearization architectures, part either active passive circuitry within system. Cell-site operators deploying multicarrier (MCPAs) that handle multiple carriers simultaneously. MCPA requires extensive linearization remove intermodulation (IM) products. AD8302 suited forms linearization architectures, including feedforward predistortion. feedforward system, AD8302 used monitor carrier cancellation within first loop distortion cancellation within erroramplifier loop. output response both compensated within gain phase shifters. Other applications include adaptive antenna circuits where dual matching both amplifiers eases design measuring forward reflective power voltage standing-wave ratio (VSWR). Along with dual directional coupler attenuators, AD8302 used form wideband VSWR/reflection-coefficient meter (figure shown; contact author details). AD8302 compares magnitude phase incident signal, supplied generator, that signal reflected from load. perfect impedance match between source, load, transmission lines, magnitude reflected signal would resultant would unity. impedance these components changed from this optimal value, magnitude reflected signal will increase, increasing SWR. Since AD8302 provides optimal accuracy when magnitudes input signals both dBm, coupling factors directional couplers attenuation factors attenuators selected provide these levels under nominal operating conditions. result, AD8302 accurately
Feedback linearization architecture Gain adjust Controller-based linearization architecture Gain phase adjust Gain phase adjust Attenuator
Drivers
Attenuator
AD8302
AD8302 Gain phase points
AD8302 used variety linearization configurations minimizing products multicarrier cellular PAs.
resolve variations reflected signal magnitude from nominal conditions. reflection coefficient, which vector quantity, defined reflected voltage/incident voltage SWR, terms reflection coefficient, (1-| arbitrarily selects coupling factors both directional couplers then attenuation factors attenuators selected follows. attenuator that drives INPB, ATTENB, selected ensure that signal level termination resistor under nominal conditions. Then, attenuation factor other attenuator, ATTENA, selected also deliver INPA under nominal conditions. assumes that return loss load nominally then reflected signal from load coupled towards INPB lower than incident signal amplitude, value ATTENB that would deliver INPB smaller than value selected ATTENA. example, ATTENB selected nominal return loss
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load then ATTENA should measured reflection coefficient used calculate level impedance mismatch particular load condition. This configuration proves particularly useful diagnosing varying load impedances within antenna systems. test instrument such vectornetwork analyzer (VNA), AD8302 configured measure reflection coefficient device under test (DUT) determine complex impedance DUT. AD8302 fabricated with high-performance silicon (Si) bipolarprocess transistors with cutoff frequencies GHz. device, which packaged 14-lead thin-shrink, smalloutline package (TSSOP), specified over +85°C temperature range. AD8302 power-measurement range GHz. gain-measurement range +1.8 VDC) phasemeasurement range deg. +1.8 VDC). amplitude accuracy better than across 60-dB range phase accuracy better than deg. across 180-deg. range. small-signal envelope bandwidth MHz. device typically consumes 19mA current from supply voltage +2.7 +5.5 VDC.
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Make Precise Base-Station Power Measurements fiers, enabling meas

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