Powerwave Technologies 5JS0044 Multi-Channel Power Amplifier User Manual sect 4

Powerwave Technologies Inc Multi-Channel Power Amplifier sect 4

sect 4

044-05073 Rev. A 4-1PRINCIPLES OF OPERATION4-1. INTRODUCTIONThis section contains a functional description of the Multicarrier Cellular Amplifier.4-2. RF INPUT SIGNALThe maximum input power for all carrier frequencies should not exceed the limits specified in table1-2. For proper amplifier loop balance, the out of band components of the input signals should notexceed -40 dBc. The input VSWR should be 2:1 maximum (or better).4-3. RF OUTPUT LOADThe load impedance should be as good as possible (1.5:1 or better) in the working band for goodpower transfer to the load. If the amplifier is operated into a filter, it will maintain its distortioncharacteristics outside the signal band even if the VSWR is infinite, provided the reflected powerdoes not exceed one watt. A parasitic signal of less than one watt incident on the output will notcause distortion at a higher level than the normal forward distortion (i.e. -65 dBc).4-4. SYSTEM FUNCTIONAL DESCRIPTIONThe G3S-800-150 amplifier is a linear, feed-forward power amplifier that operates in the 25 MHzfrequency band from 869 MHz to 894 MHz. A typical two-module system is shown in figure 4-1.The power output specification is listed in table 1-2. Each amplifier is a self-contained plug-inmodule and is functionally independent of the other amplifier module. The amplifier modules aredesigned for parallel operation to achieve high peak power output, and for redundancy inunmanned remote locations. Each amplifier in the system can simultaneously transmit multiplecarrier frequencies, at an average total power output of 135 watts (one amplifier module in asubrack unit) to 270 watts (two amplifier modules), with -65 dBc third order intermodulationdistortion (IMD).The output from each amplifier is an amplified composite signal of approximately 150 watts beforecombiner losses. All phase and gain corrections are performed on the signal(s) in the individualamplifier modules. In a two-module system, the amplifier outputs are fed to a power combiner andcombined to form a composite RF output of up to 270 watts. Each amplifier module has an alarmand display board that monitors the amplifier performance. If a failure or fault occurs in anamplifier module, it is displayed on the individual amplifier front panel.4-5. G3S-800-150 AMPLIFIER MODULEThe amplifier module, figure 4-2, has an average output of 150 watts power (1500 watts peakpower) with intermodulation products suppressed to better than -65 dBc below carrier levels. Theamplifier provides an amplified output signal with constant gain and phase by adding approximately30 dB of distortion cancellation on the output signal. Constant gain and phase is maintained bycontinuously comparing active paths with passive references, and correcting for small variationsthrough the RF feedback controls. All gain and phase variations, for example those due totemperature, are reduced to the passive reference variations. The amplifier module is comprisedof:Section4
044-05073 Rev. A 4-2PreamplifiersMain amplifierError amplifierTwo feed-forward loops with phase-shift and gain controlsDC/DC power regulatorAlarm monitoring, control and display panelFigure 4-1. G3S-800-150 Two Module Amplifier SystemThe main amplifier employs class AB amplification for maximum efficiency. The error amplifier andfeed forward loops are employed to correct signal nonlinearities introduced by the class AB mainamplifier. The error amplifier operates in class AB mode. The RF input signals are amplified by apreamp and coupled to an attenuator and phase shifter in the first feed-forward loop. The mainsignal is phase shifted by 180 degrees and amplified in the premain amplifier. The output from thepremain amplifier is fed to the class AB main amplifier. The output from the main amplifier istypically 220 watts. The signal is output to several couplers and a delay line.The signal output from the main amplifier is sampled using a coupler, and the sample signal iscombined with the main input signal and input to the second feed-forward loop. The error signal isattenuated, phase shifted 180 degrees, then fed to the error amplifier where it is amplified to alevel identical to the sampled output from the main amplifier. The output from the error amplifier isthen coupled back and added to the output from the main amplifier. The control loops continuouslymake adjustments to cancel out any distortion in the final output signals.RF IN J9 VVA COUPLER BPFALC_LEDMOD PORTBDM PORTRF OUT J2J8RS485/ADD.RS485/RS232RMS DET.500-001090J5/J6J3/J4INTERFACEASSY.500-1107POWER SPLITTERFORM C ALARMSJ7SIGNAL DISTRIBUTION1717ACTIVE POWER COMBINERMCA 1MCA 2IN-RUSHIN-RUSHDC_CH1DC_CH2SPLITTER &SIGNAL DIST.ASSY.500-00109580A MAX80A MAXDB9DB9J1DB92X32X32124COMBINERASSY500-0010945 5CONTROLASSEMBLY500-001105100 30
044-05073 Rev. A 4-3The primary function of the first loop is to provide an error signal for the second loop. The primaryfunction of the second loop is to amplify the error signal to cancel out spurious products developedin the main amplifier. The input signal is amplified by a preamplifier and fed to a coupler and delayline. The signal from the coupler is fed to the attenuator and phase shifter in the 1st loop. Thefirst loop control section phase shifts the main input signals by 180 degrees and constantlymonitors the output for correct phase and gain.Figure 4-2. G3S-800-150 Power Amplifier Module Functional Block DiagramThe 2nd loop control section obtains a sample of the distortion added to the output signals by themain amplifiers, phase shifts the signals by 180 degrees, then feeds it to the error amplifier.There it is amplified to the same power level as the input sample and coupled on to the mainoutput signal. The final output is monitored by the 2nd loop and adjusted to ensure that the signaldistortion and IMD on the final output is canceled out.4-5.1. MAIN AMPLIFIERThe input and output of the amplifier employ two-stage, class AB amplifiers which provideapproximately 25 dB of gain in the 25 MHz frequency band from 869 to 894 MHz. The amplifieroperates on +27 Vdc, and a bias voltage of +5 Vdc, and is mounted directly on a heat sink whichis temperature monitored by a thermostat. If the heat sink temperature exceeds 85 °C, thethermostat opens and a high temperature fault occurs. The alarm logic controls the +5 Vdc biasvoltage which shuts down the amplifier.4-5.2. ERROR AMPLIFIERThe main function of the error amplifier is to sample and amplify the signal distortion levelgenerated by the main amplifier, to a level that cancels out the distortion and IMD when the errorsignal is coupled onto the main signal at the amplifier output. The error amplifier is a balancedmultistage, class AB amplifier, has 51 dB of gain, and produces up to an 80-watt output. Theamplifier operates on 27 Vdc and a bias voltage of +5 Vdc, and is mounted directly on a heat sink.4-5.3. AMPLIFIER MONITORING
044-05073 Rev. A 4-4In the main and error amplifier modules, all normal variations are automatically compensated for bythe feedforward loop control. However, when large variations occur beyond the adjustment
044-05073 Rev. A 4-5range of the loop control, a loop fault will occur. The alarms are displayed on the front panelindicators and output via a 21-pin connector on the rear of the module to the subrack summaryboard for subsequent remote monitoring via the ALARMS connector. Refer to paragraph 2-5 aswell as figure 2-2 and table 2-2 for a description of the ALARMS connector.4-5.4. AMPLIFIER MODULE COOLINGAlthough each amplifier module contains its own heat sink, it is cooled with forced air. Four fansare used for forced air cooling and redundancy. The fans, located on the front and rear of theamplifier module, draw air in through the front of the amplifier and exhaust hot air out the back ofthe module. The fans are field replaceable.4-6. POWER DISTRIBUTIONPrimary DC power for the system is provided by the host system to the MCR20XX Series(NTL107AC) subrack. The subrack supplies each amplifier module with +27 Vdc directly and viathe RF power splitter/combiner. The amplifier module has a DC/DC converter that converts the+27 Vdc to +15 Vdc, +5 Vdc and -5 Vdc.4-7. INTERMODULATIONThe G3X-800 amplifier is designed to deliver a 150-watt composite average power, multicarriersignal, occupying a bandwidth less than or equal to 25 MHz, in the bandwidth from 869 to 894MHz. The maximum average power for linear operation, and thus the amplifier efficiency, willdepend on the type of signal amplified.4-7.1 TWO TONE INTERMODULATIONWhen measured with two equal CW tones spaced anywhere from 30 kHz to 20 MHz apart, and atany power level up to the average power, the third order intermodulation products will be below-65 dBc4-7.2 MULTITONE INTERMODULATIONAdding more tones to the signal will lower individual intermodulation products. If the frequenciesare not equally spaced, the level of intermodulation products gets very low. When the frequenciesare equally spaced, those products fall on top of each other on the same frequency grid. Theaverage power of all intermodulation beats falling on the same frequency is called the compositeintermodulation; it is -65 dBc or better.4-8. ALARMSThe presence of several plug-in amplifier alarms can be detected at the DC and logic connector onthe amplifier rear panel. Refer to table 2-1 and figure 2-2 for a description of the connector.

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