Icom IC-E91 Service Manual
Also see for IC-E91: Instruction manualInstruction manual
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5 - 8Input RegisterOSCCounter Pre-scalerPhaseDetectorChargePumpLoop filterX45015.3 MHz15.3/61.2 MHz2nd LO signal45.9 MHz2nd LO signal1Bufferamp.Q353Q45091011“CK”12×3×4“BPS” signal to the CPU(LOGIC UNIT; IC1, pin 93)15.3 MHz “REF”signal to the PLL IC(RF UNIT; IC800, pin 6)from the CPU(LOGIC UNIT; IC1)PLL IC control signalsPLL IC (IC400)MAIN UNIT“PLLDATA”“BPLSTB”5 5Q301,D300,D301VBVCOQ351,D350,D352UBVCOTCXOReferenceCounterD450 Q451Q4521st LO signals to the1st mixer (IC50, pin 3)Bufferamp.• B_BAND PLL CIRCUITThe buffer amplified signals from the buffer amplifier (MAIN UNIT;Q353) are applied to the PLL IC (MAIN UNIT; IC400, pin 8). Theapplied signals are divided at the prescaler and OSC counteraccording to the “PLLDATA” signal from the CPU (LOGIC UNIT;IC1, pin 94). The divided signal is phasecompared with thereference frequency at the phase detector.The phase difference is output from pin 5 as a pulse type signalafter being passed through the charge pump. The output signal isapplied to the B_BAND VBVCO/UBVCO (MAIN UNIT) after beingconverted into the DC voltage (lock voltage) at the loop filter (MAINUNIT; R404–R406, C410–C412, C414). The lock voltage from theloop filter is applied to each VCO.If the oscillated signal drifts, its phase changes from that of thereference frequency, causing a lock voltage change to compensatefor the drift in the oscillated frequency.• B_BAND PLL AND VCO CIRCUITS5-4 DIGITAL CIRCUITS†5-4-1 LINER CODEC (UT-121)IC350 is a liner codec IC which converts transmitting AF signalsfrom the LOGIC unit into digital signals, and outputs them to theaudio codec IC (IC101) as 16-bit audio data.IC350 also converts the 16-bit audio data from the audio codec IC(IC101) into analog signals, and outputs them to the LOGIC unit asthe receiving AF signals.5-4-2 AUDIO CODEC (UT-121)IC101 is an AMBE audio codec IC. While receiving, digital signalsfrom the LOGIC unit are expansion decoded in IC101, and outputto the liner codec IC (IC350).While transmitting, 16-bit audio data from the liner codec IC (IC350)are compression coded in IC101, and output to the LOGIC unit.5-4-3 MODEM (UT-121)IC202 is a GMSK modem IC. While receiving, demodulated AFsignals from the MAIN unit are output to the LOGIC unit as digitalsignals synchronized with clock signal.While transmitting, digital signals from the LOGIC unit are convertedinto GMSK base-band signal, and output to the LOGIC unit.†Available when the optional UT-121 is installed. |
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