TP9100 Service Manual Circuit Descriptions 57© Tait Electronics Limited May 2005Figure 3.4 Block diagram of the frequency synthesizer circuitryBufferBufferandSamplePLLMOD5 V SWITCHSYN TX LOSYN RX LO1TR SwitchDIG SYN TR SWSignal Types:RFanalogclockdigitalasynchronous serial datasynchronous serial dataPLLSummerLoopFilterVCOSupplyFilter+4 V DECFrequency SynthesizerLPFMixerVCXOTCXOModulatorBuffer AmplifierPLLVCO 15 VSwitchTR SwitchVCO (UHF only)+5V0 ANAGNDPowerSupplyCDC VCXO MODSYN CDC FCLSYN CDC LFVCDC VCO MODCODECandAudioSYN TX LOSYN RX LO1Trans-mitterSYN RX OSCReceiverDigitalDIG SYN SPI DODIG SYN SPI CLKDIG SYN TR SWDIG SYN ENDIG SYN FASTDIG SYN LATCHSYN LOCKSYN DIG FREF14 VSMPSBuffer AmplifierInterfacesInverter+7V5 LINK+3V0 AN+2V5CDCVCL SUPPLY3 V Switch+3V0 AN+5V0 AN+3V0 ANVCO 2BufferAmplifierBufferAmplifierSample5 V SwitchVCO (VHF only)MOD