FMTRANSMITTER
TR
EM1000HEDIGPLUSCOMPACT
TechnicalManual1v2November2019
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3.11.1STEREOGENERATORBOARD(OPTIONAL)
Thephasecontrolloop (PLL)circuitiscontainedentirelyintheintegratedcircuitIC2,whose
referencefrequencyisgeneratedinaTCXOcalledTCXO1inthediagram.Thesignalgenerated
by this oscillator has a frequency of 12.8MHz. To operate correctly in the chosen reference
frequency, the synthesizer circuit IC2 must be programmed serially by the Microcontroller
withcomplexinformation,ataskcarriedoutthroughthreecontrollines.
The integrated circuit IC1, through its two sections, filters the output of the frequency
comparator, both towards the modulating varicap diodes and towards the phasehook
detectioncircuit.
It may be noted that the gate bias voltage is removed from the output MOSFETs through
transistors TR4 and TR3 to suspend the RF output of the unit while the phase control loop
(PLL)isnotcorrectlyengagedinphaseattheselectedfrequency.Thecontrolloophasbeen
designed to ensure that the crosstalk added to the stereo multiplexed baseband signal is
below55dBat30Hz,beingvirtuallynegligibleathigherfrequencieswithinthebaseband.The
followingfigureshowsthechanneloscillatorcircuitandPLL.
Figure:Stereogeneratorboard
