Tait TP9100 Service Manual

Also see for TP9100: User guide Product safety and compliance information User guide Service manual Manual

Contents

TP9100 Service Manual Circuit Descriptions 51© Tait Electronics Limited May 20053.1 Transmitter CircuitryIntroduction For a block diagram of the transmitter circuitry, refer to Figure 3.2.Exciter The exciter is different between the variants of the radio. The VCO bufferoutput is amplified through a combination of BJT discrete stage Q107(B1 and H6), integrated amplifier IC100 (H5 and H6), and BJT discretestage Q100 (H5 and H6). The exciter produces approximately +20dBmoutput to the driver.Driver The LDMOS driver stage Q103 produces up to 1.5W output that is power-controlled via Q101.Power Amplifier The final-stage power amplifier consists of a single LDMOS device Q106producing up to 5W output for B1 and 4W output for H5 and H6.Final bias control comes from the IDAC channel of IC204 and one of theoperational amplifiers making up IC202. Wave shaping of the bias signal isperformed by one of the operational amplifiers of IC101. In addition, thebias signal can be inhibited by an out of lock signal from the synthesizer.Power Control Loop Calibration is used to adjust the power control loop, thus setting the outputof the transmitter to one of four preferred power levels (1, 2, 3, and 5W forB1 and 1, 2, 2.5, and 4W for H5 and H6). The control mechanism for thisloop is via a DAC channel of IC204 and one of the operational amplifiersmaking up IC202. Wave shaping, filtering and feedback from current-senseresistor R150 is then performed by two of the operational amplifiers makingup IC101. The power control loop will be inhibited if for any reason an out-of-lock signal is detected from the synthesizer. This ensures that noerroneous signals are transmitted at any time.Temperature Sensor For added protection, a temperature sensor ensures that the transmitterpower is reduced to very low levels should a temperature threshold beexceeded. If the temperature does not decrease, the transmitter is switchedoff.