Modulation Generator Sync Output Amplifier - Wavetek 193 Instruction Manual

4-15
4.5.11 Modulation Generator Sync Output
Amplifier
Refer to sweep/mod board schematic sheet 1. The
modulation generator sync output amplifier, driven by
the hysteresis switch of the modulation generator
loop, provides a TTL level output at AUX SYNC OUT
J17. The amplifier 03 is a transistor switch that is
turned off and on by the driving square wave. This
causes the collector of 03 to switch between
+
5 and
OV (no load).
pin 14 and U8 pin 11 (see sweep/mod schematic
sheet 3) which serve as active loads for the input tran-
sistors of the amplifiers. These active loads set the
emitter currents from U8 pins 4 and 7. The emitter
currents collectively pass through R129 to ground.
The voltage drop across R129 provides the reference
voltage for the amplifiers.
For the opposite polarity, the modulator demands less
current 17 at U7 pin 2 and more current 16 at U7 pin
14. This decreased current 17 decreases the voltage
E1, which decreases the current 14. But now, the
modulator output U7 pin 14 demands more current 16
all of which cannot be supplied by current 14 and the
difference in current must be supplied by 15. Output
voltage E2 now swings positive.
The bridge amplifier (sections of U8 and
04) supplies
the drive voltage E1 for the resistor bridge. It supplies
all the current for the R92, R93 legs of the bridge, and
part of current for the R101, R103 leg of the bridge.
The output amplifier (sections of U8 and 05/06) sup-
plies the receiver output signal E2. This voltage E2
serves two functions; it supplies the AM signal which
drives the main generator output amplifier, and pro-
vides a current source or sink for a portion of the
resistor bridge.
Both amplifiers are tied to a common reference
voltage. Resistors R95 and R100 bias transistors U8