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Chapter 5 Theory of Operation
Square Wave and Sync
Transistors Q601 and Q602 buffer the output of the sine wave
The amplifier gain output level is controlled by the variable current source Q605 and U307D in response to the System DAC dc signal SW_AMP. Squarewave variable gain amplifier output signal levels are unbalanced by resistors R643 and R644 to correct for the output amplifier + and - gain differences as discussed in the preattenuator section on page 90.
Latching relay K601 connects the square wave into the +FUNCTION and
5 volts for 15 ms through relay driver U301. The main controller, U102, writes data bytes to ASIC U103 which transmits this data to the relay drivers via the internal
Multiplexer U604 selects one of five sources for the SYNC output: off, modulation sync, square wave comparator output, RUN*, or Arbitrary waveform sync. ARB_SYNC is derived from the WA14 line through U210B. U215B and U210C control the pulse width of the ARB_SYNC (arbitrary waveform sync) signal. Square wave sync is taken from the 5 inverting output of square wave comparator U620. U620 also generates
the MOD_SYNC (modulation sync) through U217. Buffer U621 inverts the sync signal and provides the output current drive to the SYNC output BNC connector.
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