Agilent Technologies HP 8719D Service Manual page 347

Option 400 AS8 M/A/D, and A74 Switch Splitter
The M/A/D (Modulator/Amplifier/Detector) microcircuit accomplishes three
functions:
The modulator controls the output power proportionally to the signal produced
by the ALG circuit on the source interface board.
The amplifier can provide +30 dB of amplification for test port output power
levels up to +5 dBm for HP 8719D/20D (-10 dBm for HP 8722D).
The detector outputs a voltage that is proportional to the RF power out of the
amplifier. The voltage is used by the ALC circuit onthe source interface board.
The switch splitter (A74) divides three inputs:
a path routed directly to A64 (Rl sampler)
n
a path switched to the appropriate output port (through A70/71 step
n
attenuators, A60/61 bias tees, and A62/63 directional couplers)
Figure 12-6. Option 400 Signal Separation
Theory of Operation