Fluke 5700A Series Service Manual page 209

Theory of Operation 2
Analog Section Detailed Circuit Description
connector is connected back to the OUTPUT HI SENSE and OUTPUT LO SENSE
binding posts.
Attenuation is calibrated starting with 70 dB and decreased in 10 dB steps to 0 dB. The
Switch Matrix assembly connects the output of the Wideband AC module to its internal
cal zero amplifier circuit during all attenuator calibrations except the 0 dB and 10 dB.
The internal cal zero amplifier circuit provides a gain of 10 to Wideband output during 20
dB to 70 dB attenuation calibration. The output of this amplifier is connected to the RCL
line which is routed to the +input of the adc circuit on the DAC assembly. Output from
the DAC is connected to the -input of the adc circuit and adjusted until a null is achieved.
The exact attenuator value is then determined.
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