Agilent Technologies 2712A Analog Waveform Processing, Interrelationshipof the Circuit Assemblies

Model 8904A Service

f=pjTSAMPLERD7E

Figure 8-7.Analog Output Block Diagram

Analog Waveform Processing

The analog waveform processing block diagram is shown in figure 8-7. Instruments with Option 002 have a second, identical output assembly. The DAC receives digital inputs from the instrument’s controller and converts them to an analog voltage. Because the DAC output has significant switching transients, each new output is sampled after settling. The Sampler Amplifier buffers the output of the Sampler.

The Low-Pass Filter is needed to accurately construct the sample-generated waveform. For smooth waveforms, such as sinewaves, a sharp-cutoff filter is selected its 3 dl3 corner is approximately 670 kHz. For waveforms less smooth, such as triangle waves or tone bursts, a low-overshoot filter is selected with a 3 dE3 corner of 230 kHz.

The Audio Amplifier has 19 dEl gain and passes signals up to 600 kHz with good flatness and low distortion. Attenuator 1can be programmed for 0, 6, 12, or 24 dB attenuation. It reduces the need for large level range control in the DWSIC and thereby maintains waveform fidelity at low levels.

The Floating Output Amplifier is a single-ended-to-differential converter with a gain of 1.12. In its float mode, either the high or the low output (not shown in the block diagram) can be floated up to 10 V while the signal from the instrument itself appears on the other output. Output impedance is 50R. Attenuator 2 can be programmed for 0 or 48 dB.

Both the high and low outputs are protected from inadvertent application of a large reverse voltage by the Overvoltage Detector and Relay. When a large output voltage is sensed the Overvoltage Detector opens the relay. The relay is reset by the instrument’s controller when any key is pressed if the overvoltage condition has been removed.

If the instrument has Option 006 (balanced output), Output 1 is floated by means of a balancing transformer (not shown in figure 8-7).The transformer provides a true balanced 600n output but limits the useable frequency range and fidelity of the various non-sinusoidal waveforms.

Interrelationshipof the Circuit Assemblies

Figure 8-8and figure 8-8.1diagrams the assemblies by assembly number and shows their interrela- tionship.

reu.15DEC89 Principles of Operation (Overall) 8-21