Agilent Technologies 2712A, 2948 Principles of Operation Overall, How Waveforms Are Generated

Model 8904A Service

PRINCIPLES OF OPERATION

OVERALL

What the Multifunction Synthesizer Can Do

The HP 8904A Multifunction Synthesizer is a general purpose function generator which can output complex signals based on combinations of six waveforms:

sine	square
sawtooth	noise
triangle	dc
Control over these signals includes:
frequency,
amplitude, and
phase.

Signals can (with Option 001) be combined by summation and/or modulation. The modulation formats are:

AM	DSB
FM	pulse

@M

Long, complex sequences can (with Option 001) be output based on:

tones

DTMF (Dual Tone Multi Frequency) digital

Channel A can (with Option 003) be phase-continuous fast-hopped with external control of:

timing

frequency

amplitude phase

All of the above signal combinations can (with Option 002) be output to a second port. The output ports can be single-ended or floating.

How Waveforms Are Generated

Waveforms are generated by a numerical synthesis technique. The heart of the synthesizer is a single digital waveform synthesis integrated circuit (DWSIC). For each channel, the DWSIC generates a continuous stream of numbers which represent instantaneous levels of the waveform. This "digital" waveform is then converted to an analog signal by a digital-to-analog converter or DAC (one converter for each output port). The analog signal is conditioned by high-performance (but conventional) analog circuitry and routed to the output connector. The conditioning circuits include a sample-and-hold to remove DAC switching noise, filters to remove quantization noise (that is, smooth the transitions between samples from the DAC), amplifiers to boost the maximum output, and attenuators to increase the outputs dynamic range.

Figure 8-1 is a conceptual block diagram of the simplest configuration of the instrument-one without Options 001, 002, or 003. The blocks indicate conceptually how tlie data is handled.

Principles of Operation (Overall) 8-15