Agilent Technologies 2712A, 2948 manual Further Digital Waveform Processing with Options

Model 8904A Service

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4BITS

5BITS

6BITS

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Figure 8-5.The Output of the WaveformTable with Data Bus Widths of 4, 5, and 6 Bits

With a four-bit data bus, the poor resemblance to a sine wave is apparent. With only four-bit quantization, the resolution is very coarse. A vast improvement is made by increasing the number of quantization states by increasing the width of the data buses. Examples of 5 and 6 bit data buses are also illustrated in Figure 8-5.In the instrument, the bus width used in the DWSIC is actually 12 bits; the total number of quantization levels is 212=4096.

Controlling Amplitude

The Amplitude Multiplier scales (by digital multiplication) the amplitude of the waveform data by the factor on the AM Data bus, thus controlling the signal level. For CW outputs the scaling covers a 2:l range. Further level control occurs in the analog output circuitry.

Further Digital Waveform Processing with Options

Thus far, all data inputs have been assumed to be constants which control frequency, phase, and amplitude. In practice the data inputs may vary with time and thus modulate the waveforms. This feature requires Option 001. In the Fkequency Adder, the Frequency Data is held constant to set the CW frequency; the FM Data can be varied to generate FM. In the Phase Adder, QM Data is varied to generate QM. In the Amplitude Multiplier, the AM Data is held constant to set the CW level or it can be varied .about the level constant to generate AM.

In addition to modulation, waveforms from other channels can be summed (digitally, of course) with channel one to create waveforms of specific shapes and characteristics. Implementation of these additional capabilities is illustrated in Figure 8-6.

Figure 8-6also shows a second output channel which is included as Option 002. If Option 002 is added without Option 001, any of the six basic waveforms can be generated at the second output independent of the first output, but neither output can be modulated or summed.

Principles of Operation (Overall) 8-19