Audio Engineering

884 Chapter 30

waveform, having smaller, higher frequency staircase steps, could be obtained by connecting
two or more such shift registers in series, with appropriate values of loading resistors.

Like all digitally synthesized systems, this circuit will have an output frequency stability
that is as good as that of the clock oscillator, which will be crystal controlled. Also the
output frequency can be displayed numerically and there will be no amplitude “ bounce ”
on switch on, or on changing frequency.

A more elegant digitally synthesized sinewave generator is shown in Figure 30.10. In this
the quantized values of a digitally encoded sine waveform are drawn from a data source,
which could be a numerical algorithm, of the kind used, for example, in a “ scientifi c ”
calculator, but, more conveniently, would be a ROM-based “ look-up ” table. These are





Drive

Ck Shift register

Clock input

Rs

R 7

R 6

R 8

Op. amp.

Output waveform

A 1

R 5

R 4

R 3

R 2

R 1

Figure 30.9 : Digital waveform generation.