
78 Analog Circuits Cookbook
When the output of a generator is to be used as the local oscillator drive
for a frequency converter, the waveshape is usually unimportant, a square-
wave will do as well as a sinewave. This means in the case of a DDS that
the AM noise floor or discrete AM spurs mentioned earlier are of no
consequence; as far as the local oscillator signal is concerned a mixer
normally works way into saturation and any small variations of drive level
have no effect. However, with truncation effects present, this is no longer
the case, neither the upper trace in Figure 3.13 nor yet the lower would be
a suitable drive for a mixer, assumin ...