
236 Analog Circuits Cookbook
(The rf waveform here looks sinusoidal rather than square because I have
cheated slightly. The waveform shown was actually produced by an
MCI 495 which is a four quadrant multiplier, rather than by an MCI 496
with its cell of four switching transistors. But an active double balanced
modulator like the MCI 496 would of course usually be used with a tuned
tank circuit rather than with resistive loads as in Figure 8.14(c), providing
a sinusoidal output.) In contrast, if the AM modulation index is allowed to
exceed 100%, then there are sudden 180° phase changes apparent in the
rf waveform - see Figure 8.16(b) which