A simple digital mixer, based on two dual-Schmitt triggers (4583B) and three exclusive-OR gates, uses an RC time-delay circui
t to permit easy adjustment of the output-signal pulse width. The exclusive-OR gates can also be used separately as a symmetrical frequency doubler. As shown, a signal passing through the Schmitt triggers is delayed by t, a value equal to RC In (y#/ Vtâ€ž), where V^ and Vin are the positive and negative threshold voltages of the triggers. To function properly, the same time delay must be introduced to signals f1 and f2. Also, the time delay must be less than 50% of the period of fl. Provided that fl is more than twice the value of f2, the output of the circuit will equal the difference of the two signals (i.e., fl-f2).