Ugly Sawtooth Generator

By cross-coupling a NPN and PNP transistor, the equivalent of a Silicon Controlled Rectifier (SCR) can be formed. This SCR lends itself to sawtooth waveform generation. Except that operating the transistors as a SCR apparently induces reverse-mode avalanche operation, and in bipolar form, where currents in two directions compete for a brief instant. The waveshape during the sawtooth retrace period was very fast, but it was not linear at all. It was very ragged, such that with closer inspection using my 60 MHz digital scope, I could see harmonic undulations well into VHF frequencies. So, this circuit is probably adaptable to a RF frequency multiplier application, but it would make horrible in-band periodic noise for audio.



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