[sdiy] TZ triangle core

[David G. Dixon]

> I don't get it. Where does the modulation go, ie where is the 
> multiplier?

In the loop.  The Linear FM circuit is a balanced modulator (four-quadrant
multiplier) made up of two linearized 2164s.  The (optionally inverted)
triangle is driving two comparators with opposite inputs (each limited with
separate zener circuits), and each zener-limited comparator output is
dropped across a resistor and fed into one side of the modulator.  By using
two comparators (LM319), I didn't have to invert anything by converting
currents to voltages, which is slow.  Only currents are going around the
loop at virtual ground.  Also, with the balanced modulator, I easily get
voltage-controlled time reversal (a la the "Zeroscillator").  Also, because
one input of each comparator is grounded, I obtain variable sync simply by
spiking it.