Micro Linear Corporation

W Richard Davis

Bing F Ma

An R-C relaxation oscillator having two comparators and a silicon controlled rectifier dissipates very low average power without resulting in frequency instabilities due to circuit propagation delays. A timing capacitor C.sub.T is charged through a timing resistor R.sub.T. The first comparator compares the voltage across the timing capacitor with an upper threshold voltage V.sub.TH. When the voltage across the timing capacitor crosses the upper threshold voltage, the comparator turns on the silicon controlled rectifier, which causes the capacitor to discharge the voltage that it has stored. The second comparator turns off the silicon controlled rectifier when the voltage across the timing capacitor falls below a lower threshold voltage V.sub.TL. The silicon controlled rectifier also provides boosted comparator bias current during the discharge phase, enabling the second comparator to respond quickly to the lower threshold voltage crossing and allowing fast capacitor discharge (therefore narrow clock pulses) and increasing frequency stability.

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W Richard Davis