R1_____________1M 1/4W Resistor
R2___________100K Linear Potentiometer
C1,C2________100΅F 25V Electrolytic Capacitors
C3____________10nF 63V Polyester Capacitor
D1,D2_______1N4148 75V 150mA Diodes
IC1___________4069 Hex Inverter IC
This circuit is intended to provide good square waves converting a sine wave picked-up from an existing generator. Its major feature consists in the fact that no power-source is needed: thus it can be simply connected between a sine wave generator and the device under test. The input sine wave feeds a voltage doubler formed by C1, C2, D1 & D2 that powers the IC. IC1A amplifies the input sine wave, other inverters included in IC1 squaring the signal and delivering an output square wave of equal mark/space ratio and good rise and fall times through the entire 20Hz-20KHz range.
* Best performances are obtained with an input sine wave amplitude from 1V RMS onwards.
* Output square wave amplitude is proportional to input amplitude.
* Minimum sine wave input amplitude needed for good performance: 750mV RMS.
* Output square wave amplitude with 1V RMS input: 3V peak to peak, with R2 set at max.
* Minimum output square wave amplitude: 2V peak to peak, with R2 set at max.
* Substituting the two silicon diodes with germanium types (e.g. AA118, AA119), the minimum input threshold can be lowered.
Source: Electronics Lab