Only with a single chip active component (4069 IC), this circuit will convert sine to square waves without a power-source. To test some audio instruments, we can use this circuit. Device purpose: This circuit intended to pick up the a sine wave from an existing generator and then converts that wave into good square waves. This circuit doesn’t need power-source, so we can be simply connected between the device under test and a sine wave generator. C1,C2 D1 and D2 form a voltage doubler from the input sine wave that will used as powers by IC. The inverter IC1A is used to amplifies the input sine wave, the others inverters is used to delivering and squaring an output square wave of good rise and fall times and equal ratio through the entire range 20Hz-20KHz.
Notes: An input sine wave amplitude from 1V RMS onwards will give us best performances of this circuit. Output square wave amplitude is proportional to input amplitude. For good performance we need minimum sine wave input amplitude of 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. The minimum input threshold can be lowered by substituting the two silicon diodes with germanium types (e.g. AA118, AA119)