Pulse Frequency Doubler
Électronique / Electronic

This is a pulse frequency multiplier with one transistor. It is called a pulse frequency doubler because it doubles the frequency of the input signal.

The operational amplifier acts as a square-wave oscillator. The output from the oscillator is an AC signal of about 500 Hz.

When you complete the wiring, set the switch to position ON to turn on the power. Connect the earphone to terminals A and A' and press the key to listen to the oscillating sound of 500 Hz. Note the pitch of the tone.

Now, connect the earphone to terminals as shown in the diagrams and press the key.

Listen through the earphone; this time you hear a sound that is an octave higher than the previous sound. This means the frequency is doubled to 1000 Hz.

Now let's see how this frequency doubler works.

Transistor Q1 receives signals from the operational amplifier through its transistor base. The base voltage changes with the oscillations.

This results in the opposite phase signals appearing at the collector and emitter-when one signal is at a wave peak, the other is at the bottom. The two outputs from transistor Q1 are applied to diodes Da and Db.

The diodes pass through only the positive portion of the waves. These two signals combine to give us the doubled frequency.








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