Pulse Frequency Doubler
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
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.