Single-chip Frequency Doubler
Created: Nov 06, 2014
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A frequency doubler is a non-linear device that effectively produces an output signal that is twice the frequency of the input signal. The frequency doubler uses only a single integrated circuit. Like other doublers, this circuit uses both the rising and falling edges of the input signals to produce digital pulses, thus effectively doubling the input's frequency.
Without the RC networks at U1 inputs, U1 would not produce any output pulses. However, the RC networks delay one edge with respect to the other. The A input lags the B input for positive-going edges, and the B input lags the A input for negative-going ones. You can vary the output duty cycle from 0 to 100% by varying R3. U1's minimum output pulse width defines the maximum frequency of this circuit.
Frequency doublers are often used in frequency synthesizers and communication circuits. It is also used in nonlinear optics.