Frequency doubler operates on triangle waves
Frequency multipliers typically work with square waves. However, the circuit in Figure 1 performs frequency multiplication on triangle waveforms and maintains the input’s amplitude and uniformity.
The general idea is to apply the triangle waveform to any full-wave rectifier. The output is then a triangle wave with twice the input frequency plus some dc bias. You then can remove the dc bias using a simple highpass filter or by shifting the bias level with another op amp. You can continually repeat this trick to obtain a frequency series of 2×FIN, 4×FIN, 8×FIN, and so on.
The actual circuit in Figure 1 uses a single-supply, dual op amp to help perform the rectification. When the input is the negative half-wave signal, IC1A works as a regular inverting amplifier which R1 and R3 set to a gain of 2. The circuit then produces the algebraic sum, with a coefficient of 0.5, of the positive output signal of IC1A and the negative input signal at summing-point A. After IC1B amplifies the signal by 4, according to the values of R5 and R6, the output signal has the same peak-to-peak amplitude as the input, but with a positive sign.
Tags: Frequency Doubler, Square wave Generator
