6.8: Frequency Divider

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A frequency divider is a module that reduces the frequency of a signal. There are three main types of frequency dividers: those that work with square waves and those that work with sinusoidal signals. The square wave dividers are much simpler. A divide-by-\(2\) square wave divider is shown in Figure \(\PageIndex{1}\). The square wave input can be produced from a sinusoidal signal using zero-crossing detection or a high-gain circuit with saturating levels.

Figure \(\PageIndex{1}\): Digital frequency divider with the waveforms shown for a divide-by-\(2\) divider.

Figure \(\PageIndex{2}\): Regenerative frequency divider.

One type of analog frequency divider is the regenerative frequency divider shown in Figure \(\PageIndex{2}\). The key element of this circuit is the mixer, which here produces an output at the difference frequency of the input at frequency \(f_{i}\) and the signal is fed back at frequency \(f_{x}\). The output of the mixer is the lowpass filtered difference of \(f_{i}\) and \(f_{x}\). The loop stabilizes to produce the divided frequency at the output.

Another analog frequency divider, called a locked-oscillator frequency divider, uses injection locking of an oscillator [35]. It is relatively easy to lock many oscillators by injecting a signal near the \(n\)th harmonic of the free-running oscillation frequency. Then the oscillation frequency shifts and the output has a frequency \(1/n\)th that of the input signal.

Yet another type uses flip-flops dividing the frequency of a microwave-frequency binary clock signal.