Digital frequency multiplier (LM108, LM111)

As shown in the figure, this is a digital frequency multiplication circuit. The circuit consists of a voltage comparator, a Miller integrator, and an XOR gate. A1 is a level comparator, which is implemented by the integrated block LM111. It forms a shaping circuit to convert a waveform with a long rise time (such as a sine wave) into a square wave with a short rise time. The square wave output by A1 is transformed into a triangular wave by the Miller integrator composed of A2, R4, and C4, and then the triangular wave is converted into a square wave by the level comparator A3. There is a 90o phase difference between the output square waves of A1 and A3, so the frequency multiplication output is obtained after passing through the XOR gate DM5486. The input frequency range is 5kHz~50kHz, and the output frequency range is 10kHz~100kHz.