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Phase-locked-loop tone decoder

LM567 Internal Circuitry

Explore the internal circuitry and functional stages of LM567.

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Inside LM567

Oscillator, phase detection and a filtered output in one compact IC.

LM567C functional cutaway showing a VCO with timing pins 5 and 6, I/Q phase detection from input 3, loop filter 2, output filter 1 and open-collector output 8.
Original functional explanation of the PLL; transistor-level implementation is simplified.

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Select a stage to see its role and connections

Generate a local reference

R1 and C1 set the VCO timing near the desired tone.

Compare phase and amplitude

I/Q detector paths identify the signal and close the filtered control loop.

Drive the collector

The output filter controls the detection response before the transistor sinks pin 8.

Component view