• Ratio detector is another frequency demodulator circuit.

Operation and phase diagram:

• The ratio detector output voltage is equal to half of the difference between the output voltages from the individual diodes.

• Hence similar to the phase discriminator the output voltage is proportional to the difference between the individual output voltages.

• Due to this reason, the operation of the ratio detector is identical to the phase discriminator.

• The S type curve can be derived in an identical way. The phasor diagrams are also identical.

• The additional feature of the ratio detector is the amplitude limiting action which is incorporated due to the large capacitor $C_5$.

• Due to this the amplitude limiter is not required prior to the ratio detector.

• Advantages of ratio detector:

1. Easy to align.

2. Very good linearity.