Usedto obtain the demodulated output

However, this text will discuss only two common types of demodulator, namely the phase-looked loop (PLL) demodulator and the ratio detector.

19.6.1 The Phase-Locked Loop Demodulator

(f2)

deviation of the system. The output from the low pass fi lter, i.e., the error voltage, is used

for FM demodulation. Receivers which use this circuit generally have a bandpass limiter

as the previous stage. This improves the fi ltering before demodulation takes place as ratio

As the frequency rises above the center frequency ( fc ), the secondary becomes more inductive and VEC shifts clockwise, as shown in Figure 19.20(b) . If the frequency falls below fc the secondary becomes more capacitive and VEC will shift anticlockwise from the 90° position. This is shown in Figure 19.20(c) . Note that in Figure 19.20 VBA�VEC remains constant as the frequency varies.

Consider a DC voltage source EX replacing the capacitor CC in Figure 19.18 . When the peak-to-peak value of the incoming signal is less than EB , D1 and D2 will not conduct and

Figure 19.18 : Commonly used circuit for FM demodulation