|C||�||2 4||�||2 4||1 2||f||�||1||�||10||�||103||
|T||2 4||�||2 4||2 π||
|6 28 2||�||1 2|
|C||�||3||�||3||�||1 5||pF||f||�||10||1 5||�||92||MHz|
|T||3||�||3||6 28 2||�|
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
|FM input||Phase||(f1 – f2)||Low-pass|
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
|R4 no detector|
Figure 19.18 : Commonly used circuit for FM demodulation