ECE4371, Fall, 2009. Zhu Han Department of Electrical and Computer Engineering Class 6 Sep. 10 th , 2007. FM Modulator and Demodulator. FM modulator Direct FM Indirect FM FM demodulator Direct: use frequency discriminator (frequency-voltage converter) Ratio detector
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Department of Electrical and Computer Engineering
Sep. 10th, 2007
30 MHz output. X3 (x5)
C1:100pF, L1:2.7μH. D:1N914
L2:.22μH, L3:1.8μH, L4:330μH
so(t) linear with m(t)
(a) Block diagram for a PLL FM demodulator; (b) PLL FM demodulator using the XR-2212 PLL
Nonlinear Effects in FM Systems
1.Strong nonlinearity, e.g., square-law modulators ,
hard limiter, frequency multipliers.
2.Weak nonlinearity, e.g., imperfections
Nonlinear input-output relation
An FM system is extremely sensitive to phase nonlinearity.
Common types of source: AM-to-PM conversion
A: low power
B: high distortion
C: need a filter
but narrow band
FM Stereo Multiplexing
For non-stereo receiver