# FM Demodulation v out kdkd fdfd f in Frequency Discriminator f d, k d v out f in.

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FM Demodulation v out kdkd fdfd f in Frequency Discriminator f d, k d v out f in

Phase Locked Loop VCO f 0, k o,  f 0 FM in LPF ~ 5 Hz Phase Error: v PM “Average” Phase Error Phase Demodulation

Phase Locked Loop VCO f 0, k o,  f 0 FM in LPF ~ 15 KHz v FM Frequency Demodulation

Slope Detection FM IN = f c +  f(t) fcfc ff AM Detector v FM

Balanced Slope Detector FM IN fcfc ff AM Detector v FM fcfc ff AM Detector + _

k C p L p CcCc LsLs +V1_+V1_ _V2+_V2+ CsCs R DC RFC + V p @  _ R DC + V out = |V A | – |V B | (2) _ VAVA VBVB |V A | V A = V p + V 1 = V p + V s /2 (1a) V B = V p + V 2 = V p – V s /2 (1b) |V B | Foster Seeley Discriminator Analysis V s = V 1 – V 2 V 1 = V s /2 V 2 = -V s /2 VpVp Redraw secondary circuit for Analysis @  High Frequencies Low Frequencies

Find secondary voltage (V s ) as a function of Primary Voltage (V p ). LsLs CsCs R DC /2 V i = V p k(n s /n p ) R DC /2 +_+_ QuXTQuXT LsLs CsCs +_+_ XT/QsXT/Qs +VS_+VS_ Can neglect for high Q s Cannot neglect, or denominator will go to zero at resonance Simplify Secondary Circuit for RF: +VS_+VS_

LsLs CsCs +_+_ XL/QsXL/Qs +VS_+VS_ V i = V p k(n s /n p ) (2) V out = |V A | – |V B |

VpVp V s /2 -V s /2 VAVA VBVB VsVs

Ratio Detector k C p L p CcCc LsLs CsCs R DC RFC + V p @  _ R DC V out VpVp

Quadrature/Coincidence Detectors FM IN v out

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