FSK_MODEM

FSK MODEM – FSK1
FSK Signal – Time Domain
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Signal 1

Signal 2

S(t) = cos(2π*fo*t + Data*Kvco*2 π *t + Φ)

Pg 1 October 11

FSK MODEM – FSK2
FSK Signal – Frequency Domain
S(f) = ΣSinc((fo+Data*Km) – f)/T)
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Pg 3 October

FSK MODEM – FSK3

FSK Signal – Modulation

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Filter

VCO

PA

11

FSK MODEM – FSK4
FSK Signal – Demodulation1
R(t) = cos(2π*fo*t + Data*Kvco*2 π *t + Φ) + No C(t) = cos(2π*fc*t + α) Sl(t) = R(t)*C(t) = cos(2π*?f*t + Data*Kvco*2 π *t + θ) + No + HF After Low Pass Filtering,
DES(t) = cos(2π*?f*t + Data*Kvco*2 π *t + θ) + N
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Pg 4 October 11

Pg 5 October

FSK MODEM – FSK5

FSK Signal – Demodulation2

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11

FSK MODEM – FSK6
FSK Signal – Demodulation3
R(t) = cos(2π*fo*t - Data*Kvco*2 π *t + Φ) + No C(t) = cos(2π*fc*t + α) Sl(t) = R(t)*C(t) = cos(2π*?f*t - Data*Kvco*2 π *t + θ) + No + HF After Low Pass Filtering,
DES(t) = cos(2π*?f*t - Data*Kvco*2 π *t + θ) + N
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镜像抑制滤波是重要的 (3dB noise + image signal interference) )

Pg 6 October 11

FSK MODEM – FSK7
FSK Signal – Demodulation4
R(t) = cos(2π*fo*t + Data*Kvco*2 π *t + Φ) + No Cc(t) = cos(2π*fc*t + α) ; Cs(t) = sin(2π*fc*t + α) Si(t) = R(t)*Cs(t) = cos(Data*Kvco*2 π *t + θ) + No + HF Sq(t) = R(t)*Cs(t) = sin(Data*Kvco*2 π *t + θ) + No + HF
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After Low Pass Filtering,
DEC(t) = cos(Data*Kvco*2 π *t + θ) + N DES(t) = sin(Data*Kvco*2 π *t + θ) + N
Pg 7 October 11

Pg 8 October

FSK MODEM – FSK8

FSK Signal – Demodulation5

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11

FSK MODEM – FSK9
FSK Signal – Demodulation6
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零中频解调: 零中频解调: 1)电路简洁 ) 2)滤波器容易设计 ) 3)抗干扰能力强 ) 4)无镜像干扰 ) 5)但需要 offset cancellation )

Pg 9 October 11

Pg 10

FSK MODEM – FSK10

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Q&A

October 11


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