Demodulation of AM signal

1
Demodulation of AM signal

• The envelope detector is a very simple method of
  demodulation

2
Envelope Detector

• Main advantage very simple and cheap. However, it
  does suffer from some practical problems.

3
Envelope Detection

• The operations of the circuit requires careful
  selection of tRC
• If RC is too large, discharging will be slow and
  the circuit cannot follow a decreasing envelope.
• When RC is too small the ripples will be high.
• 1/(2pB) ltlt t ltlt 1/wc
• The ripples are finally removed by LPF.
• The DC value is blocked by a capacitor.

4
RC value
5
RC value
6
Envelope Detector
To overcome problem, make sure
m - index modulation ?m modulating signal
frequency
Pemodulatan Amplitud
7
Demodulation AMDSB-FC
(ii) DSBFC Square Law
Remove DC
DC
Modulating signal
Harmonic signal
Final Output
8
Demodulation of DSBSC

• The modulator circuits can be used for
  demodulation, but replacing the BPF by a LPF of
  bandwidth B Hz.
• The receiver must generate a carrier frequency in
  phase and frequency synchronization with the
  incoming carrier.
• This type of demodulation is therefore called
  coherent demodulation (or detection).

9
Synchronous
DSBSC DEMOD

• Signal local carrier should be synchronous with
  information signal from transmitter.

Analisa matematik
10
Mathematic

• Multiplier output
• Identiti trigonometri
• Hence
• Final Output