In electronics communication system, modulation and demodulation are processes that embeds message signal into carrier signal at the transmitter and extracts message signal from the received signal at the receiver. Because we can embed information signal in carrier signal either using amplitude, frequency or phase we have amplitude modulation, frequency modulation and phase modulation. The electronics circuit that performs modulation is called modulator and the circuit that performs demodulation is called demodulator. In this article we list various ways in which modulation and demodulation can be achieved for AM signal generation and recovery.
AM Modulator Circuits
In AM, the carrier signal amplitude is varied in accordance with the amplitude of the message signal. AM is the simplest method of embedding information signal into the carrier signal. AM modulation can be achieved using diodes, transistors or integrated circuit(IC).
Modulators/Demodulators using Diodes
Following are methods of AM modulation using Diodes:
Double Balanced Diode Ring Mixer
Modulators/Demodulators using Transistors
Modulators/Demodulators can also be designed with transistors. Following are modulators and demodulators or mixers designed with BJT and JFET.
AM modulator using BJT Transistor
Another version of this emitter modulator is shown below.
Differential Amplifier Modulator
AM modulator using JFET transistor
AM modulator design with Two JFET transistors
AM modulator circuit using Two BJT Transistor
AM Modulator using Integrated Circuit(IC)
There are many integrated circuit avilable in the market that can be used to generate AM signal using modulation and recover AM signal with demodulation. There are dedicated IC for AM modulation and demodulation such as MC1496 and there are IC for multiplication of signals which can be used AM modulation and demodulation such as AD633 or AD734.
AM modulator using MC1496 modulator for Standard AM
MC1496 Balanced Modulator for DSB-SC AM
Standard AM with AD633 Analog Multiplier IC
DSBSC Balanced Modulator Circuit
SSB Modulation Circuit using Frequency Discrimination Method
AM Demodulator Circuits
One of the simplest AM demodulator circuit is the envelope detector circuit as shown below.
Square Law Detector for Standard AM signal demodulation
Coherent Detection using Product Modulator
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