Fabrication of modulation and demodulation circuit

The manufacture of modulation and demodulation circuit

1、 background

Sounds like this k Low frequency signal of level , Not directly transmitted as an electrical signal , This low-frequency signal needs to be converted into a high-frequency electrical signal through modulation . The process of restoring the modulated signal to the original signal is called demodulation .

2、AM modulation

The following figure Vs Is a modulated wave ,Vc As carrier , The amplitude of the modulated wave shall not exceed the amplitude of the carrier wave ,Vs/Vc The size of is the modulation depth .

Example of modulation and demodulation circuit design ：

1、 Modulation circuits

1> Resistance modulation circuit , The amplitude of the carrier signal is changed by the resistance of the load , So there's an envelope .

The modulated waveform is shown in the figure below

1、 Capacitance modulation circuit , The amplitude change of the carrier signal is realized by changing the capacitance of the parallel resonance .

2、 Design of demodulation circuit

  Schematic diagram of demodulation part

The figure above shows an example of wireless charging carrier communication , Load modulation at the receiving end , Demodulate at the transmitter , Demodulation is mainly divided into diode envelope detection , The same direction amplifier circuit , Comparison circuit , this 3 Part of the circuit .

1、 Diode envelope detection circuit

diode D4 Do half wave rectification , then R3,C3 Low pass filtering , Reduce the amplitude of the carrier signal .

2、 Amplification circuit

Go first U1A Follow , Reduce the output impedance , After following, it goes through a low-pass filter , Further reduce the amplitude of the carrier signal , then U1B Here, zoom in the same direction , Note that there is a capacitor at the reverse end , The purpose is to amplify only the AC signal , Do not amplify the DC signal , DC still follows the partial voltage before . Note that the same direction amplifier here can be modified to the common base amplifier circuit we mentioned .

3、 Comparison circuit

The comparison circuit here is different from the way we usually use the benchmark to intercept and compare .