How Digital Public Address Amplifier Work

Digital public address amplifier has the advantages of small size, light weight and high efficiency.

Digital public address amplifier can be divided into four parts: signal modulator, PWM driving signal, switching amplifier circuit and demodulation filtering output according to its composition structure. The signal flow is as follows:

Audio signal → signal modulation → PWM driving signal → switching amplifier circuit → demodulation filtering output → amplified audio signal

1. Signal modulation: 

The function of signal modulation is to convert audio signal into PWM signal. The audio signal is compared with the fixed frequency triangular wave signal to realize PWM modulation. The advantage of this modulation method is that the carrier frequency is fixed, and the design of audio restoration filter at the output end is simple.

2. PMW driving signal: 

The drive signal of the digital amplifier is mainly used to drive the MOS tube. For the power amplifier of different power levels, it is necessary to select the drive circuit reasonably.

3. Switching amplifier circuit: 

The power amplifier circuit of digital public address amplifier has only two topologies: full bridge and half bridge. There are two MOS transistors on each bridge arm of the switching amplifier circuit, which can't be on at the same time. One MOS transistor must be switched off after the other is switched on, otherwise it will cause the crosstalk loss and even burn out the power transistor. Therefore, the drive signal must be inserted in the dead time (Dead-Time) to ensure that the same bridge arm of the two power tubes are not on at the same time in the on state.

4. Demodulated filter output: 

The signal passing through the switch amplifier circuit contains both audio signal information and carrier signal.

The input analog audio signal and the feedback audio signal are sent to the error amplifier, and the amplified error audio signal is output. The triangular wave generator generates analog triangular wave signal. The amplified error signal and triangular wave signal are sent to the modulator to output PWM signal.