Overview of GPS AGC working principle

　　Automatic gain control mainly includes three parts: automatic gain control amplifier, pulse width modulation (PWM) automatic gain control and a pulse width decoder. The automatic gain control amplifier and pulse width decoder are implemented in the RF chip, and the pulse width modulation (PWM) automatic gain control is implemented in the baseband chip.

　　Its working principle is as follows: the automatic gain control amplifier is responsible for amplifying the IF signal to ensure that it is normally sampled by A/D into two digit digital signals SIGN and MAG. The duty cycle of the MAG signal reflects the amplitude of the IF signal, that is, it reflects the gain of the automatic gain control amplifier to a certain extent; The pulse width modulation (PWM) type automatic gain control controls the signal gain according to the input MAG signal (possibly the MAG signal after I | Q separation), and finally outputs a pulse width modulation signal to readjust the gain of the automatic gain control amplifier; The pulse width decoder is responsible for demodulating this pulse width modulated signal into a 5-bit binary gain control word and outputting it to each gain stage of the AGC amplifier to achieve the goal of automatically adjusting the total gain of the amplifier.

　　The AGC in the baseband is mainly used to count the number of 1 in the I and 0 MAGs. If the calculated result is greater than the set threshold value, the output gain will be increased to adjust the pulse width, which will reduce the signal gain; On the contrary, if the statistical result is less than the threshold value, the gain adjustment pulse width is reduced to increase the signal gain.

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