Implementation of a two-stage digital AGC for spectrum analyzer

A new digital Automatic gain control (AGC) circuit with two-stage gain adjustment is proposed in this paper. This AGC circuit is designed as part of an intermediate frequency (IF) processing circuit in the spectrum analyzer. The first stage controls the gain in 20 dB Steps and improves the measurement range of the RMS detector, while the second stage controls the gain in 3 dB Steps and gets a precise output signal. The gain of the two stages of amplifier is coordinated by a gain control logical module. Simulations for the control algorithm are implemented; the results show this control algorithm has some advantages in aspects of rapidity and astringency. Due to the large available gain provided by two-stage gain adjustment, a large controllable input range can be obtained. Experimental results show that the detectable range of this AGC circuit is -105 dBm to 18 dBm at a 60 MHz IF frequency.