Patent ID: 6510188
Filing Date: 2003-01-21
Classification: H03G,H04L

Abstract:
A digital automatic gain control (AGC) system having a system input and a system output, said circuit comprising:an AGC amplifier coupled to said system input, said AGC amplifier configured to scale an input signal by a scale factor, and configured to generate an analog scaled input signal; an analog-to-digital (A/D) converter coupled to said AGC amplifier, said (A/D) converter configured to sample and convert said analog scaled input signal into a digital scaled input signal; a frequency down converter coupled to said A/D converter, said frequency down converter configured to down convert in frequency said digital scaled input signal; a complex lowpass filter (LPF) coupled to said frequency down converter, said complex LPF configured to filter out at least one image of said digital scaled input signal due to sampling, configured to limit noise, and configured to generate an in phase component I of said digital scaled input signal, and a quadrature component Q of said digital scaled input signal; a power level detector circuit coupled to said complex LPF, wherein said power level detector circuit is configured to detect a power of said digital scaled input signal; a logarithmic comparison circuit (LCC) coupled to said power level detector circuit, wherein said LCC is configured to compare a log of said power of said digital scaled input signal to a predetermined reference signal and configured to generate a digital error signal; and an error processing circuit coupled to said LCC, wherein said error processing circuit is configured to process said digital error signal and configured to determine said scale factor; wherein a feedback AGC loop comprising said AGC amplifier, said analog-to-digital (A/D) converter, said frequency down converter, said complex lowpass filter (LPF), said power level detector circuit, said logarithmic comparison circuit (LCC), and said error processing circuit is closed when said scale factor is used by said AGC amplifier to scale said input signal.