Automatic gain control circuit and control method

An automatic gain control circuit capable of receiving a pair of input signals and a pair of reference signals, comprising:

• a variable gain amplifier for amplifying said pair of input signals to produce a pair of amplified signals according to a gain, wherein said gain is variable;
• a filtering circuit for filtering said pair of amplified signals to produce a pair of output signals;
• a first differential comparator for comparing a first difference of said pair of output signals and a difference of said pair of reference signals to produce a first compare result signal;
• a second differential comparator for comparing a second difference of said pair of output signals and said difference of said pair of reference signals to produce a second compare result signal;
• an OR-gate for performing an OR operation between said first compare result signal and said second compare result signal to produce a combined compare result signal;
• and
• a charge/discharge circuit for converting said combined compare result signal to a control signal that controls said gain of said variable gain amplifier.

A method for controlling a gain of a variable gain amplifier, comprising the steps of:

• amplifying a differential input signal according to said gain to produce an amplified signal, wherein said gain is variable;
• transforming said amplified signal to produce a plurality of output signals;
• and
• comparing said plurality of output signals to a plurality of output signals differentially to produce a control signal that controls said gain.