Adaptive equalizer filter with variable gain control

An adaptive equalizer circuit comprising a variable gain control circuit comprising:

• a pair of diode connected transistors comprising a first transistor M6 and a second transistor M5 coupled together in a common mode rejection configuration, wherein said first transistor M6 is capable of receiving an input current signal that is proportional to a first scale factor that has a value between zero and one, and wherein said second transistor M5 is capable of receiving an input current signal that is proportional to a second scale factor that has a value that is equal to one minus said first scale factor;
• a first differential amplifier comprising a third transistor M1 and a fourth transistor M2, said first differential amplifier coupled to said pair of diode connected transistors and capable of receiving a first control voltage Vp from said first transistor M6 at a gate of said third transistor M1 and capable of receiving a second control voltage Vn from said second transistor M5 at a gate of said fourth transistor M2;
• a second differential amplifier coupled in parallel to said first differential amplifier, said second differential amplifier comprising a fifth transistor M3 and a sixth transistor M4, said second differential amplifier coupled to said pair of diode connected transistors and capable of receiving said first control voltage Vp from said first transistor M6 at a gate of said fifth transistor M3 and capable of receiving said second control voltage Vn from said second transistor M5 at a gate of said sixth transistor M4;
• wherein said first differential amplifier is capable of rejecting common mode signals in an input current equal to IH2(f)+Ibias from a second filter circuit of said adaptive equalizer circuit and providing an output current equal to alpha times said input current IH2(f)+Ibias where alpha is equal to said first scale factor;
• and
• wherein said second differential amplifier is capable of rejecting common mode signals in an input current equal to a bias current Ibias used to bias said second filter circuit of said adaptive equalizer circuit and providing an output current that is equal to (1−α) times said bias current Ibias where alpha is equal to said first scale factor.

A method for providing variable gain control in an adaptive equalizer circuit comprising the steps of:

• coupling together a pair of diode connected transistors comprising a first transistor and a second transistor in a common mode rejection configuration, wherein said first transistor is capable of receiving an input current signal that is proportional to a first scale factor that has a value between zero and one, and wherein said second transistor is capable of receiving an input current signal that is proportional to a second scale factor that has a value that is equal to one minus said first scale factor;
• coupling to said pair of diode connected transistors a first differential amplifier comprising a third transistor and a fourth transistor;
• providing to said first differential amplifier a first control voltage from said first transistor and a second control voltage from said second transistor;
• coupling to said pair of diode connected transistors a second differential amplifier comprising a fifth transistor and a sixth transistor;
• providing to said second differential amplifier said first control voltage from said first transistor and said second control voltage from said second transistor;
• rejecting common mode signals in said first differential amplifier;
• providing an output current from said first differential amplifier that is proportional to said first scale factor;
• rejecting common mode signals in said second differential amplifier;
• and
• providing an output current from said second differential amplifier that is proportional to said first second factor.