Transmit amplitude independent adaptive equalizer

1. An equalizer, comprising:

a variable gain amplifier coupled to an input signal from a transmission medium and a variable gain control signal that applies a variable gain to the input signal to generate an equalizer core input signal having a pre-determined, fixed signal swing;

a variable gain amplifier control loop coupled to the input signal and the equalizer core input signal that compares the input signal with the equalizer core input signal and generates the variable gain control signal; and

an equalizer core coupled to the equalizer core input signal that applies a frequency dependant gain to the equalizer core input signal to compensate for attenuation of the input signal caused by losses incurred in the transmission medium;

wherein the variable gain amplifier control loop comprises:

a first filter coupled to the input signal that filters the input signal to a frequency range at which the input signal incurs minimal attenuation from the transmission medium and generates a first low-frequency signal;

a fixed-swing slicer coupled to the equalizer core input signal that converts the equalizer core input signal into a digital signal having the pre-determined, fixed signal swing; and

a second filter coupled to the digital signal that filters the digital signal to the frequency range at which the input signal incurs minimal attenuation from the transmission medium and generates a second low-frequency signal;

wherein the first and second low-frequency signals are processed to generate the variable gain control signal.

2. The equalizer of claim 1 , wherein the variable gain amplifier control loop comprises:

a received data swing control detect circuit coupled to the input signal that detects a first energy level in the input signal and generates a first energy-level output; and

a core input swing detect circuit coupled to the equalizer core input signal that detects a second energy level in the equalizer core input signal and generates a second energy-level output;

wherein the first and second energy-level outputs are compared by the variable gain amplifier control loop to generate the variable gain control signal.

3. The equalizer of claim 2 , wherein the variable gain amplifier control loop further comprises:

an adder coupled to the first and second energy-level outputs that generates the variable gain control signal.

4. The equalizer of claim 1 , wherein the variable gain amplifier control loop further comprises:

a plurality of envelope detectors that determine energy levels in the first and second low-frequency signals, wherein the energy levels in the first and second low-frequency signals are compared to generate the variable gain control signal.

5. An equalization method, comprising:

applying a variable gain to an input signal received from a transmission medium to generate

an equalizer core input signal having a pre-determined, fixed swing;

comparing the input signal with the equalizer core input signal by: (i) filtering the input signal to a frequency range at which the input signal incurs minimal attenuation from the transmission medium and generates a first low-frequency signal; (ii) converting the equalizer core input signal into a digital signal having the pre-determined, fixed swing; (iii) filtering the digital signal to the frequency range at which the input signal incurs minimal attenuation from the transmission medium and generates a second low-frequency signal; and (iv) processing the first and second low-frequency signals to generate a variable gain control signal;

adjusting the variable gain based on the variable am control signal; and

applying a frequency dependant gain to the equalizer core input signal to compensate for attenuation of the input signal caused by losses incurred in the transmission medium.

6. The method of claim 5 , wherein the comparing the input signal with the equalizer core input signal comprises:

detecting a first energy level in the input signal and generating a first energy level output;

detecting a second energy level in the equalizer core input signal and generating a second energy level output; and

comparing the first and second energy level output signals to generate the variable gain control signal.

7. The method of claim 5 , wherein the comparing the input signal with the equalizer core input signal comprises:

envelope detecting to determine energy levels in the first and second low-frequency signals.

8. An equalizer, comprising:

means for applying a variable gain to an input signal received from a transmission medium to generate

an equalizer core input signal having a pre-determined, fixed swing;

means for comparing the input signal with the equalizer core input signal by (i) filtering the input signal and generating a first low-frequency signal; (ii) converting the equalizer core input signal into a digital signal having the pre-determined, fixed swing; (iii) filtering the digital signal and generating a second low-frequency signal; and (iv) processing the first and second low-frequency signals to generate a variable gain control signal;

means for adjusting the variable gain based on the variable gain control signal; and

means for applying a frequency dependant gain to the equalizer core input signal to compensate for attenuation of the input signal caused by losses incurred in the transmission medium.

9. The equalizer of claim 8 , wherein the means for comparing comprises:

means for detecting a first energy level in the input signal and generating a first energy level output;

means for detecting a second energy level in the equalizer core input signal and generating a second energy level output; and

means for comparing the first and second energy level output signal to generate the variable gain control signal.

10. An equalizer processing device, comprising:

a variable gain amplifier coupled to an input signal from a transmission medium and a variable gain control signal that applies a variable gain to the input signal to generate an equalizer core input signal having a predetermined, fixed signal swing;

a first signal processing circuit that receives the input signal and generates a first control signal;

a second signal processing circuit that receives the equalizer core input signal and generates a second control signal, the second signal processing circuit comprising a slicer configured to receive the equalizer core input signal and generate a sliced signal; a bandpass filter configured to receive the sliced signal and bandpass filter the sliced signal to generate a bandpass filtered sliced signal; and an envelope detector configured to receive the bandpass filtered sliced signal and generate the second control signal; and

a third signal processing circuit that receives the first and second control signals and generates the variable gain control signal from the first and second control signals.

11. The equalizer processing device of claim 10 , further comprising:

an equalizer core coupled to the equalizer core input signal that applies a frequency dependant gain to the equalizer core input signal to compensate for attenuation of the input signal caused by losses incurred in the transmission medium.

12. The equalizer processing device of claim 10 , wherein the first signal processing circuitry comprises:

a bandpass filter configured to receive the input signal and bandpass filter the input signal to generate a bandpass filtered input signal; and

an envelope detector configured to receive the bandpass filtered input signal and generate the first control signal.

13. The equalizer processing device of claim 10 , wherein the third signal processing circuitry comprises:

a summing circuit configured to receive the first and second control signals and generate the variable gain control signal.