AC coupling circuit integrated with receiver with hybrid stable common-mode voltage generation and baseline-wander compensation

• US 20080063091A1
• Filed: 12/06/2006
• Published: 03/13/2008
• Est. Priority Date: 09/08/2006
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: LSI Corporation (Broadcom, Inc.)
• Inventors: Dong, Yikui (Jen), Liu, Cathy Ye, Zhong, Freeman Yingquan, Hsu, Shao Ming
• Granted Patent: US 7,961,817 B2
• Time in Patent Office: Days
• US Class Current: 375/257
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection

Abstract

In a receiver, an AC-coupling solution uses a fully integrated circuit for simultaneously providing both baseline wander compensation and common-mode voltage generation. Usefully, an integrated capacitor is placed between the receiver input pin and the input buffer, and a high resistive impedance element is connected to the internal high-speed data node after the capacitor. An on-chip voltage generation and correction circuit is connected to the other side of the impedance element to generate a common-mode voltage, and to provide dynamic, fine adjustment for the received data voltage level. The voltage correction circuit is controlled by the feedback of data detected by the clock and data recovery unit (CDRU) of the receiver. The feedback data passes through a weighting element, wherein the amount of feedback gain is adjustable to provide a summing weight and thereby achieve a desired BLW compensation. Register bits are used to control an on-chip reference voltage generator that consists of a resistor ladder to generate the reference voltage.

Claims

1. In association with a receiver having an input signal, an input signal compensation circuit comprising:

a first feedback loop adapted to receive a feedback signal, corresponding to data detected from said receiver input signal, and further adapted to generate a baseline wander correction component in response to said feedback signal;

a second feedback loop configured to generate a common-mode voltage related to a selected reference voltage associated with said receiver input signal; and

a mechanism for combining said baseline wander correction component with said common-mode voltage, for use in providing a reconstructed correction component for said receiver input signal.

2. The circuit of claim 1, wherein:

said input signal is AC coupled to said receiver, and said reconstructed component provides compensation for interference comprising baseline wander (BLW).

3. The circuit of claim 2, wherein:

a selected capacitor element is used to AC couple said input signal to said receiver, and is also used in a low pass filter operable to provide said feedback signal for said first feedback loop.

4. The circuit of claim 1, wherein:

said receiver input signal comprises a differential input having positive and negative components, and an associated common-mode voltage.

5. The circuit of claim 1, wherein:

said feedback signal is in digital form.

6. The circuit of claim 5, wherein:

said first feedback loop further comprises one or more switches, wherein each of said switches is operated by said digital feedback signal to generate a pulsed current that represents said feedback signal, and further represents a selected gain adjustment to compensate for baseline wander in said receiver input signal.

7. The circuit of claim 6, wherein:

said first feedback loop is provided with a BLW compensation gain control to supply a current i_blwc, wherein the current i_blwc is disposed to flow through said switches when said switches are respectively closed by said feedback signal, in order to generate said pulsed current.

8. The circuit of claim 6, wherein:

said combining mechanism includes a summer for combining said pulsed current with a current supplied by said second feedback loop that represents said common-mode voltage.

9. The circuit of claim 8, wherein:

said second feedback loop comprises a comparator and a dynamic common-mode current injection device connected to receive the comparator output, and to supply current that represents said common-mode voltage in response to said comparator output.

10. The circuit of claim 9, wherein:

said reference voltage is connected as a first input to said comparator, and a compensation component is connected as a second input to said comparator, wherein said compensation component is derived using said current combined by said summer.

11. The circuit of claim 1, wherein:

said receiver includes a data compressor to convert parallel-form data into serial-form data, in order to provide said low frequency feedback signal for said first feedback loop.

12. The circuit of claim 1, wherein:

said receiver comprises a high frequency receiver, and said receiver and said compensation circuit are respectively integrated into a common integrated circuit.

13. For use in a receiver disposed to receive a transmitted input signal affected by baseline wander (BLW) during transmission, circuit apparatus comprising:

a circuit component configured to generate a feedback signal representing data contained in said receiver input signal;

a first set of circuit elements operable by said feedback signal to produce a first signal provided with a BLW compensation value;

a second set of circuit elements for generating a second signal representing a common-mode voltage adaptable to said receiver; and

a circuit component for producing a component from said first and second signals, and for combining said component with said receiver input to compensate said signal for BLW effects.

14. The apparatus of claim 13, wherein:

said receiver and said apparatus are contained in a common integrated circuit (IC), and said receiver input is AC-coupled to said receiver by means of a capacitor contained in said common IC.

15. The apparatus of claim 13, wherein:

said first set of circuit elements comprises a BLW compensation gain control, and one or more switches operable by said feedback signal to generate a pulsed current that represents a selected gain adjustment to compensate for baseline wander in said receiver input signal.

16. The apparatus of claim 13, wherein:

said second set of circuit elements comprises a reference voltage generator, a comparator and a dynamic common-mode current injection device connected to receive the comparator output, and to supply current that represents said common-mode voltage in response to said comparator output.

17. In association with a receiver having an input signal, a method comprising the steps of:

receiving a feedback signal corresponding to data contained in said receiver input signal;

generating a baseline wander correction component in response to said feedback signal;

generating a common-mode voltage related to a selected reference voltage associated with said receiver input signal; and

combining said baseline wander correction component with said common-mode voltage, in order to provide a reconstructed compensation component for said receiver input signal.

18. The method of claim 17, wherein:

said input signal is AC coupled to said receiver, and said reconstructed component provides compensation for interference comprising baseline wander.

19. The method of claim 17, wherein:

said low frequency digital feedback signal is used to generate a pulsed current that represents said feedback signal, and further represents a selected gain adjustment to compensate for baseline wander in said receiver input signal.

20. The method of claim 19, wherein:

said pulsed current is combined with a current that represents said common-mode voltage, in order to provide said compensation component.