Dynamic AC-Coupled DC Offset Correction

• US 20120238231A1
• Filed: 05/02/2012
• Published: 09/20/2012
• Est. Priority Date: 05/21/2004
• Status: Abandoned Application

• Current Assignee: Realtek Semiconductor Corp.
• Original Assignee: Realtek Semiconductor Corp.
• Inventors: Aytur, Turgut
• Application Number:
  US13/461,981
• Publication Number:
  US 20120238231A1
• Time in Patent Office: Days
• US Class Current: 455/296
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A method, using an AC-coupled filter, reduces DC offset in a downconverted signal in a wireless receiver receiving a signal including a preamble, the method including: changing the corner frequency of the AC-coupled filter a plurality of times during reception of the preamble. In another implementation, a receiver includes a DC offset correction system. The receiver includes a mixer downconverting a received signal to form a downconverted signal; a first AC-coupled high pass filter having an input in at least one-way data communication with the mixer, the first AC-coupled high pass filter having a switchable corner frequency dependent on a frame state of a received signal; and a plurality of second AC-coupled high pass filters coupled to an output of the first AC-coupled high pass filter, each of the plurality of second AC-coupled high pass filters have a switchable corner frequency.

Claims

1. A method, using an AC-coupled filter, of reducing DC offset in a downconverted signal in a wireless receiver receiving a signal including a preamble, the method comprising:

changing the corner frequency of the AC-coupled filter a plurality of times during reception of the preamble.

2. The method of claim 1 wherein the AC-coupled filter is a high pass filter, and changing the corner frequency of the AC-coupled filter a plurality of times during reception of the preamble comprises changing the corner frequency to a succession of lower frequencies.

3. The method of claim 2 wherein the preamble includes periodic components and the corner frequencies are changed within a period of at least one of the periodic components.

4. The method of claim 3 wherein the number of corner frequencies is at least two times the number of periodic components in the preamble.

5. The method of claim 1 wherein the signal includes frames, at least some of the frames being preceded by a preamble, the receiver receiving a plurality of preambles over time, and the method further comprises changing the corner frequency of the AC-coupled filter a plurality of times during reception of each preamble.

6. A receiver including a DC offset correction system, comprising:

a mixer downconverting a received signal to form a downconverted signal;

a first AC-coupled high pass filter having an input in at least one-way data communication with the mixer, the first AC-coupled high pass filter having a switchable corner frequency dependent on a frame state of a received signal; and

a plurality of second AC-coupled high pass filters coupled to an output of the first AC-coupled high pass filter, each of the plurality of second AC-coupled high pass filters 20 having a switchable corner frequency dependent on the frame state of the received signal.

7. The DC offset correction system of claim 6, wherein the plurality of second AC-coupled high pass filters are parallel high pass filters.

8. The DC offset correction system of claim 6, wherein each of the filters comprises a capacitance in series with a 30 resistance, with a switch controlling the magnitude of the resistance.

9. A method for correcting DC offset in a wireless receiver, the method comprising:

high pass filtering a downconverted signal to substantially reduce signal components below a first frequency during a first time period;

high pass filtering the downconverted signal to substantially reduce signal components below a second frequency during a second time period; and

high pass filtering the downconverted signal to substantially reduce signal components below a third frequency during a third time period.