DC-offset compensation

• US 7,079,590 B2
• Filed: 09/06/2005
• Issued: 07/18/2006
• Est. Priority Date: 10/16/2000
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Wilhelmsson, Leif, Mattisson, Sven, Markenlöv, Peter
• Primary Examiner(s): Bayard, Emmanuel
• Assistant Examiner(s): Williams, Lawrence B.
• Application Number:
  US11/220,034
• Publication Number:
  US 20060002492A1
• Time in Patent Office: 315 Days
• Field of Search: 375/295, 375/346, 370/462, 370/342, 455/296, 702/189, 327/307, 327/362
• US Class Current: 375/295
• CPC Class Codes: H03F 3/45986 using switching means, e.g. sample and hold
• CPC Class Codes: H03K 5/003 Changing the DC level reinsertion of dc component of a television signal H04N5/16
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only
• CPC Class Codes: H04L 27/142 Compensating direct current components occurring during the demodulation and which are caused by mistuning

Abstract

A method of estimating a DC offset value of a signal includes estimating a DC offset value of a preamble part of the signal using a pair of diodes (D1, D2) and a resistor (R) connected in parallel. During receipt of the data part of the signal, the diode pair (D1, D2) is switched out of the circuit by a switch (SW). During reception of the data part, the DC level is estimated using a low pass filter (R,C).

Claims

1. A method of estimating a DC offset level of an input signal having a first part and a second part, the method comprising:

during reception of a first part of an input signal, using an estimation method which does not rely on a DC-free signal to estimate the DC offset value of the input signal; and

during reception of a second part of the input signal, using an estimation method which relies on a DC-free signal to estimate the DC offset value of the input signal.

2. A method of estimating a DC offset value of a frequency modulated input signal which comprises a first portion and a second portion, the method comprising:

estimating a DC offset value of the first portion of the input signal using a resistance and first and second diodes connected in parallel; and

estimating a DC offset value of the second part of the input signal using a low pass filter which includes the resistance.

3. A method as claimed in claim 2, wherein the voltage drop across each diode, when the diode is on, is set to equal the voltage deviation corresponding to a maximum frequency deviation of the input signal.

4. A circuit for estimating a DC offset value of an input signal comprising:

input and output terminals;

a low pass filter including a resistor and a capacitor, the resistor being connected between the input and output terminals and the capacitor being connected between the output terminal and ground;

a pair of diodes operatively connected in parallel between the input and output terminals of the circuit; and

switch means operable to switch a connection to the output terminal, such that the pair of diodes is connected to the output terminal during receipt of a first part of an input signal, and is not connected to the output terminal during receipt of a second part of the input signal.