Method and circuit arrangement for processing a received signal

• US 6,324,389 B1
• Filed: 10/09/1998
• Issued: 11/27/2001
• Est. Priority Date: 02/08/1996
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Väisänen, Risto
• Primary Examiner(s): Maung, Nay
• Application Number:
  US09/117,881
• Time in Patent Office: 1,145 Days
• Field of Search: 455/214, 455/226.1, 455/296, 455/303, 455/309, 455/312, 455/334, 455/338, 455/234.1, 455/324, 375/317, 375/319, 375/346
• US Class Current: 455/324
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A direct voltage component of a signal which has been received and converted to a baseband is separated by a first separator in a signal line. Also the direct voltage components of both the signal preceding the separator and the signal following the separator are controlled by control signals. Thus a baseband signal line preceding the first separator can be direct current coupled.

Claims

1. A circuit arrangement for processing a received radio frequency signal in a direct conversion receiver, said circuit arrangement comprising a demodulator for directly demodulating the received radio frequency signal into a baseband signal, a control circuit coupled to said demodulator for controlling the strength of the baseband signal, first separating means coupled to said control circuit for separating of direct voltage occurring in the baseband signal, an analog-to-digital converter coupled to said first separating means, means for controlling the direct voltage component of a first baseband signal preceding said first separating means on the basis of a first control signal, and means for controlling the direct voltage component of a second baseband signal following the separating means on the basis of a second control signal.

2. A circuit arrangement according to claim 1, further comprising a second separating means for separating the direct voltage component which occurs in said control circuit from the constant potential.

3. A circuit arrangement according to claim 2, further comprising means for controlling the charge state of said second separating means by said second control signal for controlling the direct voltage component which occurs in the control circuit.

4. A circuit arrangement according to claim 1, wherein the signal line between the demodulator and the first separating means has been direct voltage coupled.

5. A circuit arrangement according to claim 1, wherein the demodulator is an I/Q demodulator and to the output of its quadrature signal, a first branch has been connected for processing a baseband quadrature signal and to the output of the in-phase signal, a second branch has been connected for processing the in-phase baseband signal.

6. A circuit arrangement according to claim 1, further comprising means for connecting a second signal to the output of the separating means and means for forming said second signal on the basis of a first signal preceding the separating means.

7. A circuit arrangement according to claim 1, wherein the first and second control signals are identical.

8. A mobile station receiver comprising the circuit arrangement of claim 1.

9. A digital time division mobile communication system comprising the circuit arrangement of claim 1.

10. A method for processing a received radio frequency signal in a direct conversion receiver, said method comprising:

directly demodulating the received signal to an analog baseband signal;

controlling the strength of the analog baseband signal using a control circuit;

separating DC from said analog baseband signal using a first separating means;

converting the analog baseband signal to a digital signal;

controlling the DC component of a baseband signal at the input of the separating step in accordance with a first control signal; and

controlling the DC component of a baseband signal at the output of the first separating means in accordance with a second control signal.

11. A method according to claim 10, wherein the signal which is demodulated to a baseband is conducted to said first separating means as direct voltage coupled.

12. A method according to claim 10, wherein the direct voltage component which occurs in said strength control circuit is separated from the constant potential by a second separating means of direct voltage and the charge state of said second separating means of direct voltage is controlled by a second control signal for controlling the direct voltage component occurring in the control circuit.

13. A method according to claim 10, wherein said first and second control signals are switched to an active state at least partially coincident in time.

14. A method according to claim 10, wherein said first and second control signals are switched to an active state before the start of the time slot which contains information of the received signal.

15. A method according to claim 10, wherein for reducing of the offset voltage, to the output of said first separating means a second signal is connected which is formed on the basis of the first signal preceding said separating means.

16. The method of claim 10, wherein said first and second control signals are identical.

17. A mobile station receiver operated in accordance with the method of claim 10.

18. A mobile digital time division communication system operated in accordance with the method of claim 10.