Offset compensation in a direct-conversion receiver

• US 6,862,439 B2
• Filed: 06/28/2002
• Issued: 03/01/2005
• Est. Priority Date: 06/28/2002
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Feng, Shen
• Primary Examiner(s): Vuong, Quochien B.
• Application Number:
  US10/185,337
• Publication Number:
  US 20040002311A1
• Time in Patent Office: 977 Days
• Field of Search: 455/232.1, 455/234.1, 455/251.1, 455/313, 455/323, 455/324, 455/334, 455/341, 375/319, 375/345
• US Class Current: 455/234.1
• 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 conversion receiver comprises a low noise amplifier, a bandpass filter, a mixer circuit and a baseband processing assembly. The low noise amplifier is capable of receiving communication signals from an antenna and, in turn, the bandpass filter is capable of filtering the received signals to a bandpass including a reception frequency band. The mixer circuit is electrically connected to an output of the bandpass filter, and can demodulate the received signals into differential signals in two channels. The baseband processing assembly is electrically connected to the mixer circuit opposite said bandpass filter. In this regard, the baseband processing assembly can process the demodulated differential signals in at least one of the channels. And to compensate DC offset from the demodulated differential signals, for each channel the baseband processing assembly includes a pair of dynamic offset compensation elements and a static offset compensation element.

Claims

1. A baseband processing assembly capable of compensating received and demodulated differential signals in at least one channel of a direct conversion receiver for DC offset, wherein, for each of the at least one channel, said baseband processing assembly comprises:

a baseband amplifier capable of amplifying the demodulated differential signals;

a variable-gain amplifier capable of receiving and further amplifying the amplified demodulated differential signals from said baseband amplifier;

a pair of dynamic offset compensation elements each comprising a capacitor, wherein one dynamic offset compensation element is electrically connected to said baseband amplifier and the other dynamic offset compensation element is electrically connected to said variable-gain amplifier, wherein said dynamic offset compensation elements are capable of compensating at least a portion of dynamic offset from the demodulated differential signals at the respective amplifier; and

a static offset compensation element electrically connected to said variable-gain amplifier opposite said baseband amplifier, wherein said static offset compensation element is capable of receiving a differential control code representative of static offset and thereafter compensating at least a portion of static offset from the further amplified demodulated differential signals based upon a combination of the differential control code with the further amplified demodulated differential signals from the variable-gain amplifier.

2. A baseband processing assembly according to claim 1, wherein the differential signals comprise positive signals and negative signals, wherein said baseband amplifier comprises an instrumental amplifier including two operational amplifiers, wherein one of the operational amplifiers is capable of amplifying the demodulated positive signals and the other operational amplifier is capable of amplifying the demodulated negative signals, and wherein one of the dynamic offset compensation elements is electrically connected between the operational amplifiers.

3. A baseband processing assembly according to claim 1, wherein the differential signals comprise positive signals and negative signals, wherein said variable-gain amplifier comprises an instrumental amplifier including two operational amplifiers, wherein one of the operational amplifiers is capable of further amplifying the amplified demodulated positive signals and the other operational amplifier is capable of further amplifying the amplified demodulated negative signals, and wherein one of the dynamic offset compensation elements is electrically connected between the operational amplifiers.

4. A baseband processing assembly according to claim 1, wherein the differential signals comprise positive signals and negative signals, wherein said static offset compensation element comprises two operational amplifiers, wherein one of the operational amplifiers is capable of receiving the further amplified demodulated positive signals and the other operational amplifier is capable of receiving the further amplified demodulated negative signals, and wherein each operational amplifier is also capable of receiving signals comprising a combination of a portion of the differential control code and an output of the respective operational amplifier.

5. A baseband processing assembly according to claim 4, wherein the operational amplifier receiving the positive signals is also capable of receiving signals comprising the combination of a positive portion of the differential control code and the output of the operational amplifier receiving the positive signals, and wherein the operational amplifier receiving the negative signals is also capable of receiving signals comprising the combination of a negative portion of the differential control code and the output of the operational amplifier receiving the negative signals.

6. A baseband processing assembly according to claim 4, wherein the further amplified demodulated differential signals comprise analog signals, wherein the differential control code comprises a digital control code, and wherein said static compensation element further comprises a digital-to-analog converter capable of receiving the digital differential control code and thereafter converting the digital differential control code to an analog differential control code.

7. A baseband processing assembly according to claim 6, wherein said static offset compensation element further comprises an analog-to-digital converter capable of receiving the further amplified demodulated differential signals, wherein the direct conversion receiver is capable of operating in an initialization mode where the direct conversion receiver operates independent of communication signals, and wherein said analog-to-digital converter is capable of operating in the initialization mode to measure an amount of offset at an output of said variable-gain amplifier and thereafter generate the digital control code based upon the measured amount of offset.

8. A baseband processing assembly according to claim 6, wherein the differential control code comprises a plurality of differential control signals, wherein said digital-to-analog converter comprises a plurality of pairs of switching elements electrically connected to a current sink capable of drawing a different reference current, and wherein each pair of switching elements is capable of receiving respective differential control signals.

9. A baseband processing assembly according to claim 8, wherein the differential signals comprise positive signals and negative signals, wherein said static offset compensation element includes two operational amplifiers each comprising a switching element electrically connected to each pair of switching elements of the digital-to-analog converter, and wherein one of the switching elements of one of the operational amplifiers is capable of receiving the further amplified demodulated positive signals and the other switching element of the other operational amplifier is capable of receiving the further amplified demodulated negative signals.

10. A baseband processing assembly capable of compensating received and demodulated analog differential signals in at least one channel of a direct conversion receiver for DC offset, wherein, for each of the at least one channel, said baseband processing assembly comprises:

a baseband amplifier capable of amplifying the demodulated differential signals;

a variable-gain amplifier capable of receiving and further amplifying the amplified demodulated differential signals from said baseband amplifier;

a pair of dynamic offset compensation elements each comprising a capacitor, wherein one dynamic offset compensation element is electrically connected to said baseband amplifier and the other dynamic offset compensation element is electrically connected to said variable-gain amplifier; and

a static offset compensation element electrically connected to said variable-gain amplifier opposite said baseband amplifier, wherein said static offset compensation element comprises;

an analog-to-digital converter electrically connected to an output of said variable-gain amplifier opposite said baseband amplifier, wherein the direct conversion receiver is capable of operating in an initialization mode where the direct conversion receiver operates independent of communication signals and the analog-to-digital converter is capable measuring an amount of offset at the output of said variable-gain amplifier and thereafter generating a digital differential control code based upon the measured amount of offset; and

a digital-to-analog converter capable of receiving the digital differential control code and thereafter converting the digital differential control code into an analog differential control code,

wherein said static offset compensation element is capable of compensating at least a portion of static offset from the further amplified demodulated differential signals based upon a combination of the analog differential control code with the further amplified demodulated differential signals from the variable-gain amplifier.

11. A baseband processing assembly according to claim 10, wherein the differential signals comprise positive signals and negative signals, wherein said baseband amplifier comprises an instrumental amplifier including two operational amplifiers, wherein one of the operational amplifiers is capable of amplifying the positive demodulated signals and the other operational amplifier is capable of amplifying the negative demodulated signals, and wherein one of the dynamic offset compensation elements is electrically connected between the operational amplifiers.

12. A baseband processing assembly according to claim 10, wherein the differential signals comprise positive signals and negative signals, wherein said variable-gain amplifier comprises an instrumental amplifier including two operational amplifiers, wherein one of the operational amplifiers is capable of further amplifying the positive amplified demodulated signals and the other operational amplifier is capable of amplifying the negative amplified demodulated signals, and wherein one of the dynamic offset compensation elements is electrically connected between the operational amplifiers.

13. A baseband processing assembly according to claim 10, wherein the differential signals comprise positive signals and negative signals, wherein said static offset compensation element further comprises two operational amplifiers, wherein the analog-to-digital converter is electrically connected to an output of each of the operational amplifiers, wherein one of the operational amplifiers is capable of receiving the further amplified demodulated positive signals and the other operational amplifier is capable of receiving the further amplified demodulated negative signals, and wherein each operational amplifier is also capable of receiving signals comprising a combination of a portion of the analog differential control code and an output of the respective operational amplifier.

14. A baseband processing assembly according to claim 13, wherein the operational amplifier receiving the positive signals is also capable of receiving signals comprising the combination of a positive portion of the differential control code and the output of the operational amplifier receiving the positive signals, and wherein the operational amplifier receiving the negative signals is also capable of receiving signals comprising the combination of a negative portion of the differential control code and the output of the operational amplifier receiving the negative signals.

15. A baseband processing assembly according to claim 10, wherein the differential control code comprises a plurality of differential control signals, wherein the digital-to-analog converter comprises a plurality of pairs of switching elements electrically connected to a current sink capable of drawing a difference reference current, and wherein each pair of switching elements is capable of receiving respective differential control signals.

16. A baseband processing assembly according to claim 15, wherein the differential signals comprise positive signals and negative signals, wherein said static offset compensation element includes two operational amplifiers each comprising a switching element electrically connected to each pair of switching elements of the digital-to-analog converter, wherein one of the switching elements of one of the operational amplifiers is capable of receiving the further amplified demodulated positive signals and the other switching element of the other operational amplifier is capable of receiving the further amplified demodulated negative signals.

17. A direct conversion receiver comprising:

a low noise amplifier capable of receiving communication signals from an antenna;

a bandpass filter capable of filtering the received signals to within a reception frequency band;

a mixer circuit electrically connected to an output of said bandpass filter capable of demodulating the received signals into differential signals in two channels; and

a baseband processing assembly electrically connected to said mixer circuit opposite said bandpass filter, for each channel said baseband processing assembly comprising;

a baseband amplifier;

a variable-gain amplifier electrically connected to said baseband amplifier opposite said mixer circuit;

a pair of dynamic offset compensation elements each comprising a capacitor, wherein one dynamic offset compensation element is electrically connected to said baseband amplifier and the other dynamic offset compensation element is electrically connected to said variable-gain amplifier; and

a static offset compensation element electrically connected to said variable-gain amplifier opposite said baseband amplifier, wherein said static offset compensation element is capable of receiving a differential control code representative of static offset and thereafter combining the differential control code with output differential signals from the variable-gain amplifier.

18. A direct conversion receiver according to claim 17, wherein said static offset compensation element comprises:

an analog-to-digital converter capable of receiving the output differential signals from the variable-gain amplifier, wherein the direct conversion receiver is capable of operating in an initialization mode where the direct conversion receiver operates independent of communication signals from the antenna and the analog-to-digital converter is capable measuring an amount of offset at an output of said variable-gain amplifier and thereafter generating a digital differential control code based upon the measured amount of offset; and

a digital-to-analog converter capable of receiving the digital differential control code and thereafter converting the digital differential control code into an analog differential control code,

wherein said static offset compensation element is capable of combining the analog differential control code with the further amplified demodulated differential signals from the variable-gain amplifier.

19. A direct conversion receiver according to claim 17 is employed in connection with a mobile station.

20. A direct conversion receiver according to claim 17 is employed in connection with a terminal.