Common mode management between a current-steering DAC and transconductance filter in a transmission system

• US 7,348,911 B2
• Filed: 08/08/2006
• Issued: 03/25/2008
• Est. Priority Date: 08/08/2006
• Status: Expired due to Fees

• Current Assignee: Atmel Rousset S.A.S. (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Marais, Emmanuel
• Primary Examiner(s): JEANGLAUDE, JEAN BRUNER
• Application Number:
  US11/500,655
• Publication Number:
  US 20080036634A1
• Time in Patent Office: 595 Days
• Field of Search: 341/144, 327/543, 327/561, 360/66, 330/9, 330/260
• US Class Current: 341/144
• CPC Class Codes: H03M 1/0604 at one point, i.e. by adjusting a single reference value, e.g. bias or gain error gain setting for range control H03M1/18
• CPC Class Codes: H03M 1/742 using current sources as quantisation value generators

Abstract

Common mode management between a DAC, such as a current-steering DAC, and a transconductance filter in a high-frequency transmission system. In one aspect of the invention, a transmission circuit includes a DAC that provides an analog signal from an input digital signal, and a filter such as a transconductance filter connected to the DAC, the filter receiving the analog signal and filtering the analog signal for transmission. A common mode management circuit connected to the DAC and the transconductance filter provides common mode compatibility in the interface connecting the DAC and the transconductance filter.

Claims

1. A transmission circuit comprising:

a current-steering DAC that provides an analog signal from an input digital signal;

a transconductance filter connected to the current-steering DAC, the transconductance filter receiving the analog signal and filtering the analog signal for transmission; and

a common mode circuit connected to the current-steering DAC and the transconductance filter that provides a reference signal to the current-steering DAC to provide common mode compatibility between the current-steering DAC and the transconductance filter.

2. The transmission circuit of claim 1 wherein the transconductance filter includes Nauta'"'"'s transconductor.

3. The transmission circuit of claim 1 wherein the common mode compatibility includes causing a common mode voltage output from the current-steering DAC to match an input common mode voltage of the transconductance filter at a transmission signal input of the transconductance filter.

4. The transmission circuit of claim 3 wherein the input common mode voltage of the transconductance filter includes a common mode voltage of inverters of a transconductor of the transconductance filter, the common mode voltage of the inverters providing a maximum input range and linearity for the performance of the transconductor.

5. The transmission circuit of claim 3 wherein the common mode circuit includes a reference voltage generation circuit that generates the reference signal as a reference voltage input to the current-steering DAC based on a control voltage, the control voltage being input to the reference voltage generation circuit and supplied to the transconductance filter to tune the transconductance filter.

6. The transmission circuit of claim 5 wherein the control voltage supplied to the transconductance filter is a tuning voltage auto-tuned with a frequency automatic tuning block to provide desired filter operation, wherein based on the control voltage, the reference voltage adjusts to cause the current-steering DAC to output the best suitable input common mode voltage for the transconductance filter.

7. The transmission circuit of claim 5 wherein the input common mode voltage of the transconductance filter is the control voltage divided in half, corresponding approximately to the middle of the gain zone of inverters of the transconductor.

8. The transmission circuit of claim 7 wherein the common mode circuit includes a resistor bridge coupled to the control voltage.

9. The transmission circuit of claim 8 wherein the common mode circuit includes an operational amplifier receiving a divided voltage from the resistor bridge, the operational amplifier having as its output the reference voltage for the current-steering DAC.

10. The transmission circuit of claim 3 wherein the current steering DAC is a differential DAC providing a differential input signal to the transconductance filter.

11. A transmission circuit comprising:

a current-steering DAC that provides a differential analog signal from an input digital signal;

a transconductance filter that receives the differential analog signal and filters the differential analog signal for RF transmission, wherein a control voltage supplied to the transconductance filter is a tuning voltage auto-tuned with a frequency automatic tuning block connected to the transconductance filter; and

a reference voltage generation circuit connected to the current-steering DAC and the transconductance filter that provides common mode compatibility between the current-steering DAC and the transconductance filter by generating a reference voltage input to the current-steering DAC based on the control voltage supplied to the transconductance filter.

12. The transmission circuit of claim 11 wherein the transconductance filter includes Nauta'"'"'s transconductor, and wherein the common mode compatibility includes a match of the output common mode voltage of the current-steering DAC to an input common mode voltage of the transconductance filter at a transmission signal input of the transconductance filter.

13. The transmission circuit of claim 12 wherein the input common mode voltage of the transconductance filter is the control voltage divided in half, corresponding to approximately the middle of the gain zone of inverters of the transconductor.

14. The transmission circuit of claim 11 wherein the reference voltage generation circuit includes a resistor bridge coupled to the control voltage and an operational amplifier receiving a divided voltage from the resistor bridge, the operational amplifier having as its output the reference voltage for the current-steering DAC.

15. A method for reducing distortion in a transmission circuit, comprising:

providing a common mode circuit connected to a current-steering DAC and to a transconductance filter, wherein the current-steering DAC provides an analog signal to the transconductance filter that filters the analog signal for transmission; and

providing common mode compatibility between the current-steering DAC and the transconductance filter by matching an output common mode voltage of the current-steering DAC to an input common mode voltage of the transconductance filter at a transmission signal input of the transconductance filter.

16. The method of claim 15 wherein the common mode circuit includes a reference voltage generation circuit that generates a reference voltage input to the current-steering DAC based on a control voltage, the control voltage being input to the reference voltage generation circuit and supplied to the transconductance filter to tune the transconductance filter.

17. The method of claim 15 wherein the transconductance filter includes Nauta'"'"'s transconductor.

18. The method of claim 15 wherein the input common mode voltage of the transconductance filter includes a common mode voltage of inverters of a transconductor of the transconductance filter, the common mode voltage of the inverters providing a maximum input range and linearity for the performance of the transconductor.

19. The method of claim 15 wherein providing the common mode compatibility includes providing the common mode voltage of inverters of the transconductor as the control voltage divided in half, corresponding approximately to the middle of the gain zone of the inverters.

20. The method of claim 16 wherein the control voltage supplied to the transconductance filter is a tuning voltage auto-tuned by a frequency automatic tuning block to provide desired filter operation, wherein based on the control voltage, the reference voltage adjusts to cause the current-steering DAC to output the best suitable common mode voltage for the transconductance filter.

21. A transmission circuit comprising:

a DAC that provides an analog signal from an input digital signal;

a filter connected to the DAC, the filter receiving the analog signal and filtering the analog signal for transmission; and

a common mode circuit connected to the DAC and the filter that provides a reference signal to the current-steering DAC to provide common mode compatibility between the DAC and the filter.

22. The transmission circuit of claim 21 wherein the filter includes Nauta'"'"'s transconductor.

23. The transmission circuit of claim 21 wherein the common mode compatibility includes causing a common mode voltage output from the DAC to match a desired input common mode voltage of the filter at a transmission signal input of the transconductance filter.

24. The transmission circuit of claim 23 wherein the common mode circuit includes a reference voltage generation circuit that generates the reference signal as a reference voltage input to the DAC based on a control voltage, the control voltage being input to the reference voltage generation circuit and supplied to the filter to tune the filter.

25. The transmission circuit of claim 24 wherein the control voltage supplied to the filter is a tuning voltage auto-tuned to provide desired filter operation, wherein based on the control voltage, the reference voltage adjusts to cause the DAC to output a common mode voltage matched to a desired input common mode voltage of the filter.