Wideband monolithic tunable high-Q notch filter for image rejection in RF application

• US 6,990,327 B2
• Filed: 04/30/2003
• Issued: 01/24/2006
• Est. Priority Date: 04/30/2003
• Status: Expired due to Fees

• Current Assignee: Agency For Science Technology and Research
• Original Assignee: Agency For Science Technology and Research
• Inventors: Zheng, Yuanjin, Xu, Yong, Wong, Sheng Jau
• Primary Examiner(s): Vo, Nguyen T.
• Assistant Examiner(s): Le, Nhan T.
• Application Number:
  US10/426,426
• Publication Number:
  US 20040219900A1
• Time in Patent Office: 1,000 Days
• Field of Search: 455/302, 455/307, 455/323, 455/333, 333/175, 333/176, 333/195
• US Class Current: 455/307
• CPC Class Codes: H03H 11/1213 using transistor amplifiers H03H11/1204 takes precedence; parallel-T filters H03H11/1295
• CPC Class Codes: H03H 7/03 comprising means for compensation of loss
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal

Abstract

A notch filter with a high Q factor, which is integrated with a first and a second cascoded LNA, is totally contained on an integrated chip. The notch filter, comprising two Q-enhancement circuits, is coupled to the second differential LNA. The two Q-enhancement circuits are combined to generate sufficient negative impedance to compensate for the loss in the on-chip low Q inductors. To improve the image rejection of the notch filter in a wide frequency band, the notch filter uses an automatic current tuning circuit which consists of an analog multiplier and fixed and voltage controlled current sources. Furthermore, by modifying the connection and location of the tunable varactor, another wideband tunable notch filter is implemented. The notch filter can be applied in all current wireless receiver systems.

Claims

1. A wideband tunable high Q image rejection notch filter comprising:

a Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising;

a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are the input terminals of said Q-enhancement circuit, where the sources of said first and said second transistor are coupled together via a first and a second terminal of a capacitance tunable varactor means, where a third terminal of said capacitance tunable varactor means is coupled to an input port providing an input signal, and where the drain of said first and said second transistor is coupled via capacitive means to the gate of said first and said second transistor, respectively, where said differential series LC resonator is a transconductor based negative resistance generator resonating at an image frequency to compensate for the resistance of said inductive means; and

a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively.

2. The notch filter of claim 1, wherein a current source is coupled between a reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

3. The notch filter of claim 1, wherein a tunable current source is coupled between said input port and the source of said third and said fourth transistor, said tunable current source comprising an analog multiplier, two voltage controlled current sources and a fixed current source, said tunable current source improving the image rejection of said notch filter in a wide frequency band by providing for said Q-enhancement circuit a bias current which is the quadratic function of the tuning voltage across said tunable varactor means.

4. The notch filter of claim 1, wherein said inductive means of said LC resonator is an on-chip low Q inductor.

5. The notch filter of claim 1, wherein said capacitive means of said LC resonator are used to adjust the frequency distance between poles and zeros of said notch filter.

6. The notch filter of claim 1, wherein adjustment of the transconductance g_m of said first and said second transistor of said LC resonator increases the quality factor Q of said inductive means of said LC resonator.

7. The notch filter of claim 1, wherein changes of said bias current change the value of the negative resistance of said Q-enhancement circuit.

8. The notch filter of claim 1, wherein said Q-enhancement circuit operates in the range from 2 to 5 GHz (GHz=10⁹ Hz).

9. The notch filter of claim 1, wherein said Q-enhancement circuit has an image rejection ranging from 55 to 65 dB.

10. The notch filter of claim 1, wherein said Q-enhancement circuit has an image frequency tuning range of 100 MHz (MHz=10⁶ Hz).

11. A wideband tunable high Q image rejection notch filter comprising:

a Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising;

a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are the input terminals of said Q-enhancement circuit, where the sources of said first and said second transistor are coupled together via capacitance means, where the source and gate of said first transistor is coupled via first and second terminals of a first capacitance tunable varactor means, where the source and gate of said second transistor is coupled via first and second terminals of a second capacitance tunable varactor means, and where a third terminal of said first and said second capacitance tunable varactor means is coupled to an input port providing an input signal, said varactors extending the notch frequency band of said Q-enhancement circuit, and where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;

a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and

a current source coupled between a reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

12. The notch filter of claim 11, wherein said inductive means of said LC resonator is an on-chip low Q inductor.

13. The notch filter of claim 11, wherein said first and said second capacitive means of said LC resonator are used to adjust the frequency distance between poles and zeros of said notch filter.

14. The notch filter of claim 11, wherein adjustment of the transconductance g_m of said first and said second transistor of said LC resonator increases the quality factor Q of said inductive means of said LC resonator.

15. The notch filter of claim 11, wherein changes in said bias current change the value of the negative resistance of said Q-enhancement circuit.

16. The notch filter of claim 11, wherein said Q-enhancement circuit operates in the range from 2 to 5 GHz (GHz=10⁹ Hz).

17. The notch filter of claim 11, wherein said Q-enhancement circuit has an image rejection ranging from 35 to 50 dB.

18. The notch filter of claim 11, wherein said Q-enhancement circuit has an image frequency tuning range of 200 MHz (MHz=10⁶ Hz).

19. The notch filter of claim 11, wherein said Q-enhancement circuit has an image frequency tuning range of 350 MHz (MHz=10⁶ Hz).

20. A wideband tunable high Q image rejection notch filter comprising:

a first cascoded LNA having an input and an output, said first cascoded LNA receiving an RF input signal at said input and providing at its output an amplified signal of said RF input signal;

a second cascoded LNA having an input and an output, said second cascoded LNA input coupled to said output of said first LNA, said second LNA rejecting on-chip common-mode noise;

a Q-enhancement circuit coupled to said second cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising;

a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via a first and a second terminal of a capacitance tunable varactor means, where a third terminal of said capacitance tunable varactor means is coupled to a third port providing an input signal, and where the drain of said first and said second transistor is coupled via capacitive means to the gate of said first and said second transistor, respectively, where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;

a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and

a tunable current source coupled between said third port and the source of said third and said fourth transistor, said tunable current source comprising an analog multiplier, two voltage controlled current sources and a fixed current source, said tunable current source improving the image rejection of said notch filter in a wide frequency band by providing for said Q-enhancement circuit a bias current which is the quadratic function of the tuning voltage across said tunable varactor means.

21. The notch filter of claim 20, wherein said first cascoded LNA is a differential LNA with a differential input and a differential output.

22. The notch filter of claim 20, wherein said second cascoded LNA is a differential LNA with a differential input and a differential output.

23. The notch filter of claim 20, wherein said inductive means of said LC resonator is an on-chip low Q inductor.

24. The notch filter of claim 20, wherein said capacitive means of said LC resonator are used to adjust the frequency distance between poles and zeros of said notch filter.

25. The notch filter of claim 20, wherein adjustment of the transconductance g_m of said first and said second transistor of said LC resonator increases the quality factor Q of said inductive means of said LC resonator.

26. The notch filter of claim 20, wherein changes of said bias current change the value of the negative resistance of said Q-enhancement circuit.

27. The notch filter of claim 20, wherein said Q-enhancement circuit operates in the range from 2 to 5 GHz (GHz=10⁹ Hz).

28. The notch filter of claim 20, wherein said Q-enhancement circuit has an image rejection ranging from 55 to 65 dB in Bluetooth applications.

29. The notch filter of claim 20, wherein said Q-enhancement circuit has an image frequency tuning range of 100 MHz (MHz=10⁶ Hz) in Bluetooth applications.

30. A wideband tunable high Q image rejection notch filter comprising:

a first cascoded LNA having an input and an output, said first cascoded LNA receiving an RF input signal at said input and providing at its output an amplified signal of said RF input signal;

a second cascoded LNA having an input and an output, said second cascoded LNA input coupled to said output of said first LNA, said second LNA rejecting on-chip common-mode noise;

a Q-enhancement circuit coupled to said second cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising;

a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via capacitance means, where the source and gate of said first transistor is coupled via first and second terminals of a first capacitance tunable varactor means, where the source and gate of said second transistor is coupled via first and second terminals of a second capacitance tunable varactor means, and where a third terminal of said first and said second capacitance tunable varactor means is coupled to a third port providing an input signal, said varactors extending the notch frequency band of said Q-enhancement circuit, and where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;

a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and

a current source coupled between a reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

31. The notch filter of claim 30, wherein said first cascoded LNA is a differential LNA with a differential input and a differential output.

32. The notch filter of claim 30, wherein said second cascoded LNA is a differential LNA with a differential input and a differential output.

33. The notch filter of claim 30, wherein said inductive means of said LC resonator is an on-chip low Q inductor.

34. The notch filter of claim 30, wherein said first and said second capacitive means of said LC resonator are used to adjust the frequency distance between poles and zeros of said notch filter.

35. The notch filter of claim 30, wherein adjustment of the transconductance g_m of said first and said second transistor of said LC resonator increases the quality factor Q of said inductive means of said LC resonator.

36. The notch filter of claim 30, wherein changes in said bias current change the value of the negative resistance of said Q-enhancement circuit.

37. The notch filter of claim 30, wherein said Q-enhancement circuit operates in the range from 2 to 5 GHz (GHz=10⁹ Hz).

38. The notch filter of claim 30, wherein said Q-enhancement circuit has an image rejection ranging from 35 to 50 dB.

39. The notch filter of claim 30, wherein said Q-enhancement circuit has an image frequency tuning range of 200 MHz (MHz=10⁶ Hz) in Bluetooth applications.

40. The notch filter of claim 30, wherein said Q-enhancement circuit has an image frequency tuning range of 350 MHz (MHz=10⁶ Hz) in Wireless LAN applications.

41. A wideband tunable high Q image rejection notch filter comprising:

a single ended cascoded LNA having an input and a single output, said single ended cascoded LNA receiving an RF input signal at said single input and providing at said single output an amplified signal of said RF input signal;

a differential cascoded LNA having a single input and a differential output, said single input of said differential cascoded LNA coupled to said single output of said single ended cascoded LNA, said differential cascoded LNA rejecting on-chip common-mode noise;

a Q-enhancement circuit coupled to said differential cascoded LNA, said Q-enhancement circuit used in a notch filter by creating a negative resistance to compensate for resistive losses in inductive components of said Q-enhancement circuit, said Q-enhancement circuit comprising;

a differential series LC resonator comprising a first and a second transistor, where the source and the drain of said first and said second transistor are paralleled by a first and a second capacitive means, respectively, where a first and a second inductive means is coupled across the gate and the drain of said first and said second transistor, respectively, where the drains of said first and said second transistor are coupled to said second cascoded LNA, where the sources of said first and said second transistor are coupled together via a first and a second terminal of a capacitance tunable varactor means, where a third terminal of said capacitance tunable varactor means is coupled to a reference potential, and where the drain of said first and said second transistor is coupled via capacitive means to the gate of said first and said second transistor, respectively, where said differential series LC resonator is a transconductor based negative resistance generator resonating at the image frequency to compensate for the resistance of said inductive means;

a differential Q compensation circuit providing extra negative impedance to further compensate for the resistance of said inductive means of said differential series LC resonator, said differential Q compensation circuit comprising a cross-coupled differential third and fourth transistor, the drain of said third and fourth transistor coupled to the source of said first and said second transistor, respectively, and

a current source coupled between said reference voltage and the source of said third and said fourth transistor, said current source providing a bias current for said Q-enhancement circuit.

42. The notch filter of claim 41, wherein said inductive means of said LC resonator is an on-chip low Q inductor.

43. The notch filter of claim 41, wherein said capacitive means of said LC resonator are used to adjust the frequency distance between poles and zeros of said notch filter.

44. The notch filter of claim 41, wherein adjustment of the transconductance g_m of said first and said second transistor of said LC resonator increases the quality factor Q of said inductive means of said LC resonator.

45. The notch filter of claim 41, wherein changes of said bias current change the value of the negative resistance of said Q-enhancement circuit.

46. The notch filter of claim 41, wherein said Q-enhancement circuit operates in the range from 2 to 5 GHz (GHz=10⁹ Hz).

47. The notch filter of claim 41, wherein said Q-enhancement circuit has an image rejection ranging from 60 to 70 dB in Bluetooth applications.

48. The notch filter of claim 41, wherein said Q-enhancement circuit has an image frequency tuning range of 200 MHz (MHz=10⁶ Hz) in Bluetooth applications.