A Tunable Upconverter Mixer With Image Rejection

• US 20030199259A1
• Filed: 01/20/2003
• Published: 10/23/2003
• Est. Priority Date: 04/22/2002
• Status: Active Grant

• Current Assignee: IPR Licensing Incorporated (InterDigital, Inc.)
• Original Assignee: Cognio, Inc. (Cisco Systems, Inc.)
• Inventors: Rahn, David G., Fong, Neric H. W., Macedo, Jose A.
• Granted Patent: US 6,959,178 B2
• Time in Patent Office: Days
• US Class Current: 455/141
• CPC Class Codes: H03D 2200/0023 Balun circuits
• CPC Class Codes: H03D 2200/0043 Bias and operating point
• CPC Class Codes: H03D 2200/0088 Reduction of intermodulation, nonlinearities, adjacent channel interference; intercept points of harmonics or intermodulation products
• CPC Class Codes: H03D 7/1425 with transistors
• CPC Class Codes: H03D 7/1433 using bipolar transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1458 Double balanced arrangements, i.e. where both input signals are differential
• CPC Class Codes: H04B 1/005 adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
• CPC Class Codes: H04B 1/0057 using diplexing or multiplexing filters for selecting the desired band
• CPC Class Codes: H04B 1/006 using switches for selecting the desired band H04B1/0057 takes precedence

Abstract

Tunable upconversion mixers that have a controllable passband response and provide substantial image rejection, making costly post-mixing filtering at least optional, if not unnecessary for many applications. A single mixer is able to support several frequency bands (and/or be accurately tuned within one frequency band) by means of varying the capacitance in a tunable load circuit for the mixer circuit. The tunable mixer comprises a mixer circuit having inputs for receiving a signal to be upconverted and an oscillator signal to be mixed with the signal to be upconverted. The mixer generates a mixer output signal at a desired sideband frequency and an image signal at an image frequency. A tunable load circuit is coupled to the mixer circuit and responsive to a control signal to resonate and pass signals in a desired passband corresponding to the mixer output signal at the desired sideband frequency, and which attenuates signals in an attenuation band that includes the image signal at the undesired image frequency.

Claims

1. A tunable mixer comprising:

a. a mixer circuit having inputs for receiving a signal to be upconverted and an oscillator signal to be mixed with the signal to be upconverted, the mixer generates a mixer output signal at a desired sideband frequency and an image signal at an image frequency; and

b. a tunable load circuit coupled to the mixer circuit and responsive to a control signal to resonate and pass signals in a desired passband corresponding to the mixer output signal at the desired sideband frequency, and which attenuates signals in an attenuation band outside the desired passband that includes the image signal at the image frequency.

2. The tunable mixer of claim 1, wherein the tunable load circuit comprises a inductance-capacitance resonant circuit, wherein a capacitance circuit forms a capacitance of the resonant circuit and is responsive to the control signal to change its capacitance for tuning the tunable load circuit.

3. The tunable mixer of claim 2, wherein the inductance-capacitance resonant circuit is a parallel resonant circuit.

4. The tunable mixer of claim 2, wherein the capacitance circuit comprises a bank of one or more capacitors, and one or more switches responsive to the control signal to selectively connect one or more of the capacitors in and out of the tunable load circuit.

5. The tunable mixer of claim 4, wherein the capacitance circuit further comprises one or more varactors, and wherein the control signal includes a control voltage coupled to the one or more varactors to further tune the tunable load circuit.

6. The tunable mixer of claim 5, wherein the one or more varactors are responsive to a direct current voltage signal that is digitally switched or continuously adjusted.

7. The tunable mixer of claim 5, wherein the one or more switches are responsive to the control signal for coarse tuning of the tunable load circuit and the one or more varactors are responsive to the control voltage for fine tuning of the tunable load circuit.

8. The tunable mixer of claim 1, wherein the capacitance circuit comprises one or more varactors coupled to at least one inductor, and wherein the control signal includes a control voltage coupled to the one or more varactors to tune the tunable load circuit.

9. The tunable mixer of claim 8, wherein the one or more varactors are responsive to the control signal including a direct current voltage signal that is digitally switched or continuously adjusted.

10. The tunable mixer of claim 1, wherein the mixer circuit comprises a double-balanced Gilbert cell having a differential pair of input transistors and four switching transistors, wherein a differential signal to be upconverted is coupled to bases of respective ones of the input transistors, and a differential oscillator signal is applied to bases of respective ones of the four switching transistors.

11. The tunable mixer of claim 10, wherein the tunable load circuit comprises first and second inductors each connected to the collectors of two of the four switching transistors and a capacitance circuit connected in parallel with said collectors.

12. The tunable mixer of claim 1, wherein the mixer circuit is a single-ended mixer circuit.

13. An upconverter comprising the tunable mixer of claim 1, and further comprising:

c. a pre-amplifier coupled to the output of the mixer circuit to increase the power of the mixer output signal, wherein the pre-amplifier outputs a pre-amplified signal; and

d. a pre-amplifier tunable load circuit coupled to the output of the pre-amplifier and responsive to a control signal to resonate and pass signals in the desired passband, and which attenuates signals in the attenuation band.

14. The upconverter of claim 13, wherein the pre-amplifier tunable load circuit comprises an inductance-capacitance resonant circuit coupled to the output of the pre-amplifier.

15. The upconverter of claim 14, wherein a capacitance of the resonant circuit is adjustable to tune the pre-amplifier tunable load circuit.

16. The upconverter of claim 14, wherein the pre-amplifier is a differential preamplifier outputting a differential pre-amplified signal, and wherein the pre-amplifier tunable load circuit is coupled in parallel with the differential outputs of the differential pre-amplified signal.

17. The upconverter of claim 16, wherein an inductance of the pre-amplifier tunable load circuit comprises a primary winding of a balun which is coupled in parallel with the differential outputs of the pre-amplifier, and a capacitance of the resonant circuit comprises a capacitance circuit connected in parallel with the primary winding of the balun that interacts with the primary winding of the balun to resonate.

18. The upconverter of claim 17, wherein the capacitance circuit comprises a bank of one or more capacitors, and one or more switches responsive to the control signal to selectively connect one or more of the capacitors to tune the pre-amplifier tunable load circuit.

19. The upconverter of claim 18, wherein the capacitance circuit further comprises one or more varactors responsive to a control voltage to further tune the pre-amplifier tunable load circuit.

20. The upconverter of claim 17, wherein the capacitance circuit comprises one or more varactors responsive to a control voltage to tune the pre-amplifier tunable load circuit.

21. The upconverter of claim 13, wherein the tunable load circuit for the mixer circuit comprises an inductance-capacitance resonant circuit, wherein a capacitance circuit forms a capacitance of the resonant circuit and is responsive to the control signal to adjust its capacitance for purposes of tuning the tunable load circuit.

22. The upconverter of claim 21, wherein the inductance-capacitance resonant circuit is a parallel resonant circuit.

23. The upconverter of claim 21, wherein the capacitance circuit comprises a bank of one or more capacitors, and one or more switches responsive to the control signal to selectively connect one or more of the capacitors in and out of the tunable load circuit to tune the tunable load circuit.

24. The upconverter of claim 23, wherein the capacitance circuit further comprises one or more varactors, and wherein the control signal includes a control voltage coupled to the one or more varactors to further tune the tunable load circuit.

25. The upconverter of claim 24, wherein the one or more varactors are responsive to a direct current voltage signal that is digitally switched or continuously adjusted.

26. The upconverter of claim 24, wherein the one or more switches are responsive to the control signal for coarse tuning of the tunable load circuit and the one or more varactors are responsive to the control voltage for fine tuning of the tunable load circuit.

27. The upconverter of claim 13, wherein the capacitance circuit comprises one or more varactors, and wherein the control signal includes a control voltage coupled to the one or more varactors to tune the tunable load circuit.

28. The upconverter of claim 27, wherein the one or more varactors are responsive to the control signal including a direct current voltage signal that is digitally switched or continuously adjusted.

29. The upconverter of claim 13, wherein the mixer circuit comprises a double-balanced Gilbert cell having a differential pair of input transistors and four switching transistors, wherein a differential signal to be upconverted is coupled to bases of respective ones of the input transistors, and a differential oscillator signal is applied to bases of respective ones of the four switching transistors.

30. The upconverter of claim 29, wherein the tunable load circuit comprises first and second inductors each connected to the collectors of two of the four switching transistors and a capacitance circuit connected in parallel with said collectors.

31. The upconverter of claim 13, wherein the mixer circuit is a single-ended mixer circuit.

41. A radio transmitter comprising the tunable mixer of claim 1, and further comprising a power amplifier coupled to the tunable mixer to amplify the mixer output signal and couple an amplified signal to an antenna.

32. An upconverter with image rejection capabilities, comprising:

a. a mixer circuit having inputs for receiving a signal to be upconverted and an oscillator signal to be mixed with the signal to be upconverted, the mixer generates a mixer output signal at a desired sideband frequency and an image signal at an image frequency; and

b. a mixer tuned load circuit coupled to the mixer circuit that resonates and passes signals in a desired passband corresponding to the mixer output signal at the desired sideband frequency, and attenuates signals in an attenuation band that includes the image signal at the undesired image frequency;

c. a pre-amplifier coupled to the output of the mixer circuit to increase the power of the mixer output signal, wherein the pre-amplifier outputs a pre-amplified signal; and

d. a pre-amplifier tuned load circuit coupled to the output of the pre amplifier to resonate and pass signals in the desired passband and, which attenuates signals in the attenuation band.

33. The upconverter of claim 32, wherein the pre-amplifier tuned load circuit comprises an inductive-capacitance resonant circuit coupled to the output of the pre-amplifier.

34. The upconverter of claim 33, wherein a capacitance of the pre-amplifier tuned load circuit is adjustable to tune the passband of the pre-amplifier tuned load circuit.

35. The upconverter of claim 33, wherein the pre-amplifier is a differential pre-amplifier outputting a differential pre-amplified signal, and wherein the pre-amplifier tuned load circuit is coupled in parallel with the differential outputs of the differential pre-amplified signal.

36. The upconverter of claim 35, wherein an inductance of the pre-amplifier tuned load circuit comprises a primary winding of a balun which is coupled in parallel with the differential outputs of the pre-amplifier, and a capacitance of the pre-amplifier tuned load circuit comprises a capacitance circuit connected in parallel with the primary winding of the balun that interacts with the primary winding of the balun to resonate.

37. The upconverter of claim 35, wherein a capacitance of the capacitance circuit is adjustable in response to a control signal to tune the pre-amplifier tuned load circuit.

38. The upconverter of claim 37, wherein the capacitance circuit comprises a bank of one or more capacitors, and one or more switches responsive to the control signal to selectively connect one or more of the capacitors to tune the pre-amplifier tuned load circuit.

39. The upconverter of claim 38, wherein the capacitance circuit further comprises one or more varactors responsive to a control voltage to further tune the pre-amplifier tuned load circuit.

40. The upconverter of claim 37, wherein the capacitance circuit comprises one or more varactors responsive to a control voltage to tune the pre-amplifier tuned load circuit.

42. A radio transmitter comprising at least first and second transmitter paths each coupled to an associated antenna to process a signal for substantially simultaneous transmission, each of the first and second transmitter paths comprising:

a. a tunable upconversion mixer that receives as input a baseband or intermediate frequency signal to be upconverted, a local oscillator signal and a tuning control signal, and which upconverts the baseband or intermediate frequency signal to a frequency based on a frequency of the local oscillator signal and in response to the tuning control signal, resonates to pass signals in a desired passband corresponding to a desired sideband frequency, and which attenuates signals in an attenuation band that includes an image signal at an undesired image frequency, and outputting an upconverted signal; and

b. at least one power amplifier coupled to the output of the tunable upconversion mixer to amplify the upconverted signal and couple an amplified signal to an associated antenna.

43. The radio transmitter of claim 42, wherein each of the first and second transmitter paths further comprises:

c. a pre-amplifier coupled to the output of the tunable upconversion mixer to increase the power of a mixer output signal output by the tunable upconversion mixer, wherein the pre-amplifier outputs a pre-amplified signal; and

d. a pre-amplifier tunable load circuit coupled to the output of the pre-amplifier and responsive to a control signal to resonate and pass signals in the desired passband, and which attenuates signals in the attenuation band, an output of the pre-amplifier coupled to the at least one power amplifier.

44. The radio transmitter of claim 42, wherein each of the first and second transmitter paths further comprises a plurality of power amplifiers, each associated with a frequency band of operation of the radio transmitter, each power amplifier coupled to the output of the tunable upconversion mixer.

45. A method for upmixing a signal comprising steps of:

a. applying a signal to be upmixed to a mixer circuit; and

b. adjusting a tunable load circuit of the mixer circuit to control the passband of the tunable load circuit to coincide with an output signal at a desired frequency generated by the mixer circuit, wherein the tunable load circuit also attenuates signals in an attenuation band that includes an image signal generated by the mixer circuit.

46. The method of claim 45, wherein the step of adjusting the tunable load circuit comprises varying a capacitance of a parallel LC network.

47. The method of claim 46, wherein the step of varying the capacitance comprises supplying a control signal to one or more varactors in the parallel LC network.

48. The method of claim 45, wherein the step of varying the capacitance further comprises switching one or more capacitors in and/or out of the parallel LC network.