Apparatus and method for frequency conversion with minimized intermodulation distortion

Abstract

A frequency conversion unit includes a local oscillator, a phase compensator, and a mixer. The local oscillator generates differential original oscillating signals. The phase compensator generates differential compensated oscillating signals mixed with differential received signals by the mixer to generate differential baseband signals. The respective duty cycles of the compensated oscillating signals are adjusted for minimizing intermodulation distortion in the baseband signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent when described in detailed exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a circuit diagram of a conventional Gilbert cell mixer;

FIG. 2 is a circuit diagram of a conventional IP2 calibration circuit using a calibration resistor;

FIG. 3 is a block diagram of a DCR (direct-conversion receiver) according to an embodiment of the present invention;

FIG. 4 is a circuit diagram of a phase compensator in FIG. 3, according to embodiment of the present invention;

FIG. 5 is a circuit diagram of the phase compensator in FIG. 3, according to another embodiment of the present invention;

FIG. 6 shows a waveform diagram of example output signals of the phase compensator of FIG. 4;

FIGS. 7A, 7B, 7C, and 7D show waveform diagrams of input and output signals of the phase compensator of FIG. 4, according to another embodiment of the present invention;

FIG. 8 is a graph of IP2 values versus Δη when ΔR varies in Expression 5;

FIG. 9 is a graph of IP2 values versus ΔR when Δη varies in Expression 5; and

FIG. 10 shows a flow chart of steps during operation of the DCR of FIG. 3, according to an embodiment of the present invention.

Claims

1. An apparatus for frequency conversion, comprising: a local oscillator that generates differential original oscillating signals;a phase compensator that generates differential compensated oscillating signals from the original oscillating signals with a respective duty cycle of each of the compensated oscillating signals being adjusted by the phase compensator; anda mixer that mixes the compensated oscillating signals with differential received signals to generate differential baseband signals.

2. The apparatus of claim 1, wherein the respective duty cycle of each of the compensated oscillating signals is adjusted for minimizing intermodulation distortion in the baseband signals.

3. The apparatus of claim 1, wherein the phase compensator includes: a first differential amplifier, biased with a first current, and including first inputs with the original oscillating signals applied thereon, and including first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; anda second differential amplifier, biased with a second current, and including second inputs with the original oscillating signals applied thereon, and including second outputs coupled to said differential pair of output terminals,wherein the first and second currents are adjusted for setting the respective duty cycle of each of the compensated oscillating signals.

4. The apparatus of claim 3, wherein a sum of the first and second currents is maintained to be constant.

5. The apparatus of claim 3, wherein the phase compensator further includes: a first BJT (bipolar junction transistor) for generating the first current and having a first base with a first base voltage applied thereon for setting the first current;a second BJT (bipolar junction transistor) for generating the second current and having a second base with a second base voltage applied thereon for setting the second current; anda current source coupled to the first and second BJTs and generating a fixed current such that a sum of the first and second currents is the fixed current.

6. The apparatus of claim 1, wherein the phase compensator includes: a first differential amplifier, biased with a first current, and including a first pair of transistors with the original oscillating signals applied thereon, and including first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; anda second differential amplifier, biased with a second current, and including a second pair of transistors with the original oscillating signals applied thereon, and including second outputs coupled to said differential output terminals,wherein a first size ratio between the first pair of transistors and a second size ratio between the second pair of transistors are set for determining the respective duty cycle of each of the compensated oscillating signals.

7. The apparatus of claim 6, wherein a sum of the first and second currents is maintained to be constant.

8. A direct-conversion receiver (DCR) comprising: a receiving unit for receiving differential RF signals;a frequency conversion unit including: a local oscillator that generates differential original oscillating signals;a phase compensator that generates differential compensated oscillating signals from the original oscillating signals with a respective duty cycle of each of the compensated oscillating signals being adjusted by the phase compensator; anda mixer that mixes the compensated oscillating signals with the received signals to generate differential baseband signals; anda baseband signal processor for receiving and processing the baseband signals.

9. The DCR of claim 8, wherein the respective duty cycle of each of the compensated oscillating signals is adjusted for minimizing intermodulation distortion in the baseband signals.

10. The DCR of claim 9, further comprising: a phase compensator controller that generates at least one control signal from the baseband signals, the phase compensator adjusting the respective duty cycle of each of the compensated oscillating signals in response to the at least one control signal.

11. The DCR of claim 8, wherein the phase compensator includes: a first differential amplifier, biased with a first current, and including first inputs with the original oscillating signals applied thereon, and including first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; anda second differential amplifier, biased with a second current, and including second inputs with the original oscillating signals applied thereon, and including second outputs coupled to said differential pair of output terminals,wherein the first and second currents are adjusted for setting the respective duty cycle of each of the compensated oscillating signals.

12. The DCR of claim 11, wherein a sum of the first and second currents is maintained to be constant.

13. The DCR of claim 11, wherein the phase compensator further includes: a first BJT (bipolar junction transistor) for generating the first current and having a first base with a first base voltage applied thereon for setting the first current;a second BJT (bipolar junction transistor) for generating the second current and having a second base with a second base voltage applied thereon for setting the second current; anda current source coupled to the first and second BJTs and generating a fixed current such that a sum of the first and second currents is the fixed current.

14. The DCR of claim 8, wherein the phase compensator includes: a first differential amplifier, biased with a first current, and including a first pair of transistors with the original oscillating signals applied thereon, and including first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; anda second differential amplifier, biased with a second current, and including a second pair of transistors with the original oscillating signals applied thereon, and including second outputs coupled to said differential output terminals,wherein a first size ratio between the first pair of transistors and a second size ratio between the second pair of transistors are set for determining the respective duty cycle of each of the compensated oscillating signals.

15. The DCR of claim 14, wherein a sum of the first and second currents is maintained to be constant.

16. A method of frequency conversion, comprising: generating differential original oscillating signals;generating differential compensated oscillating signals from the original oscillating signals;adjusting a respective duty cycle of each of the compensated oscillating signals; andmixing the compensated oscillating signals with differential received signals to generate differential baseband signals.

17. The method of claim 16, further comprising: adjusting the respective duty cycle of each of the compensated oscillating signals for minimizing intermodulation distortion in the baseband signals.

18. The method of claim 16, further including: setting a first current through a first differential amplifier having first inputs with the original oscillating signals applied thereon and having first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; andsetting a second current through a second differential amplifier having second inputs with the original oscillating signals applied thereon and having second outputs coupled to said differential pair of output terminals,wherein the first and second currents are adjusted for setting the respective duty cycle of each of the compensated oscillating signals.

19. The method of claim 18, further comprising: maintaining a sum of the first and second currents to be constant.

20. The method of claim 16, further comprising: setting a first size ratio between a first pair of transistors forming a first differential amplifier biased with a first current and having the original oscillating signals applied thereon, the first differential amplifier having first outputs coupled to differential output terminals having the compensated oscillating signals generated thereon; andsetting a second size ratio between a second pair of transistors forming a second differential amplifier biased with a second current and including a second pair of transistors with the original oscillating signals applied thereon, the second differential amplifier having second outputs coupled to said differential output terminals,wherein the first size ratio and the second size ratio are set for determining the respective duty cycle of each of the compensated oscillating signals.

21. The method of claim 20, wherein a sum of the first and second currents is maintained to be constant.