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An LR polyphase filter implemented with inductors and resistors and capable of operating at high frequencies is described. In one design, the LR polyphase filter includes first and second paths, with each path including an inductor coupled to a resistor. The first and second paths receive a first in

An LR polyphase filter implemented with inductors and resistors and capable of operating at high frequencies is described. In one design, the LR polyphase filter includes first and second paths, with each path including an inductor coupled to a resistor. The first and second paths receive a first input signal and provide first and second output signals, respectively, which may be in quadrature. For a differential design, the polyphase filter further includes third and fourth paths, which receive a second input signal and provide third and fourth output signals, respectively. The four output signals may be 90° out of phase. The first and second input signals are for a differential input signal. The first and third output signals are for a first differential output signal, and the second and fourth output signals are for a second differential output signal. Each inductor may be implemented with a transmission line.

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1. An apparatus comprising: a voltage controlled oscillator (VCO) configured to generate a first input signal; anda polyphase filter comprising: a first path comprising a first inductor coupled to a first resistor, the first path receiving the first input signal and providing a first output signal,a

1. An apparatus comprising: a voltage controlled oscillator (VCO) configured to generate a first input signal; anda polyphase filter comprising: a first path comprising a first inductor coupled to a first resistor, the first path receiving the first input signal and providing a first output signal,a second path comprising a second inductor coupled to a second resistor, the second path receiving the first input signal and providing a second output signal, the second output signal having a target phase offset from the first output signal at a selected frequency,a third path comprising a third inductor coupled to a third resistor, the third path receiving a second input signal and providing a third output signal, anda fourth path comprising a fourth inductor coupled to a fourth resistor, the fourth path receiving the second input signal and providing a fourth output signal. 2. The apparatus of claim 1, wherein the first inductor is coupled between an input node and a first output node, the first resistor is coupled between the first output node and circuit ground, the second resistor is coupled between the input node and a second output node, and the second inductor is coupled between the second output node and circuit ground, wherein the first input signal is applied to the input node, and wherein the first and second output signals are provided by the first and second output nodes, respectively. 3. The apparatus of claim 1, wherein the first and second input signals are for a differential input signal, the first and third output signals are for a first differential output signal, and the second and fourth output signals are for a second differential output signal, and wherein the first, second, third and fourth output signals are 90 degrees out of phase. 4. The apparatus of claim 1, wherein the first, second, third and fourth inductors are coupled to first, second, third and fourth input nodes, respectively, and are further coupled to first, second, third and fourth output nodes, respectively, wherein the first, second, third and fourth resistors are coupled to the first, second, third and fourth output nodes, respectively, and are further coupled to second, third, fourth and first input nodes, respectively, wherein the first input signal is applied to the first and second input nodes and the second input signal is applied to the third and fourth input nodes, and wherein the first, second, third and fourth output signals are provided by the first, second, third and fourth output nodes, respectively. 5. The apparatus of claim 1, the polyphase filter comprising multiple stages coupled in series, each stage comprising the first, second, third and fourth paths, wherein a first stage receives the first and second input signals and a last stage provides the first, second, third and fourth output signals. 6. The apparatus of claim 5, wherein inductors in the first path in the multiple stages are implemented with a first transmission line, wherein inductors in the second path in the multiple stages are implemented with a second transmission line, wherein inductors in the third path in the multiple stages are implemented with a third transmission line, wherein inductors in the fourth path in the multiple stages are implemented with a fourth transmission line, and wherein each inductor is implemented with a quarter wavelength segment of one transmission line. 7. The apparatus of claim 1, wherein the first inductor is implemented with a first transmission line and the second inductor is implemented with a second transmission line. 8. The apparatus of claim 7, wherein the first and second transmission lines are implemented with microstrips. 9. The apparatus of claim 7, wherein the first and second transmission lines are implemented with strip lines. 10. The apparatus of claim 7, wherein the first and second transmission lines are implemented with coplanar waveguides. 11. The apparatus of claim 7, wherein each transmission line has a length of one quarter wavelength at the selected frequency. 12. The apparatus of claim 1, wherein the first, second, third and fourth inductors are implemented with first, second, third and fourth transmission lines, respectively. 13. The apparatus of claim 12, wherein the first, second, third and fourth transmission lines are formed by routing traces from an oscillator to at least one mixer. 14. The apparatus of claim 1, wherein the VCO is a differential VCO configured to generate a differential oscillator signal comprising the first input signal and the second input signal. 15. The apparatus of claim 1, further comprising: a first mixer downconverting a differential input radio frequency (RF) signal with a differential inphase (I) local oscillator (LO) signal comprising the first and third output signals and providing a differential I downconverted signal; anda second mixer downconverting the differential input RF signal with a differential quadrature (Q) LO signal comprising the second and fourth output signals and providing a differential Q downconverted signal. 16. The apparatus of claim 1, further comprising: a first mixer upconverting a differential inphase (I) baseband signal with a differential I local oscillator (LO) signal comprising the first and third output signals;a second mixer upconverting a differential quadrature (Q) baseband signal with a differential Q LO signal comprising the second and fourth output signals; anda summer summing outputs of the first and second mixers and providing a differential upconverted signal. 17. The apparatus of claim 1, wherein the selected frequency is in a 60 gigahertz (GHz) band. 18. An integrated circuit comprising: a polyphase filter comprising: a first path comprising a first inductor coupled to a first resistor, the first path receiving a first input signal and providing a first output signal,a second path comprising a second inductor coupled to a second resistor, the second path receiving the first input signal and providing a second output signal, the second output signal having a target phase offset from the first output signal at a selected frequency,a third path comprising a third inductor coupled to a third resistor, the third path receiving a second input signal and providing a third output signal, anda fourth path comprising a fourth inductor coupled to a fourth resistor, the fourth path receiving the second input signal and providing a fourth output signal. 19. The integrated circuit of claim 18, wherein the first inductor is implemented with a first transmission line and the second inductor is implemented with a second transmission line. 20. The integrated circuit of claim 18, wherein the first, second, third and fourth inductors are implemented with first, second, third and fourth transmission lines, respectively. 21. A wireless communication device comprising: a voltage controlled oscillator (VCO) generating a differential oscillator signal comprising first and second input signals;a polyphase filter receiving the differential oscillator signal and providing a differential inphase (I) local oscillator (LO) signal comprising first and third output signals and a differential quadrature (Q) LO signal comprising second and fourth output signals, the polyphase filter comprising first, second, third and fourth paths, each path comprising an inductor coupled to a resistor, wherein the first input signal is applied to the first and second paths and the second input signal is applied to the third and fourth paths, and wherein the first, second, third and fourth output signals are provided by the first, second, third and fourth paths, respectively;a first mixer performing frequency conversion between radio frequency (RF) and baseband with the differential I LO signal; anda second mixer performing frequency conversion between RF and baseband with the differential Q LO signal. 22. The wireless communication device of claim 21, wherein the first, second, third and fourth inductors are implemented with first, second, third and fourth transmission lines, respectively. 23. The wireless communication device of claim 21, wherein the first and second mixers are for a downconverter in a receiver within the wireless device. 24. The wireless communication device of claim 21, wherein the first and second mixers are for an upconverter in a transmitter within the wireless device. 25. A method of performing polyphase filtering, comprising: passing a first input signal via a first path comprising a first inductor coupled to a first resistor to obtain a first output signal;passing the first input signal via a second path comprising a second inductor coupled to a second resistor to obtain a second output signal, the second output signal having a target phase offset from the first output signal at a selected frequency, wherein the selected frequency is in a 60 gigahertz (GHz) band;passing a second input signal via a third path comprising a third inductor coupled to a third resistor to obtain a third output signal; andpassing the second input signal via a fourth path comprising a fourth inductor coupled to a fourth resistor to obtain a fourth output signal. 26. The method of claim 25, wherein the first and second input signals are 180 degrees out of phase, and wherein the first, second, third and fourth output signals are 90 degrees out of phase. 27. The method of claim 25, further comprising: generating a differential oscillator signal comprising the first and second input signals. 28. The method of claim 25, further comprising: performing frequency conversion between radio frequency (RF) and baseband for an inphase (I) signal path with a differential I local oscillator (LO) signal comprising the first and third output signals; andperforming frequency conversion between RF and baseband for a quadrature (Q) signal path with a differential Q LO signal comprising the second and fourth output signals. 29. An apparatus comprising: a polyphase filter comprising: a first path comprising a first inductor coupled to a first resistor, the first path coupled to receive a first input signal and further coupled to provide a first output signal;a second path comprising a second inductor coupled to a second resistor, the second path coupled to receive the first input signal and further coupled to provide a second output signal, the second output signal having a target phase offset from the first output signal at a selected frequency, wherein the first inductor comprises a first transmission line and the second inductor comprises a second transmission line;a third path comprising a third inductor coupled to a third resistor, the third path coupled to receive a second input signal and further coupled to provide a third output signal; anda fourth path comprising a fourth inductor coupled to a fourth resistor, the fourth path coupled to receive the second input signal and further coupled to provide a fourth output signal. 30. The apparatus of claim 29, further comprising: a first mixer coupled to downconvert a differential input radio frequency (RF) signal with a differential inphase local oscillator (LO) signal comprising the first and third output signals and further coupled to provide a differential inphase downconverted signal; anda second mixer coupled to downconvert the differential input RF signal with a differential quadrature LO signal comprising the second and fourth output signals and further coupled to provide a differential quadrature downconverted signal. 31. The apparatus of claim 29, further comprising: a first mixer coupled to upconvert a differential inphase baseband signal with a differential inphase local oscillator (LO) signal comprising the first and third output signals;a second mixer coupled to upconvert a differential quadrature baseband signal with a differential quadrature LO signal comprising the second and fourth output signals; anda summer coupled to sum outputs of the first and second mixers and further coupled to provide a differential upconverted signal. 32. A wireless communication device comprising: means for generating a differential oscillator signal comprising first and second input signals;means for receiving the differential oscillator signal and for providing a differential inphase (I) local oscillator (LO) signal comprising first and third output signals and a differential quadrature (Q) LO signal comprising second and fourth output signals, the means for receiving the differential oscillator signal comprising first, second, third and fourth paths, each path comprising an inductor coupled to a resistor, wherein the first input signal is applied to the first and second paths and the second input signal is applied to the third and fourth paths, and wherein the first, second, third and fourth output signals are provided by the first, second, third and fourth paths, respectively;means for performing frequency conversion between radio frequency (RF) and baseband with the differential I LO signal; andmeans for performing frequency conversion between RF and baseband with the differential Q LO signal. 33. A computer-readable tangible medium including instructions executable by a processor to cause the processor to: generate a differential oscillator signal comprising first and second input signals;provide a differential inphase (I) local oscillator (LO) signal comprising first and third output signals and a differential quadrature (Q) LO signal comprising second and fourth output signals, the differential I LO signal and the differential Q LO signal provided to a polyphase filter comprising first, second, third and fourth paths, each path comprising an inductor coupled to a resistor, wherein the first input signal is applied to the first and second paths and the second input signal is applied to the third and fourth paths, and wherein the first, second, third and fourth output signals are provided by the first, second, third and fourth paths, respectively;perform frequency conversion between radio frequency (RF) and baseband with the differential I LO signal; andperform frequency conversion between RF and baseband with the differential Q LO signal.