Method and apparatus for down conversion of radio frequency (RF) signals

1. A demodulator circuit for emulating the down conversion of an input signal x(t) with a local oscillator (LO) signal, said demodulator circuit comprising:

a first mixer for receiving said input signal x(t), and mixing said input signal x(t) with a multi-tonal mixing signal φ 1 , to generate an output signal φ 1 x(t);

a second mixer for receiving said signal φ 1 x(t) as an input, and mixing said signal φ 1 x(t) with a mono-tonal mixing signal φ 2 , to generate an output signal φ 1 φ 2 (t);

a first signal generator for generating an oscillator signal f 1 ;

a second signal generator for generating said mono-tonal mixing signal φ 2 , where the frequency of f 1 is a multiple of the frequency of φ 2 ; and

a logic circuit for receiving said oscillator signal f 1 and said mono-tonal mixing signal φ 2 , and generating said multi-tonal mixing signal φ 1 , where φ 1 *φ 2 has significant power at the frequency of said local oscillator signal being emulated, neither of said φ 1 nor said φ 2 having significant power at the carrier frequency of said input signal x(t) or said LO signal being emulated.

2. The circuit of claim 1 wherein said logic circuit comprises an exclusive OR gate (XOR), and φ 1 =f 1 XOR φ 2 .

3. The-circuit of claim 1 wherein unwanted power at baseband is minimized by adjusting the frequency of said φ 2 signal such that unwanted RF tones do not fall on top of said input signal x(t) at baseband.

4. The circuit of claim 1 wherein unwanted power at baseband is minimized by frequency hopping said φ 2 signal so that the probability of unwanted RF tones falling on top of φ 1 *φ 2 x(t) insignificantly reduced.

5. The circuit of claim 1 wherein said first signal generator comprises:

an oscillator for-generating an oscillator signal; and

a regenerative divider for receiving said oscillator signal and converting said oscillator signal to said f 1 signal.

6. The circuit of claim 5 wherein said oscillator is a voltage-controlled oscillator.

7. The circuit of claim 5 wherein said oscillator that is tuned to a multiple of the carrier frequency of said input signal x(t) and said regenerative divider comprises a divide-by-n element.

8. The circuit of claim 6 wherein said oscillator further comprises a high pass filter.

9. The circuit of claim 1 wherein said first signal generator comprises an oscillator that is tuned to a divisor of the carrier frequency of said input signal x(t) and a multiply-by-n element.

10. The circuit of claim 1 wherein said second signal generator comprises:

a frequency controller; and

a square wave generator.

11. The circuit of claim 10 wherein said second signal generator further comprises:

a divide-by-2 element to ensure that a fifty percent duty cycle is provided.

12. The circuit of claim 10 wherein said frequency controller is operable to hop said φ 2 signal from one frequency to another, reducing the probability of the output of said circuit having power at an unwanted frequency.

13. The circuit of claim 10 wherein said frequency controller is responsive to noise in said output signal φ 1 φ 2 x(t) by adjusting the frequency of φ 2 .

14. The circuit of claim 10 wherein said first mixer comprises an active mixer.

15. The circuit of claim 14 wherein said first mixer comprises an active mixer having adjustable performance.

16. The circuit of claim 15 , wherein said active mixer has adjustable gain.

17. The circuit of claim 15 , wherein said active mixer has adjustable linearity.

18. The circuit of claim 15 , wherein said active mixer comprises a current-source whose parameters can be adjusted to control gain and linearity of said active mixer.

19. The circuit of claim 15 , wherein said active mixer comprises multiple driver components, each for receiving a different input signal in a multi-standard radio.

20. The circuit of claim 14 further comprising a high pass filter electrically connected between said first mixer and said second mixer.

21. The circuit of claim 20 wherein said second mixer comprises a passive mixer.

22. The circuit of claim 21 , wherein each of said active mixer, said high pass filter and said-passive mixer is a differential device.

23. The circuit of claim 22 , wherein said high pass filter comprises a resistor dividing network for setting the common mode voltage output.

24. The circuit of claim 5 wherein said oscillator, said regenerative divider and said logic circuit are differential.

25. The circuit of claim 24 wherein said logic circuit comprises two exclusive OR (XOR) gates.

26. The circuit of claim 24 wherein said logic circuit comprises two exclusive-NOR (XNOR) gates.

27. The circuit of claim 24 wherein said logic circuit comprises four AND gates and two OR gates arranged to generate:

φ1 P =(φ2 P AND f 1 P ) OR (φ2 N AND f 1 N ); and

φ1 N =(φ2 P AND f 1 N ) OR (φ2 N AND f 1 P ).

28. The circuit of claim 24 wherein said logic circuit comprises four semiconductor switches arranged to generate:

φ1 P =(φ2 P AND f 1 P ) OR (φ2 N AND f 1 N ); and

φ1 N =(φ2 P AND f 1 N ) OR (φ2 N AND f 1 P ).

29. A method of emulating the demodulation of an input signal x(t) to the product of said input signal with a local oscillator (LO) signal, said method comprising the steps of:

generating an oscillator signal f 1 ;

generating a mixing signal φ 2 , where f 1 is four times the frequency of φ 2 ;

generating an aperiodic mixing signal φ 1 , using a logic circuit which receives said oscillator signal f 1 and said second mixing signal φ 2 , as inputs, where φ 1 *φ 2 has significant power at the frequency of a local oscillator signal being emulated, and neither of said φ 1 nor said φ 2 having significant power at the frequency of said input signal x(t), said LO signal being emulated, or said output signal φ 1 φ 2 x(t);

mixing said input signal x(t) with said aperiodic mixing signal φ 1 , to generate an output signal φ 1 x(t); and

mixing said signal φ 1 x(t) with a second mixing signal φ 2 , to generate an output signal φ 1 , φ 2 x(t).