3G radio

1. A transmitter for GSM and UMTS comprising

an in-phase/quadrature up-converter for mixing in-phase and quadrature inputs with an intermediate frequency local oscillator signal;

a GSM path including a phase locked loop; and

a UMTS path; wherein

a frequency generator is further provided to generate a first signal at a frequency F 1 , and

the first signal is supplied as an input to an image reject mixer in the GSM path, to a mixer in the UMTS path, and as an input to divider which divides the first signal by three to create an intermediate frequency local oscillator signal which is supplied to the in-phase/quadrature up converter;

and wherein the image reject mixer in the GSM path is controllable to select either an upper or lower side band such that the GSM path operates at either (1+⅓)F 1 or (1−⅓)F 1 ; and wherein the mixer in the UMTS path selects the upper side band so as to have a output at (1+⅓)F 1 .

2. A transmitter as claimed in claim 1 , in which the frequency generator is tuneable.

3. A transmitter as claimed in claim 2 , in which the frequency generator is tuneable over a range of 10% with respect to a centre frequency.

4. A transmitter as claimed in claim 2 , in which the frequency generator is tuneable to have an output frequency in the range 2.56 to 2.97 GHz.

5. A transmitter as claimed in claim 1 , wherein the frequency generator includes a local oscillator, an output of which is provided to a divide by two counter which generates first and second frequency divided representations of the output of the local oscillator, the second frequency divided representation being 90° out of phase which respect to the first frequency divided representation.

6. A transmitter as claimed in claim 5 , in which the first and second frequency divided representations constitute the first signal.

7. A transmitter as claimed in claim 1 , in which the first signal comprises an “in-phase” signal and a “quadrature” signal.

8. A transmitter as claimed in claim 1 , in which the divide by three divider acts independently on the in-phase and quadrature components of the first signal.

9. A transmitter as claimed in claim 1 , in which the divide by three divider is a regenerative divider.

10. A transmitter as claimed in claim 1 , in which the intermediate frequency is substantially 450 MHz.

11. A transmitter as claimed in claim 1 , in which the in-phase and quadrature inputs are up converted to the intermediate frequency and then combined prior to being made available to the GSM path and the UMTS path.

12. A transmitter as claimed in claim 1 , in which the GSM path comprises a phase sensitive detector having a first input arranged to receive a modulated intermediate frequency signal and an output connected to a frequency control input of a voltage controlled oscillator; an output of the oscillator being supplied to an antenna path and also to a signal input of the image reject mixer; and wherein an output of the image reject mixer is supplied to a second input of the phase sensitive detector.

13. A transmitter as claimed in claim 1 , in which in the GSM mode a carrier frequency is substantially 900 MHz or 1.8 GHz and the image reject mixer is arranged to either add or subtract a substantially 450 MHz intermediate frequency signal from a substantially 1.35 GHz signal generated by the frequency generator.

14. A transmitter as claimed in claim 1 , wherein the UMTS path comprises an up converter for forming a signal whose frequency is the sum of intermediate frequency and the signal generated by the frequency generator.

15. A transmitter as claimed in claim 1 , in which the UMTS path operates at substantially 1.8 GHz.

16. A transmitter as claimed in claim 1 , in which the frequency generator, the divider for generating the local oscillator signal, the GSM path and the UMTS path are, with the exception of power amplifier stages for the GSM and UMTS paths, integrated into a single integrated circuit.

17. A transmitter as claimed in claim 1 , in which the transmitter is integrated into a single integrated circuit.

18. A multi-mode transmitter operable for UMTS and GSM transmissions, comprising:

a. a signal input for receiving a signal to be up converted on to a carrier signal by the transmitter;

b. an oscillator for generating a first radio frequency signal having a frequency F 1 , where F 1 is 1.5 or ¾ times a desired carrier frequency F C ;

c. a first divider for receiving the first radio frequency signal F 1 and dividing it by three so as to form an intermediate frequency, I F , having a frequency substantially at 0.25 or 0.5 times the desired carrier frequency;

d. at least one mixer for mixing the signal from the signal input with the intermediate frequency local oscillator signal to create a modulated intermediate frequency signal;

e. a GSM path responsive to the modulated intermediate frequency signal; and

f. a UMTS path responsive to the modulated intermediate frequency signal; wherein

the GSM path comprises a voltage controlled oscillator within a phase locked loop, the phase locked loop including an image reject mixer receiving at a first input thereof the output of the voltage controlled oscillator, and at second inputs thereof the first radio frequency signal, such that it selectively outputs either the upper or lower side band of the mixing of the signals supplied to it as a signal in the phase locked loop; and wherein

the UMTS path comprises at least one variable gain amplifier and a mixer for mixing the first radio frequency signal with the intermediate signal and outputting one of the side bands of the mixing process.

19. A transmitter as claimed in claim 18 in which the oscillator is tuneable.

20. A transmitter as claimed in claim 19 , in which the oscillator is tuneable over a range of substantially 10% with respect to a nominal centre frequency.

21. A transmitter as claimed in claim 18 in which the oscillator is associated with a divider so as to produce in-phase and quadrature signals.

22. A transmitter as claimed in claim 21 , in which the in-phase and quadrature signals have a frequency F 1 .

23. A transmitter as claimed in claim 18 , in which the first radio frequency signal comprises an in-phase signal and a quadrature signal.

24. A transmitter as claimed in claim 23 , wherein the in-phase and quadrature signals are frequency divided to generate in-phase and quadrature local oscillator signals.

25. A transmitter as claimed in claim 18 , wherein the transmitter is provided as part of an integrated circuit.

26. A transmitter as claimed in claim 18 , wherein, with the exception of output power amplifiers, the transmitter is provided as part of an integrated circuit.

27. A mobile telephone including a transmitter as claimed in claim 1 or 18 .

28. A mobile telephone as claimed in claim 18 , wherein a receiver is provided, and the receiver is a homodyne receiver and receives the signal F 1 for performing down conversion.