Multistage modulation architecture and method in a radio

• US 20020164965A1
• Filed: 05/03/2001
• Published: 11/07/2002
• Est. Priority Date: 05/03/2001
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Larson, Lawrence E., Chominski, Paul P., Kennedy, Jonathan L., Park, Joshua C.
• Granted Patent: US 6,915,117 B2
• Time in Patent Office: Days
• US Class Current: 455/118
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/40 Circuits

Abstract

In a multiple stage transmitter, and analog signal is modulated and mixed to produce a radio frequency output. A separate mixing frequency signal is provided to each stage. A single frequency synthesizer is used rather than a plurality of frequency synthesizers. In a two-stage system, first and second dividers each receive the output of the frequency synthesizer and deliver a mixing signal to the first and second stages respectively. The modulus of each divider may be selected to minimize spurious signals.

Claims

1. In a double conversion transmitter transmitting a radio frequency signal in response to an analog signal input and comprising a modulator including a first mixer providing an intermediate frequency output and a second mixer providing a radio frequency output, said mixers being supplied with first and second mixing signals respectively and mixing signal means for providing said first and second mixing signals, the improvement wherein said mixing signal means comprises:

a first frequency divider and a second frequency divider connected to said first mixer and said second mixer respectively, each of said first and second frequency dividers having a respective, selected modulus; and

a frequency synthesizer providing a signal at a local oscillator frequency to said first and second frequency dividers.

2. The transmitter according to claim 1 wherein said modulator comprises both in-phase and quadrature channels and said first mixer comprises a mixer in each said channel and wherein said first frequency divider provides an input to said mixer to each said channel.

3. The transmitter according to claim 2 wherein said first and second frequency dividers are each constructed with a different modulus.

4. The transmitter according to claim 3 wherein the modulus of the first and second frequency dividers are related by the expression:

f_RF=[(M1+M2)/(M1*M2)]*f_VCO

where f_RF is the frequency of the radio frequency signal, M1 and M2 are the first and second moduli respectively and f_VCO is the output frequency of the frequency synthesizer.

5. The transmitter according to claim 4 wherein M1 is a multiple of 4.

6. The transmitter according to claim 5 where M2−

M1±

N where N is a positive integer.

7. In a transmitter transmitting a radio frequency signal in response to an analog signal input and comprising a plurality of stages, a first said stage receiving said analog signal and including a modulator, each said stage further comprising a mixer providing an output having a frequency which is a function of an input frequency to said stage and output and a respective mixing signals to supplied to said mixer and mixing signal means for providing said mixing signals, the improvement wherein said mixing signal means comprises:

a plurality of frequency dividers each connected to a respective said mixer; and

a frequency synthesizer providing a signal at a local oscillator frequency to each said frequency divider.

8. The transmitter according to claim 7 wherein said modulator comprises both in-phase and quadrature channels and said first stage mixer comprises a mixer in each said channel and wherein said frequency divider connected to said first stage provides an input to said mixer to each said channel.

9. The transmitter according to claim 8 wherein said first and second frequency dividers are each constructed with a different modulus.

10. A double conversion transmitter transmitting a radio frequency signal in response to an analog signal input and comprising a modulator including a first mixer providing an intermediate frequency output and a second mixer providing a radio frequency output, said mixers being supplied with first and second mixing signals respectively, a frequency synthesizer providing a signal at a local oscillator frequency, first and second frequency dividers each receiving an input from said frequency synthesizer and coupled for providing said first and second mixing signals to said first mixer and said second mixer respectively.

11. The transmitter according to claim 10 wherein said modulator comprises both in-phase and quadrature channels and said first mixer comprises a mixer in each said channel and wherein said first frequency divider provides an input to said mixer to each said channel.

12. The transmitter according to claim 11 wherein said first and second frequency dividers are each constructed with a different modulus.

13. The transmitter according to claim 12 wherein the modulus of the first and second frequency dividers are related by the expression:

f_RF=[(M1+M2)/(M1*M2)]*f_VCO

where f_RF is the frequency of the radio frequency signal, M1 and M2 are the first and second moduli respectively and f_VCO is the frequency of the frequency synthesizer.

14. The transmitter according to claim 13 wherein M1 is a multiple of 4.

15. The transmitter according to claim 14 where M2=M1±

N where N is a positive integer.

17. The method of claim 16 wherein the step of modulating comprises modulating in-phase and quadrature components of said analog signal and wherein said step of mixing comprises mixing each said component with said first mixing frequency.

18. The method of claim 17 wherein the step of dividing comprises utilizing first and second moduli to produce said first and second mixing frequencies.

19. The method of claim 18 wherein the moduli in the step of division are related by the expression:

f_RF=[(M1+M2)/(M1*M2)]*f_VCO

where f_RF is the frequency of the radio frequency signal, M1 and M2 are the first and second moduli respectively and f_VCO is the frequency of the frequency synthesizer.

20. The method of claim 19 wherein the step of dividing comprises utilizing an M1 which is a multiple of 4.

21. The method of claim 20 wherein the step of dividing comprises utilizing moduli where M2=M1±

N where N is an integer.

16. In a method for translation an analog signal to a radio frequency signal comprising the steps of modulating an analog signal and mixing the analog signal with a first mixing frequency signal to provide a first intermediate frequency signal and mixing said first intermediate frequency signal with a second mixing frequency signal to provide a radio frequency output, the improvement comprising:

providing a one frequency synthesizer as a source for said first and second mixing frequency signals; and

dividing the output of said frequency synthesizer by first and second divisors to produce said first and second mixing frequencies.