Digital transmitter and method

• US 20040192229A1
• Filed: 03/31/2003
• Published: 09/30/2004
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Fuller, Arthur Thomas Gerald, Morris, Bradley John
• Granted Patent: US 6,987,953 B2
• Time in Patent Office: Days
• US Class Current: 455/91
• CPC Class Codes: H04B 1/0483 Transmitters with multiple parallel paths

Abstract

A transmitter and method is provided for digitally upconverting a baseband digital signal to a modulated intermediate frequency (IF) digital signal and sigma-delta modulating the IF digital signal. The baseband digital signal is split into N phases, as can be accomplished using a polyphase interpolation technique (polyphase filter), and modulated. The modulated N phases are not recombined and each phase is further modulated, as can be accomplished using a digital-to-digital sigma-delta modulator that generates digital output signals at the same rate. A high speed digital multiplexer multiplexes the digital output signals into a single bit stream at a higher rate for subsequent power amplification and RF transmission.

Claims

1. A transmitter, comprising:

a digital upconverter for receiving a baseband digital signal having a first rate and upconverting the baseband digital signal to an upconverted digital signal having a second rate;

circuitry for receiving the upconverted digital signal and separating the upconverted digital signal to generate a plurality of parallel digital signals;

a modulator for receiving and modulating the parallel digital signals to generate a plurality of modulated digital signals;

a digital-to-digital modulator for receiving the plurality of modulated digital signals and generating a plurality of modulated digital signals; and

a multiplexer operable to generate a digital output signal.

2. The transmitter in accordance with claim 1 further comprising:

an analog bandpass filter for receiving the digital output signal and converting the digital output signal to an analog output signal; and

a power amplifier for receiving the analog output signal and generating an radio frequency (RF) output signal.

3. The transmitter in accordance with claim 1 further comprising:

a switching amplifier for receiving the digital output signal and generating an amplified digital output signal; and

an analog bandpass filter for receiving the amplified digital output signal and converting the amplified digital output signal to a radio frequency (RF) output signal.

4. The transmitter in accordance with claim 1 further comprising:

a local oscillator for generating a LO signal for use by the multiplexer in selecting the inputs to the multiplexer for output.

5. The transmitter in accordance with claim 1 wherein the upconverted digital signal comprises I and Q signals and the modulator further functions to combine the I and Q signals to generate the plurality of modulated digital signals.

6. The transmitter in accordance with claim 1 wherein the circuitry comprises a polyphase circuit is an interpolator and operable to separate the upconverted digital signal into a number N of parallel digital signals, and the interpolator further comprises:

a number N of subfilters for filtering each of the N parallel digital signals.

7. The transmitter in accordance with claim 1 wherein the circuitry comprises a polyphase filter operable to separate the upconverted digital signal into a number N phase signals, where N is a integer multiple of four, and the circuitry further comprises:

a number N of subfilters for filtering each of the N phase signals.

8. The transmitter in accordance with claim 7 wherein the circuitry comprises N subfilters with each subfilter having a set of coefficients, and wherein the coefficients of the subfilters correspond with a set of coefficients of the polyphase filter.

9. The transmitter in accordance with claim 8 wherein the circuitry comprises a digital finite impulse response filter.

10. The transmitter in accordance with claim 8 wherein the upconverted digital signal comprises I and Q signals, and wherein the filter coefficients of the subfilters are modified such that the subfilters implement the modulator for the I and Q signals.

11. The transmitter in accordance with claim 1 wherein the plurality of modulated digital signals received by the modulator comprise a first sample having one or more binary bits and the generated plurality of modulated digital signals comprise a second sample having one or more binary bits and which correspond to the first sample.

12. The transmitter in accordance with claim 11 wherein the second sample comprises a single bit.

13. The transmitter in accordance with claim 1 wherein the modulator further comprises a plurality of sigma-delta modulators.

14. A transmitter, comprising:

means for receiving a baseband digital signal having a first rate and upconverting the baseband digital signal to an upconverted digital signal having a second rate;

means for receiving the upconverted digital signal and separating the upconverted digital signal to generate a plurality of parallel digital signals;

means for receiving and modulating the parallel digital signals to generate a plurality of modulated digital signals;

means for receiving the plurality of modulated digital signals and generating a plurality of second modulated digital signals; and

means for receiving and multiplexing the plurality of second modulated digital signals to generate a digital output signal.

15. The transmitter in accordance with claim 14 further comprising:

means for receiving the digital output signal and converting the digital output signal to an analog output signal; and

means for receiving the analog output signal and generating an radio frequency (RF) output signal.

16. The transmitter in accordance with claim 14 further comprising:

means for receiving the digital output signal and generating an amplified digital output signal; and

means for receiving the amplified digital output signal and converting the amplified digital output signal to a radio frequency (RF) output signal.

17. A method of upconverting a digital signal for RF transmission, comprising:

receiving a baseband digital signal having a first rate;

upconverting the baseband digital signal to an upconverted digital signal having a second rate;

separating the upconverted digital signal into a plurality of phased digital signals;

modulating the phased digital signals to generate a plurality of modulated digital signals;

modulating the plurality of modulated digital signals to generate a plurality of second modulated digital signals; and

multiplexing the plurality of second modulated digital signals and to generate and output a digital output.

18. The method in accordance with claim 17 wherein the upconverted digital signal comprises I and Q signals and the I and Q signals are modulated to generate the plurality of modulated digital signals.

19. The method in accordance with claim 17 wherein a polyphase interpolator separates the upconverted digital signal into a number N of phase signals, and the method further comprises:

filtering each of the N phase signals with a subfilter.

20. The transmitter in accordance with claim 19 wherein N is an integer multiple of four, and the subfilters comprise a digital finite impulse response function.

21. A wireless communications device, comprising:

a transmitter, comprising,

a digital upconverter for receiving a baseband digital signal having a first rate and upconverting the baseband digital signal to an upconverted digital signal having a second rate,

circuitry for receiving the upconverted digital signal and separating the upconverted digital signal to generate a plurality of parallel digital signals,

a modulator for receiving and modulating the parallel digital signals to generate a plurality of modulated digital signals,

a digital-to-digital modulator for receiving the plurality of modulated digital signals and generating a plurality of modulated digital signals, and

a multiplexer operable to generate a digital output signal.

22. The wireless communications device in accordance with claim 21 wherein the device is a mobile terminal.

23. The wireless communications device in accordance with claim 21 wherein the device is a base station.