Digital transmitter and method
View Patent ↗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.
1. A signal processing apparatus comprising:
circuitry for receiving a digital signal having a first rate and separating the digital signal to generate a plurality of parallel digital signals;
a modulator for receiving and modulating the plurality of parallel digital signals to generate a plurality of modulated digital signals; and
a digital-to-digital modulator for receiving the plurality of modulated digital signals and generating a plurality of second modulated digital signals.
2. The apparatus in accordance with claim 1 further comprising a multiplexer operable for receiving the plurality of second modulated digital signals and generating a digital output signal.
3. The apparatus in accordance with claim 2 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.
4. The apparatus in accordance with claim 2 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.
5. The apparatus in accordance with claim 1 wherein the 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 apparatus in accordance with claim 1 wherein the circuitry further comprises an interpolator operable to separate the 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 apparatus in accordance with claim 1 wherein the circuitry comprises a polyphase filter operable to separate the 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 apparatus 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 apparatus in accordance with claim 8 wherein the 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.
10. The apparatus 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.
11. The transmitter in accordance with claim 10 wherein the second sample comprises a single bit.
12. The apparatus in accordance with claim 1 wherein the digital-digital modulator further comprises a plurality of sigma-delta modulators.
13. The apparatus in accordance with claim 1 further comprising:
a digital upconverter for receiving a baseband digital signal having a second rate and upconverting the baseband digital signal to the digital signal having the first rate; and
a multiplexor operable for receiving the plurality of second modulated signals and generating a digital output signal.
14. A signal processing apparatus comprising:
means for receiving a digital signal having a first rate and separating the digital signal to generate a plurality of parallel digital signals;
means for receiving and modulating the plurality of parallel digital signals to generate a plurality of modulated digital signals; and
means for receiving the plurality of modulated digital signals and generating a plurality of second modulated digital signals.
15. The signal processing apparatus in accordance with claim 14 further comprising:
means for receiving and multiplexing the plurality of second modulated digital signals to generate a digital output signal;
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 apparatus in accordance with claim 14 further comprising:
means for receiving and multiplexing the plurality of second modulated digital signals to generate a digital output signal;
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 processing a digital signal for RF transmission, comprising:
separating the 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 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 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 method 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,
circuitry for receiving a digital signal having a first rate and separating the digital signal to generate a plurality of parallel digital signals;
a modulator for receiving and modulating the plurality of parallel digital signals to generate a plurality of modulated digital signals; and
a digital-to-digital modulator for receiving the plurality of modulated digital signals and generating a plurality of second modulated digital signals.
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.
24. The wireless communications device in accordance with claim 21 further comprising:
a digital upconverter for receiving a baseband digital signal having a second rate and upconverting the baseband digital signal to the digital signal having the first rate; and
a multiplexor operable for receiving the plurality of second modulated signals and generating a digital output signal.