Broadband digital transmitter using π/4 phase offset local oscillator (LO) signals

1. A digital transmitter, comprising:

a vector decomposer circuit configured to receive baseband in-phase (I) and quadrature (Q) signals and to decompose the baseband I and Q signals into an offset envelope signal and a non-offset envelope signal;

a phase selector circuit configured to receive a plurality of phase offset local oscillator (LO) signals and to output, responsive to the baseband I and Q signals, first and second offset LO signals and first and second non-offset LO signals; and

a digital power amplifier (DPA) comprising:

an offset DPA circuit configured to generate a first signal based on the offset envelope signal and the first and second offset LO signals;

a non-offset DPA circuit configured to generate a second signal based on the non-offset envelope signal and the first and second non-offset LO signals; and

a combiner circuit configured to combine the first signal and the second signal to generate an output signal of the digital transmitter.

2. The digital transmitter of claim 1 , wherein the vector decomposer circuit comprises:

first circuitry configured to generate an I envelope signal and a Q envelope signal based on the baseband I and Q signals respectively; and

second circuitry configured to generate the offset envelope signal and the non-offset envelope signal from the I envelope signal and the Q envelope signal.

3. The digital transmitter of claim 2 , wherein the second circuitry is further configured to:

determine the smaller signal between the I envelope signal and the Q envelope signal; and

multiply the smaller signal by the square root of two to generate the offset envelope signal.

4. The digital transmitter of claim 2 , wherein the second circuitry is further configured to:

generate a difference signal between the I envelope signal and the Q envelope signal; and

generate the non-offset envelope signal as an envelope of the difference signal.

5. The digital transmitter of claim 1 , wherein the vector decomposer circuit is configured to generate a phase control signal based on the baseband I and Q signals.

6. The digital transmitter of claim 5 , wherein the phase selector circuit is configured to output the first and second offset LO signals and first and second non-offset LO signals based on the phase control signal.

7. The digital transmitter of claim 6 , wherein the plurality of phase offset LO signals include a first set of offset LO signals and a second set of non-offset LO signals, and wherein the phase selector circuit is further configured to:

select the first and second offset LO signals from the first set of offset LO signals based on a first control signal included in the phase control signal; and

select the first and second non-offset LO signals from the second set of non-offset LO signals based on a second control signal included the phase control signal.

8. The digital transmitter of claim 7 , wherein the phase selector circuit is further configured to:

swap the first and second offset LO signals before outputting the first and second offset LO signals responsive to a third control signal, included in the phase control signal, having a first pre-determined logic level; and

swap the first and second non-offset LO signals before outputting the first and second non-offset LO signals responsive to a fourth control signal, included in the phase control signal, having a second pre-determined logic level.

9. A method for digital transmission, comprising:

receiving baseband in-phase (I) and quadrature (Q) signals;

decomposing the baseband I and Q signals into an offset envelope signal and a non-offset envelope signal;

selecting from a plurality of phase offset local oscillator (LO) signals, responsive to the baseband I and Q signals, first and second offset LO signals and first and second non-offset LO signals; and

generating an output signal using the offset envelope signal, the non-offset envelope signal, the first and second offset LO signals and the first and second non-offset LO signals,

wherein the first offset LO signal, the second offset LO signal, the first non-offset LO signal and the second non-offset LO signals all have different phases relative to each other.

10. The method of claim 9 , wherein decomposing the baseband I and Q signals comprises:

generating an I envelope signal and a Q envelope signal based on the baseband I and Q signals respectively; and

generating the offset envelope signal and the non-offset envelope signal from the I envelope signal and the Q envelope signal.

11. The method of claim 10 , wherein generating the offset envelope signal comprises:

determining the smaller signal between the I envelope signal and the Q envelope signal; and

multiplying the smaller signal by the square root of two to generate the offset envelope signal.

12. The method of claim 10 , wherein generating the non-offset envelope signal comprises:

generating a difference signal between the I envelope signal and the Q envelope signal; and

generating the non-offset envelope signal as an envelope of the difference signal.

13. A method for digital transmission comprising:

receiving baseband in-phase (I) and quadrature (Q) signals;

generating a phase control signal based on the baseband I and Q signals;

decomposing the baseband I and O signals into an offset envelope signal and a non-offset envelope signal;

selecting from a plurality of phase offset local oscillator (LO) signals, based on the phase control signal, first and second offset LO signals and first and second non-offset LO signals; and

generating an output signal using the offset envelope signal, the non-offset envelope signal, the first and second offset LO signals and the first and second non-offset LO signals.

14. The method of claim 13 , wherein the plurality of phase offset LO signals include a first set of offset LO signals and a second set of non-offset LO signals, and wherein selecting the first and second offset LO signals and the first and second non-offset LO signals further comprises:

selecting the first and second offset LO signals from the first set of offset LO signals based on a first control signal included in the phase control signal; and

selecting the first and second non-offset LO signals from the second set of non-offset LO signals based on a second control signal included in the phase control signal.

15. The method of claim 14 , wherein the plurality of phase offset LO signals include a first set of offset LO signals and a second set of non-offset LO signals, and wherein selecting the first and second offset LOs and first and second non-offset LOs further comprises:

selecting the first and second offset LO signals from the first set of offset LO signals based on a first control signal included in the phase control signal; and

selecting the first and second non-offset LO signals from the second set of non-offset LO signals based on a second control signal included the phase control signal.

16. The method of claim 9 , further comprising:

generating a first signal based on the offset envelope signal and the first and second offset LO signals;

generating a second signal based on the non-offset envelope signal and the first and second non-offset LO signals; and

combining the first signal and the second signal to generate the output signal.

17. A digital transmitter, comprising:

a vector decomposer circuit configured to receive baseband in-phase (I) and quadrature (Q) signals, generate a phase control signal based on the baseband I and Q signals, and decompose the baseband I and Q signals into an offset envelope signal and a non-offset envelope signal;

a phase selector circuit configured to receive a plurality of phase offset local oscillator (LO) signals and to output, based on the phase control signal, first and second offset LO signals and first and second non-offset LO signals; and

a digital power amplifier (DPA) configured to generate an output signal of the digital transmitter using the offset envelope signal, the non-offset envelope signal, the first and second offset LO signals and the first and second non-offset LO signals.

18. The digital transmitter of claim 17 , wherein the plurality of phase offset LO signals include a first set of offset LO signals and a second set of non-offset LO signals, and wherein the phase selector circuit is further configured to:

output the first and second offset LO signals from the first set of offset LO signals based on a first control signal included in the phase control signal; and

output the first and second non-offset LO signals from the second set of non-offset LO signals based on a second control signal included the phase control signal.

19. The digital transmitter of claim 18 , wherein the phase selector circuit is further configured to:

swap the first and second offset LO signals responsive to a third control signal, included in the phase control signal, having a first pre-determined logic level; and

swap the first and second non-offset LO signals responsive to a fourth control signal, included in the phase control signal, having a second pre-determined logic level.

20. The digital transmitter of claim 17 , wherein the first and second offset LO signals and the first and second non-offset LO signals all have different phases relative to each other.