Radio frequency transmitter energy shifting during ramp-down

1. Radio frequency (RF) circuitry comprising:

control circuitry adapted to select one of a plurality of operating modes, such that the plurality of operating modes comprises a data burst mode, and an energy-shifted ramp-down mode; and

IQ modulation circuitry adapted to:

during the data burst mode, modulate an RF carrier signal having an RF carrier frequency to provide a modulated RF signal, such that a maximum energy spectrum peak of the modulated RF signal is about coincident with the RF carrier frequency; and

during the energy-shifted ramp-down mode, modulate the RF carrier signal to provide the modulated RF signal, such that the maximum energy spectrum peak is shifted away the RF carrier frequency.

2. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode:

the maximum energy spectrum peak is associated with an energy spectrum of the modulated RF signal; and

an energy level of the energy spectrum at the RF carrier frequency is at least 10 decibels (dB) less than the maximum energy spectrum peak.

3. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode:

the maximum energy spectrum peak is associated with an energy spectrum of the modulated RF signal; and

an energy level of the energy spectrum at the RF carrier frequency is at least 20 decibels (dB) less than the maximum energy spectrum peak.

4. The RF circuitry of claim 1 wherein:

the plurality of operating modes further comprises a standard ramp-down mode and a ramp-up mode;

the ramp-up mode is immediately followed by the data burst mode; and

the standard ramp-down mode is immediately preceded by the data burst mode.

5. The RF circuitry of claim 1 further comprising RF down-conversion circuitry adapted to during a receive mode, receive and down-convert an RF receive signal to provide a baseband receive signal, such that RF power amplifier circuitry is adapted to during the data burst mode and the energy-shifted ramp-down mode, receive and amplify the modulated RF signal to provide an RF transmit signal, wherein the plurality of operating modes further comprises the receive mode.

6. The RF circuitry of claim 5 wherein a carrier frequency of the RF transmit signal is about equal to a carrier frequency of the RF receive signal.

7. The RF circuitry of claim 6 wherein the RF down-conversion circuitry comprises direct current (DC) offset correction circuitry adapted to:

during the energy-shifted ramp-down mode and a receive preparation mode, measure a DC offset of the RF down-conversion circuitry to obtain a measured DC offset; and

during the receive mode, apply a DC offset correction to the RF down-conversion circuitry based on the measured DC offset, wherein the plurality of operating modes further comprises the receive preparation mode.

8. The RF circuitry of claim 7 wherein a bandwidth of the DC offset correction circuitry is wider during the receive preparation mode than during the energy-shifted ramp-down mode.

9. The RF circuitry of claim 6 further comprising a common frequency synthesizer adapted to:

during the data burst mode, provide the RF carrier signal to an IQ modulator to create the modulated RF signal; and

during the energy-shifted ramp-down mode, provide an RF local oscillator (LO) signal to the RF down-conversion circuitry, such that the RF carrier signal to provide the modulated RF signal adjusts a frequency of the RF LO signal to correspond to a desired receive frequency of the RF receive signal to compensate for pulling of the common frequency synthesizer; and

during the receive mode, provide the RF LO signal to the RF down-conversion circuitry for down-conversion of the RF receive signal, such that the frequency of the RF LO signal corresponds to the desired receive frequency of the RF receive signal.

10. The RF circuitry of claim 6 further comprising:

a receive frequency synthesizer adapted to:

during the energy-shifted ramp-down mode, provide an RF local oscillator (LO) signal to the RF down-conversion circuitry, such that a frequency of the RF LO signal corresponds to a desired receive frequency of the RF receive signal; and

during the receive mode, provide the RF LO signal to the RF down-conversion circuitry for down-conversion of the RF receive signal, such that the frequency of the RF LO signal corresponds to the desired receive frequency of the RF receive signal; and

a transmit frequency synthesizer adapted to:

during the data burst mode, provide the RF carrier signal to an IQ modulator to create the modulated RF signal; and

during the energy-shifted ramp-down mode, adjust the frequency of the RF LO signal to correspond to the desired receive frequency of the RF receive signal using the RF carrier signal to provide the modulated RF signal to compensate for pulling of the receive frequency synthesizer.

11. The RF circuitry of claim 6 wherein the RF transmit signal and the RF receive signal are time division duplexing (TDD) signals.

12. The RF circuitry of claim 11 wherein the RF transmit signal and the RF receive signal are long term evolution (LTE) signals.

13. The RF circuitry of claim 11 wherein the RF transmit signal and the RF receive signal are time division synchronous code division multiple access (TD-SCDMA) signals.

14. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode, the RF carrier signal to provide the modulated RF signal includes shifting a frequency of the RF carrier signal.

15. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode, the RF carrier signal to provide the modulated RF signal includes amplitude modulating the RF carrier signal.

16. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode, the RF carrier signal to provide the modulated RF signal includes phase modulating the RF carrier signal.

17. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode, the RF carrier signal to provide the modulated RF signal includes amplitude modulating and phase modulating the RF carrier signal.

18. The RF circuitry of claim 1 wherein during the energy-shifted ramp-down mode, the RF carrier signal to provide the modulated RF signal includes sending a string of data via the modulated RF signal.

19. The RF circuitry of claim 18 wherein the string of data includes alternating ones and zeros.

20. The RF circuitry of claim 1 wherein a duration of the energy-shifted ramp-down mode is equal to between about 5.5 and about 7.5 microseconds, and a duration of a receive preparation mode is equal to between about 5 and about 7 microseconds, wherein the plurality of operating modes further comprises the receive preparation mode.

21. The RF circuitry of claim 1 wherein a duration of the energy-shifted ramp-down mode is equal to about 6.5 microseconds and a duration of a receive preparation mode is equal to about 6 microseconds, wherein the plurality of operating modes further comprises the receive preparation mode.

22. The RF circuitry of claim 1 further comprising:

RF power amplifier circuitry adapted to during the data burst mode and the energy-shifted ramp-down mode, receive and amplify the modulated RF signal to provide an RF transmit signal; and

RF down-conversion circuitry adapted to during a receive mode, receive and down-convert an RF receive signal to provide a baseband receive signal, wherein the plurality of operating modes further comprises the receive mode.

23. A method comprising:

selecting one of a plurality of operating modes, such that the plurality of operating modes comprises a data burst mode, and an energy-shifted ramp-down mode;

providing IQ modulation circuitry;

during the data burst mode, modulating an RF carrier signal having an RF carrier frequency to provide a modulated RF signal, such that a maximum energy spectrum peak of the modulated RF signal is about coincident with the RF carrier frequency; and

during the energy-shifted ramp-down mode, modulating the RF carrier signal to provide the modulated RF signal, such that the maximum energy spectrum peak is shifted away the RF carrier frequency.