Bandwidth enhancement for envelope elimination and restoration transmission systems
View Patent ↗Systems and methods for increasing bandwidth capability of an envelope elimination and restoration (EER) transmitter. A frequency response of a power supply modulator of the transmitter is approximated. An inverse response is applied to the envelope signal prior to digital-to-analog conversion (DAC) and before the signal reaches the power supply modulator to pre-emphasize the signal thereby counteracting distorting affects of the modulator. The filter is implemented using any of a variety of different digital techniques including programmable logic, DSP, etc.
1. An envelope elimination and restoration (EER) radio frequency (RF) transmitter comprising:
a data source input adapted to receive a data signal to be transmitted;
an envelope signal path comprising a power supply modulator;
a phase signal path comprising a local oscillator;
a power amplifier at the terminal end of the envelope and phase signal paths that recombines the two signals for RF transmission; and
a pre-emphasis filter in the envelope signal path adapted to pre-emphasize the envelope signal before it reaches the power supply modulator.
2. The transmitter according to claim 1 , wherein the pre-emphasis filter is a digital pre-emphasis filter.
3. The transmitter according to claim 1 , wherein the pre-emphasis filter increases the bandwidth of the transmitter by reducing an intermodulation distortion level cause by the power supply modulator.
4. The transmitter according to claim 3 , wherein the pre-emphasis filter approximates an inverse frequency response of the power supply modulator.
5. The transmitter according to claim 1 , wherein the pre-emphasis filter is a digital infinite impulse response filter implemented in a programmable circuit logic.
6. The transmitter according to claim 1 , wherein the pre-emphasis filter is a digital infinite impulse response filter implemented in a digital signal processor routine.
7. A system for power amplification of an input signal prior to RF transmission of the input signal comprising:
an envelope detector circuit adapted to generate an envelope voltage level from the input signal;
a power supply modulator coupled to the envelope detector circuit adapted to determine a supply voltage from the envelope voltage level signal;
an input signal conditioning circuit adapted to remove amplitude information from the input signal and to mix the stripped signal with a local oscillator signal;
a power amplifier that receives as inputs signals from the power supply modulator and the input signal conditioning circuit and whose output is connected to an RF antenna; and
a pre-emphasis module adapted to perform a pre-emphasis operation on the envelope voltage level signal prior to input to the power supply modulator.
8. The system according to claim 7 , wherein the pre-emphasis module is implemented in digital electronics.
9. The system according to claim 7 , wherein the pre-emphasis module is implemented as programmable circuit logic.
10. The system according to claim 7 , wherein the pre-emphasis module is implemented as a routine executed by a digital signal processor.
11. The system according to claim 7 , wherein the pre-emphasis filter increases the bandwidth of the transmitter by reducing an intermodulation distortion level caused by the power supply modulator.
12. The transmitter according to claim 11 , wherein the pre-emphasis filter approximates an inverse frequency response of the power supply modulator.
13. A method of extending the bandwidth capabilities of an envelope elimination and restoration RF transmitter comprising:
applying a pre-emphasis filter to an envelope signal prior to that signal being input to a supply modulator that is coupled to a power amplifier of the RF transmitter.
14. The method according to claim 13 , wherein applying a pre-emphasis filter comprises determining a frequency response of the power supply modulator and applying a filter that approximates an inverse of the modulator's frequency response.
15. The method according to claim 13 , wherein applying a pre-emphasis filter comprises applying a digital pre-emphasis filter implemented in digital circuitry of the RF transmitter.
16. The method according to claim 13 , wherein applying a pre-emphasis filter comprises applying a digital pre-emphasis filter implemented in a programmable logic circuit.
17. The method according to claim 13 , wherein applying a pre-emphasis filter comprises subjecting the envelope signal to a routine executed on a digital signal processor.
18. A method of generating a supply modulator signal for a power amplifier of an RF transmitter comprising:
separating a digital data source signal into respective envelope and phase data paths;
subjecting the digital data source signal on the envelope data path to an envelope detection process that generates a signal corresponding an envelope of the digital data source signal;
applying a pre-emphasis filter to this envelope signal to generate a pre-emphasized envelope signal;
performing a digital to analog conversion of the pre-emphasized envelope signal; and
supplying the pre-emphasized envelope signal to a power supply modulator connected to the input of the power amplifier.
19. The method according to claim 18 , wherein applying a pre-emphasis filter comprises determining a frequency response of the power supply modulator and applying a filter that approximates an inverse of the modulator's frequency response.
20. The method according to claim 18 , wherein applying a pre-emphasis filter comprises applying a digital pre-emphasis filter implemented in a programmable logic circuit.
21. The method according to claim 18 , wherein applying a pre-emphasis filter comprises subjecting the envelope signal to a routine executed on a digital signal processor.