Constant gain nonlinear envelope tracking high efficiency linear amplifier
An envelope tracking radio frequency (RF) power amplifier having an adaptive envelope signal processing circuit is disclosed. An RF input voltage is sampled by the adaptive envelope signal processing circuit which provides control signals to the power supply which supplies voltages to RF power devices in order to simultaneously satisfy two operating conditions: a) provide best possible efficiency of the power amplifier stages depending on the input signal characteristics and b) provide compensation for RF transistor AM-AM and AM-PM distortion compensation across the power range. In particular, the voltage control provides for constant power amplifier gain across the input signal dynamic range, thus minimizing power amplifier amplitude distortions and extending the useful power amplifier linear dynamic range up to saturation point. The power amplifier thus exhibits better linearity and efficiency than offered by conventional techniques and topologies.
1. A power amplifier system, comprising:
an input for receiving an RF input signal including a modulated RF carrier having a dynamically varying envelope;
an RF amplifier receiving and amplifying the RF input signal including said carrier and envelope, the RF amplifier having a power supply input and the RF amplifier having a saturation region;
a DC power supply;
a variable power supply circuit coupled to the input, the DC power supply and the RF amplifier power supply input for providing a supply voltage to the RF amplifier which increases with the input signal power to maintain substantially constant RF amplifier gain up to the beginning of said amplifier saturation region; and
a phase compensation circuit coupled to the input for adjusting the phase of the input signal to compensate for phase variations due to the variable power supply.
2. A power amplifier system as set out in claim 1 , wherein said variable power supply circuit provides a substantially constant power supply voltage over a first lower power input signal region and provides a continuously increasing power supply voltage in a second higher power input signal region.
3. A power amplifier system as set out in claim 2 , wherein said power supply voltage varies from about 10 volts in said first region to about 30 volts in said saturation region.
4. A power amplifier system as set out in claim 2 , wherein the phase compensation circuit comprises a phase adjuster, coupled between the input and RF amplifier for adjusting the phase of the input signal, and a predistorter providing a control signal to said phase adjuster based on the input signal magnitude.
5. A power amplifier system as set out in claim 4 , wherein said predistorter controls said phase adjuster to provide little or no phase adjustment in said first input signal region and a continuously increasing phase adjustment in said second input signal region.
6. A power amplifier system as set out in claim 5 , wherein said phase adjustment in said second region varies over a range of about 30 degrees.
7. A power amplifier system as set out in claim 1 , wherein said RF amplifier comprises one or more LDMOS amplifier devices.
8. A power amplifier system as set out in claim 7 , wherein said one or more LDMOS amplifier devices are biased in class AB.
9. A power amplifier system, comprising;
an input for receiving an RF input signal including a modulated RF carrier having having a dynamically varying envelope;
an RF amplifier receiving and amplifying the RF input signal including said carrier and envelope, the RF amplifier having a power supply input and the RF amplifier having a saturation region;
a DC power supply;
a variable power supply circuit coupled to the input, the DC power supply and the RF amplifier power supply input for providing a supply voltage to the RF amplifier which increases with the input signal power to maintain substantially constant RF amplifier gain up to the beginning of said amplifier saturation region; and
a phase compensation circuit coupled to the input for adjusting the phase of the input signal to compensate for phase variations due to the variable power supply,
wherein said variable power supply circuit comprises an envelope detector coupled to the input and an envelope amplifier responsive to the output of the envelope detector and coupled to the DC power supply and RF amplifier.
10. A method for amplifying a high frequency modulated signal, comprising:
receiving a high frequency modulated input signal having a carrier and a dynamically varying envelope providing a varying input signal power;
amplifying said high frequency modulated input signal, including said carrier and varying envelope, with a power amplifier module, said power amplifier module having a saturation region;
providing a DC supply voltage to said power amplifier module;
detecting a signal related to the power of the high frequency modulated input signal;
controlling the DC supply voltage of said power amplifier module in response to the detected signal to maintain substantially constant gain up to the beginning of said saturation region; and
adjusting the phase of the input signal to compensate for phase variations introduced by controlling the supply voltage of the power amplifier module.
11. A method for amplifying a high frequency modulated signal as set out in claim 10 , wherein controlling the DC supply voltage comprises maintaining a substantially constant supply voltage over a first input signal power range and continuously increasing the DC supply voltage over a second higher power input signal power range.
12. A method for amplifying a high frequency modulated signal as set out in claim 11 , wherein said second input signal power range extends from a transition region to the beginning of said saturation region of the power amplifier module.
13. A method for amplifying a high frequency modulated signal as set out in claim 11 , wherein continuously increasing the DC supply voltage comprises increasing the supply voltage from about 10 volts to about 30 volts.
14. A method for amplifying a high frequency modulated signal having a carrier and a dynamically varying envelope as set out in claim 10 , wherein detecting a signal related to the power of the input signal comprises detecting the envelope of the input signal.
15. A method for amplifying a high frequency modulated signal as set out in claim 10 , wherein said high frequency signal is an RF CDMA or WCDMA signal.
16. A method for amplifying a high frequency modulated signal, comprising:
receiving a high frequency modulated input signal having a carrier and a dynamically varying envelope providing a varying input signal power;
amplifying said high frequency modulated input signal, including said carrier and varying envelope, with a power amplifier module, said power amplifier module having a saturation region;
detecting a signal related to the power of the high frequency modulated input signal;
providing a variable DC supply voltage to said power amplifier module in response to the detected signal which continuously increases in a higher power input signal range extending up to the beginning of said saturation region; and
adjusting the phase of said input signal with a continuously increasing phase adjustment in said higher power signal range;
wherein the gain and phase are maintained substantially constant up to the beginning of said saturation region.
17. A method for amplifying a high frequency modulated signal as set out in claim 16 , wherein providing a variable DC supply voltage further comprises maintaining a substantially constant supply voltage over a lower power input signal range below said higher power input signal power range.
18. A method for amplifying a high frequency modulated signal as set out in claim 17 , wherein said input signal is a CDMA or WCDMA modulated RF signal.
19. A method for amplifying a high frequency modulated signal as set out in claim 17 , wherein adjusting the phase comprises adjusting the phase from about 0 degrees to about 30 degrees continuously through the higher power input signal range.
20. A method for amplifying a high frequency modulated signal as set out in claim 16 , wherein detecting a signal related to the power of the input signal comprises detecting the envelope of the input signal.