Advanced gain shaping for envelope tracking power amplifiers
Envelope tracking power amplifiers with advanced gain shaping are provided. In certain implementations, a power amplifier system includes a power amplifier that amplifies a radio frequency (RF) signal and an envelope tracker that controls a voltage level of a supply voltage of the power amplifier based on an envelope of the RF signal. The power amplifier system further includes a gain shaping circuit that generates a gain shaping current that changes with the voltage level of the supply voltage from the envelope tracker. For example, the gain shaping circuit can include an analog look-up table (LUT) mapping a particular voltage level of the supply voltage to a particular current level of gain shaping current. Additionally, the gain shaping circuit biases the power amplifier based on the gain shaping current.
1. A power amplifier system comprising:
a power amplifier configured to amplify a radio frequency signal;
an envelope tracker configured to control a voltage level of a supply voltage of the power amplifier based on an envelope of the radio frequency signal; and
a gain shaping circuit configured to generate a gain shaping current based on the voltage level of the supply voltage from the envelope tracker, and to bias the power amplifier based on the gain shaping current, the gain shaping circuit including a plurality of current steering circuits each configured to control the gain shaping current.
2. The power amplifier system of claim 1 wherein the gain shaping circuit is operable to map a plurality of supply voltage levels of the supply voltage to a corresponding plurality of current levels of the gain shaping current.
3. The power amplifier system of claim 1 wherein the gain shaping circuit reduces the gain shaping current in response to an increase in the voltage level of the supply voltage of the power amplifier.
4. The power amplifier system of claim 1 wherein the gain shaping circuit includes a regulator configured to generate a plurality of reference voltages of different voltage levels, the plurality of current steering circuits each configured to compare the supply voltage to a corresponding one of the plurality of reference voltages.
5. The power amplifier system of claim 1 further comprising a regulator configured to generate a common reference voltage and a resistor ladder configured to receive the supply voltage and to generate a plurality of scaled supply voltages, the plurality of current steering circuits each configured to compare the common reference voltage to a corresponding one of the plurality of scaled supply voltages.
6. A power amplifier system comprising:
a power amplifier configured to amplify a radio frequency signal;
an envelope tracker configured to control a voltage level of a supply voltage of the power amplifier based on an envelope of the radio frequency signal; and
a gain shaping circuit configured to generate a gain shaping current based on the voltage level of the supply voltage from the envelope tracker, and to bias the power amplifier based on the gain shaping current, the gain shaping circuit operable to bias a driver stage of the power amplifier.
7. The power amplifier system of claim 6 further comprising an input matching network connected between an input terminal and the driver stage, the gain shaping current configured to couple a portion of the radio frequency signal at the input terminal to a bias input of the driver stage.
8. The power amplifier system of claim 1 wherein the gain shaping circuit is further configured to generate a reference current, and to bias the power amplifier based on the reference current.
9. The power amplifier system of claim 8 the gain shaping circuit is configured to bias the power amplifier based on combining the reference current and the gain shaping current.
10. A method of amplification in a mobile device, the method comprising:
amplifying a radio frequency signal using a power amplifier;
controlling a voltage level of a supply voltage of the power amplifier based on an envelope of the radio frequency signal using an envelope tracker;
biasing the power amplifier based on a gain shaping current using a gain shaping circuit, including controlling the gain shaping current based on the voltage level of the supply voltage from the envelope tracker; and
generating a reference current using the gain shaping circuit, and further biasing the power amplifier based on combining the reference current and the gain shaping current.
11. The method of claim 10 further comprising mapping a plurality of supply voltage levels of the supply voltage to a corresponding plurality of current levels of the gain shaping current.
12. The method of claim 10 further comprising reducing the gain shaping current in response to an increase in the voltage level of the supply voltage of the power amplifier.
13. The method of claim 10 wherein controlling the gain shaping current includes individually selecting one or more of a plurality of current steering circuits based on the voltage level of the supply voltage.
14. The method of claim 10 wherein biasing the power amplifier with the gain shaping current includes biasing a driver stage of the power amplifier, the method further comprising providing input matching using an input matching network that is coupled between an input terminal and the driver stage, and coupling a portion of the radio frequency signal at the input terminal to a bias input of the driver stage using the gain shaping circuit.
15. A mobile device comprising:
a power management system including an envelope tracker configured to control a voltage level of a supply voltage based on an envelope of a radio frequency signal;
a transceiver configured to generate the radio frequency signal; and
a front end system including a power amplifier configured to amplify the radio frequency signal, and a gain shaping circuit configured to generate a gain shaping current based on the voltage level of the supply voltage from the envelope tracker, and to bias the power amplifier based on the gain shaping current, the gain shaping circuit including a plurality of current steering circuits each configured to control the gain shaping current based on a comparison.
16. The mobile device of claim 15 wherein the gain shaping circuit is operable to map a plurality of supply voltage levels of the supply voltage to a corresponding plurality of current levels of the gain shaping current.
17. The mobile device of claim 15 wherein the gain shaping circuit reduces the gain shaping current in response to an increase in the voltage level of the supply voltage of the power amplifier.
18. The power amplifier system of claim 6 wherein the gain shaping circuit is operable to map a plurality of supply voltage levels of the supply voltage to a corresponding plurality of current levels of the gain shaping current.
19. The power amplifier system of claim 6 wherein the gain shaping circuit reduces the gain shaping current in response to an increase in the voltage level of the supply voltage of the power amplifier.
20. The power amplifier system of claim 6 wherein the gain shaping circuit is further configured to generate a reference current, and to bias the power amplifier based on the reference current.