Envelope tracking power amplifier apparatus
An envelope tracking (ET) power amplifier apparatus is provided. The ET power amplifier apparatus includes a pair of power amplifiers configured to amplify a pair of radio frequency (RF) signals based on a pair of ET voltages. In one aspect, each of the RF signals is split before amplification and recombined after amplification. As such, the power amplifiers can operate based on half the peak power of the RF signals to help improve operating efficiency of the power amplifiers. In another aspect, the RF signals are pre-processed prior to amplification to form a pair of composite RF signals with similar average power such that the power amplifiers can operate based on substantially similar ET voltages. As a result, it may be possible to employ a single ET integrated circuit (ETIC) to provide the ET voltages, thus helping to reduce cost and footprint of the ET power amplifier apparatus.
1. An envelope tracking (ET) power amplifier apparatus comprising:
a first signal output coupled to a first antenna;
a second signal output coupled to a second antenna;
a first power amplifier configured to amplify a first composite radio frequency (RF) signal comprising a quadrature component of a first RF signal and an in-phase component of a second RF signal based on a first ET voltage;
a second power amplifier configured to amplify a second composite RF signal comprising an in-phase component of the first RF signal and a quadrature component of the second RF signal based on a second ET voltage;
an input circuit coupled to a signal processing circuit and configured to:
receive the first RF signal and the second RF signal from the signal processing circuit;
generate the first composite RF signal comprising the quadrature component of the first RF signal and the in-phase component of the second RF signal;
generate the second composite RF signal comprising the in-phase component of the first RF signal and the quadrature component of the second RF signal; and
provide the first composite RF signal and the second composite RF signal to the first power amplifier and the second power amplifier, respectively; and
an output circuit configured to:
receive the first composite RF signal and the second composite RF signal from the first power amplifier and the second power amplifier, respectively;
regenerate the first RF signal and the second RF signal from the first composite RF signal and the second composite RF signal; and
provide the first RF signal and the second RF signal to the first signal output and the second signal output, respectively.
2. The ET power amplifier apparatus of claim 1 wherein the first power amplifier and the second power amplifier are further configured to receive the first composite RF signal and the second composite RF signal, respectively, from the signal processing circuit coupled to the ET power amplifier apparatus.
3. The ET power amplifier apparatus of claim 1 wherein the first composite RF signal and the second composite RF signal are generated to have a substantially equal average power.
4. The ET power amplifier apparatus of claim 3 wherein the first RF signal and the second RF signal are associated with an identical power envelope.
5. The ET power amplifier apparatus of claim 3 wherein the first RF signal and the second RF signal are associated with different power envelopes.
6. The ET power amplifier apparatus of claim 1 further comprising at least one phase adjuster configured to phase shift at least one of the first RF signal and the second RF signal based on a feedback signal indicative of an average differential between the first ET voltage and the second ET voltage.
7. The ET power amplifier apparatus of claim 6 further comprising a measurement circuit coupled to the output circuit and configured to measure the average differential between the first ET voltage and the second ET voltage.
8. The ET power amplifier apparatus of claim 1 further comprising an ET integrated circuit (ETIC), the ETIC comprises:
a multi-level charge pump (MCP) configured to generate a low-frequency voltage at a plurality of levels based on a battery voltage; and
an inductor circuit configured to:
generate a low-frequency current based on the low-frequency voltage; and
provide the low-frequency current to the first power amplifier and the second power amplifier.
9. The ET power amplifier apparatus of claim 8 wherein the ETIC further comprises an ET voltage circuit configured to generate and provide the first ET voltage and the second ET voltage to the first power amplifier and the second power amplifier, respectively.
10. The ET power amplifier apparatus of claim 9 wherein the ET voltage circuit comprises:
a first voltage amplifier configured to generate a first initial ET voltage based on a first ET target voltage;
a first offset capacitor configured to raise the first initial ET voltage by a first offset voltage to generate the first ET voltage;
a second voltage amplifier configured to generate a second initial ET voltage based on a second ET target voltage; and
a second offset capacitor configured to raise the second initial ET voltage by a second offset voltage to generate the second ET voltage.
11. The ET power amplifier apparatus of claim 8 further comprising a distributed ETIC, the distributed ETIC comprising an ET voltage circuit configured to generate and provide the first ET voltage and the second ET voltage to the first power amplifier and the second power amplifier, respectively.
12. The ET power amplifier apparatus of claim 11 wherein the ET voltage circuit comprises:
a first voltage amplifier configured to generate a first initial ET voltage based on a first ET target voltage;
a first offset capacitor configured to raise the first initial ET voltage by a first offset voltage to generate the first ET voltage;
a second voltage amplifier configured to generate a second initial ET voltage based on a second ET target voltage; and
a second offset capacitor configured to raise the second initial ET voltage by a second offset voltage to generate the second ET voltage.
13. The ET power amplifier apparatus of claim 11 wherein the distributed ETIC is separated from the ETIC.
14. The ET power amplifier apparatus of claim 8 wherein the inductor circuit comprises:
a first power inductor coupled between the MCP and the first power amplifier, the first power inductor configured to induce the low-frequency current based on the low-frequency voltage and provide the low-frequency current to the first power amplifier; and
a second power inductor coupled between the MCP and the second power amplifier, the second power inductor configured to induce the low-frequency current based on the low-frequency voltage and provide the low-frequency current to the second power amplifier.
15. The ET power amplifier apparatus of claim 14 wherein the first power inductor and the second power inductor are negatively coupled.
16. The ET power amplifier apparatus of claim 8 wherein the inductor circuit comprises a power inductor configured to generate the low-frequency current based on the low-frequency voltage.
17. The ET power amplifier apparatus of claim 16 further comprising a direct current (DC) control circuit, the DC control circuit comprising:
a first low-dropout regulator (LDO) coupled between the power inductor and the first power amplifier and configured to regulate the low-frequency current flowing into the first power amplifier;
a second LDO coupled between the power inductor and the second power amplifier and configured to regulate the low-frequency current flowing into the second power amplifier; and
a control circuit coupled to the first LDO and the second LDO and configured to:
detect a maximum instantaneous voltage differential between the first ET voltage and the second ET voltage; and
control the first LDO and the second LDO to regulate the low-frequency current based on the detected maximum instantaneous voltage differential.
18. The ET power amplifier apparatus of claim 17 wherein the control circuit is further configured to control any one of the first LDO and the second LDO to prevent the low-frequency current from flowing into any one of the first power amplifier and the second power amplifier.