PPA linearization
A linearization circuit improves the linearity of a power amplifier based on an envelope of an input RF signal. The linearization circuit comprises an RF signal generation circuit, a replica circuit, and an adaptive amplifier. The RF signal generation circuit generates the RF signal from a phase and an amplitude of an input digital signal. The replica circuit extracts the envelope from the RF signal and generates a sensing voltage based on the extracted envelope. The adaptive amplifier generates an adaptive bias voltage for the power amplifier based on the sensing voltage, and applies the adaptive bias voltage to the power amplifier and to the replica circuit to improve the linearity of the power amplifier by regulating the power amplifier and the replica circuit according to the envelope.
1. A linearization circuit for improving linearity of a class B or class AB or class C power amplifier based on an envelope of a radio frequency (RF) signal input to the power amplifier and generated from a phase and amplitude of an input digital signal, the linearization circuit comprising:
a replica circuit configured to receive the generated RF signal and configured to extract the envelope from the RF signal, and generate a sensing voltage based on the extracted envelope; and
an adaptive amplifier operatively connected to the replica circuit and the power amplifier, the adaptive amplifier configured to generate an adaptive bias voltage for the power amplifier based on the sensing voltage;
wherein the adaptive amplifier applies the adaptive bias voltage to the power amplifier and to the replica circuit to improve the linearity of the power amplifier by regulating the power amplifier and the replica circuit according to the envelope; and
wherein an operational point of the power amplifier is set such that an average amplifier current increases with increasing amplitude of the RF signal.
2. The linearization circuit of claim 1 wherein the power amplifier comprises a pre-power amplifier.
3. The linearization circuit of claim 1 wherein the power amplifier comprises a plurality of power amplifier cells, and wherein the RF signal and the adaptive bias voltage are applied to each of the power amplifier cells to improve the linearity of each of the power amplifier cells.
4. The linearization circuit of claim 1 wherein:
the power amplifier comprises an In-phase power amplifier and a Quadrature power amplifier connected in parallel; and
the linearization circuit comprises an In-phase path for improving the linearity of the In-phase power amplifier based on the envelope of an In-phase portion of the RF signal connected in parallel with a Quadrature path for improving the linearity of the Quadrature power amplifier based on the envelope of a Quadrature portion of the RF signal;
the In-phase path comprises an In-phase replica circuit configured to receive the In-phase portion of the RF signal, and an In-phase adaptive amplifier operatively connected to the In-phase replica circuit and the In-phase power amplifier; and
the Quadrature path comprises a Quadrature replica circuit configured to receive the Quadrature portion of the RF signal, and a Quadrature adaptive amplifier operatively connected to the Quadrature replica circuit and the Quadrature power amplifier.
5. The linearization circuit of claim 1 wherein the replica circuit comprises:
a differential input transconductance stage comprising a positive half-cell transistor and a negative half-cell transistor;
wherein the RF signal comprises a positive RF signal and a negative RF signal;
wherein the positive RF signal is applied to an input of the positive half-cell transistor and the negative RF signal is applied to an input of the negative half-cell transistor; and
wherein outputs of the differential input transconductance stage are connected to provide the sensing voltage to an input of the adaptive amplifier.
6. An amplifier system comprising:
a power amplifier, wherein an operational point of the power amplifier is set such that an average amplifier current increases with increasing amplitude of an RF signal input to the power amplifier;
an RF signal generation circuit operatively connected to the power amplifier 20 and configured to generate an RF signal from a phase and amplitude of a digital signal input to the RF signal generation circuit; and
a linearization circuit for improving linearity of the power amplifier based on an envelope of the radio frequency (RF) signal input to the power amplifier, the linearization circuit comprising:
a replica circuit operatively connected to the RF signal generation circuit, the replica circuit configured to extract the envelope from the RF signal, and generate a sensing voltage based on the extracted envelope; and
a adaptive amplifier operatively connected to the replica circuit and the power amplifier, the adaptive amplifier configured to generate an adaptive bias voltage for the power amplifier based on the sensing voltage, wherein the adaptive amplifier applies the adaptive bias voltage to the power amplifier and to the replica circuit to improve the linearity of the power amplifier by regulating the power amplifier and the replica circuit according to the envelope.
7. The amplifier system of claim 6 wherein the power amplifier comprises a pre-power amplifier.
8. The amplifier system of claim 6 wherein the power amplifier comprises a plurality of power amplifier cells, and wherein the RF signal and the adaptive bias voltage are applied to each of the power amplifier cells to improve the linearity of each of the power amplifier cells.
9. The amplifier system of claim 6 wherein:
the power amplifier comprises an In-phase power amplifier and a Quadrature power amplifier connected in parallel; and
the linearization circuit comprises an In-phase path for improving the linearity of the In-phase power amplifier based on the envelope of an In-phase portion of the RF signal connected in parallel with a Quadrature path for improving the linearity of the Quadrature power amplifier based on the envelope of a Quadrature portion of the RF signal;
the In-phase path comprises an In-phase replica circuit operatively connected to the an In-phase output of the RF signal generation circuit, and an In-phase adaptive amplifier operatively connected to the In-phase replica circuit and the In-phase power amplifier; and
the Quadrature path comprises a Quadrature replica circuit operatively connected to a Quadrature output of the RF signal generation circuit, and a Quadrature adaptive amplifier operatively connected to the Quadrature replica circuit and the Quadrature power amplifier.
10. The amplifier system of claim 9 wherein the replica circuit comprises:
a differential input transconductance stage comprising a positive half-cell transistor and a negative half-cell transistor;
wherein the RF signal comprises a positive RF signal and a negative RF signal;
wherein the positive RF signal is applied to an input of the positive half-cell transistor and the negative RF signal is applied to an input of the negative half-cell transistor; and
wherein the outputs of the differential transconductance stage are connected to provide the sensing voltage to an input of the adaptive amplifier.
11. A method of improving linearity of a class B or class AB or class C power amplifier based on an envelope of an analog radio frequency (RF) signal input to the power amplifier and generated from a phase and amplitude of an input digital signal, the method comprising:
extracting the envelope from the RF signal and generating a sensing voltage based on the extracted envelope; and
generating an adaptive bias voltage for the power amplifier based on the sensing voltage;
wherein the adaptive bias voltage is applied to the power amplifier to improve the linearity of the power amplifier by regulating the power amplifier and the replicating operations according to the envelope; and
wherein an operational point of the power amplifier is set such that an average amplifier current increases with increasing amplitude of the RF signal input to the power amplifier.
12. A transceiver comprising an amplifier system, said amplifier system comprising:
a power amplifier, wherein an operational point of the power amplifier is set such that an average amplifier current increases with increasing amplitude of an RF signal input to the power amplifier;
an RF signal generation circuit operatively connected to the power amplifier 20 and configured to generate an RF signal from a phase and amplitude of a digital signal input to the RF signal generation circuit; and
a linearization circuit for improving linearity of the power amplifier based on an envelope of the radio frequency (RF) signal input to the power amplifier, the linearization circuit comprising:
a replica circuit operatively connected to the RF signal generation circuit, the replica circuit configured to extract the envelope from the RF signal, and generate a sensing voltage based on the extracted envelope; and
a adaptive amplifier operatively connected to the replica circuit and the power amplifier, the adaptive amplifier configured to generate an adaptive bias voltage for the power amplifier based on the sensing voltage, wherein the adaptive amplifier applies the adaptive bias voltage to the power amplifier and to the replica circuit to improve the linearity of the power amplifier by regulating the power amplifier and the replica circuit according to the envelope.
13. The transceiver of claim 12 wherein the power amplifier comprises a pre-power amplifier.
14. The transceiver of claim 12 wherein the power amplifier comprises a plurality of power amplifier cells, and wherein the RF signal and the adaptive bias voltage are applied to each of the power amplifier cells to improve the linearity of each of the power amplifier cells.
15. The transceiver of claim 12 wherein:
the power amplifier comprises an In-phase power amplifier and a Quadrature power amplifier connected in parallel; and
the linearization circuit comprises an In-phase path for improving the linearity of the In-phase power amplifier based on the envelope of an In-phase portion of the RF signal connected in parallel with a Quadrature path for improving the linearity of the Quadrature power amplifier based on the envelope of a Quadrature portion of the RF signal;
the In-phase path comprises an In-phase replica circuit operatively connected to the an In-phase output of the RF signal generation circuit, and an In-phase adaptive amplifier operatively connected to the In-phase replica circuit and the In-phase power amplifier; and
the Quadrature path comprises a Quadrature replica circuit operatively connected to a Quadrature output of the RF signal generation circuit, and a Quadrature adaptive amplifier operatively connected to the Quadrature replica circuit and the Quadrature power amplifier.
16. The transceiver of claim 15 wherein the replica circuit comprises:
a differential input transconductance stage comprising a positive half-cell transistor and a negative half-cell transistor;
wherein the RF signal comprises a positive RF signal and a negative RF signal;
wherein the positive RF signal is applied to an input of the positive half-cell transistor and the negative RF signal is applied to an input of the negative half-cell transistor; and
wherein the outputs of the differential transconductance stage are connected to provide the sensing voltage to an input of the adaptive amplifier.
17. The linearization circuit of claim 1 wherein the sensing voltage represents an operating point of the power amplifier generated from the extracted envelope.