Envelope tracking with low frequency loss correction
A low frequency loss correction circuit that improves the efficiency of a power amplifier at near-DC low frequencies The low frequency loss correction circuit can include a signal error detection circuit configured to produce an error signal in response to detecting one or more frequency components of a tracking signal below a cutoff frequency that are substantially attenuated through a capacitive path. The low frequency loss correction circuit can include a drive circuit configured to convert the error signal into a low frequency correction signal, and provide the low frequency correction signal to a voltage supply line, the low frequency correction signal including at least some of the one or more frequency components of the tracking signal below a cutoff frequency that are substantially attenuated through the capacitive path.
1. A low frequency loss correction circuit comprising:
a signal error detection circuit connectable across a capacitance along a path for providing an envelope signal to an amplifier, and configured to produce an error signal in response to detecting a frequency component of the envelope signal below a cutoff frequency and attenuated by the capacitance; and
a drive circuit configured to generate a low frequency correction signal based on the error signal, and provide the low frequency correction signal to a voltage supply line for the amplifier, such that the low frequency correction signal corrects for the attenuated frequency component of the envelope signal.
2. The low frequency loss correction circuit of claim 1 wherein the signal error detection circuit includes first and second detection nodes connectable across the capacitance to sense respective first and second signals.
3. The low frequency loss correction circuit of claim 2 wherein the signal error detection circuit further includes a comparator configured to produce the error signal as a function of the first and second signals.
4. The low frequency loss correction circuit of claim 1 wherein the drive circuit includes a controllable current source coupled to the voltage supply line.
5. The low frequency loss correction circuit of claim 4 wherein a terminal of the controllable current source is coupled to a portion of a voltage divider between the voltage supply line and a source of the envelope signal.
6. The low frequency loss correction circuit of claim 1 wherein the drive circuit includes a differential amplifier arranged to produce an output representative of the low frequency correction signal based on the error signal and a reference signal.
7. The low frequency loss correction circuit of claim 1 wherein the amplifier is a power amplifier configured to operate in an envelope tracking mode.
8. A power amplifier module comprising:
a packaging substrate configured to receive a plurality of components;
a power amplifier implemented on a die that is mounted on the packaging substrate, the power amplifier configured to operate with a supply voltage provided through a supply line;
a signal error detection circuit connected across a capacitance along a path for providing an envelope signal to the power amplifier, and configured to produce an error signal in response to detecting a frequency component of the envelope signal below a cutoff frequency and attenuated by the capacitance; and
a drive circuit configured to generate a low frequency correction signal based on the error signal, and provide the low frequency correction signal to the supply line, such that the low frequency correction signal corrects for the attenuated frequency component of the envelope signal.
9. The power amplifier module of claim 8 further comprising a tracking circuit configured to provide the envelope signal, the envelope signal characterizing a voltage envelope of a signal being amplified by the power amplifier.
10. The power amplifier module of claim 8 wherein the signal error detection circuit includes first and second detection nodes connected across the capacitance to sense respective first and second signals.
11. The power amplifier module of claim 10 wherein the signal error detection circuit further includes a comparator configured to produce the error signal as a function of the first and second signals.
12. The power amplifier module of claim 8 wherein the drive circuit includes a controllable current source coupled to the supply line.
13. The power amplifier module of claim 12 wherein a terminal of the controllable current source is coupled to a portion of a voltage divider between the supply line and a source of the envelope signal.
14. The power amplifier module of claim 8 wherein the drive circuit includes a differential amplifier arranged to produce an output representative of the low frequency correction signal based on the error signal and a reference signal.
15. A wireless device comprising:
a transceiver configured to generate a signal;
a power amplifier module configured to amplify the signal, and including a power amplifier configured to operate with a supply voltage provided through a supply line to amplify the signal, the power amplifier module further including a signal error detection circuit connected across a capacitance along a path for providing an envelope signal to the power amplifier, and configured to produce an error signal in response to detecting a frequency component of the envelope signal below a cutoff frequency and attenuated by the capacitance, the power amplifier module further including a drive circuit configured to generate a low frequency correction signal based on the error signal, and provide the low frequency correction signal to the supply line, such that the low frequency correction signal corrects for the attenuated frequency component of the envelope signal; and
an antenna in communication with the power amplifier module and configured to facilitate transmission of the amplified signal.
16. The wireless device of claim 15 further comprising a tracking circuit configured to provide the envelope signal, the envelope signal characterizing a voltage envelope of the signal being amplified by the power amplifier.
17. The wireless device of claim 15 wherein the signal error detection circuit includes first and second detection nodes connected across the capacitance to sense respective first and second signals.
18. The wireless device of claim 15 wherein the drive circuit includes a controllable current source coupled to the supply line.
19. The wireless device of claim 18 wherein a terminal of the controllable current source is coupled to a portion of a voltage divider between the supply line and a source of the envelope signal.
20. The wireless device of claim 15 wherein the drive circuit includes a differential amplifier arranged to produce an output representative of the low frequency correction signal based on the error signal and a reference signal.