Wideband transmission circuit
A wideband transmission circuit is provided. The wideband transmission circuit includes a transceiver circuit and a power amplifier circuit(s). The transceiver circuit generates a radio frequency (RF) signal(s) from a time-variant input vector and provides the RF signal(s) to the power amplifier circuit(s). The power amplifier circuit(s) amplifies the RF signal(s) based on a modulated voltage and provides the amplified RF signal(s) to a coupled RF front-end circuit (e.g., filter/multiplexer circuit). In embodiments disclosed herein, the transceiver circuit is configured to apply an equalization filter to the time-variant input vector to thereby compensate for a voltage distortion filter caused by a coupling of the power amplifier circuit(s) and the RF front-end circuit. As a result, it is possible to reduce undesired instantaneous excessive compression and/or spectrum regrowth resulting from the voltage distortion filter to thereby improve efficiency and linearity of the power amplifier circuit(s).
1. A wideband transmission circuit comprising:
a power amplifier circuit coupled to a transmitter circuit via a radio frequency (RF) front-end circuit and configured to amplify an RF signal based on a modulated voltage and provide the amplified RF signal to the RF front-end circuit;
an envelope tracking (ET) integrated circuit (ETIC) configured to generate the modulated voltage based on a modulated target voltage; and
a transceiver circuit comprising:
a signal processing circuit configured to generate the RF signal from a time-variant input vector;
a target voltage circuit configured to detect a time-variant amplitude envelope of the RF signal from the time-variant input vector and generate the modulated target voltage based on the detected time-variant amplitude envelope; and
an equalizer circuit configured to apply an equalization filter to the time-variant input vector to compensate for a voltage distortion filter created on an output stage of the power amplifier circuit by coupling the power amplifier circuit with the RF front-end circuit, wherein the voltage distortion filter is a function of a reflection coefficient applied to the power amplifier circuit and a reflection coefficient applied to the RF front-end circuit.
2. The wideband transmission circuit of claim 1 , wherein the equalization filter is configured to match a combined signal path filter that includes a transfer function of the signal processing circuit, a voltage gain transfer function of the power amplifier circuit, and the voltage distortion filter.
3. The wideband transmission circuit of claim 2 , wherein:
the equalizer circuit is further configured to apply the equalization filter to the time-variant input vector to generate an equalized time-variant input vector; and
the target voltage circuit is further configured to detect the time-variant amplitude envelope from the equalized time-variant input vector.
4. The wideband transmission circuit of claim 3 , wherein the target voltage circuit comprises:
an amplitude detector circuit configured to detect the time-variant amplitude envelope from the equalized time-variant input vector;
an ET lookup table (LUT) circuit configured to generate a time-variant digital target voltage based on the detected time-variant amplitude envelope; and
a digital-to-analog converter (DAC) configured to convert the time-variant digital target voltage into the modulated target voltage.
5. The wideband transmission circuit of claim 3 , wherein the signal processing circuit comprises:
a memory digital predistortion (mDPD) circuit configured to digitally pre-distort the time-variant input vector to generate a pre-distorted time-variant input vector; and
a modulator circuit configured to generate the RF signal from the pre-distorted time-variant input vector and provide the RF signal to the power amplifier circuit.
6. The wideband transmission circuit of claim 5 , wherein the mDPD circuit is further configured to digitally pre-distort the time-variant input vector based on the detected time-variant amplitude envelope.
7. The wideband transmission circuit of claim 3 , wherein the equalization filter is expressed as: H ET (s)=H IQ (s)*H PA (s)*H IV (s), wherein:
H ET (s) represents the equalization filter;
H IQ (s) represents the transfer function of the signal processing circuit;
H PA (s) represents the voltage gain transfer function of the power amplifier circuit; and
H IV (s) represents the voltage distortion filter.
8. The wideband transmission circuit of claim 7 , wherein the voltage distortion filter is expressed as: H IV (s)=½*[1−T PA (s)*T I (s)/[1−T PA (s)]*T I (s)], wherein:
T PA (s) represents the reflection coefficient applied to the power amplifier circuit; and
T I (s) represents the reflection coefficient applied to the RF front-end circuit.
9. The wideband transmission circuit of claim 8 , wherein:
the transceiver circuit further comprises a coefficient lookup table (LUT) configured to store the reflection coefficient applied to the power amplifier circuit and the reflection coefficient applied to the RF front-end circuit; and
the equalizer circuit is further configured to dynamically create the equalization filter based on the coefficient LUT.
10. The wideband transmission circuit of claim 2 , wherein:
the equalizer circuit is further configured to apply the equalization filter to the time-variant input vector to generate an equalized time-variant input vector; and
the signal processing circuit is further configured to generate the RF signal from the equalized time-variant input vector.
11. The wideband transmission circuit of claim 10 , wherein the signal processing circuit comprises:
a memory digital predistortion (mDPD) circuit configured to digitally pre-distort the equalized time-variant input vector to generate a pre-distorted equalized time-variant input vector; and
a modulator circuit configured to generate the RF signal from the pre-distorted equalized time-variant input vector and provide the RF signal to the power amplifier circuit.
12. The wideband transmission circuit of claim 11 , wherein the mDPD circuit is further configured to digitally pre-distort the equalized time-variant input vector based on the detected time-variant amplitude envelope.
13. The wideband transmission circuit of claim 10 , wherein the target voltage circuit comprises:
an amplitude detector circuit configured to detect the time-variant amplitude envelope from the time-variant input vector;
an ET lookup table (LUT) circuit configured to generate a time-variant digital target voltage based on the detected time-variant amplitude envelope; and
a digital-to-analog converter (DAC) configured to convert the time-variant digital target voltage into the modulated target voltage.
14. The wideband transmission circuit of claim 10 , wherein the equalization filter is expressed as: 1/H ET (s)=1/[H IQ (s)*H PA (s)*H IV (s)], wherein:
H ET (s) represents the equalization filter;
H IQ (s) represents the transfer function of the signal processing circuit;
H PA (s) represents the voltage gain transfer function of the power amplifier circuit; and
H IV (s) represents the voltage distortion filter.
15. The wideband transmission circuit of claim 14 , wherein the voltage distortion filter is expressed as: H IV (s)=½*[1−T PA (s)]*[1+T I (s)]/[1−T PA (s)*T I (s)], wherein:
T PA (s) represents the reflection coefficient applied to the power amplifier circuit; and
T I (s) represents the reflection coefficient applied to the RF front-end circuit.
16. The wideband transmission circuit of claim 1 , wherein the RF front-end circuit comprises one or more of: a filter circuit and a multiplexer circuit.