Techniques for linearizing phase independently of amplitude in a communications system
The present disclosure, for example, relates to one or more techniques for linearizing a signal in a communications system. An input signal may be obtained at a beginning of a signal path of a radio frequency (RF) communication device. The RF communication device may estimate subsequent distortion of the input signal due to the signal path. The estimated distortion may include estimated phase distortion and estimated amplitude distortion of the input signal. The RF communication device may adjust phase and amplitude within the signal path to compensate for the estimated phase distortion and the estimated amplitude distortion to produce an adjusted signal. The phase within the signal path of the input signal may be adjusted separately from the amplitude within the signal path of the input signal. The RF communication device may generate a linearized signal at an end of the signal path based at least in part on the adjusted signal.
1. A method comprising:
estimating distortion of a communication signal due to a signal path of a radio frequency (RF) communication device, the estimated distortion comprising estimated phase distortion and estimated amplitude distortion of the communication signal;
adjusting an amplitude of the communication signal to compensate for the estimated amplitude distortion by modifying the communication signal with an amplitude modification circuit of the RF communication device; and
adjusting a phase of the communication signal by modifying a phase of a local oscillator (LO) signal in an LO chain of the RF communication device based on the estimated phase distortion and applying the modified LO signal to the communication signal.
2. The method of claim 1 , wherein adjusting the amplitude comprises:
modifying the current from a digital current source based at least in part on the estimated amplitude distortion;
controlling a gain of a variable gain amplifier based at least in part on the current from the digital current source; and
amplifying the communication signal with the variable gain amplifier.
3. The method of claim 2 , wherein the digital current source comprises a plurality of current sources, and modifying the current from the digital current source comprises:
enabling one or more of the plurality of current sources based at least in part on the estimated amplitude distortion; and
combining the currents from the one or more enabled current sources to form the current from the digital current source.
4. The method of claim 3 , further comprising:
shaping a trigger pulse to have an opposite shape of the estimated amplitude distortion; and
digitizing the shaped trigger pulse to enable one or more of the plurality of current sources.
5. The method of claim 4 , wherein the shaped trigger pulse is digitized with a comparator network.
6. The method of claim 2 , wherein the variable gain amplifier comprises a main amplifier and a secondary amplifier, and controlling the gain of the variable gain amplifier comprises:
modifying the gain of the secondary amplifier based at least in part on the current of the digital current source; and
amplifying the communication signal with the main amplifier and the secondary amplifier.
7. The method of claim 6 , wherein the main amplifier and the secondary amplifier comprise differential amplifiers, and the secondary amplifier is 180° out of phase with the main amplifier.
8. The method of claim 1 , wherein the amplitude of the communication signal is adjusted in an RF chain of the RF communication device.
9. The method of claim 1 , wherein modifying the phase of the LO signal comprises:
shaping a biasing voltage of an amplifier in the LO chain; and
saturating at least one subsequent amplifier in the LO chain to preserve the amplitude and modified phase of the LO signal.
10. The method of claim 1 , wherein the phase of the LO signal is modified by an output matching network of the LO chain.
11. The method of claim 10 , wherein the output matching network comprises a plurality of varactors, and wherein modifying the phase of the LO signal comprises:
applying a control voltage to the plurality of varactors.
12. The method of claim 11 , further comprising:
scaling the control voltage; and
applying the scaled control voltage to a subset of the plurality of varactors.
13. The method of claim 11 , further comprising:
shaping the control voltage based at least in part on the estimated phase distortion.
14. The method of claim 1 , wherein applying the modified LO signal to the communication signal comprises:
generating a first phase adjusted signal in a first mixer based at least in part on the modified LO signal; and
generating a second phase adjusted signal in an upconverter based at least in part on the modified LO signal.
15. The method of claim 14 , further comprising:
generating a third phase adjusted signal in a second mixer based at least in part on the first phase adjusted signal and the second phase adjusted signal.
16. A radio frequency (RF) communication device comprising:
a distortion estimation circuit to generate a distortion estimation signal, the distortion estimation signal indicating an estimated distortion of a communication signal due to a signal path of the RF communication device, the estimated distortion comprising estimated phase distortion and estimated amplitude distortion of the communication signal;
an amplitude modification circuit to modify, based at least in part on the distortion estimation signal, amplitude of the communication signal to compensate for the estimated amplitude distortion; and
a phase modification circuit to modify, based at least in part on the distortion estimation signal, a phase of a local oscillator (LO) signal in an LO chain of the RF communication device based on the distortion estimation signal, and to apply the modified LO signal to the communication signal.
17. The RF communication device of claim 16 , wherein the amplitude modification circuit comprises:
a digital current source supplying a current based at least in part on the distortion estimation signal; and
a variable gain amplifier having a gain based at least in part on the current from the digital current source, wherein the variable gain amplifier amplifies the communication signal.
18. The RF communication device of claim 17 , wherein the digital current source comprises a plurality of current sources, and the current from the digital current source is supplied by:
enabling one or more of the plurality of current sources based at least in part on the distortion estimation signal; and
combining the currents from the one or more enabled current sources to form the current from the digital current source.
19. The RF communication device of claim 18 , further comprising:
a trigger pulse shaping circuit to shape a trigger pulse to have an opposite shape of the estimated amplitude distortion; and
a digitizer to digitize the shaped trigger pulse to enable one or more of the plurality of current sources.
20. The RF communication device of claim 19 , wherein the digitizer comprises a comparator network.
21. The RF communication device of claim 17 , wherein the variable gain amplifier comprises a main amplifier and a secondary amplifier, and the gain of the variable gain amplifier is modified by:
modifying the gain of the secondary amplifier based at least in part on the current of the digital current source; and
amplifying the communication signal with the main amplifier and the secondary amplifier.
22. The RF communication device of claim 21 , wherein the main amplifier and the secondary amplifier comprise differential amplifiers, and the secondary amplifier is 180° out of phase with the main amplifier.
23. The RF communication device of claim 16 , wherein the amplitude modification circuit is in an RF chain of the RF communication device.
24. The RF communication device of claim 16 , wherein the phase modification circuit adjusts the phase of the LO signal by shaping a biasing voltage of an amplifier in the LO chain and saturating at least one subsequent amplifier in the LO chain to preserve the amplitude and modified phase of the LO signal.
25. The RF communication device of claim 16 , wherein the phase modification circuit comprises an output matching network, and the output matching network modifies the phase of the LO signal.
26. The RF communication device of claim 25 , wherein the output matching network comprises a plurality of varactors, and wherein the phase modification circuit adjusts the phase of the LO signal by applying a control voltage to the plurality of varactors.
27. The RF communication device of claim 26 , wherein the phase modification circuit comprises:
a voltage divider that scales the control voltage,
and wherein the phase modification circuit applies the scaled control voltage to a subset of the plurality of varactors.
28. The RF communication device of claim 26 , wherein the phase modification circuit shapes the control voltage based at least in part on the estimated phase distortion.
29. The RF communication device of claim 16 , wherein the phase modification circuit comprises:
a first mixer to generate a first phase adjusted signal based at least in part on the modified LO signal; and
an upconverter to generate a second phase adjusted signal based at least in part on the modified LO signal.
30. The RF communication device of claim 29 , further comprising:
a second mixer to generate a third phase adjusted signal based at least in part on the first phase adjusted signal and the second phase adjusted signal.