Methods and systems for pre-emphasis of an envelope tracking power amplifier supply voltage
View Patent ↗Embodiments provide systems and methods for producing an envelope tracking (ET) PA supply voltage with minimum headroom relative to the desired RF output signal of the PA. In an embodiment, the PA supply voltage is generated by applying an ET signal to an ET path of the wireless device, and by further applying pre-emphasis to the ET signal to compensate for a frequency response of the ET path. Embodiments operate by estimating the frequency response of the ET path and determining the pre-emphasis based on the estimate of the frequency response of the ET path. In embodiments, the pre-emphasis is applied using a pre-emphasis filter, which may be within or outside of the ET path. Further, the pre-emphasis may be applied to the ET signal in digital or analog form.
1. A method for controlling a power amplifier (PA) in a wireless device, comprising:
generating an envelope tracking (ET) signal based on an envelope of a complex transmit signal;
applying the ET signal to an ET path of the wireless device to generate a supply voltage signal;
applying pre-emphasis to the ET signal, wherein the pre-emphasis compensates for a frequency response of the ET path of the wireless device;
providing the supply voltage signal to the PA; and
estimating the frequency response of the ET path, the estimating including:
applying tone samples of pre-determined frequency to the ET path;
sampling the supply voltage signal, resulting from the applied tone samples, to generate supply voltage samples;
correlating the tone samples with the supply voltage samples to produce a correlation product;
integrating the correlation product over a pre-determined time window to generate a complex gain of the ET path at the pre-determined frequency; and
generating an estimate of the frequency response of the ET path based on the complex gain of the ET path at the pre-determined frequency;
wherein the pre-emphasis is determined based on an inverse of the estimate of the frequency response of the ET path.
2. The method of claim 1 , wherein generating the ET signal comprises computing a magnitude of the complex transmit signal and compensating the computed magnitude.
3. The method of claim 1 , wherein applying the ET signal to the ET path of the wireless device comprises up-sampling the ET signal to reduce digital-to-analog converter (DAC) produced images of the ET signal.
4. The method of claim 1 , wherein applying the ET signal to the ET path of the wireless device comprises applying the ET signal to a power supply that produces the supply voltage signal.
5. The method of claim 1 , further comprising:
repeating the estimating of the frequency response of the ET path over a range of pre-determine frequencies to generate a plurality of complex gain values.
6. The method of claim 1 , wherein applying the pre-emphasis to the ET signal comprises applying the ET signal to a pre-emphasis filter.
7. The method of claim 6 , wherein the pre-emphasis filter boosts components of an upper frequency range of the ET signal, thereby preserving substantially all of a bandwidth of the ET signal after being applied to the ET path.
8. The method of claim 6 , further comprising:
determining coefficients of the pre-emphasis filter based on an estimate of the frequency response of the ET path.
9. The method of claim 1 , wherein the tone samples include one of:
a sinusoidal signal;
a continuous wave signal;
a chirp signal; and
the ET signal.
10. The method of claim 1 , wherein the tone samples are not proportional to the envelope of the complex transmit signal.
11. A wireless device, comprising:
a transmit path, including a power amplifier (PA), that receives a complex transmit signal and generates a radio frequency (RF) output signal at an output of the PA;
an envelope tracking (ET) path that receives an ET signal, based on an envelope of the complex transmit signal, and generates a supply voltage signal applied to the PA, wherein the ET path comprises a pre-emphasis filter that compensates for a frequency response of the ET path of the wireless device;
a tone generator that applies tone samples of a pre-determined frequency to the ET path;
an analog-to-digital converter (ADC) that samples the supply voltage signal, resulting from the applied tone samples, to generate supply voltage samples;
a correlator that correlates the tone samples with the supply voltage samples to produce a correlation product;
an accumulator that integrates the correlation product over a pre-determined time window to generate a complex gain of the ET path at the pre-determined frequency; and
an estimator that estimates the frequency response of the ET path based on the complex gain of the ET path at the pre-determined frequency;
wherein the pre-emphasis filter is configured to have a frequency response substantially equal to an inverse of the estimate of the frequency response of the ET path.
12. The wireless device of claim 11 , wherein the ET signal is generated using a magnitude of the complex transmit signal.
13. The wireless device of claim 11 , wherein the ET path further comprises a digital-to-analog converter (DAC).
14. The wireless device of claim 13 , wherein the ET path further comprises an up-sampler that up-samples the ET signal to reduce DAC produced images of the ET signal.
15. The wireless device of claim 11 , wherein the ET path includes a power supply that produces the supply voltage signal applied to the PA.
16. The wireless device of claim 11 , further comprising:
means for sweeping the pre-determined frequency over a range of frequencies to generate a plurality of complex gain values.
17. The wireless device of claim 11 , wherein the pre-emphasis filter boosts components of an upper frequency range of the ET signal, thereby preserving substantially all of a bandwidth of the ET signal after being applied to the ET path.
18. The wireless device of 11 , wherein the pre-emphasis filter includes a finite impulse response (FIR) filter.