Loop delay and gain control methods in closed-loop transmitters and wireless devices
Embodiments include transmitters, wireless devices, and methods for performing loop delay and gain control. In a transmitter, a gain application element receives and combines digital input samples and a digital gain signal to generate gain-compensated digital samples. A power amplifier receives and amplifies an analog version of the gain-compensated digital samples to generate an antenna output signal. A feedback path generates an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal, and generates the digital gain signal from the sequence of digital feedback samples and a loop gain estimate. A loop delay and gain calculator calculates a loop delay estimate from the gain-compensated digital samples and the sequence of digital feedback samples, and calculates the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples.
1. A transmitter of a wireless device, the transmitter comprising:
a gain application element adapted to receive a sequence of digital input samples and a digital gain signal, and to combine the digital gain signal with the digital input samples to generate a sequence of gain-compensated digital samples;
a power amplifier adapted to receive and amplify an analog version of the gain-compensated digital samples in order to generate an antenna output signal;
a feedback path adapted to generate an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal, and to generate the digital gain signal from the sequence of digital feedback samples and a loop gain estimate; and
a loop delay and gain calculator adapted to calculate a loop delay estimate from the gain-compensated digital samples and the sequence of digital feedback samples, and to calculate the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples, wherein the loop delay estimate represents a loop delay between the gain-compensated digital samples and the digital feedback samples.
2. A transmitter of a wireless device, the transmitter comprising:
a gain application element adapted to receive a sequence of digital input samples and a digital gain signal, and to combine the digital gain signal with the digital input samples to generate a sequence of gain-compensated digital samples;
a power amplifier adapted to receive and amplify an analog version of the gain-compensated digital samples in order to generate an antenna output signal;
a feedback path adapted to generate an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal, and to generate the digital gain signal from the sequence of digital feedback samples and a loop gain estimate; and
a loop delay and gain calculator adapted to calculate a loop delay estimate from the gain-compensated digital samples and the sequence of digital feedback samples, and to calculate the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples, wherein the loop delay and gain calculator comprises:
a magnitude calculator adapted to generate a sequence of input sample magnitudes from the sequence of gain-compensated digital samples;
a cross-correlator adapted to correlate a set of the digital feedback samples with a set of the input sample magnitudes to generate a plurality of cross-correlation values; and
a correlation peak calculator adapted to determine a correlation peak from the plurality of cross-correlation values, wherein the correlation peak corresponds to the loop delay estimate.
3. The transmitter of claim 2 , further comprising a loop gain estimator adapted to time-align a feedback signal envelope reflected by the set of the digital feedback samples with an input signal envelope reflected by set of input sample magnitudes, and to calculate the loop gain estimate from the time-aligned feedback signal envelope and input signal envelope.
4. The transmitter of claim 3 , wherein the loop gain estimator calculates the loop gain estimate from the time-aligned feedback signal envelope and input signal envelope by converting the time-aligned feedback signal envelope and the input signal envelope to a decibel (dB) domain and performing a dB domain subtraction to obtain instantaneous gain estimates.
5. The transmitter of claim 2 , wherein the loop delay and gain calculator further comprises:
a transmit sample buffer adapted to buffer the input sample magnitudes; and
a feedback sample buffer adapted to buffer the digital feedback samples.
6. The transmitter of claim 2 , wherein the loop delay and gain calculator further comprises:
a downsampler adapted to receive and downsample the input sample magnitudes in order to produce a sequence of downsampled, input sample magnitudes that are used by the cross-correlator as the set of input sample magnitudes.
7. The transmitter of claim 1 , wherein the feedback path comprises a transmit power controller adapted to generate the digital gain signal from the sequence of digital feedback samples and the loop gain estimate by comparing the digital feedback samples with an internal reference ramp signal and accumulating the error signal between them to generate the digital gain signal.
8. The transmitter of claim 1 , further comprising:
a digital-to-analog converter adapted to receive the gain-compensated digital samples and to convert the gain-compensated digital samples into a gain-compensated analog signal;
a radio frequency (RF) modulator adapted to receive the gain-compensated analog signal and to modulate the gain-compensated analog signal to an RF carrier frequency to generate a pre-adjusted analog signal; and
a stepped variable gain amplifier (SVGA) adapted to apply gains indicated in a gain ramp signal to the pre-adjusted analog signal in order to generate the analog version of the gain-compensated digital samples.
9. The transmitter of claim 1 , wherein the gain application element is adapted to receive the digital input samples as a sequence of signal bursts produced using wideband code division multiple access.
10. The transmitter of claim 1 , further comprising:
an antenna adapted to receive the antenna output signal and to transmit the antenna output signal over an air interface.
11. A wireless device comprising:
a processing subsystem adapted to generate an outgoing digital signal as a sequence of digital input samples;
a closed-loop transmitter that includes;
a gain application element adapted to receive the sequence of digital input samples and a digital gain signal, and to combine the digital gain signal with the digital input samples to generate a sequence of gain-compensated digital samples,
a power amplifier adapted to receive and amplify an analog version of the gain-compensated digital samples in order to generate an antenna output signal,
a feedback path adapted to generate an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal, and to generate the digital gain signal from the sequence of digital feedback samples and a loop gain estimate, and
a loop delay and gain calculator adapted to calculate a loop delay estimate by cross-correlating versions of the gain-compensated digital samples and the digital feedback samples, and to calculate the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples; and
an antenna adapted to receive the antenna output signal and to transmit the antenna output signal over an air interface.
12. The wireless device of claim 11 , wherein the outgoing digital signal is generated as a sequence of signal bursts produced using wideband code division multiple access technology.
13. The wireless device of claim 11 , wherein the wireless device forms at least a portion of a device selected from a group of devices that includes a cellular telephone, a radio, a personal data assistant, and a computer.
14. A method for performing loop delay and gain control in a wireless device transmitter, the method comprising the steps of:
receiving a sequence of digital input samples and a digital gain signal;
combining the digital gain signal with the digital input samples to generate a sequence of gain-compensated digital samples;
amplifying an analog version of the gain-compensated digital samples in order to generate an antenna output signal;
generating an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal;
generating the digital gain signal from the sequence of digital feedback samples and a loop gain estimate;
calculating a loop delay estimate from the gain-compensated digital samples and the sequence of digital feedback samples, wherein the loop delay estimate represents a loop delay between the gain-compensated digital samples and the digital feedback samples; and
calculating the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples.
15. A method for performing loop delay and gain control in a wireless device transmitter, the method comprising the steps of:
receiving a sequence of digital input samples and a digital gain signal;
combining the digital gain signal with the digital input samples to generate a sequence of gain-compensated digital samples;
amplifying an analog version of the gain-compensated digital samples in order to generate an antenna output signal;
generating an analog feedback signal from the antenna output signal, to produce a sequence of digital feedback samples from the analog feedback signal;
generating the digital gain signal from the sequence of digital feedback samples and a loop gain estimate;
calculating a loop delay estimate from the gain-compensated digital samples and the sequence of digital feedback samples by
generating a sequence of input sample magnitudes from the sequence of gain-compensated digital samples,
cross-correlating a set of the digital feedback samples with a set of the input sample magnitudes to generate a plurality of cross-correlation values, and
determining a correlation peak from the plurality of cross-correlation values, wherein the correlation peak corresponds to the loop delay estimate; and
calculating the loop gain estimate using the loop delay estimate, the gain-compensated digital samples, and the sequence of digital feedback samples.
16. The method of claim 15 , further comprising the step of:
time-aligning a feedback signal envelope reflected by the set of the digital feedback samples with an input signal envelope reflected by set of input sample magnitudes, and
wherein calculating the loop gain estimate comprises calculating the loop gain estimate from the time-aligned feedback signal envelope and input signal envelope.
17. The method of claim 16 , wherein calculating the loop gain estimate comprises calculating the loop gain estimate from the time-aligned feedback signal envelope and input signal envelope by converting the time-aligned feedback signal envelope and the input signal envelope to a decibel (dB) domain and performing a dB domain subtraction to obtain instantaneous gain estimates.
18. The method of claim 15 , further comprising the steps of:
buffering the input sample magnitudes; and
buffering the digital feedback samples.
19. The method of claim 15 , further comprising the step of:
downsampling the input sample magnitudes in order to produce a sequence of downsampled, input sample magnitudes that are used in the cross-correlating step as the set of input sample magnitudes.
20. The method of claim 14 , further comprising the step of generating the digital gain signal from the sequence of digital feedback samples and the loop gain estimate by comparing the digital feedback samples with an internal reference ramp signal and accumulating the error signal between them to generate the digital gain signal.