Digital pre-emphasis quadrature imbalance compensating filter

1. A transmitter comprising:

a pre-emphasis digital filter configured to filter a series of respective digital input data samples according to a plurality of coefficients to generate a series of respective corresponding preemphasized data samples;

a digital-to-analog converter (DAC) configured to sample the series of pre-emphasized data samples to generate an analog signal;

an analog filter configured to:

filter the analog signal to generate a filtered signal, and

provide the filtered signal to an input of a power amplifier of the transmitter; and estimator circuitry configured to:

receive a pre-emphasized data sample from the pre-emphasis digital filter,

receive a corresponding sample of the filtered signal,

calculate the plurality of coefficients using the sample of the filtered signal and the pre-emphasized data sample, and

provide the coefficients to the pre-emphasis digital filter.

2. The transmitter of claim 1 , comprising an observation path configured to feedback a sample of the filtered signal to the estimator circuitry, wherein the observation path comprises an analog-to-digital converter (ADC) that inputs the filtered signal and generates the sample of the filtered signal.

3. The transmitter of claim 1 , comprising an observation path configured to feedback a sample of the filtered signal to the estimator circuitry, wherein the observation path comprises:

an up-converter configured to convert the filtered signal from a baseband frequency to radio frequency (RF) to generate an RF filtered signal for transmission by the transmitter;

a down-converter configured to convert the RF filtered signal back to the baseband frequency to generate a filtered baseband signal; and

an analog-to-digital converter (ADC) configured to:

generate a sample of the filtered baseband signal; and

feedback the sample to the estimator circuitry.

4. The transmitter of claim 1 , wherein the pre-emphasis digital filter comprises:

leakage compensation circuitry configured to generate, for each input data sample, a leakage compensated I component and a leakage compensated Q component; and

skew and bandwidth compensation circuitry configured to generate, for each input data sample, a skew and bandwidth compensated I component and a skew and bandwidth compensated Q component;

wherein the pre-emphasis digital filter is configured to:

add an I component of the input data sample to the leakage compensated I component and the skew and bandwidth compensated I component to generate a pre-emphasized I component;

add a Q component of the input data sample to the leakage compensated Q component and the skew and bandwidth compensated Q component to generate a pre-emphasized Q component; and

combine the pre-emphasized I component with the pre-emphasized Q component to generate the pre-emphasized data sample.

5. The transmitter of claim 1 , comprising monitor circuitry configured to:

input the sample of the filtered signal;

input a corresponding input data sample;

compare the sample of the filtered signal to the input data sample;

determine if a difference between the sample of the filtered signal and the input data sample exceeds a threshold; and

trigger the estimator circuitry to re-calculate the coefficient based on present pre-emphasized data samples and present samples of the filtered signal when the difference exceeds the threshold.

6. The transmitter of claim 1 wherein the transmitter is configured to transmit in a selected one of two or more bandwidths, and wherein a bandwidth of the analog filter is selected as a narrowest bandwidth of the two or more bandwidths.

7. The transmitter of claim 1 , wherein the estimator circuitry is configured to calculate the plurality of coefficients by adjusting the plurality of coefficients to bring the filtered signal into equivalence with the pre-emphasized data sample.

8. The transmitter of claim 4 , wherein the leakage compensation circuitry is configured to:

add a first portion of a Q component of an input data sample to a second portion of an I component of the input data sample to generate the leakage compensated I component, wherein the first portion and second portion are controlled by a first coefficient and a second coefficient, respectively, of the plurality of coefficients; and

add a third portion of the I component of the input data sample to a fourth portion of the Q component of the input data sample to generate the leakage compensated Q component, wherein the third portion and fourth portion are controlled by a third coefficient and a fourth coefficient, respectively, of the plurality of coefficients.

9. The transmitter of claim 4 , wherein the skew and bandwidth compensation circuitry configured to:

add a fifth portion of an I component of the input data sample to a sixth portion of an I component of an immediately prior input data sample to generate a first summed I component, wherein the fifth portion and sixth portion are controlled by a fifth coefficient and a sixth coefficient, respectively, of the plurality of coefficients;

add a seventh portion of a Q component of the input data sample to an eighth portion of a Q component of an immediately prior input data sample to generate a first summed Q component, wherein the seventh portion and eighth portion are controlled by a seventh coefficient and an eighth coefficient, respectively, of the plurality of coefficients;

add the first summed I component and the first summed Q component to generate the skew and bandwidth compensated I component;

add a ninth portion of an I component of the input data sample to a tenth portion of an I component of an immediately prior input data sample to generate a second summed I component, wherein the ninth portion and tenth portion are controlled by a ninth coefficient and a tenth coefficient, respectively, of the plurality of coefficients; and

add an eleventh portion of a Q component of the input data signal to a twelfth portion of a Q component of an immediately prior input data sample signal to generate a second summed Q component, wherein the eleventh portion and twelfth portion are controlled by an eleventh coefficient and a twelfth coefficient, respectively, of the plurality of coefficients; and

add the second summed I component and the second summed Q component to generate the skew and bandwidth compensated Q component.

10. A method comprising:

filtering, with a pre-emphasis digital filter, a series of respective digital input data samples according to a plurality of coefficients to generate a series of respective corresponding pre-emphasized data samples;

sampling the series of pre-emphasized data samples to generate an analog signal;

filtering the analog signal to generate a filtered signal;

providing the filtered signal to an input of a power amplifier of a transmitter;

receiving a pre-emphasized data sample from the pre-emphasis digital filter;

receiving a corresponding sample of the filtered signal; and

calculating the plurality of coefficients using the sample of the filtered signal and the pre-emphasized data sample, and

providing the coefficients to the pre-emphasis digital filter.

11. The method of claim 10 , comprising: generating the sample of the filtered signal by inputting the filtered signal to an ADC.

12. The method of claim 10 , comprising:

converting the filtered signal from a baseband frequency to radio frequency (RF) to generate an RF filtered signal for transmission by a transmitter;

converting the RF filtered signal back to the baseband frequency to generate a filtered baseband signal; and

inputting the filtered baseband signal to an ADC to generate the sample of the filtered signal; and

providing the sample of the filtered baseband signal to estimator circuitry.

13. The method of claim 10 , comprising:

generating, for each input data sample, a leakage compensated I component and a leakage compensated Q component; and

generating, for each input data sample, a skew and bandwidth compensated I component and a skew and bandwidth compensated Q component;

adding an I component of the input data sample to the leakage compensated I component and the skew and bandwidth compensated I component to generate a pre-emphasized I component;

adding a Q component of the input data sample to the leakage compensated Q component and the skew and bandwidth compensated Q component to generate a pre-emphasized Q component; and

combining the pre-emphasized I component with the pre-emphasized Q component to generate the pre-emphasized data sample.

14. The method of claim 10 , comprising:

inputting the sample of the filtered signal;

inputting an input data sample that resulted in the sample of the filtered signal;

comparing the sample of the filtered signal to the input data sample;

when a difference between the sample of the filtered signal and the input data sample exceeds a threshold, triggering estimator circuitry to re-calculate the coefficient based on present pre-emphasized data samples and present samples of the filtered signal.

15. A pre-emphasis digital filter configured to filter a series of digital input data samples according to a plurality of coefficients to generate a series of pre-emphasized data samples, the pre-emphasis digital filter comprising:

leakage compensation circuitry configured to generate, for each input data sample, a leakage compensated I component and a leakage compensated Q component; and

skew and bandwidth compensation circuitry configured to generate, for each input data sample, a skew and bandwidth compensated I component and a skew and bandwidth compensated Q component;

wherein the pre-emphasis digital filter is configured to: add an I component of the input data sample to the leakage compensated I component and the skew and bandwidth compensated I component to generate a pre-emphasized I component,

add a Q component of the input data sample to the leakage compensated Q component and the skew and bandwidth compensated Q component to generate a pre-emphasized Q component, and

combine the pre-emphasized I component with the pre-emphasized Q component to generate the pre-emphasized data sample; and estimator circuitry configured to:

receive a sample of a filtered signal that is an input to a power amplifier of a transmitter, wherein the filtered signal is generated by sampling the series of pre-emphasized data samples to generate an analog signal and filtering the analog signal with an analog filter;

receive a corresponding pre-emphasized digital samples from the pre-emphasis digital filter;

calculate the plurality of coefficients using the filtered signal and the pre-emphasized data sample, and

provide the coefficients to the pre-emphasis digital filter.

16. The pre-emphasis digital filter of claim 15 , wherein the estimator circuitry is configured to calculate the plurality of coefficients by solving for a filter function that, when applied to the pre-emphasized data sample, will bring the filtered signal into equivalence with the pre-emphasized data sample.

17. The pre-emphasis digital filter of claim 15 , comprising monitor circuitry configured to:

input an input data sample;

input a corresponding sample of the filtered signal;

determine a difference between the sample of the filtered signal and the input data sample; and

trigger the estimator circuitry to re-calculate the coefficients based on present pre-emphasized data samples and present samples of the filtered signal when the difference exceeds a threshold.

18. The pre-emphasis digital filter of claim 15 , wherein the leakage compensation circuitry is configured to:

add a first portion of a Q component of an input data sample to a second portion of an I component of the input data sample to generate the leakage compensated I component, wherein the first portion and second portion are controlled by a first coefficient and a second coefficient, respectively, of the plurality of coefficients; and

add a third portion of the I component of the input data sample to a fourth portion of the Q component of the input data sample to generate the leakage compensated Q component, wherein the third portion and fourth portion are controlled by a third coefficient and a fourth coefficient, respectively, of the plurality of coefficients.

19. The pre-emphasis digital filter of claim 18 , wherein the skew and bandwidth compensation circuitry configured to:

add a fifth portion of an I component of the input data sample to a sixth portion of an I component of an immediately prior input data sample to generate a first summed I component, wherein the fifth portion and sixth portion are controlled by a fifth coefficient and a sixth coefficient, respectively, of the plurality of coefficients;

add a seventh portion of a Q component of the input data sample to an eighth portion of a Q component of an immediately prior input data sample to generate a first summed Q component, wherein the seventh portion and eighth portion are controlled by a seventh coefficient and an eighth coefficient, respectively, of the plurality of coefficients;

add the first summed I component and the first summed Q component to generate the skew and bandwidth compensated I component;

add a ninth portion of an I component of the input data sample to a tenth portion of an I component of an immediately prior input data sample to generate a second summed I component, wherein the ninth portion and tenth portion are controlled by a ninth coefficient and a tenth coefficient, respectively, of the plurality of coefficients;

add an eleventh portion of a Q component of the input data signal to a twelfth portion of a Q component of an immediately prior input data sample signal to generate a second summed Q component, wherein the eleventh portion and twelfth portion are controlled by an eleventh coefficient and a twelfth coefficient, respectively, of the plurality of coefficients; and

add the second summed I component and the second summed Q component to generate the skew and bandwidth compensated Q component.

20. A method of filtering a series of digital input data samples according to a plurality of coefficients to generate a series of pre-emphasized data samples, the method comprising:

with a pre-emphasis digital filter,

generating, for each input data sample, a leakage compensated I component and a leakage compensated Q component,

generating, for each input data sample, a skew and bandwidth compensated I component and a skew and bandwidth compensated Q component, adding an 1 component of the input data sample to the leakage compensated I component and the skew and bandwidth compensated component to generate a pre-emphasized I component,

adding a Q component of the input data sample to the leakage compensated Q component and the skew and bandwidth compensated Q component to generate a pre-emphasized Q component, and

combining the pre-emphasized I component with the pre-emphasized Q component to generate the pre-emphasized data sample;

receiving a sample of a filtered signal that is an input to a power amplifier of a transmitter,

wherein the filtered signal is generated by sampling the series of pre-emphasized data samples to generate an analog signal and filtering the analog signal with an analog filter;

receiving, from the pre-emphasis digital filter, a corresponding pre-emphasized data sample of the series of pre-emphasized data samples; and

calculating the plurality of coefficients using the filtered signal and the pre-emphasized data sample, and

providing the coefficients to the pre-emphasis digital filter.

21. The method of claim 20 , comprising calculating the plurality of coefficients by solving for a filter function that, when applied to the pre-emphasized data sample, will bring the filtered signal into equivalence with the pre-emphasized data sample.

22. The method of claim 20 , comprising:

inputting the sample of the filtered signal;

inputting a corresponding input data sample;

determining a difference between the sample of the filtered signal and the input data sample; and

triggering estimator circuitry to re-calculate the coefficient based on present pre-emphasized data samples and present samples of the filtered signal when the difference exceeds a threshold.

23. The method of claim 10 , comprising calculating the plurality of coefficients by adjusting the plurality of coefficients to bring the filtered signal into equivalence with the pre-emphasized data sample.