Method and apparatus for nonlinear signal processing
The present disclosure relates to a concept of nonlinear signal processing which may be used for predistortion for RF power amplifiers. The concept includes generating time variant filter coefficients for a linear filter circuit based on a nonlinear mapping of an input signal, and filtering the input signal with the linear filter circuit using the time variant filter coefficients in order to generate a filtered output signal. Thus, it is proposed to implement a non-linear filter by a time-varying linear filter where the time-varying coefficients are derived from the input signal.
1. A nonlinear signal processing device, comprising:
a linear filter circuit configured to filter an input signal to generate a filtered output signal; and
a coefficient generation circuit configured to generate time variant filter coefficients for the linear filter circuit based on a nonlinear mapping of the input signal.
2. The nonlinear signal processing device of claim 1 , wherein the coefficient generation circuit is configured to extract at least one time variant numerical feature from the input signal and to generate the time variant filter coefficients based on a time invariant nonlinear mapping of the extracted at least one time variant numerical feature.
3. The nonlinear signal processing device of claim 2 , wherein the at least one time variant numerical feature comprises an absolute value, a magnitude, a distance, or a norm of the input signal.
4. The nonlinear signal processing device of claim 2 , wherein the input signal is a digital input signal and wherein the coefficient generation circuit is configured to extract the at least one time variant numerical feature for each sample of the digital input signal.
5. The nonlinear signal processing device of claim 2 , wherein the coefficient generation circuit comprises a nonlinear filter circuit configured to map the at least one extracted time variant numerical feature to the time variant filter coefficients.
6. The nonlinear signal processing device of claim 5 , wherein the nonlinear filter circuit comprises a plurality of nonlinear finite impulse response (FIR) filter taps, wherein each nonlinear FIR filter tap is configured to delay and map the at least one time variant numerical feature to a respective filter tap output vector based on a respective time invariant nonlinear function.
7. The nonlinear signal processing device of claim 6 , wherein the nonlinear filter circuit is configured to generate the time variant filter coefficients based on a sum of the filter tap output vectors of the plurality of nonlinear FIR filter taps.
8. The nonlinear signal processing device of claim 6 , wherein the respective nonlinear functions corresponding to the plurality of nonlinear FIR filter taps are implemented based on lookup-tables and/or polynomials.
9. The nonlinear signal processing device of claim 5 , wherein the nonlinear filter circuit comprises a nonlinear FIR filter implemented in direct or transposed form.
10. The nonlinear signal processing device of claim 1 , wherein the linear filter circuit comprises a linear FIR filter implemented in transposed form.
11. The nonlinear signal processing device of claim 1 , further comprising delay circuitry coupled between an input terminal and the linear filter circuit, wherein the delay circuitry is configured to delay the input signal by one or more samples.
12. The nonlinear signal processing device of claim 11 , wherein a delay of the delay circuitry corresponds to a signal processing delay of the coefficient generation circuit.
13. A method of nonlinear signal processing, the method comprising:
generating time variant filter coefficients for a linear filter circuit based on a nonlinear mapping of an input signal; and
filtering the input signal with the linear filter circuit using the time variant filter coefficients to generate a filtered output signal.
14. A transmitter circuit, comprising:
a linear digital filter circuit configured to filter a complex-valued baseband signal to generate a complex-valued predistorted baseband signal; and
a coefficient generation circuit configured to generate time variant complex filter coefficients for the linear filter circuit based on a nonlinear mapping of the complex input signal,
wherein the linear digital filter circuit and the time variant complex filter coefficients mimic a nonlinear distortion of a radio frequency (RF) power amplifier.
15. The transmitter circuit of claim 14 , further comprising RF circuitry including the RF power amplifier configured to amplify an RF version of the complex-valued predistorted baseband signal.
16. The transmitter circuit of claim 14 , wherein the transmitter circuit is a Wi-Fi transmitter circuit.