Configurable non-linear filter for digital pre-distortion
Some embodiments herein describe a radio frequency communication system that can include a transmitter to output an radio frequency (RF) transmit signal, the transmitter including a digital pre-distortion system (DPD) that pre-distorts the RF transmit signal. The DPD system can include a configurable non-linear filter, such as a Laguerre filter, having multiple rows where at least one row operates with a configurable decimation ratio. The DPD system can further include decimators and a crossbar switch coupled between the decimators.
1. A radio frequency (RF) communication system comprising:
a transmitter configured to output an RF transmit signal; and
a power amplifier configured to amplify the RF transmit signal,
wherein the transmitter comprises a digital pre-distortion (DPD) system configured to pre-distort the RF transmit signal, the DPD system including a configurable non-linear filter having a plurality of rows in which at least one row operates with a configurable decimation ratio.
2. The RF communication system of claim 1 , wherein the DPD system comprises a plurality of decimators, and a crossbar switch coupled between the plurality of decimators and the plurality of rows of the configurable non-linear filter.
3. The RF communication system of claim 2 , wherein at least a portion of the plurality of decimators have a separately controllable decimation ratio.
4. The RF communication system of claim 1 , wherein the configurable non-linear filter operates with a plurality of different time constants.
5. The RF communication system of claim 1 , wherein the configurable non-linear filter compensates for charge trapping effects of the power amplifier.
6. The RF communication system of claim 1 , wherein the configurable non-linear filter is a Laguerre filter.
7. The RF communication system of claim 6 , wherein the Laguerre filter operates with a programmable number of filter stages corresponding to matrix columns.
8. The RF communication system of claim 1 , wherein a plurality of coefficients of the plurality of rows are programmable.
9. The RF communication system of claim 1 , wherein the configurable non-linear filter further comprises a bank of input decimation filters configured to selectively reduce an operating rate of the non-linear filter, and a bank of output interpolation filters configured to compensate for the reduced operating rate provided by the bank of input decimation filters.
10. The RF communication system of claim 1 , wherein the configurable non-linear filter comprises two or more rows that share an infinite impulse response (IIR) filter.
11. The RF communication system of claim 10 , wherein the IIR filter includes a transposed pipeline structure with a floating memory stage.
12. The RF communication system of claim 1 , wherein the configurable non-linear filter further comprises a first plurality of a look-up tables (LUTs) configured to provide data to the plurality of rows of the configurable non-linear filter.
13. The RF communication system of claim 12 , wherein the first plurality of LUTs are configured to provide piece-wise linear interpolation of a non-linear transfer function.
14. The RF communication system of claim 12 , wherein the configurable non-linear filter further comprises a second plurality of LUTs configured to process data outputted from the plurality of rows.
15. The RF communication system of claim 1 , wherein the DPD system further comprises a generalized memory polynomial (GMP) circuit that operates in combination with the configurable non-linear filter to provide DPD.
16. The RF communication system of claim 15 , wherein the configurable non-linear filter is rate matched to the GMP circuit.
17. The RF communication system of claim 15 , wherein the GMP circuit operates on a data stream and the configurable non-linear filter operates on an early version of the data stream.
18. A transmitter for an RF communication system, the transmitter comprising:
a digital transmit circuit configured to generate an in-phase (I) transmit signal and a quadrature-phase (Q) transmit signal,
wherein the digital transmit circuit comprises a digital pre-distortion (DPD) system configured to pre-distort the I transmit signal and the Q transmit signal to compensate for downstream power amplifier non-linearity,
wherein the digital pre-distortion system includes a non-linear filter having a plurality of rows in which at least one row operates with a configurable decimation ratio.
19. The transmitter of claim 18 , wherein the DPD system comprises a plurality of decimators, and a crossbar switch coupled between the plurality of decimators and the plurality of rows of the configurable non-linear filter.
20. The transmitter of claim 18 , wherein the configurable non-linear filter operates with a plurality of different time constants.
21. The transmitter of claim 18 , wherein the configurable non-linear filter is a Laguerre filter.
22. A method of digital pre-distortion in an RF communication system, the method comprising:
generating an in-phase (I) transmit signal and a quadrature-phase (Q) transmit signal;
pre-distorting the I transmit signal and the Q transmit signal to compensate for a non-linearity of a power amplifier using a digital pre-distortion (DPD) system; and
configuring a decimation ratio of at least one row of a non-linear filter of the digital pre-distortion system.