Post-distortion filter for reducing sensitivity to receiver nonlinearities
View Patent ↗Methods and apparatus for reducing sensitivity to nonlinearities in the receiver of a digital communications system are disclosed. One aspect can be referred to as a Post-Distortion Decision Feedback Equalizer (PDFE). A gain stage is often implemented as a variable gain amplifier (VGA), and can introduce significant nonlinearities, a problem exacerbated by signals with a large peak-to-average ratio (PAR). One embodiment provides feed forward information from the VGA regarding its status to a DFE, and the DFE adjusts its filtering based on the provided information. The advantages are also applicable to fixed-gain amplifiers and to transversal filters.
1. A receiver for receiving a signal having embedded therein symbols, the receiver comprising:
an input amplifier configured to receive an input signal, wherein the input amplifier is configured to generate an amplified output and a signal strength indicator, wherein the signal strength indicator comprises an indication of a gain nonlinearity of the input amplifier, wherein the signal strength indicator comprises a control signal; and
a filter operatively coupled to the input amplifier to receive the amplified output and to receive the signal strength indicator for control, wherein the filter is configured to vary filter coefficients used for filtering depending on a state of the signal strength indicator, and wherein the filter is configured to determine symbols embedded in the signal.
2. The receiver of claim 1 , wherein the filter is downstream of the input amplifier.
3. The receiver of claim 1 , further comprising a delay element disposed in a signal path between the amplified output of the input amplifier and an input to the filter.
4. The receiver of claim 1 , further comprising an adaptation engine coupled to the filter for adaptive control of filter coefficients.
5. The receiver of claim 4 , wherein the adaptation engine is configured to adapt a filter coefficient for a state of the signal strength indicator, and is further configured to determine one or more other filter coefficients based at least partially on the adapted filter coefficient for the state.
6. The receiver of claim 4 , wherein the adaptation engine is configured to adapt filter coefficients for each state of the signal strength indicator independently.
7. The receiver of claim 1 , wherein the input amplifier is configured to generate the signal strength indicator in more than a binary number of states.
8. The receiver of claim 1 , wherein the filter comprises a transversal filter.
9. The receiver of claim 1 , wherein the input amplifier comprises a variable gain amplifier.
10. The receiver of claim 1 , wherein the input amplifier comprises a fixed-gain amplifier.
11. The receiver of claim 1 , wherein the nonlinearity comprises compression.
12. The receiver of claim 1 , wherein the nonlinearity comprises expansion.
13. The receiver of claim 1 , wherein the receiver is embodied in a seralizer/deserializer.
14. The receiver of claim 1 , wherein the nonlinearity comprises memory-less effects.
15. The receiver of claim 1 , wherein the nonlinearity comprises memory effects.
16. The receiver of claim 1 , wherein the input amplifier is configured to generate the signal strength indicator such that the signal strength indicator indicates a presence or absence of at least a threshold amount of gain nonlinearity.
17. The receiver of claim 1 , wherein the input amplifier is configured to receive the input signal as a wireless signal.
18. The receiver of claim 1 , wherein the input amplifier is configured to receive the input signal as a wired signal.
19. The receiver of claim 1 , wherein the filter is configured to generate an output signal as an output of the receiver.
20. The receiver of claim 1 , wherein a response of the filter changes when the filter coefficients of the filter vary.