Subtracting linear impairments for non-linear impairment digital pre-distortion error signal

• US 9,136,887 B2
• Filed: 02/20/2014
• Issued: 09/15/2015
• Est. Priority Date: 02/20/2014
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Zhao, Hongzhi, Chen, Xiaohan, Yang, Zigang
• Primary Examiner(s): Torres, Juan A
• Application Number:
  US14/185,888
• Publication Number:
  US 20150236730A1
• Time in Patent Office: 572 Days
• Field of Search: 375/296
• US Class Current: 1/1
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion

Abstract

Example embodiment of the systems and methods of linear impairment modeling to improve digital pre-distortion adaptation performance includes a DPD module that is modified during each sample by a DPD adaptation engine. A linear impairment modeling module separates the linear and non-linear errors introduced in the power amplifier. The linear impairment model is adjusted during each sample using inputs from the input signal and from a FB post processing module. The linear impairment modeling module removes the linear errors such that the DPD adaptation engine only adapts the DPD module based on the non-linear errors. This increases system stability and allows for the correction of IQ imbalance inside the linear impairment modeling, simplifying the feedback post-processing.

Claims

1. A process comprising:

receiving a digital input signal;

producing a digital pre-distortion signal from the digital input signal in response to a non-linear impairment digital pre-distortion error signal;

amplifying the digital pre-distortion signal with a power amplifier to produce a radio frequency output signal;

producing from the radio frequency output signal a digital feedback signal that includes linear impairments and non-linear impairments;

separating the linear impairments from the non-linear impairments;

subtracting the linear impairments from the digital feedback signal to result in a non-linear impairment digital pre-distortion error signal; and

updating the producing a digital pre-distortion signal from the digital input signal in response to the non-linear impairment digital pre-distortion error signal from the subtracting.

2. The process of claim 1 including converting the digital pre-distortion signal into an analog signal, mixing the analog signal with a signal from a local oscillator, power amplifying the mixed analog signal to form the radio frequency output signal, and applying radio frequency output signal to an antennae.

3. The process of claim 1 in which the producing from the radio frequency output signal includes receiving an analog signal from an amplified signal applied to an antennae, de-mixing the analog feedback signal with a signal from a local oscillator, and converting the de-mixed signal to the digital feedback signal.

4. A system comprising:

a digital pre-distortion module having a digital signal input, an update input, and a filtered signal output;

a power amplifier having a filtered signal input coupled to the filtered signal output, and having a radio frequency signal output;

a feedback post-processing module having an input coupled to the radio frequency signal output, and having a processed signal output;

a linear impairment modeling module having an input coupled to the digital signal input and having a linear error signal output;

an error module having an input coupled to the processed signal output, an input coupled to the linear error signal output, and a non-linear error signal output; and

a digital pre-distortion adaptation engine having an input coupled to the non-linear error signal output and an output coupled to the update input.

5. The system of claim 4 in which at least one of the digital pre-distortion module, the feedback post-processing module, the linear impairment modeling module, and the digital pre-distortion adaptation engine are embodied in a digital signal processor.

6. The system of claim 4 in which the linear impairment modeling module includes an input coupled to the feedback post-processing module.