Time-Interleaved DAC Calibration for Channel Mismatch Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Time interleaved digital-to-analog converters (TI DACs) suffer from linear and non-linear distortions and mismatches between channels, limiting the accuracy of the analog output signal.
Innovation Solution
A digital pre-distortion (DPD) method is employed using background or foreground calibration to correct these distortions, utilizing an analog-to-digital converter (ADC) to capture the TI DAC output, form an error signal, and apply least mean squares (LMS) adaptation of DPD coefficients to compensate for channel mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a time interleaved DAC system is used to achieve higher sampling rate, then the effective DAC sample rate is multiplied, but linear and non-linear distortions and channel mismatches occur
Solution Approach 1:
The system divides the high-speed DAC operation into multiple parallel channels (M channels), each operating at a lower sampling rate. The output of each channel is time-interleaved to achieve the overall high sampling rate. This segmentation allows each channel to operate within its linear region while collectively achieving high-speed performance.
Solution Approach 2:
An ADC captures the TI DAC output and feeds it back to an error signal generator. The error signal is produced by comparing the captured output with the properly processed input signal. This feedback loop enables continuous monitoring and correction of distortions and mismatches in the time-interleaved system.
Solution Approach 3:
The patent employs digital pre-distortion coefficients that are dynamically adjusted through LMS adaptation. By changing the pre-distortion parameters based on real-time error signals, the system compensates for linear and non-linear distortions, maintaining output accuracy despite the high sampling rate operation.
2Manufacturing precision
If digital pre-distortion is applied to correct distortions, then output accuracy is improved, but device complexity increases
Solution Approach 1:
The system performs self-calibration using the LMS adaptation algorithm. The error signal generated from the ADC feedback is automatically used to update the pre-distortion coefficients without external intervention. This self-service mechanism reduces the need for manual calibration and simplifies the overall system operation despite the complexity of the pre-distortion circuitry.
Solution Approach 2:
The ADC serves multiple functions: it captures the TI DAC output for monitoring, generates error signals for correction, and enables coefficient adaptation. This multi-functionality reduces the need for separate dedicated components, thereby managing system complexity while maintaining high output accuracy through pre-distortion.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A time-interleaved digital-to-analog converter system, comprising a digital pre-distorter configured to receive an input digital signal and an error signal and output a distorted digital signal based on them input digital signal and the error signal; a time-interleaved digital-to-analog converter having a first sample rate, the time-interleaved digital-to-analog converter configured to convert the distorted digital signal to an analog signal; and a calibration system. The calibration system includes an analog-to-digital converter having a second sample rate equal to or lower than the first sample rate, the analog-to-digital converter configured to receive the analog signal and covert the analog signal to a down-sampled digital signal, a discrete-time linear model configured to receive the input digital signal and the error signal and output a model signal, and a combiner to subtract the down-sampled digital signal from the model signal to generate the error signal.