Time-Interleaved DAC Calibration Using Adaptive Digital Predistortion
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Solution Overview
Problem
Time-interleaved digital-to-analog converters (TI DACs) face challenges with linear and non-linear distortions and mismatches between channels, leading to inaccurate analog output signals, which existing calibration methods fail to adequately address.
Innovation Solution
The implementation of a digital pre-distortion (DPD) system using background or foreground calibration, where a digital pre-distortion unit processes input data through delay lines and adaptation blocks to correct distortions, with an analog-to-digital converter capturing the output to form an error signal for least mean squares (LMS) adaptation of coefficients, effectively compensating for channel mismatches and distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a time-interleaved DAC system is used to achieve higher sample rate, then the effective DAC sample rate is multiplied, but linear and non-linear distortions and channel mismatches occur
Solution Approach 1:
The patent applies digital pre-distortion (DPD) to predistort the input signal before it enters the time-interleaved DAC channels. This preliminary action compensates for anticipated linear and non-linear distortions and channel mismatches, ensuring that after the signal passes through the imperfect TI DAC channels, the output is accurately reconstructed. The predistortion coefficients are calculated based on measured channel characteristics and applied to correct the signal path.
Solution Approach 2:
The patent implements feedback calibration where the TI DAC output is captured by an ADC and compared to the properly processed DAC input to form an error signal. This error signal is used for least mean squares (LMS) adaptation of DPD coefficients, creating a closed-loop system that continuously refines the predistortion parameters to minimize output errors and maintain high accuracy despite channel imperfections.
2Productivity
If multiple TI DAC channels are used to multiply sampling rate, then productivity increases, but channel mismatches and distortions worsen
Solution Approach 1:
The patent applies local quality by implementing separate predistortion processing for each TI DAC channel based on their individual characteristics. Each channel's linear and non-linear distortions and mismatches are measured and compensated with channel-specific predistortion coefficients, allowing each channel to be optimized independently while working together as a unified high-rate system.
Solution Approach 2:
The patent changes parameters by dynamically adjusting predistortion coefficients to compensate for channel mismatches. The system measures actual channel performance parameters (gain, phase, timing) and modifies the predistortion parameters accordingly, transforming the system from having fixed imperfections to having adaptive compensation that maintains reliability across all channels.
3Manufacturing precision
If digital pre-distortion with calibration is implemented, then output accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies self-service by implementing background calibration that operates during normal TI DAC operation. The system uses its own output (captured by an ADC) to generate error signals that automatically adjust predistortion coefficients without requiring external intervention or system shutdown. This self-calibrating approach maintains high accuracy while minimizing operational disruption and reducing the need for complex external calibration equipment.
Solution Approach 2:
The patent performs preliminary calibration to establish baseline predistortion coefficients before normal operation, storing these coefficients for use during regular operation. This preliminary setup phase separates the complex calibration process from ongoing operations, allowing the system to achieve high accuracy through pre-computed correction parameters while keeping the operational complexity low.
Data Source
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 the 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.