Sigma-Delta DAC Calibration Using Random Error Injection
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Solution Overview
Problem
DACs experience output noise and input to output non-linearity, making existing calibration methods ineffective for wide band applications, particularly those with low OSR, and requiring additional components like extra sigma-delta modulators for efficient calibration.
Innovation Solution
The implementation of a calibration method that injects a random sequence signal into the DAC to estimate and compensate for errors in sigma delta modulators, using additional DAC elements and transfer functions to correct output errors without disrupting normal operation, and storing error data in memory for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If spectral shaping is used to reduce in-band noise, then linearity is improved, but it is ineffective for wide band applications with low OSR
Solution Approach 1:
The patent changes the calibration approach from spectral shaping (frequency-domain method) to time-domain error measurement and compensation. By injecting random sequences and measuring output errors directly in the time domain, the system achieves effective calibration for wide band applications with low OSR where spectral shaping fails.
Solution Approach 2:
The patent introduces an intermediary calibration process that uses random sequence injection and error measurement to bridge the gap between DAC output and desired linearity performance. This intermediary measurement system allows direct observation and compensation of DAC errors without relying on spectral shaping techniques.
2Measurement precision
If an extra sigma-delta modulator is added for efficient calibration, then calibration accuracy is improved, but device complexity increases
Solution Approach 1:
The patent enables the existing sigma-delta modulator to perform self-calibration by injecting random sequences at its input and measuring its own output errors. This self-service approach eliminates the need for an extra calibration modulator, reducing device complexity while maintaining calibration accuracy.
Solution Approach 2:
The patent makes the existing sigma-delta modulator multi-functional by enabling it to perform both signal processing and self-calibration functions. The same modulator structure is used for both operational modes, eliminating the need for dedicated calibration hardware.
3Manufacturing precision
If calibration is performed to reduce DAC errors, then linearity is improved, but additional components and calibration circuitry are required
Solution Approach 1:
The patent merges the calibration function with the existing DAC structure by using the same digital-to-analog conversion path for both normal operation and calibration measurements. The random sequence injection and error measurement are integrated into the existing signal path, avoiding additional calibration circuitry.
Solution Approach 2:
The DAC performs self-calibration by measuring its own output errors during normal operation. The system uses its existing components to generate test signals, measure errors, and apply corrections without requiring external calibration equipment or additional circuitry.
Data Source
AI summary
Mechanisms to calibrate a digital to analog converter (DAC) of an SDM (sigma delta modulator) are disclosed. An extra DAC element in addition to the DAC is used to function in place of a DAC element under calibration. A signal (e.g., a random sequence of −1 and +1) is injected to the DAC element under calibration, and the estimated error and compensation are acquired.