Compensated DAC Circuit for Stable Current and Higher SNR
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Solution Overview
Problem
Current steering DACs introduce harmonics and noise due to threshold voltage mismatch and feedback effects, degrading the signal-to-noise ratio (SNR) and distorting output signals in sigma delta modulators and ADCs.
Innovation Solution
A compensation circuit including a capacitor and an N-type or P-type metal oxide semiconductor field effect transistor is introduced to stabilize the current flow through the DAC, ensuring that the current through the transistors remains approximately equal to the reference current, thereby reducing harmonics and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current steering DAC is used to convert digital signals to analog signals, then the conversion function is achieved, but threshold voltage mismatch and feedback effects introduce harmonics and noise that degrade the signal-to-noise ratio
Solution Approach 1:
The patent implements a feedback mechanism where the output of the DAC is fed back through a capacitor to the input side. This feedback loop compensates for threshold voltage mismatch and feedback effects by continuously adjusting the current based on the output signal, thereby reducing harmonics and noise while improving the signal-to-noise ratio
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the DAC output and input. This capacitor acts as a mediator that stores and releases charge to compensate for voltage fluctuations and threshold mismatches, reducing the harmful effects of harmonics and noise without requiring complex circuit modifications
2Device complexity
If threshold voltage mismatch in DAC transistors is present, then the DAC structure is simple, but the current through transistors varies causing signal distortion
Solution Approach 1:
The feedback path through the capacitor continuously monitors the output current and adjusts the input signal to compensate for threshold voltage variations in the transistors. This maintains consistent current flow through the DAC transistors without requiring precise manufacturing tolerances or complex compensation circuits
Solution Approach 2:
The DAC circuit uses its own output signal to generate the compensation needed for threshold voltage mismatch. The feedback mechanism allows the circuit to self-correct for transistor variations, eliminating the need for external calibration or highly precise manufacturing while maintaining current consistency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The compensation circuit significantly improves the signal-to-noise ratio (SNR) of the current steering DAC, reducing noise floor and signal distortion, especially at higher offset voltages, by ensuring consistent current flow during digital input transitions.
Implementation Method 1
The capacitor has first and second terminals, with the first terminal of the capacitor coupled to the first terminal of the DAC
Implementation Method 2
The transistor has a source coupled to the second terminal of the capacitor, and has a gate coupled to the second terminal of the DAC
Data Source
AI summary
A circuit includes a digital-to-analog converter (DAC) and a compensation circuit. The DAC has first and second terminals. The compensation circuit includes a capacitor and a transistor. The capacitor has first and second terminals, with the first terminal of the capacitor coupled to the first terminal of the DAC. The transistor has a source coupled to the second terminal of the capacitor, and has a gate coupled to the second terminal of the DAC.