Chopped Capacitively Coupled Delta-Sigma Modulator for Offset Error
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Solution Overview
Problem
Delta-sigma modulators experience offset voltage generation and sensitivity to input voltage errors due to varying output impedance and switch injection differences, leading to inaccurate final outputs.
Innovation Solution
Incorporation of a capacitively-coupled amplifier, first and second integrators, a quantizer, digital-to-analog converters, and control circuit with chopping switches to modulate and demodulate signals, reducing offset influence by alternating signal polarity and lowering switch operation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a capacitively-coupled amplifier is used to amplify analog signals, then signal amplification is achieved, but offset voltage is generated at the output
Solution Approach 1:
The patent applies periodic chopping action by alternately switching the amplifier output between inverted and non-inverted states. This periodic switching moves the offset voltage to a higher frequency component that can be filtered out, while the desired signal is recovered through synchronous demodulation. The chopping switches periodically exchange connections between capacitive elements, creating a time-varying signal that separates the offset from the useful signal.
2Measurement precision
If integrators are used to integrate analog differential signals, then signal integration is achieved, but the system becomes sensitive to input voltage errors
Solution Approach 1:
The patent extracts and removes the harmful offset voltage component from the signal path before it reaches the integrators. By using chopping switches to separate the offset voltage from the amplified signal and routing them through different paths, the offset is eliminated prior to integration, preventing it from affecting integration accuracy.
3Measurement precision
If switch operation frequency is increased to reduce offset influence, then offset cancellation improves, but current flow and detection errors increase
Solution Approach 1:
The patent changes the operating parameters by using relatively low-frequency chopping switches rather than high-frequency switching. This parameter change achieves sufficient offset cancellation while minimizing the harmful effects of high-frequency operation such as increased current flow and detection errors. The chopping frequency is optimized to balance offset rejection with minimal impact on signal integrity.
Data Source
AI summary
A delta-sigma modulator includes a capacitively-coupled amplifier, a first integrator, a second integrator, a quantizer, a first switch, a second switch, and a control circuit. The first switch is connected between an input of the capacitively-coupled amplifier and a sampling capacitor of the capacitively-coupled amplifier to execute a chopping operation. The second switch is connected between an output of the capacitively-coupled amplifier and an input of the first integrator to execute a chopping operation. The control circuit executes modulation through the first switch at the input of the capacitively-coupled amplifier, executes demodulation through the second switch at the output of the capacitively-coupled amplifier, and imports an output signal of the capacitively-coupled amplifier into the first integrator after the demodulation.