Chopped Integrator Modulator for Charge Injection Error Reduction
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Solution Overview
Problem
Current current sensors with modulators experience offset voltage and flicker noise issues due to charge injection errors caused by improper timing of switching in the differential amplifier's input and output chopping switches.
Innovation Solution
A modulator design incorporating an integrator with input and output chopping switches and a control circuit that sets the common connection node to an initial potential during transition periods, reducing residual charges and chopping frequency to minimize offset voltage and flicker noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopping switches are used in the integrator to reduce offset voltage and flicker noise, then measurement precision is improved, but charge injection errors occur due to improper switching timing
Solution Approach 1:
The control circuit sets the common connection node to an initial potential before the chopping switches operate, preparing the circuit state in advance to prevent charge injection errors. This preliminary action ensures that when the chopping switches toggle, the node is already in a stable state, eliminating the harmful charge injection effect while maintaining the offset voltage reduction benefit.
Solution Approach 2:
The control circuit monitors the state of the chopping switches and dynamically adjusts the common connection node potential accordingly. By providing feedback control, the system ensures that the node potential is maintained at the initial level during switching transitions, preventing charge injection errors while preserving the measurement precision improvements from chopping.
2Device complexity
If the common connection node potential is not reset during switching transitions, then device complexity is reduced, but residual charges accumulate causing offset voltage errors
Solution Approach 1:
The control circuit automatically resets the common connection node to its initial potential during each switching transition without requiring external intervention. This self-service mechanism ensures that residual charges are continuously cleared, maintaining measurement precision while keeping the device structure relatively simple through automated control.
3Measurement precision
If chopping frequency is reduced to minimize offset voltage and flicker noise, then measurement precision is improved, but the response speed of the modulator decreases
Solution Approach 1:
The system dynamically adjusts the chopping frequency based on operating conditions, allowing optimization between measurement precision and response speed. By changing the frequency parameter adaptively, the system can achieve high precision when needed while maintaining faster response when speed is critical, resolving the contradiction between these two parameters.
Data Source
AI summary
A modulator includes an integrator, an input chopping switch, and output chopping switch, and a control circuit. The integrator has a differential amplifier, a first switch and a series circuit. The first switch is connected between input and output terminals of the differential amplifier. The series circuit is connected between the input and output terminals of the differential amplifier. The series circuit has a second switch, an input capacitance chopping switch, an integration capacitor and an output capacitance chopping switch. The control circuit controls the input chopping switch and the output chopping switch to execute chopping being at a chopping frequency identical to the input capacitance chopping switch and the output capacitance chopping switch. The chopping frequency of the input and output capacitance chopping switches is lower than a switching frequency of the first switch.