Capacitive-Coupled Chopper Amplifier Clamping for Fast Common-Mode Settling
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Solution Overview
Problem
Conventional capacitive-coupled chopper instrumentation amplifiers (CCIAs) perform poorly in responding to quick changes in common-mode voltage, leading to glitches and distortion in output due to slow common-mode voltage settling times, especially in applications with large common-mode components like high-side current sensing.
Innovation Solution
The development of new CCIAs that repeatedly clamp common-mode voltage at a capacitively isolated portion to a reference voltage, isolating the gain stage from inputs during transient events, and using auto-zeroing circuitry to minimize settling time and output ripple, thereby reducing glitches and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CCIAs are used to achieve electrical isolation and low input offset voltage, then input offset voltage is reduced, but common-mode settling time increases causing output distortion
Solution Approach 1:
The patent applies preliminary action by clamping the common-mode voltage at the input of the gain stage to a reference voltage before the amplification process. This clamping action pre-establishes the common-mode voltage level, preventing settling issues during the actual signal amplification. The clamping circuit is activated in response to detected common-mode voltage changes, ensuring the common-mode voltage is already stabilized before it can cause output distortion.
2Reliability
If conventional CCIAs are used to achieve electrical isolation, then electrical isolation is obtained, but output voltage distortion increases during transient events
Solution Approach 1:
The patent implements feedback by detecting changes in common-mode voltage and using this detection to control the clamping circuit. The system continuously monitors the common-mode voltage level and activates the clamping function in response to detected changes, creating a closed-loop control system that dynamically prevents output distortion while maintaining electrical isolation through the capacitive coupling.
3Reliability
If conventional CCIAs are used in high-side current sensing applications, then electrical isolation from large common-mode voltage is achieved, but common-mode rejection ratio decreases due to slow settling
Solution Approach 1:
The patent applies preliminary action by pre-clamping the common-mode voltage at the gain stage input before signal amplification occurs. This preliminary clamping action ensures that when large common-mode voltage transients occur in high-side current sensing applications, the common-mode voltage is already stabilized at the reference level, preventing the settling time issue that would otherwise degrade the common-mode rejection ratio.
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 solution significantly reduces output voltage distortion and settling time, enhancing the common-mode rejection ratio (CMRR) and enabling accurate current sensing in applications with high slew rates, such as those driven by PWM or PFM voltages.
Implementation Method 1
capacitive isolation stage 106 blocks transmission of a direct current (DC) component of an input signal
Implementation Method 2
first and second choppers 102 and 104 alternate between straight signal transmission and reverse signal transmission. Such operation of first and second choppers 102 and 104 shifts input offset voltage of first gain stage 108, as well as noise at inputs 120 and 122 of first gain stage 108, to a frequency greater than that of signals intended to be amplified
Data Source
AI summary
A capacitive-coupled chopper instrumentation amplifier includes a first chopper, a first gain stage, a capacitive isolation stage electrically coupled between inputs of the first gain stage and the first chopper, a second gain stage, a second chopper electrically coupled between outputs of the first gain stage and inputs of the second gain stage, clamping circuitry electrically coupled between the inputs of the first gain stage and a reference voltage rail, and a controller. The controller is configured to (a) detect a change in a first common-mode voltage exceeding a threshold value, the first common-mode voltage being a common-mode voltage at the inputs of the amplifier, and (b) in response to detecting the change in the first common-mode voltage exceeding the threshold value, cause the clamping circuitry to clamp the inputs of the first gain stage to the reference voltage rail.