Capacitive-Coupled Chopper Amplifier Clamping for Common-Mode Glitches
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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 input voltages.
Innovation Solution
The implementation of a new CCIA configuration that repeatedly clamps common-mode voltage at a capacitively isolated portion to a reference voltage, isolates the gain stage from amplifier inputs, and uses auto-zeroing circuitry to minimize common-mode voltage settling time and output ripple, achieved through the use of clamping circuitry and auto-zeroing circuitry controlled by clock signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive-coupled chopper instrumentation amplifier configuration is used, then electrical isolation and low input offset voltage are achieved, but common-mode voltage settling time is slow leading to output glitches and distortion
Solution Approach 1:
The clamping circuitry is activated before the common-mode voltage transient can propagate through the capacitive isolation stage to the gain stage. By preemptively clamping the common-mode voltage at the gain stage inputs to the reference voltage, the circuit prevents the settling time issue from occurring in the first place, eliminating output glitches and distortion.
Solution Approach 2:
The clamping circuitry acts as an intermediary between the capacitive isolation stage and the gain stage. It introduces a new element (the clamping circuit with switches and reference voltage) that mediates the interaction between these two stages, controlling the common-mode voltage to prevent it from causing settling time problems while allowing the capacitive isolation to maintain electrical isolation.
2Reliability
If capacitive isolation stage is used to block DC component, then electrical isolation is achieved, but common-mode voltage control is lost requiring reference resistors that increase device complexity
Solution Approach 1:
The invention extracts the common-mode voltage control function from the reference resistors and implements it separately through the clamping circuitry. Instead of relying on reference resistors to set the common-mode voltage, the clamping circuit actively enforces the reference voltage, allowing the reference resistors to be removed or minimized, thus reducing device complexity while maintaining electrical isolation.
Solution Approach 2:
The clamping circuitry serves as an intermediary that replaces the need for reference resistors. It introduces a new mechanism (switches controlled by clock signals and a clamping circuit) that mediates between the capacitive isolation stage and the need for common-mode voltage control, eliminating the requirement for large-value reference resistors and reducing overall circuit complexity.
3Reliability
If reference resistors are used to set common-mode voltage, then common-mode voltage control is achieved, but resistor noise is introduced degrading signal quality
Solution Approach 1:
The invention replaces the passive resistive mechanism (reference resistors) with an active switching mechanism (clamping circuitry controlled by clock signals). Instead of using resistors to set the common-mode voltage, switches actively connect the gain stage inputs to the reference voltage, eliminating the thermal noise inherent in resistors while maintaining common-mode voltage control.
Solution Approach 2:
The invention changes the operating parameter from resistive voltage division to active voltage clamping. By transitioning from a passive resistive network to an active switching circuit, the common-mode voltage is enforced through switching action rather than resistive division, fundamentally changing how the parameter is controlled and eliminating the associated noise.
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
This configuration significantly reduces output voltage distortion and increases the AC common-mode rejection ratio (CMRR), enabling accurate current sensing in applications with high common-mode voltages and rapid changes, 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.