Common-Mode Coupled AC Amplifier for Small-Signal Gain Without Saturation
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Solution Overview
Problem
Instrumentation Amplifiers (In-Amps) face challenges in amplifying small alternating current (AC) signals in the presence of large direct current (DC) signals, leading to potential saturation and loss of useful information, especially in medical devices like EKGs and ECGs that use multiple channels, where common-mode noise is prevalent.
Innovation Solution
A multi-channel common-mode coupled alternating current (AC) gain amplifier (MC-CM-AC Amp) configuration using one or more gain setting resistors AC coupled to maintain high input impedance and low input bias, allowing the AC signal to be amplified without substantially amplifying the DC signal, thereby reducing the risk of saturation and enhancing common-mode rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional instrumentation amplifier is used to amplify small AC signals, then the AC signal gain is improved, but the amplifier saturates due to large DC signals
Solution Approach 1:
The amplifier is divided into multiple independent channels, each with separate gain control. This allows the AC coupling capacitors to be selectively placed in specific channels to block DC signals while preserving AC signal amplification, preventing saturation in those channels.
Solution Approach 2:
DC signals are extracted and blocked from specific amplifier channels using AC coupling capacitors. This separates the DC component removal from the AC signal amplification function, allowing small AC signals to be amplified without the risk of DC-induced saturation.
2Reliability
If AC coupling is applied to block DC signals, then saturation risk is reduced, but input impedance decreases
Solution Approach 1:
AC coupling capacitors are selectively applied only to specific channels where DC signal blocking is needed, rather than uniformly to all channels. This localized application maintains high input impedance in channels where it is critical while preventing saturation only where necessary.
Solution Approach 2:
The amplifier channels are configured asymmetrically with respect to AC coupling - some channels have AC coupling capacitors while others do not. This asymmetric configuration allows optimization of input impedance for different signal sources while preventing saturation in channels requiring DC blocking.
3Adaptability or versatility
If multi-channel configuration is used for medical devices, then application versatility is improved, but common-mode noise rejection becomes more difficult
Solution Approach 1:
Multiple amplifier channels are merged into a single integrated circuit with shared common-mode rejection mechanisms. The common-mode rejection network processes signals from all channels simultaneously, maintaining high common-mode rejection ratio across multiple channels while preserving application versatility.
Data Source
AI summary
Devices, systems, and methods for multi-channel common-mode coupled alternating current (AC) gain amplifiers (MC-CM-AC Amp) are disclosed. The MC-CM-AC Amp can comprise a first operational amplifier including: a first non-inverting input port configured to be coupled to a first input signal, and a first inverting input port configured to be coupled to a first capacitor. The MC-CM-AC Amp can comprise a second operational amplifier including a second non-inverting input port configured to be coupled to a second input signal, and a second inverting input port configured to be coupled to a second capacitor. The MC-CM-AC Amp can comprise one or more gain-setting resistors configured to be coupled between the first capacitor and the second capacitor.