Dual-Port Transimpedance Amplifier With Separate AC/DC Feedback
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Solution Overview
Problem
Transimpedance amplifiers (TIAs) face challenges in achieving high linearity and minimizing signal distortion while requiring a small area on integrated circuits, especially when dealing with capacitive sensors, due to the need for high impedance resistors that can result in significant parasitic capacitance and limited output voltage range.
Innovation Solution
The implementation of a transimpedance amplifier circuit with a separate AC signal path and DC bias path, utilizing pseudo-resistors to achieve high impedance with low surface area and low parasitic capacitance, allowing for high gain without reducing output voltage or introducing distortion, and using low-pass filters to manage DC bias feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high impedance resistors are used to achieve high gain, then signal amplification capability is improved, but parasitic capacitance increases and output voltage range is limited
Solution Approach 1:
The feedback path is segmented into two separate paths: an AC signal path for high-frequency signal feedback and a DC bias path for low-frequency bias feedback. This segmentation allows each path to be optimized independently, enabling high impedance for signal amplification while minimizing parasitic capacitance effects through separate routing and component selection.
Solution Approach 2:
A capacitor is introduced as an intermediary element in the AC signal path to block DC components while allowing AC signals to pass. This intermediary enables the AC feedback path to provide high impedance for signal amplification without being affected by DC bias conditions, thereby reducing the impact of parasitic capacitance.
2Measurement precision
If separate AC signal path and DC bias path are implemented, then linearity and signal quality are improved, but circuit complexity increases
Solution Approach 1:
The AC signal path and DC bias path are merged at the feedback node where they both connect to the inverting input of the operational amplifier. This merging point allows both paths to work together seamlessly, providing improved linearity through combined feedback action while minimizing circuit complexity by sharing common components and nodes.
Solution Approach 2:
The feedback network is designed with multi-functionality where the same feedback node serves both AC signal feedback and DC bias feedback purposes. The operational amplifier's inverting input acts as a universal node that processes both AC and DC components, allowing the circuit to achieve improved linearity without requiring completely separate processing paths.
Data Source
AI summary
A transimpedance amplifier circuit with an AC signal path and a DC bias path separate from the AC signal path that may be used with a wide variety of sensors such as MEMS accelerometers, photo detectors and pressure sensors. The circuit includes a high impedance input pseudo-resistor that minimizes the area needed on an integrated circuit and configured to minimize losses, noise injection, noise gain and distortion while maintaining amplifier bandwidth, linearity and output voltage range.