Integrated Instrumentation Amplifier Biasing for Stable Gain
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Solution Overview
Problem
Existing instrumentation amplifiers face challenges in maintaining high accuracy and stability over temperature variations and process changes due to the use of external resistors, which degrade performance and introduce noise, especially when dealing with small signals in noisy environments.
Innovation Solution
An integrated amplifier device utilizing a replica amplifier and transconductance biasing cell to provide biasing to both the main amplifier and the replica amplifier, ensuring stable gain and low noise across a wide bandwidth, while rejecting common-mode signals without loading the signal source, and can be implemented in standard CMOS for mixed-signal systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If external resistors are used to set gain, then gain setting flexibility is improved, but accuracy and noise performance deteriorate due to mismatch with internal resistors and different temperature coefficients
Solution Approach 1:
The patent merges the gain-setting function with internal integrated circuit resistors by providing multiple predetermined gain configurations (G1, G2, G3) that are built into the amplifier circuit. This eliminates the need for external resistors while maintaining accuracy through matched temperature coefficients and process characteristics.
Solution Approach 2:
The amplifier is designed with multi-functionality by incorporating switchable gain stages that can operate in multiple gain modes (G1, G2, G3) using the same internal resistor network. This universal design allows the circuit to adapt to different gain requirements while maintaining precision through integrated components.
2Measurement precision
If operational amplifier buffers are used at each input, then input impedance is improved, but speed requirements and complexity increase to maintain virtual node stability
Solution Approach 1:
The patent extracts the high input impedance function from traditional operational amplifier buffers and implements it through a differential input stage with high-impedance transistor inputs. This eliminates the need for complex operational amplifier buffers while maintaining the required input impedance characteristics.
3Reliability
If bipolar or BiCMOS processes are used, then performance objectives are met, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the process parameter from bipolar/BiCMOS to standard CMOS technology. This parameter change maintains the required performance objectives while significantly simplifying manufacturing and reducing cost, as standard CMOS is a more common and less complex process.
4Measurement precision
If laser trimming of on-chip resistors is used, then accuracy requirements are met, but device complexity and manufacturing steps increase
Solution Approach 1:
The patent implements self-service by designing the circuit to achieve required accuracy through inherent properties of integrated resistors and switchable gain configurations, eliminating the need for additional laser trimming steps. The circuit compensates for variations through its internal design rather than requiring external adjustment processes.
Data Source
AI summary
An integrated amplifier device includes a main amplifier configured to be coupled to an input source. A replica amplifier is coupled to the main amplifier to provide a bias to the main amplifier. A transconductance biasing cell to the main amplifier and the replica amplifier. The transconductance biasing cell is configured to bias both the main amplifier and the replica amplifier. A method of making an integrated amplifier device is also disclosed.