Multiple-Output Transconductance Amplifier for Resistor-Matched IA Limits
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Solution Overview
Problem
Traditional instrumentation amplifiers face challenges in achieving high precision and accuracy due to the difficulty in matching resistor pairs, which affects common mode rejection and introduces distortion from voltage coefficients in polysilicon resistors.
Innovation Solution
The use of multiple-output transconductance amplifiers, specifically triple-output transconductance amplifiers, reduces the number of resistors needed and eliminates the need for precise resistor matching, providing improved common mode rejection and accuracy by using two resistors with one connected to ground and the other to an amplifier output node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional instrumentation amplifiers use multiple resistors to achieve differential gain and common mode rejection, then the amplifier can provide signal amplification and noise rejection, but the difficulty and cost of fabrication increases rapidly due to the need for precise resistor matching
Solution Approach 1:
The patent extracts the resistive elements from the critical signal path and replaces them with transconductance amplifiers. By removing the need for precision-matched resistors in the differential gain stage, the fabrication difficulty is significantly reduced while maintaining or improving common mode rejection ratio through the inherent properties of the transconductance amplifier circuitry.
Solution Approach 2:
The patent changes the fundamental operating parameters by using transconductance amplifiers with high output impedance to simulate resistive behavior without physical resistors. This parameter change allows the circuit to achieve the same functional goals (differential gain, common mode rejection) without requiring precise component matching, thereby easing fabrication.
2Ease of manufacture
If polysilicon resistors are used in traditional instrumentation amplifiers, then the amplifier can be fabricated using standard processes, but voltage coefficients in the resistors create significant distortion and non-linearity in the output voltage
Solution Approach 1:
The patent removes polysilicon resistors from the critical signal path where their voltage coefficients cause distortion. By replacing these resistors with transconductance amplifiers, the source of non-linearity is eliminated while maintaining fabrication simplicity through the use of standard integrated circuit processes for building the amplifier circuits.
Solution Approach 2:
The patent uses transconductance amplifiers to create an equivalent resistive function without the harmful properties of physical resistors. The amplifier circuits copy the functional behavior of resistors (providing impedance and gain) while eliminating the voltage coefficient distortion inherent in polysilicon resistors.
3Power
If more resistors are used to increase differential gain in traditional instrumentation amplifiers, then the amplifier can provide higher signal amplification, but the number of components and circuit complexity increases
Solution Approach 1:
The transconductance amplifiers perform multiple functions simultaneously: they provide differential gain, establish output impedance, and contribute to common mode rejection all in a single circuit stage. This multi-functionality achieves high differential gain without proportionally increasing component count, as each amplifier module handles multiple responsibilities.
Solution Approach 2:
The patent combines the functions of multiple resistors and amplifier stages into integrated transconductance amplifier modules. By merging these functions into unified circuit blocks, the design achieves high differential gain with reduced overall component count and lower circuit complexity compared to traditional multi-resistor configurations.
Data Source
AI summary
This disclosure is directed to devices and integrated circuits for instrumentation amplifiers. In one example, an instrumentation amplifier device uses two non-inverted outputs of a first multiple-output transconductance amplifier, and a non-inverted output and an inverted output of a second multiple-output transconductance amplifier. Both multiple-output transconductance amplifiers have a non-inverted output connected to an inverting input, and a non-inverting input connected to a respective input voltage terminal. A first resistor is connected between the inverting inputs of both multiple-output transconductance amplifiers. The outputs of both multiple-output transconductance amplifiers are connected together, connected through a second resistor to ground, and connected to an output voltage terminal. In other examples, two pairs of outputs from triple-output transconductance amplifiers are connected to provide two voltage output terminals, and may also be connected to buffers or a differential amplifier. These provide various advantages over traditional instrumentation amplifiers.