Differential Amplifier Gain Trimming for High Common-Mode Rejection
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Solution Overview
Problem
Existing differential amplifiers face challenges in achieving high input common mode rejection without using chopper circuits, especially in applications where choppers are impractical due to voltage limitations or power concerns, and require efficient area utilization for resistor mismatch reduction.
Innovation Solution
A differential amplifier design that incorporates resistors in both paths and a varistor in a T-network for gain trimming, allowing for the adjustment of the varistor's resistance to achieve matched gains and high common mode rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a chopper circuit is used to cancel gain and offset mismatches, then common mode rejection ratio is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the gain trimming function from the complex chopper circuit and implements it through a simple variable resistor in a T-network configuration. This removes the need for complex switching circuits while maintaining the ability to adjust and match gains in differential paths, thereby improving common mode rejection without the complexity overhead of chopper circuits.
Solution Approach 2:
The patent changes the resistance parameter of the variable resistor in the T-network to trim and match the gains of differential paths. By adjusting this single parameter, the system achieves high common mode rejection ratio without requiring complex circuit topologies, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If resistor values are increased to reduce mismatch effects, then common mode rejection is improved, but circuit area increases
Solution Approach 1:
The patent introduces a dynamically adjustable variable resistor that allows the circuit to achieve high common mode rejection through electronic trimming rather than relying on physically large fixed resistors. This dynamic adjustment capability enables precise gain matching without requiring oversized resistor components, thus resolving the area penalty associated with high-precision fixed resistor implementations.
Solution Approach 2:
The patent implements preliminary gain trimming during the manufacturing or initialization phase by adjusting the variable resistor to match the differential path gains. This preliminary action compensates for resistor mismatches before the circuit operates, allowing the use of smaller, more area-efficient resistors while still achieving high common mode rejection performance.
3Measurement precision
If chopper circuits are used for gain matching, then common mode rejection is improved, but power consumption increases
Solution Approach 1:
The patent replaces the power-hungry chopper circuit with a passive variable resistor implementation that consumes minimal power. The T-network with variable resistor provides a low-power alternative for gain trimming and common mode rejection, effectively substituting an energy-intensive active circuit with a passive, energy-efficient component.
Solution Approach 2:
The variable resistor in the T-network provides self-adjusting gain trimming capability without requiring additional active power consumption. Once adjusted, the circuit maintains its gain matching and common mode rejection performance passively, eliminating the continuous power consumption associated with active chopper circuits while preserving the measurement precision benefits.
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 approach enables high input common mode rejection with reduced resistor mismatch effects, suitable for applications where choppers are not feasible, and optimizes area usage, achieving specifications comparable to untrimmed networks with improved accuracy.
Implementation Method 1
a varistor in a T-network between both paths, to provide gain trimming
Data Source
AI summary
An amplifier comprising a differential amplifier configured to be provide a comparator function, and a gain trimming circuit is electrically configured to provide gain trimming using a T-network comprising a varistor element. In addition, a method of trimming the gain of a differential amplifier, comprising the steps of a first step, (a) providing the differential amplifier comprising resistors in both of its paths, a second step, (b) providing a varistor in a T-network between both said paths; and lastly, a third step, (c) trimming the gain of the differential amplifier by adjusting the varistor's resistance.