Differential Amplifier Trimming Circuit for Precise CMRR and Gain
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Solution Overview
Problem
Existing differential amplifier circuits face challenges in achieving high trimming accuracy for gain and common-mode rejection ratio due to the difficulty in manufacturing small resistance values required for precise resistor trimming, leading to increased costs and testing time with traditional digital methods.
Innovation Solution
The implementation of an all-digital trimming circuit using a series of unit resistors and auxiliary resistors in parallel, allowing for finer adjustments through tap switches, which reduces the need for laser trimming and lowers circuit costs by enabling larger unit resistance values with improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional digital trimming methods are used with small resistance values to achieve high trimming accuracy, then gain and common-mode rejection ratio accuracy are improved, but manufacturing difficulty increases and cost increases
Solution Approach 1:
The trimming circuit is divided into multiple identical unit resistors (e.g., 64 resistors for 8-bit trimming) connected in series to form trimming resistor strings. Each unit resistor has a larger, easier-to-manufacture resistance value, and by selectively connecting different numbers of unit resistors through trimming switches, high-resolution trimming is achieved without requiring manufacturing of very small resistance values.
Solution Approach 2:
Instead of using small resistance values to achieve fine trimming resolution, the invention changes the approach by using multiple larger resistance values in series combinations. The total resistance is divided into discrete units that can be selectively activated, transforming the problem from manufacturing small precise resistors to combining larger standard resistors in different configurations.
2Measurement precision
If laser trimming method is used to achieve high trimming accuracy, then gain and common-mode rejection ratio accuracy are improved, but cost and testing time increase
Solution Approach 1:
The invention replaces the mechanical/laser trimming process with an all-digital trimming approach. Digital trimming signals control switching elements to selectively connect different numbers of unit resistors in series, achieving precise resistance adjustment through electronic control rather than physical material removal. This eliminates the need for expensive laser trimming equipment and reduces testing time significantly.
3Manufacturing precision
If more unit resistors are used to achieve higher trimming resolution, then trimming accuracy is improved, but circuit complexity increases
Solution Approach 1:
The trimming circuit uses multiple identical unit resistors with the same resistance value, segmented into series connections. For example, 64 identical resistors can achieve 8-bit trimming resolution. The repetition of identical units simplifies manufacturing and testing while achieving high resolution through the number of segments rather than varying individual resistor values.
Solution Approach 2:
The same unit resistor design and trimming switch configuration can be used for both gain trimming and common-mode rejection ratio trimming by appropriately connecting the trimming resistor strings to different circuit nodes. This universal approach reduces overall circuit complexity compared to using different trimming mechanisms for different functions.
Data Source
AI summary
The present invention provides a common-mode rejection ratio and gain trimming circuit of differential amplifier, comprising: a first trimming unit and a second trimming unit coupled between an in-phase input voltage and a reference voltage, wherein the first trimming unit and the second trimming unit are coupled to a positive input terminal of the differential amplifier by means of tap switches; a third trimming unit and a fourth trimming unit coupled between tan inverting input voltage and an output terminal of the differential amplifier, wherein the third trimming unit and the fourth trimming unit are coupled to a negative input terminal of the differential amplifier by means of tap switches; wherein, the first trimming unit, the second trimming unit, the third trimming unit, and the fourth trimming unit comprise: a first trimming resistor string and a second trimming resistor string coupled in series; the first trimming resistor string is coupled in parallel with a first trimming auxiliary resistor string, and the second trimming resistor string is coupled in parallel with a second trimming auxiliary resistor string; wherein, the second trimming resistor string of the first trimming unit is coupled to the second trimming resistor string of the second trimming unit, and the second trimming resistor string of the third trimming unit is coupled to the second trimming resistor string of the fourth trimming unit.