Differential Input Amplifier Using Branch Current Copying for Offset Balance
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Solution Overview
Problem
Amplifiers with differential input pairs are sensitive to systematic imbalances, which affect the accuracy of signal measurement and amplification, especially for low-amplitude input signals, and are often neglected in comparison to random imbalances.
Innovation Solution
The solution involves a method and structure for differential input amplifiers that includes measuring and copying current in one branch to compensate for imbalances in another branch, using identical transistors and resistors to dynamically correct systematic imbalances, making the compensation self-adaptable to temperature and manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a differential input pair structure is used for amplification, then the amplifier can provide useful signal amplification, but systematic imbalance is introduced due to current sampling from a single branch
Solution Approach 1:
The amplifier is divided into four separate branches: first and second branches for differential input signals, third branch for current measurement, and fourth branch for current copying. This segmentation allows the systematic imbalance to be measured and compensated without affecting the main amplification function.
Solution Approach 2:
A current measurement branch (third branch) is introduced as an intermediary to measure the systematic imbalance current. This measurement is then copied to a fourth branch to compensate for the imbalance in the differential input branches, without directly interfering with the signal amplification path.
2Productivity
If current sampling from a single branch is used to provide useful signal, then amplification is achieved, but current imbalance between branches occurs altering measurement accuracy
Solution Approach 1:
The systematic imbalance current measured in the third branch is copied to the fourth branch using a current mirror circuit. This copying mechanism reproduces the imbalance current to compensate for its effect in the differential input branches, maintaining measurement accuracy without reducing processing efficiency.
Solution Approach 2:
The measurement of current in the third branch provides feedback information about the systematic imbalance. This feedback is used to adjust the current in the fourth branch, creating a closed-loop compensation system that continuously corrects the imbalance without affecting the forward signal processing path.
3Measurement precision
If random imbalance correction is improved, then random offset is reduced, but systematic imbalance becomes the dominant error source
Solution Approach 1:
The systematic imbalance, which was previously a harmful error source that was neglected, is converted into a measurable quantity. By intentionally measuring and copying this imbalance current, the harmful effect is transformed into a useful compensation mechanism that improves overall amplifier accuracy.
Solution Approach 2:
The systematic imbalance is measured and compensated in advance through the dedicated third and fourth branches, before it can significantly degrade the amplifier performance. This preliminary compensation action ensures that both random and systematic imbalances are corrected, with the systematic correction being continuously adaptive.
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 effectively reduces systematic imbalances, improving the accuracy and stability of signal amplification across different temperature conditions and manufacturing batches, ensuring consistent performance.
Implementation Method 1
a first bipolar amplifier having an input terminal connected to the second branch and having an output terminal intended to be coupled to a load... a second bipolar amplifier having an input terminal connected to the first branch
Implementation Method 2
the measurement and copying elements are respectively associated with resistors in series
Implementation Method 3
the measurement element comprises a first diode-assembled transistor and the copying element comprises a second transistor mirror-assembled on the first transistor
Data Source
AI summary
An amplifier comprises: first and second supply terminals intended to receive a DC supply voltage; a first branch coupled between the first and second supply terminals and including a first terminal of application of a differential signal to be amplified; a second branch coupled between the first and second supply terminals and including a second terminal of application of the differential signal to be amplified; a third branch coupled between the first and second supply terminals and including a first amplifier having an input terminal connected to the second branch and having an output terminal configured to be coupled to a load, and a measurement element configured to measure a current in the third branch; and a fourth branch coupled between the first and second supply terminals and including a second amplifier having an input terminal connected to the first branch, and a copying element configured to copy the current measured in the third branch.