Differential Amplifier Offset Calibration With Multi-Tanh Linearization
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Solution Overview
Problem
Differential amplifiers face challenges in accurately compensating for offset voltages due to variations in manufacturing processes, which affect the accuracy of output voltage in high-precision circuits.
Innovation Solution
An offset compensated differential amplifier system employing a multi-tan h circuit with a plurality of differential pairs and a compensation calibration circuit using a SAR ADC and DAC to generate a compensation control voltage, providing improved linearity and granularity in offset compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional differential amplifier with single differential pair is used, then the circuit is simple, but the offset compensation linearity is poor and the linear voltage range is limited
Solution Approach 1:
The patent divides a single differential pair into multiple differential pairs (first, second, third differential pairs) with different tail currents. Each differential pair operates in a different current range, providing linear compensation in respective segments. The segmentation of compensation ranges across multiple pairs achieves overall improved linearity without requiring a single complex high-current pair.
Solution Approach 2:
Each differential pair is assigned a specific tail current value (I1, I2, I3) tailored to its operating range. The first pair uses higher tail current for large offset compensation, the second pair uses medium tail current for intermediate ranges, and the third pair uses lower tail current for fine adjustments. This local optimization of current values improves linearity in each specific compensation range.
2Manufacturing precision
If the tail current is increased to improve offset compensation range, then the compensation range increases, but the granularity of compensation decreases
Solution Approach 1:
The system dynamically switches between different differential pairs based on the magnitude of the offset voltage. The switching mechanism selects which differential pair to activate, thereby dynamically adjusting the tail current to match the compensation requirement. This dynamic adaptation ensures fine granularity (low current) for small offsets and adequate range (high current) for large offsets.
Solution Approach 2:
Instead of using a single high tail current for all cases, the patent applies partial action by using multiple differential pairs with progressively lower currents. The system uses only the necessary portion of total available compensation capability for each specific offset magnitude, avoiding excessive current consumption while maintaining sufficient compensation range.
3Manufacturing precision
If a single differential pair with high tail current is used, then the compensation range is large, but the linearity in the linear region is poor
Solution Approach 1:
The transfer function is segmented across multiple differential pairs, each contributing to linearity in its specific operating region. The first differential pair handles large-signal compensation with coarser linearity requirements, while subsequent pairs handle smaller signals with finer linearity requirements. This segmentation allows each pair to operate in its optimal linear region.
Solution Approach 2:
The overall transfer function is composite, formed by combining the transfer functions of multiple differential pairs with different tail currents. Each pair contributes a linear segment to the composite characteristic, and their combination creates an extended linear range with improved overall linearity, similar to how composite materials combine properties of individual materials.
Data Source
AI summary
An offset compensated differential amplifier employing a multi-tan h circuit comprising differential pairs coupled in parallel to compensate for an offset voltage of the output voltage in the offset compensation calibration mode is disclosed. The differential pairs each include a compensation transistor coupled to the positive internal node and a reference transistor coupled to the negative internal node. Each compensation transistor receives the compensation control voltage and each reference transistor receives a different reference voltage. The multi-tan h circuit generates an offset compensation voltage on the positive and negative internal nodes based on a difference between the compensation control voltage and the different reference voltages. The multi-tan h circuit comprises a larger linear range than a hyperbolic tangent current transfer function of a single differential pair. The offset compensated differential amplifier provides offset compensation with improved linearity and a finer granularity compared to a conventional differential amplifier.