Single controller automatic calibrating circuits for reducing or canceling offset voltages in operational amplifiers in an instrumentation amplifier
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Solution Overview
Problem
In integrated circuit (IC) design, accurately measuring current across distributed load circuits is challenging due to varying voltage and current profiles, leading to inaccurate current measurements and potential circuit failures, especially with excessive current causing issues as voltage scaling slows and active components increase per unit area.
Innovation Solution
The implementation of single controller automatic calibrating circuits in instrumentation amplifiers, which include front-end and final-stage operational amplifiers with auxiliary differential inputs for offset voltage cancellation, and an automatic calibration circuit using a successive approximation register (SAR) controller and digital-to-analog converter (DAC) to generate calibration signals, effectively reducing or canceling offset voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If distributed voltage averaging circuits with multiple op-amps are used to measure current in distributed load circuits, then current measurement capability is provided, but offset voltages in the op-amps reduce measurement precision
Solution Approach 1:
The patent extracts the offset voltage from the main measurement signal by providing separate auxiliary differential inputs dedicated to offset cancellation. The automatic calibration circuit generates calibration signals that are applied exclusively to these auxiliary inputs, allowing the offset component to be isolated and eliminated without affecting the primary current measurement function.
Solution Approach 2:
The patent implements preliminary calibration action by automatically generating and applying calibration signals to cancel offset voltages before the actual current measurement takes place. The successive approximation register controller systematically adjusts the calibration signals in advance, ensuring that offset voltages are eliminated prior to measurement operations.
2Measurement precision
If multiple automatic calibration circuits with multiple controllers are used to cancel offset voltages in multiple op-amps, then offset voltage cancellation capability is improved, but device complexity increases
Solution Approach 1:
The patent makes a single automatic calibration circuit universal by enabling it to calibrate multiple op-amps through shared calibration resources. The successive approximation register controller and digital-to-analog converters can be sequentially or simultaneously applied to multiple auxiliary differential inputs, allowing one calibration circuit to serve multiple operational amplifiers without requiring separate dedicated calibration circuits for each op-amp.
Solution Approach 2:
The patent merges multiple calibration functions into a single integrated calibration circuit. By combining the controller, digital-to-analog converters, and calibration signal generation into one unified block that can service multiple op-amps, the patent reduces the overall number of components and simplifies the calibration system architecture while maintaining the ability to cancel offset voltages in all operational amplifiers.
3Measurement precision
If auxiliary differential inputs are added to op-amps for offset voltage cancellation, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent introduces asymmetry into the op-amp structure by adding auxiliary differential inputs that are distinct from the primary signal inputs. This asymmetric addition provides a dedicated pathway for offset cancellation signals without interfering with the normal differential signal processing, allowing the op-amp to perform both measurement and calibration functions through structurally differentiated input terminals.
Data Source
AI summary
Single controller automatic calibrating circuits for reducing or canceling offset voltages in operational amplifiers (op-amps) in an instrumentation amplifier are disclosed. An automatic calibrating op-amp system is provided that includes an instrumentation amplifier, which includes a front-end amplifier circuit comprising at least one front-end op-amp and a final-stage amplifier circuit comprising a final-stage op-amp. The op-amp(s) can include auxiliary differential inputs for offset voltage cancellation. The automatic calibrating op-amp system also includes an automatic calibration circuit employing a single controller to generate calibration signals on a calibration output to an auxiliary differential input(s) of an op-amp(s) in the instrumentation amplifier for offset voltage cancellation. The automatic calibration circuit includes a single controller to generate calibration signals to the instrumentation amplifier to reduce or cancel offset voltage, thereby eliminating the need to provide multiple automatic calibration circuits or an automatic calibration circuit employing multiple controllers.