Current Integrator Circuit With Isolated Offset Cancellation
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Solution Overview
Problem
Current integrators for OLED panels face errors due to input offset from operational amplifiers, which are exacerbated by non-ideal fabrication processes and circuit elements, leading to noise amplification and challenges in cost reduction due to the need for large offset cancelation capacitors.
Innovation Solution
A current integrator design with an operational amplifier featuring two input stages, where the offset cancelation capacitor is isolated from the signal path, allowing one input stage to receive the input current signal and the other to handle offset cancellation, reducing noise influence on the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an offset cancelation capacitor is coupled between the differential input terminals of the operational amplifier to cancel offset, then the offset error is reduced, but the capacitor size must be large enough to store offset charges during integration period, increasing device area and cost
Solution Approach 1:
The patent divides the operational amplifier into two separate input stages: a first input stage for receiving the input current signal and a second input stage for receiving the offset cancelation signal. This segmentation allows the offset cancelation capacitor to be coupled to the second input stage rather than between differential input terminals, enabling smaller capacitor size while maintaining offset cancellation functionality during integration.
Solution Approach 2:
The patent introduces a current source as an intermediary device that converts the offset cancelation voltage signal into an offset cancelation current signal. This current source is coupled between the second input stage and ground, serving as a mediator that enables offset cancellation through current injection rather than direct voltage coupling, thereby reducing the burden on the offset cancelation capacitor.
2Reliability
If a large offset cancelation capacitor is used to store offset information during integration period, then offset cancellation is effective, but the device size increases and cost rises
Solution Approach 1:
By segmenting the operational amplifier into two input stages and coupling the offset cancelation capacitor to the second input stage rather than using a large capacitor between differential terminals, the patent achieves effective offset cancellation with a smaller capacitor, reducing manufacturing cost and device area while maintaining reliability.
Solution Approach 2:
The patent changes the operating parameters by using a current source to convert the offset cancelation voltage to current, and by coupling the capacitor to a single-input stage rather than across differential inputs. This parameter change enables the use of smaller capacitor values while maintaining adequate charge storage capability for offset cancellation throughout the integration period.
3Measurement precision
If the offset cancelation capacitor is coupled between differential input terminals, then offset cancellation is achieved, but noise from the capacitor is amplified by the operational amplifier and coupled to the output
Solution Approach 1:
The patent segments the operational amplifier into two input stages, isolating the offset cancelation capacitor from the signal path. The capacitor is coupled to the second input stage which processes offset cancellation signals separately from the main input signal, preventing noise amplification while maintaining offset cancellation effectiveness.
Solution Approach 2:
The patent extracts the offset cancelation function from the main signal path by creating a separate second input stage dedicated to offset cancellation. The offset cancelation capacitor and its associated noise are taken out of the primary signal processing path, preventing noise amplification while preserving the offset cancellation benefit.
Data Source
AI summary
A current integrator includes an operational amplifier, an integration capacitor and an offset cancelation capacitor. The operational amplifier includes a first input stage and a second input stage. The first input stage is coupled to an input terminal of the current integrator. The integration capacitor is coupled between the first input stage of the operational amplifier and an output terminal of the current integrator. The offset cancelation capacitor is coupled to the second input stage of the operational amplifier.