Offset-Compensated Active Load for Low-Noise Offset Cancellation
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Solution Overview
Problem
Existing circuits, such as operational amplifiers and comparators, face performance issues due to component mismatches that introduce input offset voltage, with existing techniques for canceling offset voltage often introducing noise or injecting charge, which are not effectively mitigated.
Innovation Solution
The implementation of an offset-compensated active load using a semiconductor component with a plurality of transistors, switches, and charge storage elements, operating in two modes to generate and store an offset current and voltage, which is then used to compensate for input offset voltage without introducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switches are used to cancel offset voltage, then offset voltage is reduced, but noise and charge injection are introduced
Solution Approach 1:
The patent performs offset voltage measurement and compensation in a preliminary phase before the main signal processing. The offset is measured during a calibration phase when switches are temporarily activated, then stored for subsequent compensation during normal operation, avoiding continuous switch activation that would generate noise and charge injection.
Solution Approach 2:
The offset compensation is performed periodically rather than continuously. The circuit alternates between calibration phases (where switches are activated to measure and store offset) and operational phases (where stored offset is subtracted from input signals). This periodic approach minimizes the time switches are active, reducing noise and charge injection while maintaining offset compensation effectiveness.
2Measurement precision
If component mismatches are reduced to minimize input offset voltage, then circuit performance is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements a feedback mechanism where the offset voltage is measured during calibration, stored, and then fed back as a compensation signal during normal operation. This feedback loop automatically compensates for component mismatches without requiring manual adjustment or higher precision components, maintaining manufacturing simplicity while achieving low offset voltage.
Solution Approach 2:
The circuit performs self-calibration and self-compensation through integrated offset measurement and correction circuitry. The system automatically measures its own offset during calibration phases and applies compensation during operation, eliminating the need for external adjustment mechanisms or specially matched components, thereby maintaining ease of manufacture.
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 compensates for input offset voltage while maintaining circuit performance, reducing noise and charge injection, and is cost and time efficient to implement.
Implementation Method 1
a plurality of charge storage elements coupled between a control electrode of a first transistor of the active load and a control electrode of a second transistor of the active load
Data Source
AI summary
In accordance with an embodiment, an offset-compensated active load includes a pair of transistors having control electrodes connected to their drain electrodes through coupling devices. The control electrodes of the transistors are connected to each other through a plurality of charge storage elements. In accordance with another embodiment, an offset current is generated in response to coupling input terminals of an input stage together. The offset current flows towards an active load which generates an offset voltage in response to the offset current. The offset voltage is stored in the plurality of charge storage devices of the offset-compensated active load.