Comparator Circuit With Threshold-Voltage Compensation
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Solution Overview
Problem
Existing comparators exhibit significant dispersion in trip point voltage due to technological variations, leading to inconsistent performance, and existing calibration methods increase power consumption, which is undesirable, especially in image sensor applications.
Innovation Solution
A compensated comparator design featuring capacitors between transistor gates and inputs, pre-charge, sharing, and decision devices, which memorize threshold voltages and apply them during comparison, reducing dispersion and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If calibration methods are used to reduce trip point dispersion, then manufacturing precision is improved, but use of energy increases
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitors connected to the gates of differential transistors before the comparison operation. This pre-charging sets initial voltages that compensate for threshold voltage variations, thereby reducing trip point dispersion without requiring energy-consuming calibration procedures during normal operation.
Solution Approach 2:
The comparator circuit performs self-compensation through the pre-charged capacitors that automatically adjust the gate voltages to counteract transistor threshold variations. This self-service mechanism eliminates the need for external calibration systems, reducing power consumption while maintaining manufacturing precision.
2Manufacturing precision
If conventional comparator design is used, then device complexity is low, but manufacturing precision deteriorates
Solution Approach 1:
The patent introduces capacitors as intermediary elements between the input signals and the differential transistor gates. These capacitors serve as mediators that store pre-charged voltages and deliver them during operation, compensating for transistor variations without significantly increasing overall circuit complexity.
Solution Approach 2:
The invention changes the voltage parameters at the transistor gates by using pre-charged capacitors to provide compensating voltages. This parameter change approach allows the circuit to maintain consistent trip points across different manufacturing variations without requiring fundamental changes to the comparator architecture.
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
The solution effectively reduces trip point dispersion from 50 mV to 2.5 mW and minimizes power consumption, making it suitable for low-power applications like image sensors.
Implementation Method 1
first and second capacitors intercalated, respectively, between the first gate and the first input and between the second gate and the second input
Implementation Method 2
the sharing device making it possible to short circuit the gate and the drain of each of the first and second transistors, the short circuits causing a charge transfer from the first and second capacitors to the node S, the transfer being interrupted from the moment that the gate-source voltages of the first and second transistors become lower than the respective threshold voltages
Data Source
AI summary
A compensated comparator is provided, including a decision stage and a differential stage provided with two transistors connected by their sources, the differential stage being provided with compensation means to compensate the effects of a dispersion of the threshold voltages of the transistors forming the differential stage, the compensation means including first and second capacitors each connected to a gate of one of the two transistors, and being configured to memorize a voltage that is a function of a threshold voltage of the considered transistors.