Comparator Gate-Capacitor Compensation for Switching Point Stability
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Solution Overview
Problem
Existing comparators with differential stages suffer from significant dispersion in switching point due to technological variations, particularly in transistor threshold voltages, leading to high power consumption during calibration efforts, especially when integrated into image sensors.
Innovation Solution
A compensated comparator design incorporating capacitors between transistor gates and inputs, along with precharging, sharing, and decision devices controlled by a circuit, to stabilize voltage offsets and reduce power consumption by compensating for transistor threshold variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If calibration methods are used to reduce switching point dispersion, then manufacturing precision is improved, but power consumption increases
Solution Approach 1:
The patent applies preliminary action by performing charge sharing between capacitors before the decision phase. The precharge device charges capacitors during a precharge phase, and the sharing device transfers charge between capacitors during a sharing phase before the actual comparison. This preliminary charge distribution compensates for transistor threshold voltage variations without requiring power-intensive calibration operations during normal operation.
Solution Approach 2:
The comparator circuit performs self-compensation through internal charge sharing between its own capacitors. The sharing device enables the capacitors to automatically redistribute charge based on transistor threshold variations, allowing the circuit to self-correct for manufacturing dispersions without external calibration equipment or additional power consumption.
2Manufacturing precision
If traditional differential stage is used, then device complexity is low, but manufacturing precision deteriorates due to technological dispersions
Solution Approach 1:
The patent merges the compensation function into the existing differential stage by adding capacitors that are integrated with the transistor gates. The capacitors are connected in parallel with the gate terminals, combining the signal input function and the threshold compensation function in a single structural element, thereby reducing overall device complexity while improving manufacturing precision.
Solution Approach 2:
The capacitors act as intermediaries between the input signals and the transistor gates. They store and redistribute charge to compensate for threshold voltage variations, mediating the effect of technological dispersions on the comparator's switching point without requiring fundamental changes to the differential stage architecture.
3Manufacturing precision
If capacitors are added for compensation, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The capacitors are placed locally at each transistor gate terminal, providing compensation specifically where threshold voltage variations occur. This localized approach targets the exact source of manufacturing precision problems without adding complexity to the entire comparator circuit, allowing precision improvement with minimal structural overhead.
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 switching point dispersion from one comparator to another, achieving low power consumption and improved accuracy, with a dispersion reduction from 50 mV to 2.5 mV, suitable for dynamic logic operations in image sensors.
Implementation Method 1
first and second capacitors interposed, 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 transfer of charge from the first and second capacitors to the node S
Data Source
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AI summary
The invention relates to a compensated comparator (100). In particular, the present invention relates to a comparator comprising a decision stage (200) and a differential stage (300) provided with two transistors (M1, M2) connected by their sources S. The differential stage is provided with compensation means for compensating the effects of a dispersion of the threshold voltages of the transistors (M1, M2) forming the differential stage. In particular, the compensation means comprise a first and a second capacitor (C1, C2), each connected to a gate (G1, G2) of one of the two transistors (M1, M2), and intended to store a voltage as a function of the threshold voltage of the transistors (M1, M2) considered.