Differential Comparator Current Control for Low Supply Spikes
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Solution Overview
Problem
Conventional comparators experience large current spikes on voltage supplies during output transitions, leading to noise interference in high accuracy applications like analog-to-digital converters, and existing solutions either require complex structures or large numbers of circuit elements.
Innovation Solution
A differential comparator with a current control circuit comprising a pair of transistors connected in series between the VDD and ground supply, ensuring a constant current draw during transitions by using PMOS and NMOS transistors to manage current flow through a current source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional differential comparator is used, then the comparator can perform basic comparison function, but large current spikes occur on voltage supplies during output transitions
Solution Approach 1:
A current control circuit is introduced as an intermediary between the power supply and the differential comparator. This control circuit actively monitors and regulates the current supplied to the comparator, preventing large current spikes during output transitions while maintaining normal comparator operation. The control circuit acts as a mediator that smooths the power delivery without interfering with the comparator's core comparison function.
Solution Approach 2:
The current control circuit prepares and conditions the supply current before it reaches the differential comparator. By pre-regulating the current and preventing spikes before they occur, the system avoids the harmful effects of current transients during output transitions, while ensuring the comparator receives stable power for reliable operation.
2Measurement precision
If multiple comparators transition simultaneously in an image sensor chip, then high accuracy conversion can be achieved, but large current spikes create noise that adversely impacts comparators
Solution Approach 1:
The current control circuit serves as a protective intermediary for each comparator, isolating them from the noisy effects of simultaneous transitions. By regulating the supply current to each comparator individually, the control circuits prevent noise propagation through the shared power rails, allowing multiple comparators to operate simultaneously without mutual interference.
Solution Approach 2:
The harmful current spike component is extracted and removed from the power supply to each comparator through the current control circuit. This separation allows the useful comparison function to proceed while eliminating the harmful noise-generating current transients that would otherwise affect other comparators in the array.
3Power
If amplifier stages are connected in series to provide adequate gain, then gain requirement is met, but the structure becomes complex and requires capacitors in the signal path
Solution Approach 1:
The comparator and amplifier functions are merged into a single integrated stage. Rather than using multiple separate amplifier stages connected in series, the invention combines the comparison and amplification operations in one circuit, achieving the required gain without the complexity of cascaded stages and eliminating the need for capacitors in the signal path.
Solution Approach 2:
The single comparator stage is designed to perform multiple functions simultaneously - both comparison and amplification. This multi-functional approach replaces the need for separate amplifier stages, reducing the overall device complexity while maintaining the required gain performance for high-accuracy applications.
Data Source
AI summary
A current control circuit is coupled in parallel with the current paths of a differential comparator circuit to ensure that a substantially constant current is drawn from a current source during all operating phases of a comparator. The current control circuit is biased by a reference voltage, which is also used to bias a V− input terminal of the differential comparator circuit. The reference voltage is stored by a sample capacitor, which is charged by applying the reference voltage to a V+ input terminal of the differential comparator circuit while coupling an output terminal of the differential comparator circuit to the sample capacitor in a unity feedback configuration.