Dynamic Comparator Circuit for Rail-to-Rail Voltage Comparison
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Solution Overview
Problem
Dynamic comparators with input transistors of only one conductivity type are limited in comparing voltages within the full range between supply rails due to threshold voltage constraints, especially as supply voltage ranges decrease with smaller process nodes, leading to incomplete voltage range comparison.
Innovation Solution
Incorporating two sets of input transistors with opposite conductivity types and bypass transistors that allow the output signal to reach the supply rail, enabling 'rail to rail' comparison by coupling current electrodes to the power supply based on the comparison result.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If input transistors of only one conductivity type are used, then device complexity is reduced, but the comparator cannot compare voltages across the full supply voltage range
Solution Approach 1:
The patent combines two sets of input transistors with opposite conductivity types (n-type and p-type) in parallel configuration. This merging allows the comparator to handle the full supply voltage range by utilizing both transistor types' complementary characteristics, where each type handles different portions of the voltage range effectively.
Solution Approach 2:
The dual-set transistor configuration provides multi-functionality by enabling the comparator to operate across the entire supply voltage range regardless of the common-mode voltage level. The circuit universally handles both high and low voltage comparisons that a single transistor type could not achieve alone.
2Adaptability or versatility
If two sets of input transistors with opposite conductivity types are used, then full voltage range comparison is enabled, but output signal cannot reach supply rail voltage
Solution Approach 1:
Bypass transistors are introduced as intermediary elements that provide an additional current path from the output node to the supply rail. These bypass transistors act as mediators that enable the output signal to reach the supply rail voltage by bypassing the limitation imposed by the threshold voltage of the main input transistors.
3Reliability
If bypass transistors are added to enable rail-to-rail output, then output signal reaches supply rail, but device complexity increases
Solution Approach 1:
The bypass transistors are configured with dynamic control where their conductivity state changes based on the comparison phase and reset phase operations. During the comparing phase, the bypass transistors are activated to enable rail-to-rail output, while during the reset phase, they are deactivated. This dynamic operation allows the additional transistors to serve multiple purposes without continuously increasing complexity.
Data Source
AI summary
A dynamic comparator includes two sets of input transistors of opposite conductivity types, where a control electrode of one transistor of each set is coupled to a first input of the comparator and a control input of a second transistor of each set is coupled to a second input of the comparator. The comparator includes bypass transistors for pulling current electrodes of either the first set or second set of input transistors to a power supply terminal depending which input voltage is higher as determined by the output.