Differential Comparator Reset Scheme for Wider Input Range
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Solution Overview
Problem
Conventional CMOS image sensor differential comparators have a limited input range due to their reset mechanism, restricting the operational capabilities of the analog-to-digital converters.
Innovation Solution
A differential comparator circuit is designed with a differential input pair, an active load, and cross voltage generation devices that establish a cross voltage during the reset phase and act as a short circuit during operation, allowing for increased input range by managing voltage levels effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional MOS differential pair with current mirror active load is used, then the comparator can be implemented with standard CMOS technology, but the input range is limited due to the reset mechanism
Solution Approach 1:
The patent applies preliminary action by performing the reset operation before the comparison operation. The reset phase prepares the comparator by discharging the output node capacitance and setting initial conditions, allowing the subsequent comparison phase to operate over a wider voltage range without being constrained by the reset mechanism. This temporal separation of reset and compare operations expands the effective input range.
Solution Approach 2:
The patent implements dynamic operation by using clocked control signals to switch between reset and compare phases. The differential pair and active load are dynamically controlled through phase-dependent switching, allowing the circuit to adapt its configuration based on the operational phase. This dynamic approach enables wider input range while maintaining manageable complexity through systematic phase control.
2Reliability
If the reset mechanism is used to initialize the comparator, then the circuit can be reset to a known state, but the operational range is restricted
Solution Approach 1:
The patent segments the comparator operation into distinct phases: reset phase and compare phase. During the reset phase, the reset mechanism initializes the output to a known state for reliability. During the compare phase, the circuit operates with wider input range capability. This segmentation allows both reset capability and extended operational range to coexist without mutual interference.
Solution Approach 2:
The patent employs periodic action through clocked control signals that alternately activate the reset and compare functions. The periodic switching between phases ensures that the reset mechanism provides reliable initialization at regular intervals, while the compare phase maintains expanded operational range during its active period. This periodic alternation resolves the contradiction between reliability and adaptability.
Data Source
AI summary
A differential comparator circuit is provided that includes a differential input pair, an active load, a pair of cross voltage generation devices and a pair of switches. The differential input pair has a pair of input terminals and a pair of first connection terminals. The active load has a pair of second connection terminals. The cross voltage generation devices are electrically coupled between the first connection terminals and the second connection terminals, wherein the cross voltage generation devices are configured to be electrically activated to establish a cross voltage therebetween in a reset phase and electrically deactivated to become a short circuit in an operation phase. The switches are configured to electrically couple the pair of input terminals respectively to the pair of first connection terminals in the reset phase and not electrically couple the pair of input terminals respectively from the pair of first connection terminals.