Low-Power Digital Word Comparator Using Three-Transistor Bit Cells
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Solution Overview
Problem
Existing digital word comparators face limitations in speed and noise margins due to the need to pre-charge and discharge capacitance, which affects power consumption and accuracy in multi-bit comparisons.
Innovation Solution
A digital word comparator design featuring a switch responsive to a bit mismatch control signal, utilizing an exclusive-OR circuit and comparison sensing logic with pre-charging and discharging circuits to efficiently manage node states and reduce power consumption, allowing for higher speed and improved noise margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a full word comparison is performed at one time using multiple transistors per bit comparator, then comparison speed is improved, but power consumption increases due to larger capacitance that must be charged and discharged
Solution Approach 1:
The patent changes the transistor configuration from four transistors per bit comparator to three transistors per bit comparator. This parameter change reduces the total capacitance that needs to be charged and discharged during comparison operations, thereby reducing power consumption while maintaining comparison speed through optimized circuit timing and voltage management
Solution Approach 2:
The patent merges the functionality of multiple transistors into a more efficient three-transistor configuration. By combining the functions of bit comparison, latch control, and output generation into a compact three-transistor design, the circuit achieves the same computational function with reduced capacitance and lower power consumption
2Reliability
If more transistors are used in each bit comparator to improve noise margins, then comparison accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent optimizes the transistor count to exactly three per bit comparator, finding the optimal balance between noise margin performance and circuit simplicity. This parameter optimization ensures sufficient noise immunity for reliable comparison while avoiding the complexity and power overhead of additional transistors
Solution Approach 2:
The three-transistor design incorporates self-latching functionality where the circuit automatically maintains its comparison state without requiring additional transistors for separate latch control. The comparison result is inherently held in the transistor states themselves, eliminating the need for extra complexity while maintaining reliability
3Reliability
If four transistors are used per bit comparator, then noise margins are improved, but power consumption increases due to additional capacitance charging and discharging
Solution Approach 1:
The patent reduces the transistor parameter from four to three per bit comparator, directly reducing the capacitance that must be charged and discharged. This parameter change maintains adequate noise margins through optimized transistor sizing and voltage levels while significantly reducing the energy required for each comparison operation
Solution Approach 2:
The patent extracts one transistor from the traditional four-transistor design, removing the redundant component that contributes to excessive capacitance and power consumption. The remaining three transistors are optimized to perform all necessary functions with sufficient noise immunity, eliminating the harmful excess without compromising reliability
Data Source
AI summary
Apparatus and method for performing a high-speed, low-power bit-wise comparison of two digital words. For each bit, a bit comparator is shown, employing a compare node and a discharge node. After both nodes are charged, the discharge node is discharged and the condition of the compare node signals the result of the comparison. For each bit, a bit comparator is provided including a single transistor switch across the compare node and the discharge node. An exclusive-OR circuit connected to receive the corresponding bits of the words drives and selectively actuates the switch when the values of the corresponding bits are mismatched. Words may be segmented such that comparisons may be done segment-wise and the detection of a mismatch in any segment obviates the discharging of the compare node in segments containing more significant bits, to save power.