Gray-Code Counter Array for Stable High-Speed Image Sensing
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Solution Overview
Problem
Conventional up/down counters in CMOS image sensors experience increased power consumption and operating margin reduction due to high instant current changes, leading to potential faults during high-speed operations.
Innovation Solution
A counter array design that incorporates a controller, counter units with latches and switches, and a decoder to output 2-bit gray codewords, reducing the number of bits toggled simultaneously and minimizing instant current changes through a gray codeword scheme.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional BCD codeword scheme is used in up/down counters, then the counter can perform counting operations, but a large number of bits are toggled at one time causing increased instant current change
Solution Approach 1:
The patent changes the coding parameter from BCD (Binary Coded Decimal) to Gray code. This parameter change ensures that only one bit changes state between consecutive counting values, reducing the instant current change from multiple bits toggling to a single bit transition. For example, transitioning from 3 to 4 in BCD changes multiple bits (0011 to 0100), while in Gray code it changes only one bit (001 to 011).
Solution Approach 2:
The patent converts the harmful effect of bit toggling (which causes instant current changes) into a beneficial single-bit transition property inherent to Gray code. By utilizing the reflective property of Gray code where adjacent values differ by exactly one bit, the design transforms what would normally be a multi-bit simultaneous transition into a controlled single-bit change, thereby reducing power consumption and improving reliability.
2Productivity
If the counter operates at high speed, then productivity increases, but the instant current change increases causing operating margin to decrease
Solution Approach 1:
The patent applies Gray code encoding to the counter output, changing the parameter representation from BCD to Gray code. This ensures that during high-speed operation, only one bit transitions at each counting step, maintaining stable current draw even at high counting speeds. The single-bit transition property of Gray code prevents the simultaneous switching of multiple bits that would otherwise cause large current spikes during high-speed operation.
3Reliability
If multiple bits are toggled simultaneously in the counter, then the counting function is achieved, but power consumption increases
Solution Approach 1:
The patent changes the output coding scheme from BCD to Gray code, which fundamentally alters the bit transition behavior. In Gray code, consecutive numerical values differ by exactly one bit position, ensuring that during counting operations, only a single bit changes state at each step. This parameter change maintains the essential counting function while reducing power consumption by eliminating simultaneous multi-bit toggling.
Solution Approach 2:
The patent exploits the inherent property of Gray code where the 'harmful' multi-bit transition is converted into a beneficial single-bit transition. By designing the counter to output Gray code instead of BCD, the system transforms what would be a power-consuming multi-bit simultaneous switch into an energy-efficient single-bit transition, thereby reducing overall power consumption while maintaining counting functionality.
Data Source
AI summary
A counter array and an image sensor including the same may be provided. The counter array may include a controller and a plurality of counter units. The controller may output an operation control signal and a direction indication signal. The counter units hold previous output values or may perform a counting operation in response to the operation control signal and may perform an up-count operation or a down-count operation in response to the direction indication signal when performing the counting operation.