Gray-to-Binary Converter Using PIPO Latches and PISO Switching
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Solution Overview
Problem
CMOS image sensors face challenges in efficiently converting analog pixel signals to digital signals while managing high power consumption and reducing electromechanical errors during processing.
Innovation Solution
A correlated double sampling (CDS) circuit with a gray code-to-binary code converter that includes PIPO latches and a PISO circuit to convert parallel gray code to serial binary code, reducing errors and power consumption by using a series of XOR gates and switches to sequentially output bits from LSB to MSB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single ADC operates at high speed to convert analog pixel signals from all column lines, then the chip area is reduced, but power consumption increases
Solution Approach 1:
The patent divides the ADC system into multiple column ADCs, each handling a specific column of pixel signals. This segmentation allows parallel processing across columns, reducing the need for a single high-speed ADC and thereby reducing power consumption while maintaining compact area through efficient resource distribution.
Solution Approach 2:
The patent employs periodic sampling and conversion operations in column ADCs, where each ADC processes signals at a lower, periodic rate rather than continuously at high speed. This periodic action reduces instantaneous power consumption while achieving the required overall conversion throughput for the image sensor.
2Speed
If parallel gray code is converted to parallel binary code directly, then conversion speed is maintained, but electromechanical errors increase
Solution Approach 1:
The patent replaces direct parallel-to-parallel conversion mechanisms with a sequential conversion approach using PISO circuits. This substitution eliminates complex electromechanical switching required for direct parallel conversion, reducing errors while maintaining acceptable conversion speed through pipelined operation.
Solution Approach 2:
The patent introduces gray code latch circuits and PISO (parallel-in-serial-out) conversion circuits as intermediary stages between the parallel gray code input and binary output. These intermediaries buffer and systematically convert the code, reducing direct electromechanical stress and errors while maintaining conversion efficiency through staged processing.
3Use of energy by moving object
If multiple ADCs are arranged in columns to reduce power consumption, then power consumption decreases, but device complexity increases
Solution Approach 1:
The patent designs column ADCs with universal functional blocks that can be replicated across multiple columns. Each column ADC uses the same gray code latch, PISO circuit, and conversion logic, allowing standardized multi-functionality that reduces overall system complexity despite having multiple ADC instances. This modular universality simplifies design while enabling power-efficient parallel operation.
Data Source
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AI summary
A gray code-to-binary code converter includes multiple parallel-in parallel-out (PIPO) latches, each of the multiple PIPO latches configured to output a parallel output gray code by latching a parallel input gray code in response to a sampling signal, and a parallel-in serial-out (PISO) circuit including a first group of switches, the PISO circuit configured to convert the parallel output gray code, which is latched in the multiple PIPO latches, into a binary code, and sequentially output bits of the binary code in units of bit, from a least significant bit (LSB) of the binary code to a most significant bit (MSB) of the binary code, while changing an arrangement of the first group of switches.