Image Sensor Bias Wiring Layout for IR Drop Reduction
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Solution Overview
Problem
In CMOS linear color image sensors, the long power source wiring leads to significant IR drop and voltage decrease along the length of the wiring, causing a gap between the current value from the constant current source and the ideal current value, affecting the stability of the bias voltage and power source voltage.
Innovation Solution
The semiconductor integrated circuit design includes a constant current source circuit with voltage supplying sources at both ends of the row signal processing circuits, using current mirror circuits to reduce IR drop and maintain stable current flow, and separates the power source wiring to minimize voltage drop effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single power source wiring is used to supply power to all signal processing circuits, then the device complexity is reduced, but the IR drop increases significantly causing voltage instability
Solution Approach 1:
The power source wiring is segmented into multiple independent wiring structures (first power source wiring and second power source wiring) that supply power to different regions of the signal processing circuits. This segmentation reduces the current load on each individual wiring, thereby reducing IR drop and voltage instability while maintaining overall system functionality.
Solution Approach 2:
The patent introduces a spatial dimension to the power source wiring by distributing multiple wiring structures across different locations (first end and second end of the signal processing circuits). This dimensional distribution allows power to be supplied from multiple points, reducing the effective path length and resistance for current flow, thus mitigating IR drop effects.
2Reliability
If power source wiring is electrically separated for constant current circuits, then the stability of constant current power supply is improved, but the device complexity increases
Solution Approach 1:
The patent applies local quality by providing dedicated power source wiring (first power source wiring and second power source wiring) specifically for constant current circuits, while other circuits may share different wiring. This localized power supply arrangement ensures that constant current circuits receive stable voltage without being affected by IR drop from other high-current circuits, achieving improved stability without excessive complexity through targeted separation.
3Area of stationary object
If long power source wiring is used to reach all signal processing circuits, then the coverage area is increased, but the voltage drop along the wiring increases
Solution Approach 1:
The power supply coverage is segmented into multiple regions, each served by its own power source wiring (first power source wiring from first end, second power source wiring from second end). This segmentation allows each wiring to serve a localized area with shorter effective length, reducing voltage drop while maintaining comprehensive coverage across the entire array of signal processing circuits.
Solution Approach 2:
The patent transitions from a single-point power supply to a multi-point distributed power supply arrangement. By placing power source wirings at both the first end and second end of the signal processing circuits, the system creates a two-dimensional power distribution network that reduces the maximum distance any point in the circuit must be from a power source, thereby reducing voltage drop across the coverage area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design reduces the IR drop to one-fourth to one-thirteenth of the original value, maintaining stable current flow and reducing the gap between the actual and ideal current values, thereby enhancing the stability of the bias voltage and power source voltage across the sensor.
Implementation Method 1
the long power source wiring leads to significant IR drop and voltage decrease along the length of the wiring
Implementation Method 2
causing a gap between the current value from the constant current source and the ideal current value, affecting the stability of the bias voltage and power source voltage
Data Source
AI summary
A semiconductor integrated circuit includes multiple signal processing circuits including a constant current source, a first bias source that generates first bias voltage, a second bias source that generates second bias voltage, a first bias circuit that supplies a first reference current to the first bias source, a second bias circuit that supplies a second reference current to the second bias source, a bias wiring that supplies the first bias voltage and the second bias voltage to a plurality of gates of a transistor that constructs the constant current source, a power source wiring that supplies a power source voltage to each of the first bias source, the second bias source, and the constant current source, a first voltage supplying source that applies a first power source voltage to the power source wiring, and a second voltage supplying that applies a second power source voltage to the power source wiring.