Switched Resistor Capacitor Filter for Image Sensor Reference Voltage
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Solution Overview
Problem
Conventional image sensor reference voltage generators face challenges in setting a stable cutoff filter frequency, especially when sampling ratios vary, leading to difficulties in achieving a proper range of filtering across different applications.
Innovation Solution
A reference voltage generator employing a switched resistor-capacitor filter, where the resistance value is controlled by adjusting the on-time of a switch, allowing for flexible cutoff frequency setting without additional physical resources, using an existing ESD resistor to maintain a small circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional RC filter is used with fixed resistor and capacitor values, then the circuit area is small, but the cutoff frequency cannot be adjusted for different sampling ratios
Solution Approach 1:
The patent applies the dynamics principle by replacing the fixed resistor with a switched resistor that changes its effective resistance value dynamically based on the sampling ratio. The resistor is divided into multiple segments that can be selectively connected or disconnected through switches, allowing the resistance value to adapt to different sampling frequencies while maintaining a compact circuit structure.
Solution Approach 2:
The patent applies segmentation by dividing the resistor into multiple discrete segments (e.g., R1, R2, R3) that can be independently controlled. This segmentation allows the circuit to achieve multiple resistance values by selectively connecting different combinations of segments, thereby enabling cutoff frequency adjustment without requiring a completely different circuit design for each frequency.
2Adaptability or versatility
If additional resistors are added to achieve cutoff frequency adjustment, then the filtering adaptability improves, but the circuit area increases
Solution Approach 1:
Instead of adding multiple complete resistor elements, the patent uses a dynamic switching mechanism to activate different portions of a single resistor structure. This allows the circuit to achieve multiple resistance values and corresponding cutoff frequencies without proportionally increasing the physical area, as the same spatial region can serve multiple functional states through temporal switching.
Solution Approach 2:
The switched resistor structure serves multiple functions: it acts as a single physical component occupying minimal area, yet provides multiple resistance values needed for different sampling ratios. This multi-functionality eliminates the need for separate resistor components for each frequency setting, thereby maintaining compact circuit area while achieving broad filtering adaptability.
3Measurement precision
If the switch on-time is adjusted to control charging time, then the cutoff frequency can be optimized, but the control complexity increases
Solution Approach 1:
The patent employs periodic switching action where the switches are controlled by clock signals with specific duty cycles. By adjusting the on-time portion of the periodic waveform, the effective resistance value is precisely controlled, which directly determines the cutoff frequency. This periodic control mechanism provides precise frequency adjustment while using standard clock signal generation techniques that are straightforward to implement.
Solution Approach 2:
The patent changes the temporal parameter (on-time duration) of the switch control signal to adjust the effective resistance and consequently the cutoff frequency. This parameter-based control approach allows precise tuning of the filtering characteristics by simply modifying the timing parameters of existing clock signals, without requiring complex control circuitry or additional operational steps.
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
The solution provides enhanced filtering effectiveness with a stable cutoff frequency across various frequency environments, improving design flexibility and reducing noise in the reference voltage, while maintaining a compact circuit design.
Implementation Method 1
a first capacitor, and a second capacitor. The first and second capacitors may be coupled in parallel
Data Source
AI summary
A reference voltage generator including an electrostatic discharge (ESD) resistor, a first branch coupled to the ESD resistor and including a first capacitor, a second branch coupled to the ESD resistor and including a second capacitor, wherein the first and second capacitors are coupled in parallel, a first switch configured to control a first charge transfer path leading to the first branch, and a second switch configured to control a second charge transfer path leading to the second branch.