Photodiode Light Sensor Circuit With Cathode Voltage Tracking

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Solution Overview

Problem

Existing light sensor circuits face issues with junction capacitance and dark current in photodiodes, affecting the accuracy and linearity of sensor measurements, particularly in analog-to-digital converters.

Innovation Solution

A light sensor circuit design that maintains the cathode voltage of a photodiode at the same level as the anode, effectively reducing apparent junction capacitance and dark current influence by using a first and second amplifier, an active load, and switches to control the integration process without requiring a capacitor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional integrating unit operating under a reference voltage VCM is used, then the circuit can function as an analog-to-digital converter, but the junction capacitance of the photodiode cannot be reduced and dark current affects measurement accuracy

Engineering Contradiction:

Improvesensor measurement accuracyVSAvoidcircuit design complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent changes the operating voltage parameter from a fixed reference voltage VCM to a dynamically controlled voltage that tracks the anode voltage. By making the cathode voltage track the anode voltage through the amplifier circuit, the voltage difference across the photodiode junction is minimized, effectively reducing the apparent junction capacitance and dark current effects without requiring additional capacitors.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional capacitor-based voltage holding mechanism with an amplifier-based voltage tracking system. Instead of using a capacitor to maintain the cathode voltage at a fixed reference level, the invention uses an amplifier to actively track and replicate the anode voltage at the cathode, substituting passive energy storage with active voltage control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-generated harmful factors

If a capacitor is used to maintain the cathode voltage of the photodiode, then the integrating unit can operate, but the dark current and junction capacitance effects cannot be suppressed

Engineering Contradiction:

Improvedark current influenceVSAvoidcapacitor requirement

Core Design Contradiction:

Object-generated harmful factorsVSQuantity of substance

Solution Approach 1:

The patent extracts and eliminates the capacitor component from the traditional integrating unit design. By removing the capacitor and replacing it with an amplifier-based voltage tracking system, the invention not only reduces component quantity but also eliminates the fundamental problem of junction capacitance and dark current that the capacitor approach could not solve.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the harmful effect of junction capacitance and dark current into a benefit by using the amplifier's voltage tracking capability. Instead of trying to work around these effects with capacitors, the invention actively counteracts them by maintaining equal voltages at both photodiode terminals, thereby nullifying the harmful effects of junction capacitance and minimizing dark current influence.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Speed

If the cathode voltage is maintained at a reference voltage level, then the integrating unit can function, but the apparent junction capacitance cannot be reduced to improve charging and discharging speed

Engineering Contradiction:

Improvecharging and discharging speedVSAvoidanalog front-end circuit accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent transitions from a static voltage reference approach to a dynamic voltage tracking approach. The cathode voltage is no longer fixed at a reference level but dynamically adjusts to match the anode voltage in real-time, enabling the circuit to adapt to changing signal conditions and improve charging/discharging speed while maintaining measurement precision.

Inventive Principle:

Principle #15Dynamics

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 design enhances the performance and accuracy of analog-to-digital converters by minimizing junction capacitance and dark current effects, ensuring precise sensor measurements.

Implementation Method 1

the signal of a light sensor circuit is derived from the photocurrent generated by a photodiode PD

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the first amplifier 1 is configured to maintain a voltage level at a second input 12 thereof substantially equal to a voltage level at a first input 11

Methodology Applied

Scientific EffectVirtual short circuit:

Data Source

PatentUS12587153B2Integrating light sensor circuit

Publication Date: 2026.03.24 SENSORTEK TECH

AI summary

The present application discloses a light sensor circuit comprising a first amplifier, a second amplifier and an active load. An integration circuit is formed by the operation of this light sensor circuit and connected to a photodiode. The cathode of the photodiode is controlled to maintain an identical or approximate voltage level with the anode of the photodiode, which significantly reduces the influence of the dark current from the photodiode. Consequently, when applied to an analog-to-digital conversion device, the light sensor circuit effectively maintains the performance and accuracy of the device. Additionally, this design significantly reduces circuit complexity and manufacturing costs.