Current-Mirror Bias Circuit for Light-Induced Current Compensation

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Solution Overview

Problem

Light-induced current in unpackaged integrated circuits, particularly in RFID tags, disrupts the operation of low power circuits by increasing current consumption and disturbing bias voltage and current delivery due to photocurrent generation at parasitic pn junctions.

Innovation Solution

A compensation circuit with a current mirror and a second light-sensitive component is implemented to match and cancel out the light-induced current in the bias circuit, ensuring a consistent bias current is provided without the photocurrent component.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the integrated circuit is exposed to light to enable RFID tag operation, then the tag can be activated and read, but light photons create electron-hole pairs that generate photocurrent which disturbs the operation of low power circuits on the chip

Engineering Contradiction:

ImproveRFID tag operation capabilityVSAvoidcircuit operation stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces an intermediary compensation circuit between the light-sensitive bias circuit and the load circuits. This compensation circuit generates a compensating current that counteracts the photocurrent interference, allowing the RFID tag to operate under light exposure while maintaining circuit stability. The intermediary circuit acts as a buffer that isolates the harmful effect of light from the sensitive circuits.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the compensation circuit continuously monitors the bias current affected by photocurrent and adjusts the compensating current accordingly. The current mirror configuration provides automatic feedback adjustment, ensuring that the compensating current matches the photocurrent magnitude to maintain stable operation under varying light conditions.

Inventive Principle:

Principle #23Feedback

2Ease of operation

If a bias circuit is used to provide constant bias voltage and current to circuits on the IC, then proper circuit operation is enabled, but light exposure causes photocurrent to add to the bias current, increasing overall current consumption and disturbing circuit operation

Engineering Contradiction:

Improvecircuit operation capabilityVSAvoidcurrent consumption

Core Design Contradiction:

Ease of operationVSUse of energy by moving object

Solution Approach 1:

The patent converts the harmful photocurrent into a beneficial compensation mechanism. By using light-sensitive components in the compensation circuit, the system automatically generates a compensating current that matches the photocurrent magnitude. This transforms the harmful light-induced current into a useful signal that drives the compensation circuit to cancel out the interference, effectively converting harm into benefit.

Inventive Principle:

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

3Ease of manufacture

If the N-well resistor is formed with N-well material in a P-substrate to create the bias circuit, then the bias current can be generated, but a parasitic pn junction device is created that generates light-induced photocurrent when exposed to light

Engineering Contradiction:

Improvebias circuit fabricationVSAvoidphotocurrent generation

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the photocurrent generation function from the bias circuit by separating it into a dedicated compensation circuit. The compensation circuit is specifically designed to handle the photocurrent effect, allowing the original bias circuit to maintain its simple N-well resistor structure for ease of manufacture while the compensation circuit handles the harmful photocurrent through current mirroring and subtraction.

Inventive Principle:

Principle #2Taking out (Extraction)

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 compensation circuit effectively reduces current variation by 63.3% under high light intensity, maintaining accurate bias current delivery and reducing power consumption in integrated circuits.

Implementation Method 1

light photons can create electron-hole pairs, which generate charge carriers. The photo-generated charge carriers may diffuse through the backside of the semiconductor substrate and part of them may reach pn junctions resulting in a reverse current flow (or photocurrent)

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS12619850B2Compensation for light-induced current in an integrated circuit

Publication Date: 2026.05.05 NXP BV

AI summary

A circuit for compensating for the effects of light exposure is provided. The circuit includes a first circuit and a light compensation circuit. The first circuit has an output terminal for providing a first current, wherein at least a portion of the first current is a function of a first light sensitive circuit component. The compensation circuit has a current mirror and a second light sensitive circuit component. The current mirror has an input terminal coupled to receive a second current that is mirrored from the first current, and an output terminal coupled to provide a third current responsive to the second current. The second light sensitive circuit component is configured to be similar to the first light sensitive circuit component and to compensate for a light induced current provided by the first light sensitive circuit component so that the third current is provided without a light induced current component.