Ambient Light Sensor with Parallel Bipolar and MOS Amplifiers
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Solution Overview
Problem
Conventional ambient light sensors face challenges in maintaining linearity of output signals across a wide illumination range due to deviations in current mirror amplifier ratios, leading to inaccurate measurements, especially when dealing with different light sources.
Innovation Solution
An ambient light sensor design incorporating a light receiving portion and a current amplification portion with a combination of bipolar transistors and MOS Field Effect Transistors in parallel, along with a changeover control circuit to monitor and adjust the input current, ensuring consistent output across varying illumination levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current mirror amplifier is composed of a bipolar transistor, then the output signal is saturated as the light current increases, but the mirror ratio remains stable at relatively small light currents
Solution Approach 1:
The patent combines a bipolar transistor-based current mirror amplifier and a MOS transistor-based current mirror amplifier into a single integrated circuit. The bipolar amplifier provides stable mirror ratio at low light currents, while the MOS amplifier maintains linearity at high light currents, resolving the contradiction between mirror ratio stability and output signal linearity across the full illumination range.
Solution Approach 2:
The patent dynamically switches between the bipolar amplifier and MOS amplifier based on the ambient light level. A control circuit monitors the light current and selects the appropriate amplifier type, enabling the system to adapt its characteristics to match the current operating conditions and maintain optimal performance across varying illumination levels.
2Reliability
If a current mirror amplifier is composed of a MOS Field Effect Transistor, then the output signal fluctuation is large as the light current becomes small, but the mirror ratio remains stable at relatively large light currents
Solution Approach 1:
The patent combines a bipolar transistor-based current mirror amplifier and a MOS transistor-based current mirror amplifier into a single integrated circuit. The bipolar amplifier provides stable mirror ratio at low light currents, while the MOS amplifier maintains linearity at high light currents, resolving the contradiction between mirror ratio stability and output signal linearity across the full illumination range.
Solution Approach 2:
The patent dynamically switches between the bipolar amplifier and MOS amplifier based on the ambient light level. A control circuit monitors the light current and selects the appropriate amplifier type, enabling the system to adapt its characteristics to match the current operating conditions and maintain optimal performance across varying illumination levels.
3Device complexity
If calculation of difference between light currents is carried out according to a constant proportion, then the measurement is simple, but the output signal becomes zero when the difference becomes negative
Solution Approach 1:
The patent dynamically adjusts the proportion used in difference calculation based on the ambient light level. The control circuit selects between different calculation modes: constant proportion subtraction for high light levels and adaptive proportion adjustment for low light levels, ensuring accurate illumination measurement across the full range without the output becoming zero.
Solution Approach 2:
The patent changes the calculation parameters (proportion coefficients) based on the operating conditions. By adjusting the proportion used in difference calculation according to light level, the system maintains measurement accuracy across varying illumination conditions while avoiding the limitation of constant proportion methods.
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 maintains excellent linearity of output signals across a wide illumination range, enabling precise measurement of light sources regardless of their type, by dynamically adjusting the current amplification stages to match the input current values.
Implementation Method 1
a photoelectric transducing device such as a photodiode and the like is used to generate a light current depending on ambient illumination
Data Source
AI summary
In an ambient light sensor according to the present invention, a current amplification portion which amplifies a light current obtained by a light receiving portion to generate an output signal includes: a current amplification stage that has: a first current mirror amplifier which is composed of a bipolar transistor, and a second current mirror amplifier which is composed of a field effect transistor connected in parallel with the first current mirror amplifier; and a changeover control circuit which monitors an amplified current input into the current amplification stage, and performs changeover control of the first and second current mirror amplifiers according to a value of the amplified current.