Dummy Transimpedance Amplifier for Photodiode Bias Tracking
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Solution Overview
Problem
Conventional optical receivers face challenges in determining the appropriate bias for photodiodes due to variations in the inverting opamp input voltage, which can be affected by temperature and process variations, making it difficult to ensure proper operation without direct measurement.
Innovation Solution
A 'dummy' transimpedance amplifier is integrated on the same substrate as other transimpedance amplifiers, allowing the voltage on its inverting input to be used as a reference to determine the appropriate photodiode bias, eliminating the need for direct measurement of the inverting opamp input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverting opamp input voltage is used to determine photodiode bias, then the bias can be adjusted for temperature and process variations, but the voltage varies with temperature and process variations making it difficult to determine the appropriate bias without direct measurement
Solution Approach 1:
The patent creates a dummy transimpedance amplifier that copies the electrical characteristics and temperature dependence of the real TIA's inverting input. The dummy TIA includes a dummy opamp with its inverting input connected to a dummy feedback resistor, replicating the voltage behavior without needing direct measurement of the real TIA's inverting input voltage
2Measurement precision
If a dummy transimpedance amplifier is added to measure the inverting input voltage, then the photodiode bias can be accurately determined, but the device complexity increases
Solution Approach 1:
The dummy transimpedance amplifier serves multiple functions: it acts as a measurement device for the inverting input voltage, provides temperature compensation reference, and maintains the same electrical characteristics as the real TIA. This multi-functionality justifies the added complexity by eliminating the need for separate measurement circuits
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 approach enables accurate and convenient determination of the photodiode bias, ensuring proper operation by accounting for temperature and process variations, thereby stabilizing the output voltage and signal quality.
Implementation Method 1
an optical signal is often supplied to a receiver including diode, such as a photodiode, which converts the optical signal into a corresponding electrical current
Data Source
AI summary
Consistent with the present disclosure, a “dummy” transimpedance amplifier (dummy TIA) is provided on a substrate along with one or more other transimpedance amplifiers (TIAs) that are connected to photodiodes and output voltage signals for further processing. Typically, the dummy TIA is not connected to a photodiode and does not supply a useful output. The dummy TIA, however, is subject to the same processing and temperature variations as the other TIAs, and, as a result, the voltage on the dummy TIA inverting input will be the same or substantially the same as that of the other TIAs. Thus, by sensing the dummy TIA inverting input voltage, an appropriate photodiode bias can be obtained without direct measurement of the voltage on the inverting inputs of the other TIAs.