Differential TIA Circuit for High Gain and Common-Mode Noise Rejection
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Solution Overview
Problem
In optical communication systems, single-end transimpedance amplifiers face challenges in achieving high gain while maintaining low common-mode noise levels, especially when the driving current of the light source is small, as increased gain leads to more common-mode noise in the output voltage signal, making it difficult to meet the common-mode rejection requirement.
Innovation Solution
A differential transimpedance amplifier design that amplifies photocurrent from a photo diode and current noise from a dummy diode into separate positive and negative voltage signals, allowing for the suppression or elimination of common-mode noise through subtraction, utilizing a combination of differential amplification circuits, source followers, and feedback resistors, with the circuit elements primarily being transistors to enhance stability and operation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the TIA is increased to handle smaller photocurrents, then the sensitivity is improved, but the common-mode noise in the output voltage signal increases
Solution Approach 1:
The patent divides the single-end TIA into two separate single-end TIAs operating in parallel, each handling one polarity of the differential signal. This segmentation allows the system to process small photocurrents with high gain while the differential subtraction at the output stage rejects common-mode noise, thus resolving the contradiction between sensitivity and noise.
Solution Approach 2:
The patent transitions from a single-end configuration to a differential configuration, adding a new dimension to the signal processing. By using two TIAs to generate positive and negative voltage signals that are then subtracted, the system achieves both high gain for small signals and common-mode noise rejection, effectively resolving the technical contradiction.
2Productivity
If a differential structure is used to achieve high gain and high circuit operation speed, then the performance is improved, but the design and manufacture difficulty increases
Solution Approach 1:
The patent combines two single-end TIA designs into a differential configuration, where both TIAs share common components and design principles. This merging approach allows the system to achieve high gain and fast operation speed while keeping the design and manufacture relatively simple, as each individual TIA can be designed using proven single-end topologies.
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 differential transimpedance amplifier effectively suppresses or eliminates common-mode noise, achieving high gain and circuit operation speed while maintaining stability, even with low driving currents, and operates within a wider range of voltages due to the use of transistors, ensuring compliance with common-mode rejection requirements.
Implementation Method 1
a photo diode receives a light signal emitted by a light source and converts the light signal into an output voltage signal of the optical coupler
Data Source
AI summary
Disclosed is a differential transimpedance amplifier (TIA). In the differential TIA, an input end of the first source follower is coupled to the first output end of a first differential amplification circuit. The output end of the first source follower is coupled to the second input end of a second differential amplification circuit with feedback and a first feedback resistor. The input end of a second source follower is coupled to the second output end of the first differential amplification circuit. The output end of the second source follower is coupled to the first input end of the second differential amplification circuit with feedback and a second feedback resistor. A photo diode and a dummy diode are coupled respectively to two input ends of the first differential amplification circuit.