MOSFET Current Mirror Feedback for Low-Voltage Optical Receivers
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Solution Overview
Problem
Optical receivers using current mirror circuits with bipolar transistors face inaccuracies in lower optical power detection and power consumption issues due to high forward bias voltage requirements, making them unsuitable for modern low-voltage electronic equipment, and MOSFET-based circuits struggle with voltage gain and current mirror characteristics.
Innovation Solution
A current mirror circuit implemented with MOSFETs, featuring a feedback loop with differential amplifiers that maintains transistors in a substantially similar bias condition, using a reference voltage to stabilize the bias voltage applied to the photodiode, and dynamically varying gain and output impedance to ensure stable operation across a broad range of photocurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bipolar transistors are used in the current mirror circuit, then fine current-mirror characteristic is achieved, but power consumption increases due to high forward bias voltage requirement
Solution Approach 1:
The patent replaces bipolar transistors with MOSFETs in the current mirror circuit. MOSFETs use voltage-controlled operation instead of current-controlled operation, eliminating the need for high forward bias voltage (0.6-0.7V) required by bipolar transistors. This substitution maintains current mirror functionality while reducing power consumption, enabling operation at lower supply voltages (3.3V or less).
Solution Approach 2:
The patent changes the operating parameters of the transistor by switching from bipolar to MOSFET technology. This involves changing from a device requiring forward bias current and high voltage operation to one that operates with voltage control and lower power consumption, thereby resolving the contradiction between reliability and energy use.
2Use of energy by moving object
If MOSFETs are used in the current mirror circuit, then power consumption is reduced, but voltage gain decreases and current mirror characteristics deteriorate
Solution Approach 1:
The patent introduces a feedback mechanism using a sensing resistor connected to the drain of the first MOSFET and a feedback network that includes additional MOSFETs and resistors. This feedback circuit monitors the current through the first MOSFET and adjusts the gate voltage to maintain accurate current mirroring between the first and second MOSFETs, compensating for the inherently lower voltage gain of MOSFETs and restoring satisfactory current mirror characteristics.
3Device complexity
If sensing resistor is used to detect optical power, then voltage difference detection is simple, but accuracy deteriorates at lower optical powers
Solution Approach 1:
The patent uses the current mirror circuit as an intermediary between the photodiode and the sensing resistor. The current mirror accurately replicates the photocurrent from the photodiode through the first MOSFET to the second MOSFET, where it flows through the sensing resistor. This intermediary current mirror approach maintains measurement precision across a broad dynamic range while keeping the overall detection circuit relatively simple.
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 MOSFET-based current mirror circuit achieves superior current-mirror performance with a broad dynamic range, maintaining constant bias voltage for the photodiode and reducing power consumption, while maintaining stable operation even under low power supply conditions.
Implementation Method 1
An optical receiver that receives an optical signal and converts it to a corresponding electrical signal generally provides a function to monitor an average power of the optical signal. In the optical receiver including a photodiode (hereafter denoted as PD), the circuit detects an average of the photocurrent generated in the PD
Data Source
AI summary
A current mirror circuit and an optical receiver circuit implementing with the current mirror circuit are disclosed. The current mirror circuit provides two MOSFETs and two differential amplifiers. The MOSFETs are operated under the same bias condition even the power supply voltage decreases due to the virtual short-circuit characteristic between two inputs of the differential amplifier. One of the differential amplifiers provides a variable gain and output impedance characteristic to stabilize the feedback loop formed by this differential amplifier and one of the MOSFETs.