Optical Receiver Preamplifier Circuit for Wide Input Dynamic Range
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Solution Overview
Problem
Existing optical receiver preamplifiers face instability and limited input dynamic range due to direct modulation of the feedback resistor, leading to oscillation and inadequate signal detection for varying signal amplitudes.
Innovation Solution
The optical receiver preamplifier incorporates an inverting amplifier with a current-voltage conversion element, a first transistor, a second transistor, and a third transistor connected between the input and output terminals, where the third transistor reduces impedance and bypasses excessive input current, maintaining stability and expanding the input dynamic range without direct modulation of the feedback resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the current-voltage conversion gain is increased to detect a small signal, then the detection capability of small signals is improved, but the output voltage becomes saturated and the waveform is distorted when a large signal is input
Solution Approach 1:
The patent applies dynamics by making the feedback resistor value variable rather than fixed. The feedback resistor is replaced with a circuit that can dynamically adjust its resistance value based on the input signal amplitude. When a small signal is detected, the feedback resistor has a high value to provide high current-voltage conversion gain. When a large signal is detected, the feedback resistor value is reduced to prevent output voltage saturation. This dynamic adjustment resolves the contradiction between needing high gain for small signals and avoiding saturation for large signals.
2Reliability
If the current-voltage conversion gain is reduced to lower saturation of the output voltage, then the stability of the output voltage is improved, but the small signal cannot be sufficiently amplified and detection of a small signal is difficult
Solution Approach 1:
The patent uses a dynamic feedback resistor that can change its resistance value based on operating conditions. The feedback resistor is implemented using a transistor circuit where the resistance can be modulated. When the input signal is small, the feedback resistor maintains a high value to enable sufficient amplification of the small signal. When the input signal becomes large, the feedback resistor value is automatically reduced to prevent output voltage saturation. This dynamic behavior resolves the contradiction between maintaining stability and enabling small signal detection.
3Adaptability or versatility
If the value of the feedback resistor is directly modulated to expand the input dynamic range, then the adaptability to various signal amplitudes is improved, but the operation of the optical receiver preamplifier becomes unstable
Solution Approach 1:
The patent introduces an intermediary element - a transistor circuit - between the fixed feedback resistor and the variable impedance element. The transistor acts as a buffer that modulates the effective feedback resistance indirectly through its transconductance characteristics rather than directly varying the resistor value. This intermediary approach allows the feedback resistance to be effectively modulated to expand the input dynamic range while maintaining operational stability, as the transistor provides isolation and controlled impedance transformation.
Data Source
AI summary
An optical receiver preamplifier includes an inverting amplifier 1 and a current-voltage conversion element 2 connected between input and output terminals of the inverting amplifier 1. The inverting amplifier 1 includes a first transistor 3 having a gate connected to the input terminal In of the inverting amplifier 1, a second transistor 4 having a source connected to a drain of the first transistor 3 and a gate to which a predetermined voltage Vb is applied, and a load 5 connected to a drain of the second transistor 4. A third transistor 6 is connected between the input terminal In of the inverting amplifier 1 and a source of the second transistor 4.