Optical Receiver Amplifier With Variable AGC Response Time
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Solution Overview
Problem
In PON communication systems, optical receivers face challenges in stabilizing gain and threshold adjustments for intermittently received optical signals of varying magnitudes, leading to unstable amplifier responses due to differing optical losses and output powers across homes in a Fiber To The Home setup.
Innovation Solution
An amplifier with automatic gain control (AGC) and variable response time is designed for the optical line terminal, incorporating a trans-impedance amplifier, integrator, linear amplifier, comparator, delay unit, and switch, where the integrator's time constant is adjusted based on input packet data, and a buffer is added to stabilize the feedback loop, using voltage followers to control the resistance configuration and hysteresis for stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed time constant is used in the integrator, then the circuit structure is simple, but the amplifier cannot adapt to intermittently received optical signals with varying magnitudes
Solution Approach 1:
The patent applies dynamics by making the integrator's time constant variable rather than fixed. The switch dynamically changes the time constant between a longer value and a shorter value according to the reception status of packet data, enabling the amplifier to adapt to intermittent optical signals while maintaining manageable circuit complexity through controlled switching between predefined states.
2Speed
If the integrator time constant is changed frequently to follow packet data, then the response to intermittent signals is fast, but the feedback loop becomes unstable
Solution Approach 1:
The patent applies preliminary action by introducing a delay unit that delays the control signal before it reaches the switch. This delay allows the feedback loop to stabilize by preventing overly frequent switching operations, thus maintaining feedback loop stability while still enabling the integrator time constant to change in response to packet data reception.
3Speed
If voltage followers are used to control the integrator resistance configuration, then the switching speed is improved, but the device complexity increases
Solution Approach 1:
The patent applies partial action by using a limited number of voltage followers (first and second voltage followers) only where necessary to control the integrator resistance configuration. This selective application achieves improved switching speed without unnecessarily increasing device complexity by adding voltage followers throughout the entire circuit.
Data Source
AI summary
An amplifier for receiving an optical signal is disclosed. The amplifier provides a response time controller including an integrator with two time constants, a linear amplifier, a hysteresis comparator, an another integrator, and a switch to change the time constant. The switch includes two voltage followers, one of which turns off the switch to set the time constant in a longer state; while, the other of which turns on the switch and reflects the input of the integrator to set the time constant in a shorter state.