Optical Receiver Input Impedance Switching Across Transmission Rates
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Solution Overview
Problem
Existing optical receivers face challenges in accommodating wide and flexible transmission rates due to impedance mismatching issues, which affect gain and bandwidth, particularly at high transmission speeds, leading to insufficient gain and inability to optimize low cut-off frequencies.
Innovation Solution
An optical receiver design featuring a preamplifier, main amplifier, and a switching unit that dynamically adjusts the equivalent input impedance of the main amplifier by using a switching unit with field effect transistors and resistors, allowing the load impedance to match the transmission line impedance, thereby optimizing gain and bandwidth across varying transmission rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the input impedance of the main amplifier is kept low for high transmission rates, then the impedance mismatching effect is eliminated, but the total gain of the optical receiver becomes insufficient
Solution Approach 1:
The patent applies dynamics by making the input impedance of the main amplifier adjustable rather than fixed. A switching unit with multiple switches and resistors allows the impedance to be dynamically changed based on transmission rate requirements. For high transmission rates, low impedance is selected to eliminate mismatching; for low rates, high impedance is selected to maintain gain.
Solution Approach 2:
The patent changes the impedance parameter of the main amplifier based on operating conditions. By switching between different impedance values (e.g., 100 ohms for high speed, higher values for low speed), the system optimizes performance across different transmission rates without requiring separate amplifier designs.
2Reliability
If the transmission line is shortened for low transmission rates to eliminate impedance mismatching, then the low cut-off frequency requirement cannot be met
Solution Approach 1:
Instead of fixing the transmission line length, the patent dynamically adjusts the main amplifier's input impedance to match the transmission line characteristics at different frequencies. This allows the system to handle both high-speed signals (where impedance matching is critical) and low-speed signals (where low cut-off frequency performance is needed) without compromising either requirement.
Solution Approach 2:
The patent changes the impedance parameter of the main amplifier based on the transmission rate. For low transmission rates, a higher impedance is selected that works well with the existing transmission line length and coupling capacitor, maintaining the low cut-off frequency response without requiring line length changes.
3Speed
If the bandwidth of the preamplifier is increased for high transmission rates, then the 3 dB cut-off frequency shifts higher, but the gain may be reduced
Solution Approach 1:
The patent applies dynamics by making the main amplifier's input impedance adjustable. When the preamplifier bandwidth is increased for high transmission rates, the main amplifier's input impedance is switched to a lower value to maintain impedance matching and prevent gain loss. For lower rates, the impedance is increased to maximize gain when bandwidth requirements are lower.
Solution Approach 2:
The patent changes the impedance parameter of the main amplifier in coordination with preamplifier bandwidth settings. This parameter adjustment compensates for gain variations caused by bandwidth changes, ensuring optimal performance across different transmission rate requirements.
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 design enables flexible operation across transmission rates from hundreds of megabits to several gigabits per second, improving gain and adjusting bandwidth to match signal frequencies, reducing bit error ratios and impedance mismatching effects.
Implementation Method 1
The switching unit, which is configured between the transmission line and the ground, is connected in parallel to the input impedance of the main amplifier to vary the equivalent input impedance of the main amplifier
Implementation Method 2
The preamplifier converts a photocurrent generated by a light-receiving device in accordance with an optical signal to a voltage signal
Data Source
AI summary
The present invention provides an optical receiver applicable to various transmission rates. The optical receiver of the invention includes a main amplifier and a switching unit. The main amplifier amplifies a voltage signal output from the preamplifier, which converts the photocurrent to the voltage signal. The switching unit is inserted between the preamplifier and the main amplifier to vary the input impedance RIN of the main amplifier depending on the transmission rate.