Optical Receiver TIA Bypass Circuit for Wider Dynamic Range
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Solution Overview
Problem
Existing optical receivers with trans-impedance amplifiers (TIAs) face challenges in enhancing input dynamic range due to saturation issues, requiring additional circuit elements like Schottky diodes and variable resistances, which can increase size and complicate integration, while also affecting low-frequency response.
Innovation Solution
The optical receiver incorporates an additional trans-impedance circuit with a fixedly biased FET, bypassing photocurrent flowing through the intrinsic trans-impedance when the optical signal is large, allowing instantaneous response to voltage signals without filtering circuits, thus enhancing dynamic range without Schottky diodes or variable resistances, and maintaining compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a diode element is connected in parallel with the feedback impedance to prevent output saturation, then the dynamic range is enhanced, but the circuit complexity increases and low-frequency response deteriorates due to additional feedback loops
Solution Approach 1:
The patent extracts the frequency-selective function from the feedback loop by using a capacitor connected between the inverting input terminal and ground, rather than using it in the feedback path. This separates the DC feedback path (for low-frequency response) from the AC signal path (for high-frequency response), eliminating the contradiction between dynamic range enhancement and low-frequency response preservation.
Solution Approach 2:
The capacitor acts as an intermediary element that selectively bypasses AC signals while allowing DC signals to pass through the feedback impedance. This mediator enables the circuit to achieve both wide dynamic range (through AC bypassing) and good low-frequency response (through DC feedback), resolving the contradiction between these two requirements.
2Use of energy by moving object
If a Schottky diode is used to maintain low power supply condition, then power consumption is reduced, but the device becomes hard to monolithically integrate
Solution Approach 1:
The patent changes the operating parameters of standard MOS transistors by applying specific bias voltages to create variable resistance regions that function similarly to Schottky diodes. This allows the circuit to achieve low power consumption characteristics without requiring specialized Schottky devices, thus maintaining monolithic integrability while preserving energy efficiency.
3Speed
If a capacitor with large capacitance is used to lower the cut-off frequency, then the low-frequency response is improved, but the circuit size increases and monolithic integration becomes difficult
Solution Approach 1:
The patent moves the capacitance function from the feedback path to a different dimensional configuration by connecting the capacitor between the inverting input terminal and ground. This spatial reconfiguration allows the use of smaller capacitance values to achieve the same frequency response characteristics, reducing circuit area while maintaining low-frequency performance.
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 configuration dynamically enhances the dynamic range of the optical receiver, preventing saturation at high input levels, maintaining consistent noise performance, and simplifying the circuit design by eliminating the need for external capacitors and filtering circuits, while ensuring bit-by-bit frequency response alignment.
Implementation Method 1
a photodiode (PD) configured to convert an optical signal into a photocurrent
Implementation Method 2
an additional trans-impedance configured to bypass the photocurrent flowing in the intrinsic trans-impedance when the optical signal becomes large... an FET whose drain coupled with the PD, gate is fixedly biased and source is coupled with an output of the TIA
Data Source
AI summary
An optical receiver implemented with a pre-amplifier with an additional trans-impedance able to respond to the input signal in bit-by-bit is disclosed. The optical receiver provides a photodiode to convert an optical signal into a photocurrent, a trans-impedance amplifier to convert the photocurrent to a voltage signal, and an additional trans-impedance circuit able to respond instantaneously to the voltage signal. The additional trans-impedance includes a FET whose gate is fully fixedly biased and the source thereof receives the voltage signal. The FET may bypass the current flowing in the intrinsic trans-impedance instantaneously.