T-Coil Amplifier Stage for Low Power Optical Receiver Bandwidth
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Solution Overview
Problem
Conventional optical receiver circuits face challenges in achieving high bandwidth and gain while minimizing power consumption, often requiring power-intensive error correction techniques like decision feedback equalization due to large parasitic capacitance and high power consumption in trans-impedance amplifier circuits.
Innovation Solution
The optical receiver circuit employs a T-coil amplifier stage with inductive circuits to isolate parasitic capacitances and increase effective feedback impedance, reducing power consumption and eliminating the need for error correction techniques by enhancing signal-to-noise ratio through over-peaking techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional trans-impedance amplifier circuits are used to achieve sufficient bandwidth and gain, then the optical receiver can process high-speed signals, but power consumption increases undesirably
Solution Approach 1:
The patent changes the feedback impedance parameter from resistive to inductive, creating a resonant circuit that provides frequency-dependent gain enhancement. This allows the TIA to achieve higher bandwidth without proportionally increasing power consumption, as the inductive feedback creates a peaking effect that compensates for bandwidth limitations at lower power levels
Solution Approach 2:
The patent employs periodic switching of the inverter stages in the TIA circuit, where the inductive feedback creates oscillatory behavior that is controlled to produce the desired bandwidth extension. The periodic action of the resonant circuit allows energy to be reused in each cycle, improving efficiency while maintaining high-speed performance
2Reliability
If error-correction circuitry such as decision feedback equalization is added to ensure accurate reception, then data accuracy improves, but power consumption increases undesirably
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitances, which normally degrade high-frequency signal quality and require error correction, into a beneficial effect. By using inductive feedback to create resonance, the circuit transforms the capacitive loading into enhanced gain at critical frequencies, improving signal integrity without requiring additional error-correction power
Solution Approach 2:
The inductive feedback network acts as an intermediary between the photodetector and the inverter stages, mediating the signal transmission by compensating for parasitic effects. This intermediary circuit improves signal quality before it reaches subsequent stages, reducing the need for power-hungry error correction while maintaining high data accuracy
3Speed
If inductive circuits are added to isolate parasitic capacitances and increase feedback impedance, then bandwidth and signal-to-noise ratio improve, but device complexity increases
Solution Approach 1:
The patent merges the feedback function with the gain amplification function by using the same inductive network to provide both feedback and impedance transformation. This consolidation achieves bandwidth extension and parasitic isolation without adding separate dedicated circuits, thereby limiting the increase in overall device complexity while still achieving the desired performance improvements
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 approach allows for increased bandwidth and low error rates without the need for power-hungry error correction, achieving greater TIA bandwidth per unit power consumption and maintaining low data error rates.
Implementation Method 1
a first inductor coupled between the input terminal of the optical receiver circuit and an input of the first inverter, and configured to isolate parasitic capacitances from the input terminal of the optical receiver circuit
Implementation Method 2
a second inductor coupled between an input of the first inverter and a first resistor, and configured to increase an effective feedback impedance of the optical receiver circuit at one or more operating frequencies
Implementation Method 3
a photodiode configured to generate an input current based on received optical signals
Data Source
AI summary
An optical receiver circuit is disclosed, including a photodiode, an output terminal, a first amplifier stage, and an electrostatic discharge (ESD) protection circuit. The photodiode may generate a receiver current based on received optical signals. The first amplifier stage may be coupled between the photodiode and the output terminal and include a first inductor coupled between the photodiode and an input of a first inverter, and a second inductor coupled between the input of the first inverter and a first resistor. The first resistor may be coupled between the second inductor and an output of the first inverter. ESD protection circuit may be coupled to the input of the first inverter. The output terminal may generate an output signal based at least in part on the output of the first inverter.