Opto-Electronic Current Supply With Auxiliary Common-Mode Bias
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Solution Overview
Problem
Current opto-electronic systems face inefficiencies due to large capacitors required for high-frequency AC components, which reduce area efficiency and response speed, and existing solutions either add additional pins or consume significant on-chip resources when requiring a voltage source other than VDD or VSS for termination resistors.
Innovation Solution
A dual-stage current supply system is implemented, featuring a main current supply and an auxiliary current supply with a termination resistor, where the auxiliary supply maintains a common mode voltage at a common node, reducing capacitive resources and on-chip real estate by using a smaller capacitor as the AC ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large capacitors are implemented in the driver circuits to reduce ground impedance for high frequency AC components, then the ground impedance is reduced and charge level stability is maintained, but the area efficiency is reduced and the device response becomes sluggish
Solution Approach 1:
An auxiliary current supply is introduced as an intermediary component to maintain the common mode voltage at the common node. This auxiliary current supply works in conjunction with a smaller capacitor to achieve the same stability function that would otherwise require a large capacitor, thereby reducing the circuit area while maintaining charge level stability.
2Reliability
If large capacitors are implemented in the driver circuits to reduce ground impedance for high frequency AC components, then the ground impedance is reduced and charge level stability is maintained, but the device response speed is reduced
Solution Approach 1:
The auxiliary current supply acts as an intermediary that actively maintains the common mode voltage, allowing the use of a smaller capacitor with faster response characteristics. This resolves the contradiction by providing the necessary voltage stabilization without the sluggish response inherent in large capacitor-based solutions.
3Reliability
If a voltage source is added to the circuitry to maintain a common mode voltage and guarantee stable device response, then the device response stability is improved, but the device complexity and on-chip resource consumption increase
Solution Approach 1:
The auxiliary current supply is designed to perform multiple functions: it maintains the common mode voltage at the common node, works with the termination resistor to stabilize the voltage, and operates in conjunction with the main current supply. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall circuit complexity while maintaining response stability.
4Reliability
If additional pins or voltage sources are used to maintain common mode voltage with termination resistors, then the voltage stability is improved, but the on-chip resource consumption and device complexity increase
Solution Approach 1:
The auxiliary current supply is merged with the existing main current supply architecture, sharing the common node and working in conjunction with the termination resistor that is already part of the driver circuit. This merging approach eliminates the need for additional independent voltage sources or pins, reducing on-chip resource consumption while maintaining voltage stability.
Data Source
AI summary
A device, including a first current supply configured to provide a bias current to a load and a main current supply having a source terminal coupled in parallel with the load and configured to reduce a current value to the load below the bias current, is provided. The device includes a termination resistor coupled in series with the source terminal of the main current supply and configured to receive current from the source terminal of the main current supply when the source terminal of the main current supply is activated. The device also includes an auxiliary current supply having a sink terminal coupled to the termination resistor at a common node, and configured to maintain the common node at common mode voltage when current flows from the source terminal of the main current supply to the sink terminal of the auxiliary current supply and through the termination resistor.