Cascoded Reference Voltage Generator for Decoupled I/O Supplies
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Solution Overview
Problem
Existing reference voltage generators for single-ended communication systems fail to provide an optimal solution when one of the I/O power supplies is not shared between devices, leading to suboptimal sensing of signals due to perturbations in decoupled power supplies.
Innovation Solution
A cascoded current source-based reference voltage generator that isolates the reference voltage from decoupled high power supplies, ensuring it tracks only the common low power supply, thereby improving signal sensing in systems with decoupled high power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional voltage divider-based reference voltage generator is used, then the reference voltage scales with perturbations in both power supplies (Vddq and Vssq), but this leads to suboptimal data sensing in systems with decoupled power domains where one power supply is not shared between devices
Solution Approach 1:
The patent extracts the reference voltage generation from dependence on the decoupled high power supply (Vddq) by using a cascoded current source configuration. The current source isolates Vref from Vddq variations, effectively removing the harmful coupling between the decoupled power supply and the reference voltage, while maintaining necessary connection to the shared low power supply (Vssq).
Solution Approach 2:
The patent changes the operational parameters of the reference voltage generator by employing a cascoded current source instead of a simple voltage divider. This configuration alters how Vref responds to power supply variations, making it insensitive to Vddq perturbations while maintaining sensitivity to Vssq changes, thereby adapting the generator to decoupled power supply configurations.
2Reliability
If the reference voltage tracks both power supplies (Vddq and Vssq), then it maintains compatibility with traditional signaling, but it becomes sensitive to perturbations in decoupled power supplies, degrading sensing performance
Solution Approach 1:
The cascoded current source acts as an intermediary between the power supplies and the reference voltage. It mediates the relationship by allowing Vref to track Vssq (the shared supply) while blocking perturbations from Vddq (the decoupled supply), thus eliminating the harmful sensitivity without compromising reliability.
3Device complexity
If a voltage divider configuration is used for reference voltage generation, then the circuit is simple and adjustable, but it cannot effectively isolate the reference voltage from decoupled high power supplies
Solution Approach 1:
The patent replaces the passive mechanical/voltage divider-based reference voltage generation with an active cascoded current source configuration. This substitution enables effective isolation from decoupled power supplies through the high output impedance of the cascoded structure, achieving reference voltage stability that cannot be obtained with simple voltage dividers.
Data Source
AI summary
In various embodiments, a reference voltage (Vref) generator for a single-ended receiver in a communication system is disclosed. The Vref generator in one example comprises a cascoded current source for providing a current, I, to a resistor, Rb, to produce the Vref voltage (I*Rb). Because the current source isolates Vref from a first of two power supplies, Vref will vary only with the second power supply coupled to Rb. As such, the Vref generator is useful in systems employing signaling referenced to that second supply but having decoupled first supplies. For example, in a communication system in which the second supply (e.g., Vssq) is common to both devices, but the first supply (Vddq) is not, the disclosed Vref generator produces a value for Vref that tracks Vssq but not the first supply.