Cascoded Vref Generator for Decoupled Single-Ended Receivers
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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 power supplies (Vddq or Vssq) is not shared between devices, leading to suboptimal sensing of signals due to perturbations in both power supplies affecting the generated reference voltage.
Innovation Solution
A cascoded current source-based reference voltage generator that isolates the reference voltage (Vref) from the high power supply, allowing it to track only the common Vssq supply and remain independent of decoupled high supplies, ensuring accurate sensing of Vssq-referenced signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional voltage divider-based reference voltage generator is used, then the reference voltage can be generated using simple circuitry, but the reference voltage is affected by perturbations in both power supplies (Vddq and Vssq), leading to suboptimal signal sensing accuracy
Solution Approach 1:
The patent extracts the dependency on the high power supply (Vddq) from the reference voltage generation by using a cascoded current source configuration. The cascode structure isolates the reference voltage from Vddq perturbations while maintaining dependence on the low power supply (Vssq), thereby improving sensing accuracy without requiring complex additional circuitry.
Solution Approach 2:
The cascoded current source acts as an intermediary between the power supplies and the reference voltage. It mediates the power supply perturbations by blocking the propagation of Vddq noise to the reference voltage while allowing Vssq tracking, thus resolving the contradiction between simplicity and accuracy.
2Adaptability or versatility
If the reference voltage tracks both power supplies to maintain compatibility with various signaling schemes, then versatility is improved, but the reference voltage becomes sensitive to noise and perturbations from both supplies
Solution Approach 1:
The patent applies local quality by making the reference voltage selectively dependent on power supplies - it tracks Vssq (the common supply) while rejecting Vddq (the decoupled supply). This selective tracking is achieved through the cascoded current source configuration that creates different impedance paths for different power supplies, allowing the reference voltage to have different qualities of dependence on each supply.
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.