Intermediate Rail Isolation for Mixed-Voltage Device Protection
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Solution Overview
Problem
Circuitry operating in higher voltage domains with devices designed for lower voltage domains faces issues of oxide breakdown and lifetime degradation due to hot carrier injection, particularly when handling signals from older chips, and intermediate voltage supplies can cause reverse biasing and high leakage currents during power sequencing.
Innovation Solution
Incorporating an isolating circuit that connects devices to the intermediate voltage source when the high voltage rail is powered and isolates them from it when the high voltage rail is not powered, using switching devices to prevent current flow and manage voltage levels, thereby protecting devices from excessive voltage stress and reducing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an intermediate voltage supply is used to protect devices, then device reliability is improved, but leakage currents increase due to reverse biasing during power sequencing
Solution Approach 1:
An isolating circuit is introduced as an intermediary component between the intermediate voltage source and the circuit node. This isolating circuit includes switching devices that control the connection state, allowing the intermediate voltage to protect devices during normal operation while preventing reverse biasing and leakage currents during power sequencing when the high voltage rail is not yet powered.
2Reliability
If the intermediate voltage source is powered before the high voltage rail, then device protection is improved, but current flow from intermediate voltage to high voltage rail occurs via circuit nodes
Solution Approach 1:
The isolating circuit acts as a mediator that controls the electrical connection between the intermediate voltage source and the circuit node. The switching devices within the isolating circuit are configured to remain open when the high voltage rail is not powered, blocking current flow from the intermediate voltage source to the high voltage rail, while allowing connection when the high voltage rail is properly powered.
Solution Approach 2:
The isolating circuit is designed to be in place and controlled during the power sequencing process. It preliminarily prevents current flow during the critical transition period when the intermediate voltage source is powered before the high voltage rail, and then allows normal operation once the high voltage rail is established.
3Adaptability or versatility
If devices operate in higher voltage domain, then compatibility with older chips is improved, but oxide breakdown and lifetime degradation occur
Solution Approach 1:
The higher voltage domain is segmented into two separate voltage regions by introducing an intermediate voltage rail. This creates an upper voltage region (between high voltage and intermediate voltage) and a lower voltage region (between intermediate voltage and ground). Devices operating in the lower voltage region are protected from full high voltage stress, while still enabling compatibility with older chips through the upper voltage region.
Data Source
AI summary
Circuitry comprises a high voltage rail providing a high voltage level corresponding to a higher voltage domain, an intermediate voltage source, a low voltage rail, and devices that operate in a lower voltage domain. First devices in an upper voltage region are powered between the high voltage rail and an intermediate voltage rail powered by the intermediate source. Second devices in a lower voltage region are powered between the intermediate and low rails. On power up, the intermediate source is powered before the high voltage rail. An isolating circuit connects the intermediate source to a node when the high voltage rail is powered and isolates the node from the intermediate source when the high voltage rail is not powered to impede current flow from the intermediate source to the high voltage rail.