Isolation Cell Power Split for Low Leakage Across Power Domains
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Solution Overview
Problem
Conventional isolation cells experience significant leakage current when the first power domain is powered down, which is undesirable for improving battery life in portable devices due to their connection to the second power domain's voltage supply.
Innovation Solution
The isolation cell design includes a first inverter and a logic circuit with additional NMOS transistors connected to the first power domain's voltage supply, allowing the PMOS transistors to be cut off when the isolation control signal is logic '0', reducing leakage by coupling one of the logic or output inverter with the first power domain's voltage supply and the other with the second power domain's voltage supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PMOS transistors of the first inverter, logic gate and second inverter are connected to the voltage supply of the second power domain, then the isolation cell can operate normally when the first power domain is powered down, but the isolation cell suffers from considerable leakage current
Solution Approach 1:
The isolation cell is divided into two separate power domain connections: the logic circuit (NAND gate) is connected to the first power domain voltage supply, while the output inverter is connected to the second power domain voltage supply. This segmentation allows each component to be powered appropriately, eliminating the leakage current issue while maintaining operational reliability.
Solution Approach 2:
Different parts of the isolation cell are assigned different power supply connections based on their functional requirements. The logic circuit uses the first power domain supply for low leakage, while the output inverter uses the second power domain supply for proper signal level translation, optimizing both leakage performance and operational reliability locally.
Data Source
AI summary
An isolation cell clamps a signal passing from a first, powered-down power domain to a second, power-on power domain. To reduce leakage current, some of the circuits and devices are connected to a voltage supply of the first or “from” power domain, while other circuits and devices are connected to a voltage supply of the second or “to” power domain.