Volatile State Backup Circuit Using High-Voltage Transistors
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Solution Overview
Problem
Modern CMOS processes face excessive leakage currents in smaller geometry devices when power is turned off, making it difficult to achieve low standby currents, and previous solutions using analog techniques are complex and unreliable.
Innovation Solution
A digital approach is employed where non-critical circuitry is powered off in low-power mode, and high-voltage, low-leakage CMOS transistors are used for circuitry that must remain powered, switching to a secondary power source during primary power down, with the RAM core remaining powered and using high-voltage memory cells to minimize leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If smaller geometry CMOS devices are used to reduce component size, then device integration is improved, but leakage current increases significantly
Solution Approach 1:
The circuit is divided into two separate power domains: a primary low-voltage domain for normal operation and a secondary high-voltage domain for backup. This segmentation allows each domain to be optimized independently - the high-voltage domain uses larger geometry devices with lower leakage while the low-voltage domain maintains small geometry for integration.
Solution Approach 2:
Different regions of the circuit are assigned different voltage levels and device geometries based on their specific functions. The backup circuitry uses high-voltage, large-geometry transistors specifically in regions where low leakage is critical, while the main circuitry uses low-voltage, small-geometry transistors for high integration density.
2Loss of energy
If all circuit nodes are made static to reduce standby current, then power consumption is reduced, but leakage current remains excessive in modern CMOS processes
Solution Approach 1:
The invention changes the voltage parameter from the conventional single low-voltage level to a dual-voltage system. By switching the backup circuitry to a higher voltage level (e.g., 3.3V or 5V) during standby, the leakage current is reduced by one to two orders of magnitude compared to keeping the same low-voltage circuit active.
Solution Approach 2:
The circuit dynamically switches between two power modes: during normal operation, the primary low-voltage circuit is active; during standby or power extension, the system transitions to the high-voltage backup mode. This dynamic switching allows the circuit to adapt its characteristics to minimize leakage when active is not required.
3Object-generated harmful factors
If high voltage transistors are used for backup mode, then leakage current is reduced, but isolation from lower voltage circuits is required
Solution Approach 1:
Level-shifting circuits and isolation structures are introduced as intermediary elements between the high-voltage backup domain and the low-voltage operational domain. These intermediaries enable controlled interaction between the two voltage domains while maintaining the electrical isolation necessary to prevent damage to low-voltage circuits from high-voltage transients.
4Loss of energy
If primary power is turned off to save energy, then power consumption is reduced, but volatile memory states may be lost
Solution Approach 1:
The high-voltage backup circuitry is pre-configured and maintained in a ready state with higher threshold voltage transistors that exhibit lower off-state leakage. This preliminary preparation ensures that when the primary low-voltage circuit is powered down, the backup circuit can immediately take over and maintain the memory states without data loss.
Data Source
AI summary
An electrical circuit contains volatile states that are lost without continued application of power to circuit elements to preserve their volatile states. A first power source in the circuit provides power to the volatile state circuit for holding and preserving their volatile states. A power selection circuit is coupled to the circuit elements and has a plurality of selectable modes. A first mode of operation of the power selection circuit is selected when the circuit elements are to be operated at a first power level via the first power source which constitutes a first mode of operation. A second mode of operation is selected when the volatile state circuit elements are to be operated under a condition where the first power source is inactivated, such as, for example, during a circuit backup or standby operation. During the second mode of operation, the circuit elements volatile states are preserved via a power selection circuit that provides power from a second power source at a second power level, different from the first power level, to the volatile state circuit elements in place of the first power source.