Flip-Flop Latch State Preservation for Power-Gated Memory
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Solution Overview
Problem
Power gating in integrated circuits, such as programmable logic devices, results in loss of logical state when power is turned off, as existing methods do not effectively preserve and restore the state of flip-flops upon power restoration.
Innovation Solution
A circuit design that includes a flip-flop and a separate latch, where the latch maintains the state of the flip-flop's logical value during power-off mode and restores it when power is resumed, allowing the flip-flop to retain less power in a low power operational mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If power gating is applied to reduce power consumption, then power consumption decreases, but logical state information is lost
Solution Approach 1:
The circuit is segmented into two separate memory elements: a flip-flop for dynamic state storage during operation and a latch for state preservation during power gating. This segmentation allows the system to maintain logical state information even when power is gated to the flip-flop, resolving the contradiction between power reduction and information retention.
Solution Approach 2:
Before power gating occurs, the current state of the flip-flop is transferred to the latch in advance. This preliminary action ensures that the logical state is preserved before the flip-flop loses its state due to power removal, thereby preventing information loss while enabling power consumption reduction.
2Loss of energy
If power is turned off to reduce heat dissipation, then heat dissipation decreases, but operational functionality is lost
Solution Approach 1:
The state transfer from flip-flop to latch is performed preliminarily before power gating, ensuring that when power is removed to reduce heat dissipation, the operational functionality can be quickly restored by transferring the preserved state back to the flip-flop, maintaining reliability.
Solution Approach 2:
The system changes the operational parameters of the memory element by switching between a powered flip-flop (high power, dynamic operation) and a powered latch (low power, static storage). This parameter change allows the system to reduce heat dissipation while maintaining the ability to restore operational functionality when needed.
3Loss of information
If a latch is added to preserve state during power gating, then information retention improves, but device complexity increases
Solution Approach 1:
The latch is designed to serve multiple functions: it acts as a state storage element during power gating, a state transfer intermediary, and a backup memory element. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in device complexity while achieving state preservation.
Solution Approach 2:
The flip-flop and latch are merged into a coordinated power-gating circuit system where they work together as an integrated state management unit. This merging allows the two elements to share control logic and interconnect structures, reducing overall circuit complexity compared to having completely separate state management mechanisms.
Data Source
AI summary
A method and apparatus involving a circuit is disclosed. The circuit has separate first and second portions, where the first portion includes a first memory device such as a flip-flop, and the second portion includes a second memory device such as a latch. The first portion is selectively operated in first and second operational modes, the first portion consuming less power in the second operational mode than in the first operational mode. During the first operational mode a logical value is maintained in the flip-flop and can vary dynamically. During the second operational mode, the state that the logical value had at a point in time just before the first portion entered the second operational mode is maintained in the latch. Then, after the first portion switches from the second operational mode back to the first operational mode, the state of the logical value in the latch is restored to the flip-flop.