Transit State Element Circuit for Cross-Cycle Signal Timing
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Solution Overview
Problem
Long signal interconnects in integrated circuits (ICs) lead to excessive propagation delay, resistance, and capacitance, causing timing and voltage level issues at the receiver, which can result in crowbar currents and increased power consumption, even with repeater circuits, especially when signal propagation delay crosses a clock cycle boundary.
Innovation Solution
A transit state element circuit is introduced, comprising a clock input stage, an activation stage, an output stage, and a storage element that captures and stores the logic value of an input signal during one clock cycle and provides it in the next cycle, incorporating a repeater circuit functionality to address signal propagation delays across cycle boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If repeater circuits are used to overcome resistance and capacitance in long interconnects, then signal transition speed is improved, but device complexity increases
Solution Approach 1:
The circuit is divided into distinct functional stages: an activation stage that detects input transitions, a storage element that captures the transition state, and an output stage that drives the output node. This segmentation allows each stage to be optimized independently while working together to achieve fast signal transition without requiring complex inter-stage coordination.
Solution Approach 2:
A storage element is introduced as an intermediary between the activation stage and the output stage. This storage element captures the input signal state during one clock cycle and holds it until the next clock cycle, acting as a buffer that decouples the timing requirements of the input detection and output driving operations, thereby simplifying the overall circuit design.
2Loss of time
If repeater circuits are placed along signal paths to reduce propagation delay, then timing is improved, but power consumption increases due to crowbar currents
Solution Approach 1:
The circuit operates in periodic cycles synchronized with the clock signal. During each clock cycle, the storage element captures the input state, and during the next cycle, the output stage drives the output node. This periodic operation allows the circuit to achieve fast signal transition while minimizing continuous power consumption, as the output devices are only actively driving during specific phases of the clock cycle rather than continuously.
Solution Approach 2:
The storage element performs preliminary action by capturing and holding the input signal state during one clock cycle before the output stage is activated in the next cycle. This preliminary capture allows the output stage to be driven with a stable, pre-captured state, reducing the need for continuous high-current driving and thereby reducing power consumption while maintaining fast transition times.
3Device complexity
If simple repeater circuits like inverters or buffers are used, then device complexity is reduced, but they cannot adequately handle signals that propagate across clock cycle boundaries
Solution Approach 1:
The storage element serves as a mediator that bridges the timing gap between input transitions and output requirements across clock cycle boundaries. By capturing the input state during one clock cycle and holding it for the next cycle, the storage element ensures that the output stage receives a stable, synchronized signal, thereby maintaining timing reliability without requiring complex synchronization logic.
Solution Approach 2:
The circuit is segmented into distinct functional blocks with clear interfaces: the activation stage that detects transitions, the storage element that holds state across clock cycles, and the output stage that drives the output. This segmentation allows each block to be simple and well-defined, yet together they provide robust timing control that reliably handles signals propagating across clock cycle boundaries.
Data Source
AI summary
A transit state element circuit. The transit state element circuit includes a clock input stage coupled to receive a clock signal, an output stage configured to drive an output signal on an output node and an activation stage coupled to an input node. The activation stage is configured to, responsive to the clock input stage detecting a transition from a first logic level to a second logic level and detecting a logical transition of an input signal on the input node, activate the output stage to drive an output signal on the output node. A storage element is configured to capture a logic value of the input signal when the clock is at the second logic level and to store the logic value, and to provide the output signal on the output node when the clock signal is at the first logic level.