Input Buffer Circuit for TTL-CMOS Translation With Low Quiescent Current
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Solution Overview
Problem
Conventional I/O buffers in integrated circuits face limitations in bandwidth and draw significant quiescent current, leading to high power consumption, particularly in battery-powered devices.
Innovation Solution
The input-buffer circuit incorporates quiescent-current-arresting transistors, capacitive elements for DC-bypass, and feedback transistors with a hysteresis circuit to reduce quiescent current while maintaining high bandwidth, translating TTL logic signals to CMOS logic signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional I/O buffer design is used, then logic signal translation function is achieved, but quiescent current consumption is significant
Solution Approach 1:
The buffer circuit is segmented into multiple functional blocks: input stage with quiescent-current-arresting transistors, translator stage, edge-detector stage, and feedback stage. Each stage is independently optimized to reduce quiescent current while maintaining translation function. The quiescent-current-arresting transistors are specifically designed to cut off leakage paths in different operating modes.
Solution Approach 2:
The buffer employs dynamic control of transistor switching states based on input signal edges. The edge-detector stage generates control signals that dynamically adjust the conductivity of feedback transistors, allowing the circuit to adapt its quiescent current consumption to the actual signaling activity. This dynamic operation reduces static power dissipation while maintaining functional reliability.
2Speed
If conventional I/O buffer design is used, then logic signal translation function is achieved, but bandwidth is limited
Solution Approach 1:
The edge-detector stage operates in advance to detect input signal transitions before they reach the translator stage. This preliminary detection allows the feedback transistors to be activated proactively, ensuring rapid response to signal edges and maximizing bandwidth. The hysteresis circuit further prepares the circuit state in advance to prevent oscillations during transitions.
Solution Approach 2:
The feedback stage uses control signals from the edge-detector to adjust the operating state of the translator stage. This feedback mechanism optimizes the bandwidth by ensuring that the translator stage is in the optimal conducting state when signal transitions occur, thereby reducing propagation delay and increasing overall circuit speed.
3Use of energy by moving object
If quiescent-current-arresting transistors are added, then quiescent current is reduced, but device complexity increases
Solution Approach 1:
The quiescent-current-arresting transistors serve multiple functions: they block leakage current paths during logic transitions, act as switchable resistors to control signal levels, and provide feedback control signals. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in overall device complexity while achieving significant quiescent current reduction.
Solution Approach 2:
The circuit merges the quiescent-current-arresting function with the existing translator and feedback stages. The control logic for current arrest is integrated into the edge-detection and feedback mechanisms, combining multiple functions into a unified circuit architecture rather than adding completely separate current-blocking components.
Data Source
AI summary
An embodiment of an input-buffer circuit may include an input stage with an inverter having an input operable to receive a signal to be translated. The input stage may include a limiting circuit coupled to the input stage for arresting quiescent current. Additional embodiments of an input-buffer circuit formed according to the subject matter disclosed herein may include feedback transistors suited to provide additional current to the input stage and a hysteresis circuit suited to provide hysteresis current to the input stage when an input signal has a high-frequency change rate.