Buffer Circuit Pre-Charge and Pre-Discharge for Fast Output Switching
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Solution Overview
Problem
Existing high-speed buffer circuits in high-speed applications such as CPUs, GPUs, and APUs suffer from significant signal delay due to their inability to rapidly charge or discharge output nodes in response to input signals, especially under heavy load conditions.
Innovation Solution
The proposed buffer circuit design includes a first inverter, a second inverter, and switches to pre-charge or pre-discharge the output node in response to the input signal, ensuring rapid voltage level changes at the output node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional buffer circuits are used, then the circuit structure is simple, but the signal delay is significant and the output cannot rapidly reach voltage levels under heavy load
Solution Approach 1:
The patent applies preliminary action by pre-charging the output node to a voltage level close to the target voltage before the actual signal transition occurs. The pre-charge circuit raises the output node voltage in advance, so when the buffer switches, the output rapidly reaches the final voltage level without waiting for gradual charging through the buffer transistor, thereby significantly reducing signal delay.
Solution Approach 2:
The patent segments the buffer circuit into multiple functional parts: a conventional buffer stage and a separate pre-charge circuit stage. The pre-charge circuit includes its own transistor and control logic that operates independently from the main buffer, allowing the output node to be prepared in advance without interfering with the buffer's normal operation.
2Loss of time
If the output node is pre-charged to reduce signal delay, then the speed performance improves, but additional circuit components and control logic are required
Solution Approach 1:
The pre-charge transistor shares the output node with the buffer transistor, and both are controlled by signals derived from the same input. The pre-charge circuit uses the inverted input signal (already generated by the buffer's internal inverter) to control the pre-charge transistor, making the existing buffer components serve dual purposes: signal buffering and pre-charge control.
3Productivity
If pre-charge and pre-discharge circuits are added, then the output rapidly reaches voltage levels, but the circuit complexity increases
Solution Approach 1:
The patent uses the inverted input signal to control the pre-charge transistor instead of using the original input signal. When the input is low, the inverted signal is high, turning on the pre-charge transistor to raise the output voltage. This inversion approach allows the pre-charge operation to be naturally synchronized with the buffer's switching action without requiring additional complex control logic.
Data Source
AI summary
A buffer circuit is provided to output an output signal at an output node. The buffer circuit includes first and second inverters and first and second switches. The first inverter inverts an input signal. The second inverter is coupled between the first inverter and the output node. The first switch is coupled between a first voltage source terminal and the output node. The second switch is coupled between the output node and a second voltage source terminal. First and second voltages are respectively provided to the first and second voltage source terminals. In response to the input signal switching to a first level from a second level, the first switch is turned on to pre-charge the output node. In response to the input signal transiting to the second level from the first level, the second switch is turned on to pre-discharge the output node.