CMOS Output Buffer Staging for Precise Drive Capacity Trimming
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Solution Overview
Problem
The dispersion of transistor characteristics in manufacturing processes leads to variations in drive capacity among buffer circuits, affecting the timing precision and high-speed operation of semiconductor integrated circuits, as existing buffer circuits struggle to accurately set drive capacity across different states.
Innovation Solution
The implementation of a CMOS output buffer circuit with multiple stages of buffer circuits, each comprising PMOS and NMOS transistors in parallel, allows for selective driving and independent adjustment of drive capacity through trimming circuits and gate signals, ensuring consistent drive capacity across low, normal, and high drive states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple stages of buffer circuits are provided with selective driving to achieve changeable slew rate, then the drive capacity can be adjusted across different states, but manufacturing process dispersion causes variations in drive capacity that deteriorate timing precision
Solution Approach 1:
The buffer circuit is divided into multiple stages (first stage buffer circuit and second stage buffer circuit) with independently controllable enable signals. Each stage can be selectively activated to achieve different drive capacity states (low, normal, high) while maintaining consistent performance within each state despite manufacturing variations.
Solution Approach 2:
The buffer circuit employs dynamic control through enable signals (first enable signal and second enable signal) that can be independently adjusted to change the operational state of each buffer stage. This allows real-time adaptation of drive capacity while compensating for manufacturing process dispersion through selective activation of buffer stages.
2Productivity
If multiple buffer circuits are selectively driven to achieve different drive states, then slew rate can be changed in several stages, but the difference in drive capacity of each state differs from expected value
Solution Approach 1:
The buffer circuit incorporates a dispersion compensation mechanism that uses feedback from detected signal characteristics to dynamically adjust the operation of buffer stages. By monitoring the actual drive capacity and comparing it with expected values, the system compensates for manufacturing variations to achieve accurate drive capacity states.
Solution Approach 2:
The invention changes operational parameters (enable signal states, buffer stage activation) to achieve different drive capacity levels. By dynamically adjusting which buffer stages are active and their respective enable signals, the system achieves precise control over drive capacity despite fixed manufacturing variations in transistor characteristics.
3Manufacturing precision
If transistor characteristics are adjusted to compensate for manufacturing dispersion, then drive capacity consistency can be improved, but circuit complexity increases
Solution Approach 1:
The buffer circuit is segmented into multiple independently controllable stages, where each stage can be activated or deactivated based on the desired drive capacity state. This segmentation allows compensation for manufacturing dispersion through selective activation without requiring complex adjustments within each transistor, maintaining relatively simple circuit structure.
Solution Approach 2:
Multiple buffer stages share the same basic structure and control mechanism, with each stage capable of performing the same buffering function at different capacity levels. This universal design allows the system to achieve multiple drive capacity states using identical circuit blocks, reducing overall complexity compared to designing unique compensation circuits for each stage.
Data Source
AI summary
An output buffer circuit in accordance with an embodiment comprises a plurality of buffer circuits, each of the buffer circuits including a transistor operative to change an output signal of an output terminal in response to a change in an input signal, the output buffer circuit being configured to enable the plurality of buffer circuits to be driven selectively. Each of the plurality of buffer circuits includes a plurality of output transistors having respective current paths formed in parallel to one another between a fixed voltage terminal supplying a certain fixed voltage and an output terminal, and being selectively rendered in an operable state in accordance with a control signal provided from external. The plurality of output transistors included in each of the plurality of buffer circuits are formed having a certain size ratio.