Slew-Rate Output Buffer Bias Control for Stable Rise and Fall Times
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Solution Overview
Problem
Conventional output buffers exhibit significant variations in rise time and fall time due to process, voltage, temperature, and output load variations, leading to issues like crosstalk, ringing, reflection, ground bounces, and electromagnetic radiation noise.
Innovation Solution
The implementation of feedback capacitances and adjustable current sources in output buffer circuits, along with a controller to generate trimming codes based on oscillation frequency or process information, to stabilize rise and fall times across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional output buffers are used, then the circuit is simple, but the rise time and fall time have large variations over process, voltage, temperature, and output load variations
Solution Approach 1:
The patent implements feedback capacitances connected between the output node and gate nodes of the push-pull transistors. These feedback capacitances sense the output voltage changes and automatically adjust the gate voltages to compensate for variations in rise and fall times caused by PVT and load conditions, thereby stabilizing the timing characteristics without requiring complex external control circuits
Solution Approach 2:
The patent employs adjustable current sources with controllable current values that can dynamically adapt to different operating conditions. The current sources are configured to provide variable bias currents to the push-pull transistors, enabling the buffer to optimize its performance across different process, voltage, temperature, and load conditions by adjusting the driving strength dynamically
2Adaptability or versatility
If the output load is fixed to control rise time and fall time variations, then the timing is stable, but the adaptability to different load conditions is reduced
Solution Approach 1:
The feedback capacitances continuously monitor the output voltage and automatically adjust the gate drive signals to maintain consistent rise and fall times regardless of the connected load capacitance. This feedback mechanism enables the buffer to adapt to a wide range of load conditions while maintaining stable timing characteristics
Solution Approach 2:
The adjustable current sources modify their current output based on detected variations in load conditions, process parameters, voltage, or temperature. By dynamically changing the bias current parameters, the buffer maintains optimal performance across diverse operating conditions and load requirements
3Speed
If larger transistors are used to reduce rise time and fall time, then the switching speed improves, but the crosstalk, ringing, reflection, ground bounces, and electromagnetic radiation noise increase
Solution Approach 1:
The feedback capacitances provide automatic compensation that allows the use of optimally sized transistors without requiring excessive oversizing. By sensing output voltage transitions and adjusting gate signals in real-time, the feedback mechanism maintains fast switching speeds while preventing the harmful effects associated with oversized transistor designs, such as crosstalk and electromagnetic radiation
Data Source
AI summary
The present disclosure provides a semiconductor device, which includes a process monitor circuit, a controller, and an output buffer. The process monitor circuit is configured to measure process information of the semiconductor device. The controller is electrically connected to the process monitor circuit, and configured to generate a trimming code based on the measured process information. The output buffer is electrically connected to the controller, and configured to adjust a first bias current and a second bias current based on the trimming code.