Output Buffer Bias Trimming for Stable Rise and Fall Times
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Solution Overview
Problem
Conventional output buffers in digital circuits exhibit significant variations in rise time and fall time due to process, voltage, temperature, and output load variations, making it difficult to control these parameters effectively.
Innovation Solution
The implementation of feedback capacitances and adjustable current sources in the output buffer circuit, along with a controller that generates trimming codes based on process information or oscillation frequency, to adjust bias currents or resistances, thereby stabilizing the rise and fall times.
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 introduces feedback capacitances connected between the output node and gate nodes of the driver transistors. These feedback capacitances sense the output voltage changes and automatically adjust the gate voltages to compensate for variations in rise time and fall time 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 different bias currents to the driver transistors based on process, voltage, and temperature variations, enabling the output buffer to maintain stable rise and fall times across varying environmental conditions
Solution Approach 3:
The patent utilizes trim circuits that can adjust electrical parameters (such as bias currents and threshold voltages) of the output buffer components. By changing these parameters through trimming mechanisms, the circuit compensates for manufacturing variations and environmental effects, achieving stable rise and fall times without increasing overall circuit complexity
2Adaptability or versatility
If the output load is fixed to control rise time and fall time variations, then the timing parameters are stable, but the adaptability to different output loads is reduced
Solution Approach 1:
The feedback capacitances continuously monitor the output voltage and automatically adjust the driver transistor gate voltages in response to load changes. This feedback mechanism enables the output buffer to maintain stable rise and fall times across a wide range of output load conditions without requiring the load to be fixed or predetermined
Solution Approach 2:
The adjustable current sources dynamically modify their current output based on detected load conditions and environmental parameters. This dynamic adaptation allows the circuit to maintain optimal timing characteristics whether driving small or large capacitive loads, eliminating the need to fix the output load for stability
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.