Output Buffer RC Slew-Rate Control to Prevent Through-Current
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Solution Overview
Problem
Existing output buffers in microelectronic chips face challenges in minimizing interference and power loss due to simultaneous conduction of transistors, which leads to unwanted harmonics and increased power consumption.
Innovation Solution
A series connection of field effect transistors is used with an RC series connection to control the slew rate of the output signal, ensuring that only one transistor is conducting at a time, thereby reducing power loss and harmonics by using switches to manage the charging and discharging of the capacitive element for defined signal transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If both transistors are turned on simultaneously to enable fast signal transitions, then switching speed is improved, but power loss increases due to through-current
Solution Approach 1:
The control circuit prepares the second transistor for conduction before the first transistor is fully turned off by pre-charging its gate through the RC connection. This preliminary action ensures that when the first transistor turns off, the second transistor is already ready to conduct, maintaining fast switching speed while preventing simultaneous conduction and the associated power loss.
Solution Approach 2:
The switching operation is divided into distinct periodic phases: first transistor conduction phase, transition phase with RC charging, and second transistor conduction phase. This periodic action ensures that at any given time, only one transistor is fully conducting, eliminating through-current while maintaining continuous signal transmission capability.
2Productivity
If sharp transitions between signal states are used to improve switching performance, then switching efficiency is improved, but harmonics are generated in other circuit parts
Solution Approach 1:
The RC connection acts as an intermediary element between the control signal and the transistor gate. It shapes the gate voltage transition to have a controlled slew rate, which in turn produces output signal transitions with defined rise and fall times. This intermediary action reduces high-frequency harmonics while maintaining efficient switching by avoiding both sharp transitions and prolonged linear regions.
3Device complexity
If the transistor switching timing is not precisely controlled, then circuit complexity is reduced, but current losses increase due to simultaneous conduction
Solution Approach 1:
The RC connection connected to the second transistor's gate automatically charges and discharges based on the switching state, providing self-timed control for the second transistor. This self-service mechanism ensures precise timing control to prevent simultaneous conduction without requiring complex external control circuitry, thus reducing control complexity while eliminating current losses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces power loss and avoids high-frequency harmonics by ensuring that both transistors are not in a conducting state simultaneously, achieving a defined slew rate for signal transitions and minimizing interference in microelectronic circuits.
Implementation Method 1
an RC series connection coupled between the output terminal and either of the first and the second supply potential terminal, respectively, with the connection point of the RC series connection being connected to the gate terminal of the field effect transistor
Implementation Method 2
an RC series connection coupled between the output terminal and either of the first and the second supply potential terminal
Implementation Method 3
a first output transistor connected between a first power line and an output node, a second output transistor connected between the output node and a second power line
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An output buffer comprises a series connection of a first field effect transistor (MN0) and a second field effect transistor (MP0), wherein the first field effect transistor is connected to a first supply potential terminal (GND) and the second field effect transistor is connected to a second supply potential terminal (VDD). An output terminal (T-OUT) is connected to a common connection of the first transistor and the second transistor. The output buffer has a series connection of a resistive element (R1) and a capacitive element (C1), wherein the capacitive element is connected to the output terminal, and a control circuit (CTRL), to which an input signal (INP) is provided. The control circuit controls the transistors in such a way that turning off of a transistor is performed immediately, while turning on of a transistor is performed depending on the charging or discharging of the capacitive element, thus achieving a defined slew rate of the output signal at the output terminal.