Variable-Impedance Output Buffer for EMI-Reduced Signal Pads
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Solution Overview
Problem
Semiconductor devices, such as processors and microcontrollers, emit undesired electromagnetic radiation due to alternating current components on their output signal pads, which can interfere with other electronic devices and fail to meet stringent electromagnetic radiation standards.
Innovation Solution
The method involves driving a Boolean state to a signal pad of a semiconductor device through a transistor with a first drain-to-source impedance and maintaining it with a second, higher drain-to-source impedance to attenuate alternating current signals, thereby reducing electromagnetic radiation. This is achieved by using buffer circuits that selectively control the impedance of the devices through which the output signal pads are driven, particularly increasing impedance when the Boolean state is maintained for an extended period to reduce AC component propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a transistor with low drain-to-source impedance is used to drive a Boolean state to a signal pad, then the signal driving capability is improved, but electromagnetic radiation increases due to AC signal propagation
Solution Approach 1:
The patent applies dynamics by making the transistor impedance variable rather than fixed. The transistor operates in different regions (linear vs. saturation) to dynamically adjust its drain-to-source impedance based on the operational phase, enabling low impedance during signal transitions for fast driving and high impedance during steady states to reduce radiation.
Solution Approach 2:
The patent changes the electrical parameter (impedance) of the transistor over time. By controlling the gate voltage to modulate the transistor's drain-to-source impedance, the system transitions between low-impedance state (for fast signal propagation) and high-impedance state (for AC signal attenuation), thereby resolving the contradiction between speed and radiation.
2Object-generated harmful factors
If a transistor with high drain-to-source impedance is used to maintain a Boolean state on a signal pad, then electromagnetic radiation is reduced through AC signal attenuation, but signal driving capability deteriorates
Solution Approach 1:
The patent employs periodic action by alternating between two impedance states. During brief transition periods, the transistor operates in linear mode with low impedance for fast signal changes. During extended steady-state periods, it switches to saturation mode with high impedance to attenuate AC signals and reduce radiation. This time-based switching resolves the contradiction between radiation reduction and signal driving capability.
Solution Approach 2:
The patent applies preliminary action by pre-charging or pre-discharging signal pads through low-impedance paths before switching to high-impedance maintenance mode. This ensures that signal transitions are completed rapidly before the impedance increases, thereby maintaining fast signal driving capability while achieving radiation reduction during the majority of the time when the state is stable.
3Reliability
If AC signals are allowed to propagate on DC voltage busses to signal pads, then signal integrity is maintained, but electromagnetic radiation increases
Solution Approach 1:
The transistor serves as an intermediary element between the DC voltage busses and the signal pads. By controlling the transistor's impedance state, it acts as a gate that selectively permits or blocks AC signal propagation. During transitions, it allows AC components for signal integrity; during steady states, it blocks AC components to reduce radiation, thus resolving the contradiction through controlled mediation.
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 effectively reduces electromagnetic radiation from semiconductor devices by attenuating AC signals, helping to meet or exceed applicable electromagnetic radiation standards, such as those set by the FCC and SAE, by ensuring that only direct current components propagate, thus minimizing interference.
Implementation Method 1
maintaining the Boolean state applied to the signal pad through the transistor with a second drain-to-source impedance, higher than the first drain-to-source impedance. Driving with the second drain-to-source impedance attenuates alternating current (AC) signals, on the direct current (DC) voltage busses
Data Source
AI summary
Reducing electromagnetic radiation from semiconductor devices. At least some of the illustrative embodiments are methods comprising driving a Boolean state to a signal pad of a semiconductor device (the driving through a transistor with a first drain-to-source impedance during the driving), and maintaining the Boolean state applied to the signal pad through the transistor with a second drain-to-source impedance, higher than the first drain-to-source impedance.