CMOS Switch Isolation for Voltages Beyond Supply Rails
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Solution Overview
Problem
Conventional CMOS switches fail to effectively isolate input signals from output signals when input or output voltages exceed the supply or ground voltage, leading to unintended current flow and measurement inaccuracies in voltage monitoring applications.
Innovation Solution
The proposed solution involves a CMOS switch configuration with specific connections and control circuits for p-type and n-type metal oxide semiconductor transistors, where the enable signal determines whether a ground or supply voltage is applied to the transistor gates, ensuring the switch is open or closed based on voltage levels, thereby isolating or allowing signal passage regardless of voltage deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CMOS switches are used to sample voltages, then normal voltage monitoring works well, but the switches fail to isolate signals when voltages exceed supply or ground levels
Solution Approach 1:
The switch is divided into two separate transistors (first transistor for high-side switching, second transistor for low-side switching) that operate independently. Each transistor handles specific voltage conditions, allowing the system to reliably isolate signals across a broader voltage range including overvoltage and undervoltage conditions.
Solution Approach 2:
Different parts of the switch have different properties optimized for their specific functions. The first transistor is optimized for blocking high voltages from the input, while the second transistor is optimized for blocking low voltages from the output. This local optimization enables reliable signal isolation across extended voltage ranges.
2Productivity
If the switch allows signal passage during normal operation, then voltage sampling works, but unwanted current flow occurs during overvoltage/undervoltage conditions
Solution Approach 1:
The switch dynamically adapts its state based on voltage conditions. During normal operation, both transistors remain off allowing signal passage. During overvoltage conditions, the first transistor activates to block current. During undervoltage conditions, the second transistor activates to block current. This dynamic response eliminates unwanted current flow while maintaining productivity during normal conditions.
Solution Approach 2:
The two transistors act as intermediary protective elements between the input and output. They remain inactive during normal operation, allowing the signal to pass through. When voltage conditions become abnormal, they activate as intermediaries to block harmful current flow, protecting the circuit while maintaining normal signal transmission capability.
3Measurement precision
If conventional switches are used, then device complexity is low, but measurement precision fails under voltage extremes
Solution Approach 1:
The measurement function is segmented into two independent transistor circuits, each responsible for handling specific voltage extremes. This segmentation improves measurement precision across the full voltage range by ensuring accurate isolation during both overvoltage and undervoltage conditions, while keeping each individual transistor configuration relatively simple.
Data Source
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AI summary
Devices (100) for isolating an input (152) from an output (154) are disclosed. For example, a device (100) includes a first p-type metal oxide semiconductor transistor (110) and a first circuit (182). A source of the first p- type metal oxide semiconductor transistor (110) is connected to an input (152) of the device (100). The first circuit (182) is for delivering a signal on the input (152) of the device to a gate of the first p-type metal oxide semiconductor transistor (110) when an enable signal (172) is deactivated and for delivering a ground voltage (192) to the gate of the first p-type metal oxide semiconductor transistor (110) when the enable signal (172) is activated.