Buffered Analog Multiplexer Circuit for Leakage Isolation
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Solution Overview
Problem
Analog multiplexers experience leakage issues between drain and source terminals of pass gates, leading to errors in output signal voltages due to unwanted leakage from unselected portions of the multiplexer.
Innovation Solution
A multiplexer design with switch circuits connected in series, featuring an intermediate node and a buffer circuit to minimize leakage by activating third switch elements in unselected circuits, driving the output voltage to the intermediate nodes, thereby isolating the output node from leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pass gates are used to select input signals in an analog multiplexer, then signal selection capability is provided, but leakage occurs between drain and source terminals causing output voltage errors
Solution Approach 1:
A buffer circuit is introduced as an intermediary between the pass gates and the output node. The buffer isolates the output node from leakage currents generated by unselected pass gates, thereby maintaining output voltage accuracy while preserving the signal selection capability of the pass gates.
Solution Approach 2:
The multiplexer circuit is segmented into distinct functional blocks: pass gate selection circuits, a buffer circuit, and output stages. This segmentation allows the buffer to specifically address the leakage problem without affecting the selection functionality of the pass gates, resolving the contradiction between selection capability and output accuracy.
2Adaptability or versatility
If multiple switch circuits are used to provide signal selection, then selection versatility is improved, but leakage from unselected portions increases
Solution Approach 1:
The buffer circuit acts as a mediator that blocks the propagation of leakage currents from unselected switch circuits to the output node. This allows multiple switch circuits to coexist without their leakage currents degrading the output signal, thus maintaining selection versatility while eliminating harmful leakage effects.
Solution Approach 2:
The harmful leakage currents are effectively extracted or removed from the signal path by the buffer circuit, which prevents them from reaching the output node. This extraction allows multiple switch circuits to operate simultaneously without their leakage currents affecting output accuracy.
Data Source
AI summary
A multiplexer circuit includes a plurality of switch circuits coupled between respective input nodes and an output node. The switch circuits include first and second switch elements coupled in series, at an intermediate node, between the respective input node and the output node. A third switch element is coupled between an output of a buffer and the intermediate node. The buffer is configured to generate a buffered voltage based on the output voltage. When a particular switch circuit is selected, its respective first and second switch elements are active while its third switch element is inactive, resulting in a path between its input node and the output node. When the particular switch circuit is not selected, its third switch element is active while its first and second switch elements are inactive. The buffered voltage is driven to the intermediate node via the active third switch element.