CMOS analog switch
First Claim
1. A MOS circuit for switching an input signal, referenced to a ground, between a signal input terminal and a signal output terminal, comprising:
- first and second p-channel transistors formed in an at least one n-conductivity type substrate area and each having a gate, a source connected to the signal input terminal and a drain connected to the signal output terminal;
a comparator for comparing a voltage level at the signal input terminal with ground;
a switch circuit driven by an output of said comparator to selectively connect the at least one n-conductivity type substrate area to the signal input terminal for a positive input voltage level or to the ground for a negative input voltage levels; and
a control circuitry providing gate control signals for the first and second p-channel transistors.
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Accused Products
Abstract
A CMOS analog switch is provided that can handle negative input polarity. The semiconductor substrate wherein the analog switch is formed has a substrate area of n-conductivity type. First and second p-channel transistors are formed in the n-conductivity substrate area and each have a gate, a source connected to the input terminal and a drain connected to the output terminal. The analog switch further has a comparator for comparing a voltage level at the input terminal with ground level, a switch driven by an output of the comparator to selectively connect the n-conductivity area with the signal input terminal for a positive input voltage level or to ground for a negative input voltage level, and control circuitry providing gate control signals for the first and second p-channel transistors. The inherent substrate diodes are effectively kept from becoming conductive.
27 Citations
9 Claims
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1. A MOS circuit for switching an input signal, referenced to a ground, between a signal input terminal and a signal output terminal, comprising:
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first and second p-channel transistors formed in an at least one n-conductivity type substrate area and each having a gate, a source connected to the signal input terminal and a drain connected to the signal output terminal; a comparator for comparing a voltage level at the signal input terminal with ground; a switch circuit driven by an output of said comparator to selectively connect the at least one n-conductivity type substrate area to the signal input terminal for a positive input voltage level or to the ground for a negative input voltage levels; and a control circuitry providing gate control signals for the first and second p-channel transistors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A MOS circuit for switching an input signal, referenced to a ground, between a signal input terminal and a signal output terminal, comprising:
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a first and second p-channel transistors formed in an at least one n-conductivity type substrate area and each having a gate, a source connected to the signal input terminal and a drain connected to the signal output terminals; a comparator for comparing a voltage level at the signal input terminal with ground; a first switch circuit driven by an output of said comparator to selectively connect the at least one n-conductivity type substrate area to the signal input terminal for a positive input voltage level or to ground for a negative input voltage level; a control circuitry providing gate control signals for the first and second p-channel transistors;
wherein the control circuitry comprises a pair of logic gates, a first of the pair of logic gates having an input connected to the output of the comparator; and
a second of the pair of logic gates having an input connected to the output of the comparator through an inverting element;
wherein the pair of logic gates have outputs that are capacitively coupled to the p-channel transistor gates; anda second switch circuit driven by a signal source to selectively connect the signal input terminal to each of the gates of the p-channel transistors.
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Specification