Clocked high voltage switch
First Claim
1. A high voltage output level shifter using low voltage MOS devices comprising:
- a first terminal for coupling to a first voltage source, a second terminal for coupling to a second voltage source, a third terminal for coupling to a third voltage source, a fourth terminal for coupling to a clock signal, and an output terminal, wherein said second voltage source is intermediate to said first and third voltage sources;
first, second, third and fourth devices, each having a source, a drain and a gate, said second device having a channel region between said source and drain of said second device, said second device having a field implant terminating short of said source and said drain of said second device, the field implant also terminating at the edge of said channel region, said drain of said first device being coupled to said first terminal, said source of said first device and said drain of said second device being coupled together, said source of said second device and said drain of said third device being coupled to said output terminal, said source of said third device and said drain of said fourth device being coupled together, said gate of said third device being coupled to said second terminal, said source of said fourth device being coupled to said third terminal;
an input circuit for providing an input signal;
a charge pump coupled to said input circuit and to said gates of said first and second devices for charging said gates of said first and second devices to a threshold voltage above that provided by said first voltage source in response to said input signal; and
a circuit coupled to said input circuit and to said gates of said third and fourth devices for switching said third and fourth devices off in response to said input signal.
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Accused Products
Abstract
The present invention discloses methods and apparatus for implementing a clocked high voltage switch involving MOS devices. The switching is from a high voltage source typically at 21V to ground. An intermediate voltage source typically at 11V is introduced for reducing the gated breakdown voltage requirement to approximately 10V. This reduced gated breakdown voltage requirement is easily met by special layout methods applied to various transistors in the circuit. The basic layout methods include the terminating of the field implant region near the N+P junction to expose the N+ diffusion over the P substrate to increase the junction breakdown and the gated diode breakdown, and the use of short channel length to reduce the threshold voltage.
19 Citations
26 Claims
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1. A high voltage output level shifter using low voltage MOS devices comprising:
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a first terminal for coupling to a first voltage source, a second terminal for coupling to a second voltage source, a third terminal for coupling to a third voltage source, a fourth terminal for coupling to a clock signal, and an output terminal, wherein said second voltage source is intermediate to said first and third voltage sources; first, second, third and fourth devices, each having a source, a drain and a gate, said second device having a channel region between said source and drain of said second device, said second device having a field implant terminating short of said source and said drain of said second device, the field implant also terminating at the edge of said channel region, said drain of said first device being coupled to said first terminal, said source of said first device and said drain of said second device being coupled together, said source of said second device and said drain of said third device being coupled to said output terminal, said source of said third device and said drain of said fourth device being coupled together, said gate of said third device being coupled to said second terminal, said source of said fourth device being coupled to said third terminal; an input circuit for providing an input signal; a charge pump coupled to said input circuit and to said gates of said first and second devices for charging said gates of said first and second devices to a threshold voltage above that provided by said first voltage source in response to said input signal; and a circuit coupled to said input circuit and to said gates of said third and fourth devices for switching said third and fourth devices off in response to said input signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. In a circuit having a plurality of series devices, a method of distributing a voltage among a plurality of devices, the method comprising the steps of:
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(a) providing a first terminal for coupling to a first voltage source, a second terminal for coupling to a second voltage source, a third terminal for coupling to a third voltage source, a fourth terminal for coupling to a clock signal, and an output terminal, wherein said second voltage source is intermediate to said first and third voltage sources; (b) providing first, second, third and fourth devices, each having a source, a drain and a gate, said second device having a channel region between said source and drain of said second device, said second device having a field implant terminating short of said source and said drain of said second device, the field implant also terminating at the edge of said channel region, said drain of said first device being coupled to said first terminal, said source of said first device and said drain of said second device being coupled together, said source of said second device and said drain of said third device being coupled to said output terminal, said source of said third device and said drain of said fourth device being coupled together, said gate of said third device being coupled to said second terminal, said source of said fourth device being coupled to said third terminal; (c) providing an input circuit for providing an input signal; (d) providing a charge pump coupled to said input circuit and to said gates of said first and second devices for charging said gates of said first and second devices to a threshold voltage above that provided by said first voltage source in response to an input signal; and (e) providing a circuit coupled to said input circuit and to said gates of said third and fourth devices for switching said third and fourth devices off in response to said input signal. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification