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US 5,568,081 AGranted
Variable slew control for output buffers
AssigneeCypress Semiconductor Corporation
InventorsHenry Y. Lui, Sammy S. Y. Cheung
Life of this patent
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Abstract
A variable slew control for output circuits is disclosed. The slew control circuit automatically adjusts the rate in which voltage on a slew node is driven to a reference voltage, minimizing noise at the output device driver. The variable slew control decreases the slew rate of the slew node during periods when di/dt is at a high level, but allows the voltage on the slew node to drop at faster rates during times when di/dt at the output driver is low.
Claims12
An output circuit comprising:
- a first line that receives an input signal to said output circuit;
- a second line selectable to have one of a first and second state;
- a first circuit coupled to said first line having a first slew node, said first circuit responsive to said input signal that controls a voltage on said first slew node;
- a second circuit coupled to said first line having a second slew node, said second circuit responsive to said input signal that controls a voltage on said second slew node;
- a driver circuit coupled to said first circuit and to said second circuit said driver circuit having a first transistor responsive to said voltage on said first slew node and a second transistor responsive to said voltage on said second slew node that generates an output signal;
- a first variable slew control circuit coupled to said first slew node, said first circuit, and said second line, said first variable slew control circuit increases a rate at which current at said first slew node is driven to ground when said voltage at said first slew node is below a first predetermined voltage;
- and
- a second variable slew control circuit coupled to said second slew node, said second circuit and said second line, said second variable slew control circuit decreases a rate at which current at said second slew node is driven to ground when said voltage at said second slew node approaches a second predetermined voltage.
5 more elements
Dependencies are inferred from the claim text.