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US 7,795,918 B2Granted
Adjusting output buffer timing based on drive strength
AssigneeTexas Instruments Incorporated
InventorJoel J. Graber
Life of this patent
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Abstract
This invention operates to select a drive code for an adjustable drive strength transistor in a drive buffer. The drive code is determined employing a scaled-down drive transistor employing varying drive codes compared with a standard. The thus determined drive code is combined with an offset to generate the drive code for the adjustable strength transistor.
Claims7
A method of setting an adjustable buffer drive strength including the steps of:
- comparing a scaled-down drive transistor having a predetermined relationship to an actual drive transistor to a standard at a plurality of drive strengths;
- selecting one drive strength upon detection of a predetermined relationship between the scaled-down drive transistor at said one drive strength and said standard;
- determining an offset drive strength to said one drive strength;
- combining said one drive strength and said offset drive strength to determine an actual drive strength for the actual drive transistor;
- and
- setting the drive strength of the actual drive transistor as said determined actual drive strength.
3 more elements
A buffer having an adjustable drive strength corresponding to a digital code comprising:
- a standard voltage generator;
- a comparison voltage generator including a resistor having a predetermined resistance and a scaled-down drive transistor having an adjustable drive strength corresponding to said digital code, said scaled-down transistor having a predetermined relationship to an actual drive transistor;
- an analog comparator comparing said standard voltage and said comparison voltage;
- a digital code source;
- a test controller operable to
- initially cause said digital code source to supply a minimal digital code to said scaled-down drive transistor causing said digital code source to select a minimal drive strength,
- cause said digital code source to supply a next sequential digital code to said scaled-down drive transistor if said analog comparator indicates a first predetermined comparison result, and
- select a current digital code to supply said actual drive transistor in said buffer if said analog comparator indicates a second predetermined comparison result opposite to said first predetermined comparison result;
- and
- an add/subtract unit having a first input receiving said selected current digital code, a second input receiving user input offset data and an output generating a sum of said selected current digital code and said user input offset data controlling the drive strength of the adjustable drive strength buffer.
7 more elements
Dependencies are inferred from the claim text.