External pull-up resistor detection and compensation of...

Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver

Reexamination Certificate

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Details

C327S108000, C327S362000, C326S058000

Reexamination Certificate

active

06259282

ABSTRACT:

BACKGROUND OF THE INVENTION
Integrated Circuit output buffers are often coupled to an off-chip pull-up resistor. This pull-up resistor will effect the performance of the output buffer, since it speeds up the low-to-high transition and slows down the high-to-low transition of signals output by the buffer. For buffers having very tight specifications on rise and fall times, or on duty cycle distortion, the performance changes caused by the pull-up resistor are problematic. The usual solution is to design a buffer that compensates for a known pull-up resistor having a defined resistance value, so that the performance distortion caused by the known pull-up resistor is reduced.
However, there are some systems, such as the ATA bus widely used in Mass Storage applications, where the value of the pull-up resistor is unknown and can vary widely. This variation in pull-up resistor value adversely affects the performance of output buffers because the output buffers are not designed to accurately account for distortions caused by a pull-up resistor having an unknown or variable resistance. The inability of known output buffers to account for pull-up resistors having an unknown value only gets worse as the speed of data transmission increases, since the percentage of distortion increases as the pulse width narrows.
Accordingly, there exists a need for an improved output buffer that accounts for pull-up resistors having an unknown or variable resistance.
SUMMARY OF THE INVENTION
This invention overcomes the problems in conventional systems by providing for a buffer circuit capable of measuring, and responding to, a parameter at a buffer output, such as the value of a pull-up resistor. The invention, in accordance with one aspect, includes an electronic circuit including a buffer and a parameter detector. The buffer receives an input signal at a buffer input, and the buffer generates a buffered signal at a buffer output. The parameter detector measures a parameter at the buffer output when the buffer is in a high impedance output state, and the parameter detector generates a buffer control signal based upon the measured parameter. The buffer responds to the buffer control signal generated by the parameter detector.
Another aspect of the invention provides for a method of calibrating a buffer. The method includes the steps of placing the buffer in a high impedance output state, measuring a parameter at the buffer output, and adjusting the buffer based upon the measured parameter. In accordance with this aspect of the invention, the parameter at the buffer output is measured while the buffer is in a high impedance output state.


REFERENCES:
patent: 5864244 (1999-01-01), Kaplinsky
patent: 5905389 (1999-05-01), Alleven

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