National Semiconductor Corporation

David R MacQuigg

Mark J Mercer

An apparatus and method for performing curvature trim in a voltage reference circuit that allows a curvature error to be trimmed after the circuit has been packaged. The curvature trim may be performed by switching in segments of one or more non-linear resistors, such as n-type lightly doped drain (LDD) diffused resistors, having a curvature characteristic that is opposite to the normal band-gap curvature. Specifically, a network of non-linear resistors may be selected via selection bits stored in a non-volatile memory. Since various combinations of the resistors may be selected by programming the memory, the curvature of a band-gap reference can be adjusted after final packaging. This curvature correction method achieves a reliable and accurate correction for the curvature variations associated with various process changes.

CMOS voltage reference with post-assembly curvature trim

A CMOS voltage reference comprises a band-gap core, a primary amplifier and a &ldquo;nulling&rdquo; amplifier. The voltage reference may also include slope, level and curvature trim circuits to provide a low-cost CMOS voltage reference that can be trimmed after final packaging. Due to the nulling of the errors from other sources by the nulling amplifier, the trim circuits are able to adjust the variations from the band-gap core. The nulling amplifier uses switching techniques to provide an accurate null, but is configured to avoid injecting switch transients into the voltage reference output.

CMOS voltage reference with a nulling amplifier

A low noise buffer circuit for increasing the slew rates of transitions between signal states of a digital signal while drawing minimal transient power supply current during such signal state transitions. Successive alternating digital signal inversion circuits conduct respective power supply source and sink currents which: are unregulated source currents and regulated sink currents during respective low-to-high output signal transitions; transition from unregulated source currents and regulated sink currents to regulated source currents and unregulated sink currents, respectively, during respective high output signal states; are regulated source currents and unregulated sink currents during respective high-to-low output signal transitions; and transition from regulated source currents and unregulated sink currents to unregulated source currents and regulated sink currents, respectively, during respective low output signal states.

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Tuscon, AZ, United States of America

David R MacQuigg