Electrically alterable field effect transistor amplifier configuration

DETAILED DESCRIPTION The present invention eliminates the problem of the prior art by providing a single configuration incorporating electrically alterable elements for selecting the output buffer configuration after testing.
The output buffer is generally configured as an active pull-up amplifier having a pair of complementary field effect transistors with their source and drains connected in series between a pair of voltage supply terminals and their gates connected together.
An electrically alterable element is provided between the output of the amplifier and the drain of one of the field effect transistors.
Using a fusible element as the electrically alterable element, the buffer has an active pull-up configuration and is irreversibly electrically alterable to an open drain configuration.
Using a P-N junction element as the electrically alterable element, the buffer has an open drain configuration and is irreversibly electrically alterable to an active pull-up configuration.
Using an amorphous material element, the buffer is reversible electrically alterable between the two configurations.
The fusible element and the P-N junction device are electrically altered by grounding the output and raising the source voltage sufficiently to blow the fusible element or short the P-N element and thereby irreversibly convert the buffer configuration.
The impedance state of the amorphous material element is electrically altered by raising the source voltage to a value consistent with the threshold of the amorphous element and applying a pulsed current sink to the output.
OBJECTS OF THE INVENTION An object of the present invention is to provide a field effect transistor (FET) output amplifier having an electrically alterable element to permanently alter the configuration of the amplifier.
Another object is to reduce the product mix at the test stages by providing a singly configured FET amplifier which is electrically alterable to change configurations.
A further object of the invention is to reduce inventory requirements by providing an FET amplifier whose configuration may be determined permanently by the customer