Parametric tester for semiconductor devices

Claim 1

A tester for conducting parametric tests on a semiconductor device having a plurality of electrical leads, said tester comprising: a. a constant current source means having an output terminal electrically coupled to a particular lead of the semiconductor device under test, and being disposed for supplying a constant current to the lead; b. voltage maintenance means having a first input terminal coupled to a reference voltage source, a second feedback input terminal coupled to the particular lead of the device under test, and an output terminal electrically coupled to the particular lead of the device under test for maintaining the lead at a specified voltage; and, c. a current direction-sensing means electrically coupled between said voltage maintenance means and the particular lead of the device under test to detect the direction of current flow between said voltage maintenance means and the particular lead to thereby determine whether the lead draws more or less current than current supplied by said constant current source; said current direction-sensing means comprising: i. a bidirectional load electrically coupled between the particular lead and said voltage maintenance means; ii. a voltage comparator whose inputs are electrically coupled to respective ones of the terminals of said bidirectional load; and iii. an error detector electrically coupled to the output of said voltage comparator to determine whether said output of said voltage comparator signifies that said lead draws more or less current than said constant current.