Patent ID: 7952359

Claim:
A test apparatus which transmits/receives a differential signal to/from a device under test in a bidirectional manner via a differential transmission line so as to test the device under test, including: first and second input/output terminals connected to the differential transmission line; a first resistor provided between the first input/output terminal and a fixed-voltage terminal; a second resistor provided between the second input/output terminal and the fixed-voltage terminal; a first current source which generates a predetermined first tail current; a first current-switching switch which receives pattern data to be transmitted to the device under test, selects either the first input/output terminal side or the second input/output terminal side according to the value of the pattern data thus received, and couples the input/output terminal thus selected with the first current source; a third resistor with the first terminal thereof connected to the second input/output terminal; a fourth resistor with the first terminal thereof connected to the first input/output terminal; a second current source which generates a predetermined second tail current; a second current-switching switch which receives the pattern data, selects either the first input/output terminal side or the second input/output terminal side according to the value of the pattern data thus received, and couples the input/output terminal thus selected with the second current source; a level shift circuit which shifts the electric potential at the second terminal of the third resistor and the electric potential at the second terminal of the fourth resistor by a predetermined level; and a comparator circuit which compares the electric potential at the second terminal of the third resistor, which has been level-shifted by the level shift circuit, with the electric potential at the second terminal of the fourth resistor, generates a first comparison signal according to the comparison result, compares the electric potential at the second terminal of the fourth resistor, which has been level-shifted by the level shift circuit, with the electric potential at the second terminal of the third resistor, and generates a second comparison signal according to the comparison result.