Noise and dielectric absorption compensation circuit

摘要

The following specification discloses a current noise and dielectric absorption kickback compensation circuit for a force line and a sense line that are to be initially compensated with regard to unwanted currents therein. The lines are placed in a shielded cable and mutually receive the same external noise signals. The unwanted currents are incurred in the force line and the sense line which is connected to a device under test, such as an integrated circuit, that is to have a particular voltage forced thereon and a determination made or sensed as to the current drain thereof. The force and sense lines can be initially connected to a tester which is controlled by a computer. The lines lead to the device under test through various lines interconnected by relay matrices which provide a number of different functions for testing the device under test, such as timed events, voltages, and external active or passive elements used cooperatively with the device under test and the other pins thereof. The invention compensates for spurious signals which are mutually incurred on the force and sense lines through dielectric absorption kickback and noise generated thereon, such as sixty cycle ambient noise. The compensation is effectuated by the sense line being clear of any driven signals thereon. This allows the provision of any spurious currents thereon to an amplifier having a zero reference point. The foregoing amplifier of the sense line has its output connected to an inverted reference of the input of a force line amplifier. This places the spurious respective currents on the force and sense lines in diametrically opposed equal values for purposes of providing a null on the two respective lines, inasmuch as they both receive the same approximate dielectric and noise factors. The nulling effect compensates for noise, and dielectric absorption kickback that is caused by the switching matrices and the ambient noise, so that a true current reading on the force line can take place as to any current thereon that relates to the device under test.