Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-10-19
2001-12-18
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB
Reexamination Certificate
active
06331783
ABSTRACT:
BACKGROUND
Automatic test equipment or ATE is used to test semiconductor or other type devices at various stages of manufacture. An ATE tester generates signals, supplies the signals to a device under test or DUT, and monitors the responses to these signals to evaluate the fitness of the DUT. These signals include DC signals, and time varying signals such as AC, pulsed, or other periodic signals.
To provide these signals with precision, testers employ DC circuitry, and time varying signal circuitry sometimes referred to as pin electronics circuitry. Separate circuits are used because the circuits capable of providing and measuring precision DC signals are not capable of providing and measuring precision high frequency signals. Likewise, precision time varying signal circuits are not able to provide and measure precision DC signals. Thus, the tester must be capable of switching between these two circuits when testing a DUT.
Further, to maintain precise time varying signal characteristics, testers must be capable of performing self calibration. Self calibration includes signal level calibration as well as signal timing calibration. Thus, the tester also must provide this switching for calibration.
FIG. 1
shows a “T” switching circuit commonly used in prior art ATE testers to perform such switching. Relays typically are employed to provide switching. Relay switches facilitate precision testing by providing low closed resistance and low open capacitance. This allows accurate transmission and measurement of signal timing and signal levels over a wide bandwidth and range of signal levels. Thus, with appropriate relay switching, the “T” switching circuit is able to provide low resistance and low capacitance transmission paths between the time varying signal circuitry
10
and the DUT
30
, between the DC test/time varying signal calibration circuitry
20
and the DUT
30
, as well as between the time varying signal circuitry
10
and the DC test/time varying signal calibration circuitry
20
.
Relays, however, have a significant drawback. Relays have a relatively low mean time before failure or MTBF as compared to other tester components. One cause of the low MTBF of relays is polymer build-up on the surface of the relay contacts. Contacts are susceptible to polymer build-up when switched dry rather than under an applied current or voltage. Such polymer build-up increases contact resistance. Moreover, the resistance caused by polymer build-up varies each time the contacts are closed. This is particularly true in relays designed for high bandwidth applications. In such applications, relays having small contacts to provide lower capacitance along the high frequency transmission line also have a reduced spring force, which facilitates resistance variations in polymerized contacts. In testers designed to test devices 125 Mhz-500 Mhz or greater, relays normally having only a fraction of an ohm resistance, can develop several ohms of resistance. This results in each closure of the relay leading to a different resistance value, which affects measurement precision and, consequently, the reliability of the tester. As such, relays contribute to tester down time, slowing production and reducing product margins. To compete in semiconductor and other electronic devices markets, manufacturers require more reliable test equipment.
Solid state switches, on the other hand, generally have orders of magnitude higher MTBF. Solid state switches, however, are not capable of providing the same low resistance and capacitance as relays.
FIG. 2
illustrates a comparison of resistance verses capacitance characteristics of solid state switches and relays. Whereas the product of the closed resistance and open capacitance of a high frequency relay can be on the order of 0.07 pF-Ohms, the best commercially available solid state devices provide only about 15-40 pF-Ohms.
As such, although replacing RELAY
1
, RELAY
2
, and RELAY
3
, of
FIG. 1
with a solid state switch could improve MTBF, it also impermissibly impairs the capabilities of the tester. This is particularly true in high frequency applications, where the bandwidth of the time varying signal is limited by the capacitance of the time varying transmission channel. Furthermore, increased resistance limits precision of DC signal measurement and of time varying signal calibration.
SUMMARY
A preferred embodiment of the present invention provides a switching circuit for testing and calibration in automated test equipment having a time varying signal channel, a DC test channel, and a time varying signal level calibration channel. The time varying signal channel has a series-connected solid state switch interposed between a time varying signal circuit end and a device under test end of the time varying signal channel.
The DC test channel is connected to the time varying signal channel between the series-connected solid state switch and the device under test end. The DC test channel has at least one solid state switch interposed along the DC test channel so as to provide switchable coupling between a DC parametrics circuit side of the DC test channel and the time varying signal channel.
The time varying signal level calibration channel is connected to the time varying signal channel between the series-connected solid state switch and the time varying signal circuit end. The signal level calibration channel has at least one solid state switch interposed along the signal level calibration channel so as to provide switchable coupling between a DC parametrics circuit side of the signal level calibration channel and the time varying signal channel.
In more preferred embodiments, the DC test channel, the signal level calibration channel, or both, may have a force branch and a sense branch each having a solid state switch. In some embodiments, the time varying signal channel has a low resistance type solid state switch, while the DC test channel, the signal level calibration channel, or both, have low capacitance type solid state switches. Moreover, in some embodiments it is preferred to have optically coupled metal oxide semiconductor field effect transistor switches within some, or all, of the time varying signal channel, the DC test channel, and the signal level calibration channel.
REFERENCES:
patent: 4354268 (1982-10-01), Michel et al.
patent: 4799008 (1999-01-01), Kannari
patent: 4806852 (1989-02-01), Swan et al.
patent: 5101153 (1992-03-01), Morong, III
patent: 5389990 (1995-02-01), Nakamura
patent: 5402079 (1995-03-01), Levy
patent: 5621329 (1997-04-01), Tsao et al.
patent: 5812424 (1998-09-01), Chikyu
patent: 5821529 (1998-10-01), Chihara et al.
patent: 5917331 (1999-06-01), Persons
patent: 6133725 (2000-10-01), Bowhers
Patents Abstracts of Japan, vol. 1998, No. 02, Jan. 30, 1998 & JP 09281188A (Advantest Corp.), Oct. 31, 1997 abstract.
Aromat Corporation, “Photo MOS Relay is being used to replace reed relay”, view slide fax, Jun. 20, 1997 (best available copy).
Kreisman Lance
Nguyen Vinh P.
Teradyne, Inc.
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