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Test Bias Reference Generator

IP.com Disclosure Number: IPCOM000099440D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 4 page(s) / 94K

Publishing Venue

IBM

Related People

Barish, AE: AUTHOR [+3]

Abstract

Circuitry has been proposed which addresses the need for a precise current source setting reference which may be used to check for stuck- at-threshold faults in semiconductor devices. The proposed circuit provides a tightly controlled up level which, with its tight tolerance, insures good control over the test current being set. Its low level is such that it can completely turn off the test current, thereby not affecting output levels of the switch while minimizing power dissipation.

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Test Bias Reference Generator

       Circuitry has been proposed which addresses the need for a
precise current source setting reference which may be used to check
for stuck- at-threshold faults in semiconductor devices.  The
proposed circuit provides a tightly controlled up level which, with
its tight tolerance, insures good control over the test current being
set.  Its low level is such that it can completely turn off the test
current, thereby not affecting output levels of the switch while
minimizing power dissipation.

      The proposal is a support circuit for the differential current
switch logic (DCS) on a masterslice which controls a critical test
bias current source located in each DCS circuit.  This is used for
testing the DCS logic during manufacturing and for system diagnostics
in the field. During normal DCS logic operation both the proposed
reference generator and the bias current sources are OFF.

      A typical DCS circuit is shown in Fig. 1 with a "test left" and
"test right" bias current source as indicated. Voltages TL and TR are
outputs of two separate test bias generators.  Q and - are always
complementary and are referenced to each other to form one logic
signal, as indicated in Fig. 2A.  The circuit threshold will occur
when Q = - .

      During fabrication of DCS circuits, faults may occur which
create the unpredictable stuck-at-threshold condition, as indicated
in Fig.  2B.  In order to accurately catch these faults, either the
test left or test right bias current source is turned on to offset
the two signals so that the stuck-at-threshold is changed to "stuck
1" or "stuck / ".  The effect of the bias on a good circuit signal
is indicated in Fig.  2A, while the result on a faulty signal is
shown in Fig. 2B.

     ...