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Analog Multiplexer Testing Methodology

IP.com Disclosure Number: IPCOM000100815D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 115K

Publishing Venue

IBM

Related People

Kist, TA: AUTHOR [+2]

Abstract

Disclosed is a process for checking analog multiplexers to be done continually throughout the life of an application.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Analog Multiplexer Testing Methodology

       Disclosed is a process for checking analog multiplexers
to be done continually throughout the life of an application.

      The following methodology was used to test analog multiplexers
in a multi-channel data acquisition system. The test uses specially
designed hardware features combined with real-time code to test the
address and enable lines to the multiplexers for stuck faults, and to
test the multiplexers' switches for stuck-open and stuck-closed
faults.

      The address and enable faults stuck-closed switches are caught
using the following simple procedure:
1.   The multiplexers are configured as in Fig. 1.  Each mux
dedicates two of its signal inputs to test voltages TV1 and TV2.
These test inputs are located at addresses such that each bit in the
address of TV1 is of the opposite polarity of its corresponding bit
in TV2 (i.e., x'O' and x'F').  TV1 and TV2 must be distinct, known
voltages.
2.   The test points are enabled one at a time, and the output
voltage is verified.  An error during this step indicates a bad
address or enable line, or a bad test voltage or stuck-closed switch.
3.   TV1 and TV2 are enabled simultaneously from two different
multiplexers, and the output voltage is verified as (TV1 and TV2)/2.
This verifies that the resistors R are nearly equal, that the mux
resistance is not excessive, and that the address and enable lines
for the two multiplexers are independent.

      Detecting open switches is a more complex procedure, in which
four cases have been identified.

      Case A The signal inputs to the multiplexers are driven to a
given voltage by an operational amplifier (op amp) or other active
device.  This is shown in Fig. 1.

      The following procedure is used to detect stuck-open switches:
1.   The signal input being tested is enabled along with TV1 from a
different mux.
2.   The output voltage is checked.
      a.   If the voltage does not equal TV1, the switch is NOT stuck
open and the test has been passed.
      b.   If the voltage equals TV1, then the test continues with
step 3.
3.   TV1 is disabled, and TV2 is enabled.  The signal input is still
enabled.
4.   The output voltage is checked.
      a.   If the voltage does not equal TV2, the switch is NOT stuck
open and the test has been passed.
      b.   If the output voltage equals TV2, then either the switch
is stuck open or there is some other problem with the signal input.
Either way, an error condition must be flagged.

      Case B The signal inputs to the multiplexers may be floating,
but at least a capacitor is...