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74ACQ244 Fiches technique(PDF) 7 Page - Fairchild Semiconductor

No de pièce 74ACQ244
Description  Quiet Series™ Octal Buffer/Line Driver with 3-STATE Outputs
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Fabricant  FAIRCHILD [Fairchild Semiconductor]
Site Internet  http://www.fairchildsemi.com
Logo FAIRCHILD - Fairchild Semiconductor

74ACQ244 Fiches technique(HTML) 7 Page - Fairchild Semiconductor

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©1989 Fairchild Semiconductor Corporation
www.fairchildsemi.com
74ACQ244, 74ACTQ244 Rev. 1.3
7
FACT Noise Characteristics
The setup of a noise characteristics measurement is crit-
ical to the accuracy and repeatability of the tests. The
following is a brief description of the setup used to mea-
sure the noise characteristics of FACT.
Equipment:
Hewlett Packard Model 8180A Word Generator
PC-163A Test Fixture
Tektronics Model 7854 Oscilloscope
Procedure:
1. Verify Test Fixture Loading: Standard Load 50pF,
500
Ω.
2. Deskew the HFS generator so that no two channels
have greater than 150ps skew between them. This
requires that the oscilloscope be deskewed first. It is
important to deskew the HFS generator channels
before testing. This will ensure that the outputs switch
simultaneously.
3. Terminate all inputs and outputs to ensure proper
loading of the outputs and that the input levels are at
the correct voltage.
4. Set the HFS generator to toggle all but one output at
a frequency of 1MHz. Greater frequencies will
increase DUT heating and effect the results of the
measurement.
5. Set the HFS generator input levels at 0V LOW and 3V
HIGH for ACT devices and 0V LOW and 5V HIGH for
AC devices. Verify levels with an oscilloscope.
Notes:
14. VOHV and VOLP are measured with respect to ground
reference.
15. Input pulses have the following characteristics:
f
= 1MHz, tr = 3ns, tf = 3ns, skew < 150ps.
Figure 1. Quiet Output Noise Voltage Waveforms
VOLP/VOLV and VOHP/V OHV:
Determine the quiet output pin that demonstrates the
greatest noise levels. The worst case pin will usually
be the furthest from the ground pin. Monitor the output
voltages using a 50
Ω coaxial cable plugged into a
standard SMB type connector on the test fixture. Do
not use an active FET probe.
Measure VOLP and VOLV on the quiet output during
the worst case active and enable transition. Measure
VOHP and VOHV on the quiet output during the worst
case active and enable transition.
Verify that the GND reference recorded on the
oscilloscope has not drifted to ensure the accuracy
and repeatability of the measurements.
VILD and VIHD:
Monitor one of the switching outputs using a 50
coaxial cable plugged into a standard SMB type
connector on the test fixture. Do not use an active
FET probe.
First increase the input LOW voltage level, VIL, until
the output begins to oscillate or steps out a min of 2ns.
Oscillation is defined as noise on the output LOW
level that exceeds VIL limits, or on output HIGH levels
that exceed VIH limits. The input LOW voltage level at
which oscillation occurs is defined as VILD.
Next decrease the input HIGH voltage level, VIH, until
the output begins to oscillate or steps out a min of 2ns.
Oscillation is defined as noise on the output LOW
level that exceeds VIL limits, or on output HIGH levels
that exceed VIH limits. The input HIGH voltage level at
which oscillation occurs is defined as VIHD.
Verify that the GND reference recorded on the
oscilloscope has not drifted to ensure the accuracy
and repeatability of the measurements.
Figure 2. Simultaneous Switching Test Circuit


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