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DM74ALS14
Switching Characteristics over recommended operating free air temperature range
ALS Noise Characteristics
The setup of a noise characteristics measurement is critical
to the accuracy and repeatability of the tests. The following
is a brief description of the setup used to measure the
noise characteristics of ALS.
Equipment:
Word Generator
Printed Circuit Board Test Fixture Dual Trace Oscillo-
scope
Procedure:
1. Verify Test Fixture Loading: Standard Load 50 pF,
500Ω.
2. Deskew the word generator so that no two channels
have greater than 150 ps skew between them. This
requires that the oscilloscope be deskewed first. Swap
out the channels that have more than 150 ps of skew
until all channels being used are within 150 ps. It is
important to deskew the word generator channels
before testing. This will ensure that the outputs switch
simultaneously.
3. Terminate all inputs and outputs to ensure proper load-
ing of the outputs and that the input levels are at the
correct voltage.
4. Set V
CC
to 5.0V.
5. Set the word generator to toggle all but one output at a
frequency of 1 MHz. Greater frequencies will increase
DUT heating and affect the results of the measure-
ment.
6. Set the word generator input levels at 0V LOW and 3V
HIGH. Verify levels with a digital volt meter.
V
OLP
/V
OLV
and V
OHP
/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 volt-
ages using a 50Ω coaxial cable plugged into a standard
SMB type connector on the test fixture. Do not use an
active FET probe.
• Verify that the GND reference recorded on the oscillo-
scope has not drifted to ensure the accuracy and repeat-
ability of the measurements.
V
ILD
and V
IHD
:
• Monitor one of the switching outputs using a 50Ω 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, V
IL
, until the
output begins to oscillate. Oscillation is defined as noise
on the output LOW level that exceeds V
IL
limits, or on
output HIGH levels that exceed V
IH
limits. The input
LOW voltage level at which oscillation occurs is defined
as V
ILD
.
• Next decrease the input HIGH voltage level on the word
generator, V
IH
until the output begins to oscillate. Oscil-
lation is defined as noise on the output LOW level that
exceeds V
IL
limits, or on output HIGH levels that exceed
V
IH
limits. The input HIGH voltage level at which oscilla-
tion occurs is defined as V
IHD
.
• Verify that the GND reference recorded on the oscillo-
scope has not drifted to ensure the accuracy and repeat-
ability of the measurements.
V
OHV
and V
OHP
are measured with respect to V
OH
reference. V
OLV
and
V
OLP
are measured with respect to ground reference.
Input pulses have the following characteristics: f = 1 MHz, t
r
= 3 ns, t
f
=
3 ns, skew < 150 ps.
FIGURE 1. Quiet Output Noise Voltage Waveforms
FIGURE 2. Simultaneous Switching Test Circuit
Symbol Parameter Conditions Min Max Units
t
PLH
Propagation Delay Time LOW-to-HIGH Level Output V
CC
= 4.5V to 5.5V 2 12 ns
t
PHL
Propagation Delay Time HIGH-to-LOW Level Output R
L
= 500Ω, C
L
= 50 pF 2 10 ns
