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PDF AN203 Data sheet ( Hoja de datos )
| Número de pieza | AN203 | |
| Descripción | Test fixtures for high speed logic | |
| Fabricantes | Philips | |
| Logotipo |  |
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INTEGRATED CIRCUITS
AN203
Test fixtures for high speed logic
1998 Apr 02
Philips
Semiconductors
Free Datasheet http://www.datasheet4u.net/
1 page  
Philips Semiconductors
Test fixtures for high speed logic
Application note
AN203
The recommended values of capacitors are: 100pF, 0.01µF, 0.1µF.
and 10µF. We have found at times, the need to adjust these values
depending upon the product type and its performance. Some noise
sensitive circuits need more bypassing in the lower and extreme
higher values of capacitance. And third, the connection of the two
planes eliminates possible ground loops and the feed-throughs
create a ground mesh and give an excellent ground plane for the
circuit. Figure 4 illustrates the bypass connections.
ÎÎÎÎÎÎÎÎÎÎVCCPÎÎÎÎÎIN ÌÎÎÎÎÎÏÏÏÌÎÎÎÎÎÌÏÏÏÎÎÎÎÎSOLDÏÏÏÎÎÎÎÎERGAÏÏÏÎÎÎÎÎNRDDOUUCTNOÏÏÏÎÎÎÎÎVDPCPPCELPÏÏÏÎÎÎÎÎARLNAWENISREÏÏÏÎÎÎÎÎE ÏÏÏÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎGPIRNÎÎÎÎÎOUNÎÎÎÎÎD
BYPASS
CAPACITORS
SOLDER AND
COPPER WIRE
SF01268
Figure 4. Decoupling Connections
BYPASS AND DECOUPLING
It is important to understand the difference between decoupling, as
with the ferrite core, and bypassing, as with capacitors. Decoupling
occurs as High-frequency signals are removed by saturation of the
ferrite core. This prevents “noise” that may be on the VCC power
supply from getting on the VCC plane. The action of the bypassing
capacitors is to: 1) “pass” any non-DC signals that occur on the VCC
(due to the part’s operation) to ground, and 2) be able to provide the
“instantaneous” current demands of the part as it switches.
The various values of capacitors are intended to provide a
Low-impedance path at all operating frequencies. Since real-world
capacitors have resonance points at a given frequency, depending
upon their value and type of capacitor (and actually turn inductive
above the resonance point), using different values that have
different resonance points allows an across-frequency
Low-impedance path for VCC noise.
An important point in the use of bypass capacitors is the
minimization of lead length. Lead length represents inductance;
inductance in series with the capacitance. If it is too much, it can
cause resonance and oscillation problems with the part and/or
power supplies and nullify the benefit of the capacitors. It also plays
a major part in inhibiting the effect of the “instantaneous” current
response needed by the part from the bypass capacitors. It actually
can cause the ground of the device to track the change in current to
the degree of the lead inductance. The lower the inductance, the
lower the “ground bounce” effect. Hence, short or no lead lengths on
capacitors are needed to help prevent the effects of ground bounce.
SIGNAL LINES
A signal line is defined as a line that carries the input stimulus, either
DC or AC, or output response, to or from the device. Since these
signals are measured and determine the data which characterizes
the part, it is critical that they are of the highest integrity and
represent, as far as physically possible, the action of the part; not
the nuances of the fixture. To achieve this, the line must not be able
to change the signal over the measurable frequencies of the device,
nor affect the delay of the part.
The fixture as designed, has 50Ω signal lines determined by a
stripline layout method. The 50Ω value was selected for several
reasons:
1. The 50Ω value matches impedance with the pulse generators
that are used as input stimulus.
2. The output loads specified for this fixture are either a 500Ω
pull-down or a 50Ω pull-down (ECL), in parallel with a capacitive
load. This allows the 50Ω signal line to be terminated into this
load for either a 10:1 or a 1:1 match.
3. A Low-impedance line will have better characteristics with
regards to cross-talk and resisting external noise.
There are two types of signal lines on this fixture: input and output;
both of which are 50Ω transmission lines. The input line is on the top
side of the board and is always terminated in 50Ω. It is connected to
the DUT via a 0.3″ jumper, Jumper #1 for input. When this jumper is
installed, the DUT pin is available only as an input. To allow this line
to be used as an output, a 0.1″ jumper, Jumper #1 for output, is
used instead of the 0.3″ jumper. This connects the DUT pin to the
AC load when the DUP pin is an output. See Figure 6.
The output signal line can be dedicated two different ways. The first
method, used for ECL, is to leave shorted the 50Ω trace and have it
run directly into the SMB connector into the 50Ω sampling system.
The second method is to cut the trace at the DUT pin and solder the
450Ω chip resistor, R1, across the cut. This, combined with the 50Ω
scope, then appears to the part as either a 500Ω probe for the input
signal or the 500Ω output AC load for the output signal.
The signal lines are equal length and therefore do not introduce any
extraneous delay from pin to pin. We also characterized the
impedance of the lines over frequency to ensure minimal distortion
over the frequency range and any effective change in propagation
delay caused by the relationship of inductance and group delay, see
Application Note AN202. Figure 5 illustrates the frequency response
of the signal lines in impedance.
This is considered to be high bandwidth and encompasses the
frequency range exhibited by ALS, ACL, ECL, and FAST logic
families.
70
60
50
40
Ω
30
20
10
0
0 100 200 300 400 500 600 700 800 900
MHz
SF01345
Figure 5. Signal Line Frequency Response
1998 Apr 02
5
Free Datasheet http://www.datasheet4u.net/
5 Page 
Philips Semiconductors
Test fixtures for high speed logic
NOTES
Application note
AN203
1998 Apr 02
11
Free Datasheet http://www.datasheet4u.net/
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AN203.PDF ] | |
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