AD8151 Datasheet, PDF (22/36 Pages) Analog Devices – 33 x 17, 3.2 Gb/s Digital Crosspoint Switch

AD8151
On this evaluation board all unused inputs are tied to V_CC (GND).
All outputs, whether brought out to connectors or not, are tied
to V_TT through a 49.9 Ω resistor. The AD8151 device is on the
component side of the board, while input terminations and output
back terminations are on the circuit side. The input signals from
the circuit side transit through via holes to the DUT’s pads. The
component-side output signals connect to via holes and to
circuit-side 49.9 Ω termination resistors.
Board Construction
For this board FR4 material was chosen over more exotic board
materials. Tests showed exotic materials to be unnecessary. This
is a 4-layer board. Power is bused on both external and internal
layers. Test structures showed microstrip performance to be
unaffected by the dc bias levels on the plane beneath it.
The manufacturing process should produce a controlled-
impedance board. The board stack consists of a 5-mil-thick
layer between external and internal layers. This allows the use of
an 8-mil-wide microstrip trace running from SMA connector to
the DUT’s pads. The narrow trace avoids the need to neck down
the trace width as DUT’s pads are approached and it helps to
control the microstrip trace impedance. The thin 5-mil dielectric
also helps to control crosstalk by way of confining the electro-
magnetic fields more between the trace and the plane below.
Configuration Programming
The board is configurable by one of two methods. For ease of
use, custom software is provided that controls the AD8151
programming via the parallel port of a PC. This requires a user-
supplied standard printer cable that has a DB-25 connector at
one end (parallel- or printer-port interface) and a Centronix-
type connector at the other that connects to P2 of the AD8151
evaluation board. The programming with this scheme is done in
a serial fashion, so it is not the fastest way to configure the AD8151
matrix. However, the user interface makes it very convenient to
use this programming method.
If a high-speed programming interface is desired, the AD8151
address and data buses are directly available on P3. The source
of the program signals can be a piece of test equipment, like the
Tektronix HFS-9000 digital test generator, or some other user-
supplied hardware that generates programming signals.
When using the PC interface, the jumper at W1 should be
installed and no connections should be made to P3. When using
the P3 interface, no jumper is installed at W1. There are loca-
tions for termination resistors for the address and data signals if
these are necessary.
Software Installation
The software to operate the AD8151 is provided on two 3.5"
floppy disks. The software is installed by inserting Disk 1 into
the floppy drive of a PC and running the “setup.exe” program.
This will routinely install the software and prompt the user
when to change to Disk 2. The setup program will also prompt
the user to select the directory for the program.
After running the software, the user will be prompted to identify
which (of three) software driver is used with the PC’s parallel
port. The default is LPT1, which is most commonly used. How-
ever, some laptops commonly use the PRN driver. It is also
possible that some systems are configured with the LPT2 driver.
If it is not known which driver is used, it is best to select LPT1
and proceed to the next screen. This will show a full array of
“buttons” that allows the connection of any input to output of
the AD8151. All of the outputs should be in the output “OFF”
state right after the program starts running. Any of the active
buttons can be selected with a mouse click, which will send out
one burst of programming data.
After this, the PC keyboard’s left or right arrow keyboard key
can be held down to generate a steady stream of programming
signals out of the parallel port. The CLOCK test point on the
AD8151 evaluation board can be monitored with an oscillo-
scope for any activity (user-supplied printer cable must be
connected). If there is a square-wave present, the proper soft-
ware driver is selected for the PC’s parallel port.
If there is no signal present, another driver should be tried by
selecting the Parallel Port menu item under the “File” pull-
down menu selection just under the title bar. Select a different
software driver and carry out the above test until signal activity
is present at the CLOCK test point.
Software Operation
Any button can be clicked in the matrix to program the input to
output connection. This will send the proper programming
sequence out the PC parallel port. Since only one input can be
programmed to a given output at one time, clicking a button in
a horizontal row will cancel the other selection that is already
selected in that row. However, any number of outputs can share
the same input.
A shortcut for programming all outputs to the same input is to
use the broadcast feature. After clicking on the Broadcast Con-
nection button, a screen will appear that will prompt for the
user to select which input should be connected to all outputs.
The user should type in an integer from 0 to 32 and then click
on OK. This will send out the proper program data and return
to the main screen with a full column of buttons selected under
the chosen input.
The Off column can be used to disable to whichever output one
chooses. To disable all outputs, the Global Reset button can be
clicked. This will select the full column of OFF buttons.
Two scratch-pad memories (Memory 1 and Memory 2) are
provided to conveniently save a particular configuration. How-
ever, these registers are erased when the program is terminated.
For long-term storage of configurations, the disk-storage memory
should be used. The Save and Load selections can be accessed
from the “File” pull-down menu under the title bar.
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