Datasheet

AD8150
Rev. A | Page 30 of 44
EVALUATION BOARD
An evaluation board has been designed and is available to
rapidly test the main features of the AD8150. This board lets the
user analyze the analog performance of the AD8150 channels
and easily control the configuration of the board by a standard PC.
Differential inputs and outputs provide the interface for all
channels with the connections made by a 50 Ω SMB-type
connector. This type of connector was chosen for its rapid
mating and unmating action. The use of SMB-type connectors
minimizes the size and minimizes the effort of rearranging
interconnects that would be required if using SMA-type
connectors.
CONFIGURATION PROGRAMMING
The board is configurable by one of two methods. For ease of
use, custom software is provided that controls the AD8150
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 AD8150
evaluation board. The programming with this scheme is done
in a serial fashion, so it is not the fastest way to configure the
AD8150 matrix. However, the user interface makes it very
convenient to use this programming method.
If a high speed programming interface is desired, the AD8150
address and data buses are directly available on P3. The source
of the program signals can be a piece of test equipment, such as
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
locations for termination resistors for the address and data
signals if these are necessary.
POWER SUPPLIES
The AD8150 is designed to work with standard ECL logic
levels. This means that V
CC
is at ground and V
EE
is at a negative
supply. The shells of the I/O SMB connectors are at V
CC
potential. Thus, when operating in the standard ECL
configuration, test equipment can be directly connected to the
board, because the test equipment will also have its connector
shells at ground potential.
Operating in PECL mode requires V
CC
to be at a positive
voltage while V
EE
is at ground. Since this would make the shells
of the I/O connectors at a positive voltage, it can cause problems
when directly connecting to test equipment. Some equipment,
such as battery operated oscilloscopes, can be floated from
ground, but care should be taken with line-powered equipment
so that a dangerous situation is not created. Refer to the test
equipment’s manual.
The voltage difference from V
CC
to V
EE
can range from 3 V to 5 V.
Power savings can be realized by operating at a lower voltage
without any compromise in performance.
A separate connection is provided for V
TT
, the termination
potential of the outputs. This can be at a voltage as high as V
CC
,
but power savings can be realized if V
TT
is at a voltage that is
somewhat lower. Please consult elsewhere in the data sheet for
the specification for the limits of the V
TT
supply.
As a practical matter, current on the evaluation board will flow
from the V
TT
supply through the termination resistors and then
through the AD8150 from its outputs to the V
EE
supply. When
running in ECL mode, V
TT
will want to be at a negative supply.
Most power supplies will not allow their ground to connect to
V
CC
and will not allow their negative supply to connect to V
TT
.
This will require them to source current from their negative
supply, which will not return to the ground terminal. Thus, V
TT
should be referenced to V
EE
when running in ECL mode, or a
true bipolar supply should be used.
The digital supply is provided to the AD8150 by the V
DD
and
V
SS
pins. V
SS
should always be at ground potential to make it
compatible with standard CMOS or TTL logic. V
DD
can range
from 3 V to 5 V and should be matched to the supply voltage of
the logic used to control the AD8150. However, since PCs use 5 V
logic on their parallel port, V
DD
should be at 5 V when using a
PC to program the AD8150.
SOFTWARE INSTALLATION
The software to operate the AD8150 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 to
change to Disk 2. The setup program will also prompt the user
to select the directory location to store 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. However, 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
AD8150. All of the outputs should be in the output off state
immediately 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.