AD8113
When the AD8113 is optimized for video applications, all signal
inputs and outputs are terminated with 75 Ω resistors. Stripline
techniques are used to achieve a characteristic impedance on
the signal input and output lines, also of 75 Ω. Figure 20 shows
a cross-section of one of the input or output tracks along with
the arrangement of the PCB layers. It should be noted that
unused regions of the four layers are filled up with ground planes.
As a result, the input and output traces, in addition to having
controlled impedances, are well shielded.
MOLEX 0.100" CENTER
CRIMP TERMINAL HOUSING
D-SUB 25-PIN (MALE)
RESET
1
1
14
CLK
CE
UPDATE
DATA IN
DGND
6
MOLEX
TERMINAL HOUSING
D-SUB-25
SIGNAL
w = 0.008"
(0.2mm)
2
3
4
5
6
25
3
1
4
5
2
6
CE
RESET
UPDATE
25
13
DATA IN
CLK
DGND
TOP LAYER
t = 0.00135" (0.0343mm)
b = 0.0514"
(1.3mm)
a = 0.008"
(0.2mm)
SIGNAL LAYER
POWER LAYER
BOTTOM LAYER
h = 0.025"
(0.63mm)
EVALUATION BOARD
PC
Figure 21. Evaluation Board/PC Connection Cable
When you launch the crosspoint control software, you will be
asked to select the printer port you are using. Most PCs have only
one printer port, usually called LPT1. However, some laptop
computers use the PRN port.
Figure 20. Cross Section of Input and Output Traces
The board has 32 BNC type connectors: 16 inputs and 16
outputs. The connectors are arranged in a crescent around the
device. As can be seen from Figure 16, this results in all 16 input
signal traces and all 16 output traces having the same length.
This is useful in tests such as all hostile crosstalk tests, where
the phase relationship and delay between signals need to be
maintained from input to output.
Figure 22 shows the main screen of the control software in its
initial reset state (all outputs off). Using the mouse, any input
can be connected with one or more outputs by simply clicking
on the appropriate radio buttons in the 16 × 16 on-screen array.
Each time a button is clicked on, the software automatically sends
and latches the required 80-bit data stream to the evaluation
board. An output can be turned off by clicking the appropriate
button in the off column. To turn off all outputs, click on Reset.
There are separate digital (logic) and analog supplies. DVCC
should be at 5 V to be compatible with 5 V CMOS and TTL
logic. AVCC and AVEE can range from 5 V to 12 V depending
on the application.
While the computer software only supports serial programming
via a PC’s parallel port and the provided cable, the evaluation
board has a connector that can be used for parallel programming.
The SER/PAR signal should be at a logic HIGH to use parallel
programming. There is no cable or software provided with the
evaluation board for parallel programming. These are left to the
user to provide.
As a general rule, each power supply pin (or group of adjacent
power supply pins) should be locally decoupled with a 0.01 µF
capacitor. If there is a space constraint, it is more important to
decouple analog power supply pins before digital power supply
pins. A 0.1 µF capacitor, located reasonably close to the pins,
can be used to decouple a number of power supply pins. Finally
a 10 µF capacitor should be used to decouple power supplies as
they come onto the board.
The software offers volatile and nonvolatile storage of configura-
tions. For volatile storage, up to two configurations can be
stored and recalled using the Memory 1 and Memory 2 buffers.
These function in a fashion identical to the memory on a
pocket calculator. For nonvolatile storage of a configuration, the
Save Setup and Load Setup functions can be used. This stores
the configuration as a data file on disk.
Controlling the Evaluation Board from a PC
The evaluation board includes Windows® based control software
and a custom cable that connects the board’s digital interface
to the printer port of the PC. The wiring of this cable is shown in
Figure 21. The software requires Windows 3.1 or later. To install
the software, insert the disk labeled Disk #1 of 2 and run the file
called SETUP.EXE. Additional installation instructions will be
given on-screen. Before beginning installation, it is important
to terminate any other Windows applications that are running.
Overshoot on PC Printer Ports’ Data Lines
The data lines on some printer ports have excessive overshoot.
Overshoot on the pin that is used as the serial clock (Pin 6 on
the D-Sub-25 connector) can cause communication problems.
This overshoot can be eliminated by connecting a capacitor
from the CLK line on the evaluation board to ground. A pad
has been provided on the circuit side (C33) of the evaluation
board to allow this capacitor to be soldered into place. Depend-
ing upon the overshoot from the printer port, this capacitor may
need to be as large as 0.01 µF.
Audio signals are not as demanding on termination as are video
signals. Therefore, the input terminations can be removed and
changed. Likewise, the output series terminations can be shorted
or changed in value.
–26–
REV. A
ADI [ ADI ]
