The Fast-Links project: Test Board and Test Setup
Fast Links Test Board #1
A printed circuit board, shown below, was built to evaluate the
operation of the experimental signaling chips. All testing of the
chips is done on this board; a conventional IC tester would not be useful
for working with the 4 Gb/s signals.
On the left of the test board can be seen three of the test chips,
the center area is devoted to control logic, and power supply and PC
interface circuitry is on the right.
Up to three chips can be installed on the board. One chip has its
transmitter and receiver connected by a minimum-length transmission
line; the others can be interconnected by 1, 2, or 3 meter PCB traces
or by external coaxial or twisted-pair cables. All transmitter
outputs and receiver inputs have a resistive probe brought out to SMA
connectors for connection to an oscilloscope. A 400 MHz clock from an
external signal generator is gated, buffered and distributed to all
chips with discrete
ECLinPS
logic. ECL counters and delay lines allow positioning the trigger
signal for the on-chip digital and analog samplers with 20ps
resolution 655us of delay range. Oscilloscope trigger outputs at the
400MHz clock rate and at fclk/8 are provided; the former is useful for
generating eye diagrams; the latter corresponds to the period of the
transmitter's pattern RAM. A 12-bit DAC generates a reference voltage
for the analog voltage samplers. Error indications from the reciever
on each chip are accumulated in 10 bit counters. The chips' serial
scan chains and control signals for the testboard logic are are
connected to a host computer through an optically-isolated standard PC
parallel port.
Test setup
A photograph showing the test board connected to our
Tektronix 11801A
sampling scope appears on the home page;
here's a bigger version of that
photo. We most most commonly use the scope with two inputs connected to the
differential 4 Gb/s transmitter output or receiver input of one of the
chips. The display is then set to subtract the two inputs, thus
showing a differential version of the signal of interest.
Waveforms from the oscilloscope are captured as image files; many of
these can be seen on our results page. The scopes serial port is
connected to our PC, where a program called tekdump stores
a separate screen dump file each time the 11801A's hardcopy button is
pressed. Source and
documentation for
tekdump are available.
The board is connected to the parallel port of a Pentium-Pro PC. Our
department has been buying DELL machines recently, but any PC would
have worked fine. The PC is running the
Linux operating system,
in a configuration based on the
Red Hat 4.0
distribution and customized slightly by the department's linux gurus.
Control software was written almost exclusively in the
Perl programming
language version 5.0. A very small
Perl Module loads in a bit of
C code to directly read and write the
parallel port. Programming all of the test cases in perl has been
very successful; the high-level constructs built into the language and
rapid prototyping possible due to its interpretive nature are
significant advantages to this approach.
Other external equipment used in our test setup includes an HP
8656B signal generator for providing the chip clock (400 MHz) and a
pile of power supplies.
[Fast Links home page]
[MSL home page]
Last Updated July 30, 1997 by
Steve Tell.