ECL Differential Podlet Usage Hints

The Differential ECL/PECL podlet is useful to convert differential signals to single-ended signals for a logic analyzer or scope.

If the podlet is powered up, there is a faint green light visible through the front (where the leadset is connected). The podlet also has reverse power connection protection via a parallel reverse diode and polymer fuse (self-resetting). In systems where the power supply cannot supply more than 1.5 amps continuous current to the podlet, the reverse protection will pull the supply down.

Powering the Podlet

The ECL pod can be used for both PECL and standard ECL systems. PECL is powered from +5.0V and standard ECL is powered from -5.2V.

In a PECL system, the "V-" lead from the podlet should be connected to 0 volts (system ground). The "V+" lead from the podlet should be connected to the +5 volt power supply. The "Ground" lead from the back of the podlet should also be connected to 0 volts to provide a ground for the logic analyzer (or scope) ground reference. In PECL systems, a logic high is about 0.8 volts below the V+ lead; a logic low is about 1.8 volts below the V+ lead.

In an ECL system, the "V-" lead from the podlet should be connected to -5.2 volt supply. The "V+" lead from thee podlet should be connected to 0 volts (system ground). The "Ground" lead from the back of the podlet should also be connected to 0 volts to provide a ground for the logic analyzer (or scope) ground reference. In ECL systems, a logic high is about 0.8 volts below the V+ lead; a logic low is about 1.8 volts below the V+ lead.

As can be seen from the two examples above, as long as the "V+" lead is connected to the most positive supply, the "V-" lead is connected to the most negative supply, the "Ground" lead is connected to the system ground, and the logic analyzer (or scope) is adjusted to respond to the correct threshold level (midway between the logic high and the logic low for a given configuration), the podlet should provide a differential->single-ended conversion.

Terminating the Podlet

The podlet provides for several different types of termination method. We invite the user of the podlet to open the unit and adjust the termination method as is appropriate for their needs. The resistor type is the common 0603 package. Schematics and board layouts are available on this website for download.
Some termination possibilities are outlined below.

The podlet is shipped without any terminations installed and with a set of 100 ohm resistors appropriate for differential termination. The most common termination methon is no termination on the podlet using a short lead set. This works well in low speed (read slow risetime) systems that can tolerate some stub. However, there are many applications where this in not acceptable.

Another method is to remove the differential termination in the system under test, attach the leadset, and add the differential termination in the podlet.
The podlet also provides the user with the ability to setup individial parallel terminations on every line. This also makes it possible to setup individual channel biases for single-ended level translation.

Last updated January 30, 2001