1、 Flow of test signal

A two channel function generator can be connected to multiple points of a device under test. A small switch subsystem will be used to distribute the output of the function generator. The input and output of the switch and instrument are connected to a common receiving panel, and then connected to an adapter for the equipment under test. Finally, the adapter is connected to the equipment under test.

There are multiple nodes on the path through which the signal passes that will damage the signal integrity. For example, an equipment under test needs an input pulse with the minimum width and the minimum rise/fall time to start a series of events. In this simple example, the pulse signal generated by the function generator first reaches the test interface through a few feet of cable, then passes through a connection node and more cables in the test instrument, and then returns to the switch on the first floor, Once again, the switch on the second layer is reached through the interface and the test instrument, and finally the device under test is reached from the switch. Basically, more than ten feet of cable, connectors, and switch contacts have become part of the function generator.

Cables, switch contacts and connectors in the signal path are not helpful for improving signal integrity, but can cause adverse effects. The impact on signals is usually not easy to calculate or predict, especially when there are multiple possible paths designed in the system. This will lead to uncertainty of signal integrity and result measurement, thus leading to uncertainty of product quality. Therefore, when a function generator works with its nominal specification, once its output needs to pass through the signal routing system in the test system, some other measures will be taken to reduce the impact.

2、 Obstacles to automated testing

In the automatic test system, several specific specifications are usually specified for the function generator, such as rise time, bandwidth, signal source impedance and amplitude accuracy. The signal routing system will affect the capacitance, channel resistance, insertion loss and reflected power, and has a great opportunity to cause impedance mismatch and signal attenuation. If the design of the routing system is not comprehensive, the signal integrity is likely to be damaged.

It is not wise to risk signal distortion. Any system design will make the transmission system transparent to the signal as far as possible without manual setting. So, what should we do in the first step of the ATE signal routing process to ensure that we have a reliable system that is reusable, maintainable, and can minimize costs for users throughout the life cycle of the project?

What challenges will interconnected systems bring to system engineers? What measures should we take to reduce the impact of interconnection systems on signal integrity. We will focus on channel resistance, signal attenuation, and insertion loss.