Why BERTs are win-win for test and space industries

Article By : Rajan Bedi

Transmitters are using pre/de-emphasis to compensate for the electrical degradations and losses caused by PCBs and cables.

As the space industry continues to exploit higher data rates, transmitters are using pre/de-emphasis to compensate for the electrical degradations and losses caused by PCBs and cables. It used to be, the faster the data rate, the shorter the distance, with speed inversely proportional to cable/trace length. Pre/de-emphasis is a signal improving technique that opens the eye at the receiver for point-to-point applications. It does not require any additional time, maintaining the efficiency of the link for data transfer, but boosts output current during transitions to speed up edges (pre-emphasis), or decreases the low-frequency components of a signal (de-emphasis). Consequently, the received waveform exhibits less ISI after its high-frequency content has been attenuated by the channel. The M8020A offers up to eight taps of pre-emphasis to provide eye-opening enhancements to overcome link losses and/or extend the reach of interconnect as shown below.

__Figure 1:__ *Transmitter pre-emphasis function overcomes channel losses.*

All high-speed digital receivers are specified to tolerate a certain amount of ISI and the M8020A provides integrated and adjustable ISI to emulate loss on all channels during receiver characterisation as shown below.

__Figure 2:__ *You can preset adjustable ISI frequency and loss points.*

For connectors other than SMA, test adaptors can be purchased to convert between the former and your preferred connector type. To provide you with further information, a Getting Started Guide can be downloaded as well as a User Guide for the instrument and system software. There is also a very helpful, short video which shows the generation, analysis, and GUI capabilities for the M8020A, and demonstrates live how the quality of the eye at the receiver can be improved using de-emphasis or degraded by adding controlled-jitter sources.

BERTs are win-win for the test and space industries: module-to-module SERDES characterisation has become quick, repeatable, highly controllable, mission independent, and can be performed early in the product development cycle to de-risk PCB layout, hardware connectors, and cables. Measurements can be controlled using scripts to automate production testing and BERTs allow you to sign-off the development of your satellite sub-systems with confidence and deliver your avionics right-first-time, to cost, and schedule. Here is a photograph of my bench:

__Figure 3:__ *An M8020A J-BERT connected to a DSAV334A Digital Signal Analyser.*

Previously: Validating SERDES links with bit-error rate testers

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