TEST & MEASUREMENT Emulating signal loss and equalisation


Guido Schulze, Johannes Ganzert and Francisco Javier Garcia Gomez, all Rohde & Schwarz


W


hen developing designs with data interfaces such as USB 3.2, PCI Express  both the transmitter and receiver sides. The R&SRTP164B 16 GHz oscilloscope provides a range of new possibilities; for example, adding signal loss caused by signal channels  signal at the receiver.


Signal loss from transmission lines The design of the transmission channel is a major challenge when developing applications with fast data interfaces. In addition to correct dimensioning of transmission bandwidth, the control of the impedance, especially at the transitions, is also crucial as is protection against crosstalk from other signals.


The problems and limitations of the transmission channel appear as signal distortion, known as intersymbol interference. Parts of neighbouring signal symbols overlap due to the attenuation of   caused by impedance mismatches can also cause signal symbols to overlap. In the worst case, signal distortion leads to errors in


Transmitter TX FFE


 CTLE


Fig. 1: Example of signal transmission loss: The eye pattern at the receiver is closed, but equalisation 


the receiver, which can no longer distinguish data symbols correctly. Figure 1 shows an example of this signal distortion. The eye pattern at the transmitter output is wide open but completely closed at the receiver.


 improved signals


 and receiver sides can reduce signal loss with fast data interfaces and even recover


Receiver  FFE  DFE 


signal symbol information because they  losses in the transmission channel.       even further. The table below outlines the  


 ergy at symbol boundaries


Inverts the low-pass char- acteristic of the transmission channel


Overlays various delayed and weighted signal copies


Operates at the symbol rate More taps possible than TX FFE


+ Compensates for simple low- pass behaviour


+ Compensates for simple low- pass behaviour


  38 MARCH 2025 | ELECTRONICS FOR ENGINEERS


+ Reduces impedance discontinuities


- Can amplify noise


Non-linear, with feedback loop


Operates at the symbol rate  covery


Often combined with CTLE/FFE


+ Best compensation for  response


+ Can suppress noise


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