coupling from one channel to the other one within a cable. To minimize crosstalk, both the location of pins and the attribution of signals to the pin layout are critical. 5. VECTOR NETWORK ANALYZER (VNA) Data protocols provide the normative values of data transmission parameters (insertion loss, return loss, crosstalk, noise) to ensure the compatibility of the various components of a system – transmitter, receiver, cable, connector – so that they can function together appropriately. Typical protocols include Ethernet, USB, SDI, DP, and HDMI. Once a design has been optimized for a defined protocol, a physical connector- cable assembly prototype needs to be tested to validate the full characterization using a Vector Network Analyzer (VNA). This measures the wave parameters of the reflection and transmission at electrical connections of components as a function of frequency, the so-called scattering parameters, or S-parameters. Typical devices to be tested do not have coaxial interfaces, which are necessary to perform the measurement, so test fixtures often need to be inserted between an instrument’s coaxial interface and the device under test (DUT), such as a PCB, package, connector, or cable. To connect the cable-connector assembly to the VNA device, one needs to design a high-speed precision PCB based on the required bandwidth.
The differences between a connector without and with a design optimized for impedance matching.
4. CROSSTALK It is important to ascertain whether, and to what intensity, waves running in parallel channels interact with each other and cause interferences (crosstalk). One of the parameters for cable- connector assembly to achieve the usual bit error rate (BER) of 1e-12 tolerated in the physical layer, is the level of NEXT and FEXT crosstalk, i.e., the field
Comparison of two crosstalks with different ways of attributing signals in the same connector.
Examples of PCB fixtures for VNA measurement.
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