How to choose micro-coaxial connectors?

7 月 10, 2023 CONNECTOR

Have you ever been confused about how to choose the right micro-coaxial connector for high-speed transmission?

— There are many factors that can make selecting a connector challenging. To help you make a more informed decision, this article provides some examples of how you should choose the most suitable connector for your current application.

Have you ever encountered the following question, “I want to choose a micro-coaxial connector, but how do I make the decision?”

The decision you make will have a significant impact since connectors are vital electronic components that directly affect the performance of your equipment. Choosing the wrong connector may result in the inability to achieve the desired performance.

Is there a recommended method for selecting micro-coaxial connectors? If you follow the steps below, the selection process can be relatively smooth.

1.Specify the Transmission Standard.

Different devices and components adhere to different transmission standards. Before selecting a connector, determine the signal you need to transmit. The transmission speed is determined by the transmission standard. Here’s an example of how to choose a connector for the USB4 standard:

2.EMC (Electromagnetic Compatibility) Mitigation Measures.

What is Electromagnetic Compatibility (EMC)?

When a signal is transmitted, it emits noise to the surrounding environment (Electromagnetic Interference or EMI) while being influenced by noise from the surrounding environment (Electromagnetic Susceptibility or EMS). This noise generated by the signal can have adverse effects on the performance of peripheral devices. Similarly, the transmission of the signal can be negatively impacted when environmental noise interferes with it.

Our ZenShield® technology helps prevent environmental noise from affecting the signal within the connector and prevents the noise generated by the signal from affecting external components. This shielding technology allows for greater freedom in placing other electronic components and facilitates high-density installations, which is a trend in circuit board assembly.

If you’re facing noise-related challenges, here is an example of EMC shielding (ZenShield®) solution.

3.The required number of pins.

The next step is to determine the necessary pin count for your application. Choosing a larger pin count requires a larger connector, which takes up more space on the PCB. This also increases the cost. Here is an example of how to choose a 40-pin connector:

4.Connector size description.

The connector size is expressed in terms of height, pitch direction, and depth direction. Among them, the most common limitations are height and pitch size.

Why is the maximum mating height of a connector important?

The receptacle of a micro-coaxial connector is mounted on a PCB and then mated with a mating cable assembly. If the mating height is too high, it may interfere with the device casing, preventing the casing from being installed as intended.

Here is an example of how to choose a connector with a maximum height of 1.2 mm.

What is pitch?

Pitch refers to the distance from the center of one terminal pin to the center of the next terminal pin.

Why is pitch important?

For micro-coaxial connectors, the pitch determines the maximum outer diameter of the cable that can be used. It limits the available space between the pins.

Example 1: A 10-pin connector with a 0.5 mm pitch, compatible with a maximum cable outer diameter of 0.5 mm.

Example 2: A 10-pin connector with a 0.4 mm pitch, compatible with a maximum cable outer diameter of 0.4 mm.

The larger the cable diameter, the lower the loss, resulting in better transmission performance.

However, a larger cable diameter also takes up more space, resulting in thicker wire bundles.

Here is an example of how to choose a connector with a 0.4 mm pitch:

5.Deciding on the cable size

What is AWG (American Wire Gauge)?

As shown in the diagram below, AWG is a numerical representation of the center conductor diameter. The higher the AWG number, the smaller the diameter.

Imagine water flowing through a pipe. The wider the pipe, the more water can flow through it. The same principle applies to cables. The larger the diameter of the center conductor, the more current can flow through it.

The traditional belief is that you should always use thicker cables. However, as mentioned earlier, the cable size used with the connector is also limited by the connector spacing.

What is cable impedance?

In the cable size table above, the cable’s outer diameter varies based on impedance.

If we once again compare signal transmission to water flow through a pipe, smooth flow of water is disrupted at points where the pipe diameter suddenly changes.

Similarly, if the signal travels through an impedance mismatched path, reflections occur due to these disturbances. Impedance matching between the circuit board, connector, and cable is necessary for transmitting signals with minimal reflections.

If there is a mismatch in characteristic impedance (as shown in the diagram below), transmission losses occur.

When there is a match in characteristic impedance (as shown in the diagram below), transmission losses can be reduced.

For many common applications, the characteristic impedance of the signal transmission path is specified as 50 Ω. However, it may vary as impedance is determined by each respective transmission standard organization. For example, USB4 specifies a characteristic impedance of 42.5 Ω.

To minimize losses during high-speed transmission, it is crucial to select a cable that closely matches the desired characteristic impedance for the application. Here is an example of how to choose a #40 AWG ultra-fine coaxial cable:

You can also choose the size of the discrete cable.

6.Confirm the insertion and removal direction
The placement of the connector on the PCB, PCB dimensions, and other factors may vary depending on the customer and application. As a result, the required orientation of the connector can also differ.
Here is an example of how to choose a horizontal mating connector:

Therefore, you can search for CABLINE by executing steps (1) to (7) ®- CA II.

Have you selected the appropriate connector in the following order?

I-PEX is an expert in high-speed transmission connectors, and we design various types of connectors based on customer use cases to achieve optimal transmission performance.

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