1. In PCB design, if the emulator and the PCB board are powered by separate power supplies, should the grounds of the two supplies be interconnected?

If it is possible to use separate power supplies, that is usually preferable, as it minimizes the risk of interference between them. However, many devices come with specific requirements. Given that both the emulator and the PCB board operate on different power supplies, I believe their grounds should not be connected.

2. How can one verify that the PCB meets design process requirements before it leaves the factory?

Many PCB manufacturers perform a power-on network continuity test before completing the PCB processing to ensure that all connections are accurate. Additionally, an increasing number of manufacturers are employing X-ray testing to identify potential issues that may arise during etching or lamination.

For finished boards following patch processing, ICT testing is typically utilized, necessitating the addition of ICT test points during PCB design. If problems are detected, specialized X-ray inspection equipment can also be used to determine whether the manufacturing process has caused the fault.

3. On a 12-layer PCB, there are three power layers: 2.2V, 3.3V, and 5V. How should the ground wire be handled when all three power supplies are on one layer?

Typically, it is advisable to allocate the three power supplies to the third layer, as this configuration improves signal quality. This arrangement minimizes the likelihood of signal splitting across plane layers. Cross-segmentation significantly impacts signal quality, and simulation software usually overlooks this factor.

When considering power and ground layers, one must treat them as high-frequency signals. In practice, aside from signal quality, factors such as power plane coupling (which involves using adjacent ground planes to lower the AC impedance of the power plane) and stacking symmetry should also be taken into account.

4. What strategies can be implemented to avoid crosstalk in PCB design?

A changed signal (such as a step signal) propagates along the transmission line from A to B. A coupled signal will be generated on the transmission line CD. Once the changed signal concludes, meaning when the signal returns to a stable DC level, the coupled signal will cease to exist. Therefore, crosstalk occurs only during signal transitions; the faster the edge of the signal changes (conversion rate), the greater the amount of crosstalk generated. The electromagnetic field coupled in space can be conceptualized as a collection of numerous coupling capacitors and coupling inductances. The crosstalk signal produced by the coupling capacitor can be categorized into forward crosstalk and reverse crosstalk Sc on the victim network. Both signals share the same polarity. The crosstalk signal generated by the inductance is similarly divided into forward crosstalk and reverse crosstalk SL, but these signals have opposite polarities. The forward and reverse crosstalk generated by the coupled inductance and capacitance occur simultaneously and are nearly equal in magnitude. Consequently, the forward crosstalk signals on the victim network cancel each other out due to their opposing polarities, while the reverse crosstalk signals, having the same polarity, reinforce each other.

The modes of crosstalk analysis typically include default mode, tri-state mode, and worst-case mode analysis. The default mode resembles actual crosstalk testing, where the offending network driver is driven by a flip signal, and the victim network driver remains in its initial state (high or low). The crosstalk value is then calculated. This method is particularly effective for unidirectional signal crosstalk analysis. The tri-state mode involves driving the offending network with a flip signal while placing the tri-state terminal of the victim network in a high-impedance state to measure crosstalk. This approach is more suitable for bidirectional or complex topology networks. Worst-case analysis maintains the victim network driver in its initial state while the simulator calculates the cumulative crosstalk from all default infringing networks to each victim network. This method generally focuses on analyzing key networks due to the overwhelming number of combinations involved, which can slow down simulation speed.

5. Is “the protection of the organization” equivalent to protecting the case?

Yes. The cabinet should be as tightly sealed as possible, minimizing the use of conductive materials and maximizing grounding.

6. When a circuit consists of several PCB boards, should they share the same ground?

In a circuit composed of multiple PCBs, a common ground is typically required, as it is impractical to use several power supplies for one circuit. However, if specific conditions permit, different power supplies can be used, although this may result in reduced interference.

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