Harmonizing Circuit Design and EMC DesignPart 7 Evaluation Circuits and Boards (1) Using Evaluation Boards

Hello! I’m Inagaki, at ROHM.

It’s 2021. I want to redouble my efforts in this column, and I hope you’ll bear with me.

This is the first article in “Evaluation Circuits and Boards”. When actually confirming the operation and performance of semiconductor integrated circuits (LSIs, ICs), evaluation boards provided by the manufacturer can be used. The product specifications and application notes will include measurement circuit diagrams, artwork (PCB layout diagrams), matters to be noted, and the like, and these should be referenced.

To use such a board or circuit, the power supplies, input signals, control signals, and so on are connected, and the output signals are observed using an oscilloscope, a spectrum analyzer, or some other instrument. The first thing is to confirm that the semiconductor integrated circuit (LSI, IC) operates as desired. When confirming logic operations, in the case of parallel control a High signal (H voltage) and a Low signal (L voltage) are applied to control pins. In the case of serial control, a separate data generator or the like is used to create and input a serial control signal. Once basic operation has been confirmed, the electrical characteristics are next checked. From confirmation of input and output signals (large signals), which are principal parameters of the product specifications, through to examination of noise levels, crosstalk (extremely small signals) etc., measurements are made as necessary.

The best values of the electrical characteristics of a semiconductor integrated circuit (LSI or IC) are exhibited when measurements are made using an evaluation board provided by the manufacturer. Moreover, the values are those stated in the product specifications. Hence to determine the characteristics of a product (set), it is sufficient to consult values measured using the evaluation board and the typical values of the product specifications. On an evaluation board, the artwork for the power supply and ground lines, as well as the input/output signal line artwork, are all ideally drawn. Thorough consideration has been devoted to the routing of the wiring and the wire widths and lengths, and so these should be considered when fabricating a product (set) board.

As a rule, only one semiconductor integrated circuit (LSI or IC) is mounted on an evaluation board, and so the electrical characteristics in a variety of cases can be measured. For example, these may be the change in characteristics when the power supply voltage is raised or lowered from the standard value (within the recommended operating voltage range), or the change in characteristics when the device is put into a temperature chamber and the ambient temperature is made high or low (when the temperature is low, care must be taken to prevent pin shorting due to frost!). In addition, multiple different evaluation boards may be connected and used in the manufacture of simple product prototypes, and so on.

What about the case of a product (set) board? Because customers are always seeking smaller, thinner, lighter, lower-cost products, the density of artwork (PCB layout diagrams) increases. In particular, power supply lines and ground lines are likely to be greatly different. It is difficult to design ideal wiring and board layout, as in evaluation boards. When there is a change from a complete ground to an incomplete ground, differences occur in the electrical characteristics, and so caution must be used. Techniques are also needed when connecting ground lines for analog systems, digital systems, power systems, and the like.

Where electromagnetic compatibility (EMC) is concerned, it is recommended that EMC be confirmed in advance in various evaluation board states. This is because, in measurements using a product (set) board, an overall determination of conformance to EMC standards can be made, but if conformance is not achieved, it is difficult to determine which semiconductor integrated circuit (LSI, IC) is the cause. By checking these characteristics in advance, it is possible to add the countermeasure components or circuits ahead of time, and so the need for re-prototyping due to EMC after fabrication

of the product (set) board is reduced. This may appear to be an inconvenient detour, but such measures result in advance prevention of EMC problems.

Thank you very much for your attention.