Single floor plate eliminates loop area

Analog and digital components should be placed in their own dedicated PCB area. The power supply should be placed at the edge or corner of the board and between the analog and digital areas.

Power wiring is also critical to noise performance. Digital components (especially high-speed and high-power digital components) cannot be placed or placed near the path where the analog return current flows back to the power supply. This means that digital components should not be placed near lines carrying analog current or power lines to analog and mixed-signal components. Note that the power supply carries the signal current as they re-charge the bypass capacitor on the plate. The return current must flow through the common section of the separated floor plate, away from the output trace/path. This will form a radiated loop area. Sometimes analog circuits pick up this radiation.

The proposed wiring above will enable the ADC to provide the best performance. Its requirements are summarized as follows:

Use a monolithic floor slab. Do not separate the plates. If there are multiple floor plates in the multiple plate layers, they should be joined together with a through-hole grid at a distance of 2cm or less.

Separate the power supply panels, each of which is kept in the same layer. The analog circuit power plate, the digital circuit power plate, and the ADC digital output driver power plate should be separated.

The ADC digital core power supply uses analog power supply, but the ADC digital driver cannot use analog power supply.

The ADC digital output driver power supply can be the same power supply as the ADC output driver component.

Place all analog components and connections on the analog power supply panel, and all digital components and connections on the digital power supply panel.

Separate power supply for each plate. ADC digital output power supply, can come from either power supply, but should be decoupled with a series choke. ADC analog power supply is preferably linear voltage regulator.

If any digital circuit power supply and ADC output driver power supply are the same power supply, and there is a signal line to another area of the board, the capacitor is used between the two power plates. Place these capacitors close to the signal line.

Fixture problem

Depending on the line yield, workshop site and labor rate, fixtures can range from simple plywood with pins and connecting cables to complex fully automatic pin bed test fixtures connected to the assembly line by conveyor belt. Clearly, these factors suggest that there is no fixed formula.

A hand-loaded double-sided fixture, a ribbon cable is attached to the main I/O connector, and a top-mounted probe can access critical test points on the UUT. This was the ideal design for a medium-sized plant where the operator had to connect a ribbon cable, close the roof and then start testing. There is no need for manual exploration for calibration and diagnosis, as the roof can reach all relevant areas. Ribbon cables and roof probe connections should be designed to be easily replaced, as these cables often bend and suffer wear.

Keep these issues in mind when dealing with fixture suppliers, but also think about where the product will be manufactured, which is a place that many test engineers overlook. For example, let's assume that the test engineer is located in California and the product is manufactured in Thailand. Test engineers will think that the product needs expensive automated fixtures, because the high price of the California plant requires as few testers as possible, but also use automated fixtures to reduce the employment of highly skilled and high-wage operators. But in Thailand, neither of these problems exist, and it is cheaper to let people solve them, because labor costs are low, land prices are cheap, and large factories are not a problem. Therefore, sometimes first-class equipment may not be popular in some countries.

Operator skill level

In high-density Uuts, if calibration or diagnosis is required, a human probe is likely to be required, due to limited needle bed contact and faster testing (testing the UUT with a probe can quickly collect data rather than feed information back to the edge connector), so an operator is required to probe the test point on the UUT. Wherever you are, make sure the test point is clearly marked.