Do digital and analog need to be separated?

1 Why digital and analog?

On the same wire, the voltage at different points may be different, especially if the current is high. A voltage drop occurs when the current flows due to resistance in the wire. In addition, the wire has a distributed inductance, and the effect of the distributed inductance will show up in the AC signal. So we have to divide it into digital and analog, because digital signals are very noisy at high frequencies. If analog and digital are mixed together, noise will be transmitted to the analog part, causing interference. If grounded separately, high frequency noise can be isolated by power filter. But if the two reasons are mixed together, they are not easy to filter.

2 Why do digital and analog need to be separated?

When making simple circuits, it is not necessary to separate them. But why is everyone talking about separating them?

In fact, the essence is right, that is, digital ground and analog ground are both ground, and digital ground and analog ground will influence each other, not because one is called digital and the other is called analog, but they use the same elevator -- ground, and the elevator uses the well is the ground wire we laid on the PCB. The current in the analog loop passes through this line, and the current in the digital loop passes through this line. There's nothing wrong with Ben. This wire is used to conduct current, but the problem is that there is resistance on this wire! The fundamental problem is that the current flowing through this line flows into two different circuits.

Suppose there are two currents, the digital current and the mode current, starting from the ground at the same time. There are 2 devices, several pieces and modules.

If the two loops are not separated, the voltage loss is v when the digital current and the analog current return to the ground terminal of the several pieces

v= (digital current + analog current) x connection resistance, equivalent to the grounding end of the digital device relative to the ground end increased v

The digital devices are not satisfied. I'll admit it raises the voltage a little bit. I accept the digital stream part, but why add the mold stream to my head? Similarly, emulators complain.

Two solutions:

The first one: you walk PCB line has no impedance, naturally will not cause interference. When it is wide, it can be fitted with an infinitely large elevator. Nature doesn't affect each other, but everyone knows that's impossible

Second: the two circuits are separated, the digital flow and the mode flow are separated, the digital and the module are separated.

Similarly, although sometimes in the analog loop, it should also be divided into high current loop and low current loop, that is, to avoid mutual interference.

Interference is the voltage generated by the current in two different circuits of the PCB circuit, which is superimposed on each other.

Chengdu Zicheng Electronics is a professional PCB design company engaged in electronic products circuit board design (layout and wiring design). Mainly undertake multi-layer, high density PCB design drawing board and circuit board design proofing business.

The price of PCBS has been a puzzle for many buyers. Many people also ask how the prices are calculated when they order online. Here are the factors that affect PCB prices.

1. The different materials used in PCB lead to the diversity of prices.

For example, common double panels are generally FR4 (Sheng Yi, Kingboard, Guoji, three prices from top to bottom), board thickness from 0.2mm to 3.0mm, copper thickness from 0.5oz to 3oz, all of which lead to a large price difference in the board; In welding ink, ordinary thermosetting oil and photosensitive green oil also have a certain price difference.

2. Price differences caused by different surface treatment processes

Common are: OSP (antioxidant), lead spray tin, lead-free spray tin (environmental protection), gold plating, gold sinking, and some combination of processes, the price of the above process is more expensive.

3. Price difference caused by different difficulty of PCB itself

There are 1000 holes on each of the two circuit boards. The aperture of one board is greater than 0.2mm, and the aperture of the other board is less than 0.2mm, which will result in different drilling costs. For example, if two identical circuit boards have different wire widths and wire distances, one larger than 4mil and the other smaller than 4mil, the production costs will be different. Secondly, some designs do not follow the process of the ordinary plate is more expensive, such as half hole, buried blind hole, disc hole, press the keyplate printing carbon oil.

4. Different thickness of copper foil causes price differences

Common copper platinum thicknesses are: 18um (1/2OZ), 35um (1OZ), 70um (2OZ), 105um (3OZ), 140um (4OZ), etc., and the higher the thickness of copper foil, the more expensive.

5. Quality acceptance standards of customers

Commonly used are: IPC2, IPC3, enterprise standards, military standards, etc., the higher the standard, the higher the price.

6. Mold fee and test bench

(1) Mold fee. If the template and the drilling and milling contour used by the general plate factory in small batch are used, there will be no additional milling fee. In large batch, the die is needed to punch the plate, so there is a set of mold cost. The general price of plate factory is more than 1000 yuan.

(2) test fee: the prototype is generally used to fly needle test, plate factory generally charged 100-400 yuan test fee; Batch to open the test rack to test, test rack general plate factory quotation between 1000-1500 yuan

7. Price difference caused by different payment methods

The shorter the payment period, such as cash, the lower the price will be.

8. Order quantity/delivery date

(1) The less the quantity, the more expensive the price, because even if it is to make 1PCS, the plate factory needs to make engineering data and produce film, which process is necessary

(2) Delivery date: the data sent to the PCB factory should be complete (GERBER data, the number of layers of the board, the board, the thickness of the board, how to deal with surface treatment, ink color, character color and some special requirements should be written clearly).

Through the above discussion, it is not difficult to see that the diversity of PCB processing price is its inherent inevitable factors, this article is for reference only, the specific price of course or direct contact with the manufacturer. Chengdu Zicheng Electronic Equipment Co., Ltd. has been dedicated to PCB industry for 13 years, and gathered a team of engineers with more than 10 years of experience in PCB industry to provide customized one-stop service. Welcome new and old customers to inquire!