【 Weak current College 】 explore double panel wiring skills 】

Battery-powered products in a competitive market, consider the relative importance of the target cost. Multilayer PCB solutions is an engineer in designing the important consideration when necessary. This article will explore the way double panel wiring, using automatic routing and manual wiring for analog and mixed-signal circuit wiring difference, how to arrange the ground loop.

A battery-powered products in a highly competitive market, when considering the target costs always requires designers to use double-layer PCB design. Although multilayer PCB (four to six layers and eight layers) solution in terms of size, noise, and performance can be better, but the cost pressure forced the engineers must make full use of double-layer boards. In this article will discuss with or without automatic routing, with or without ground current return path concept, as well as double panel arrangement of parts.

Use the automatic routing to design a printed circuit board (PCB) is attractive. The majority of cases, the automatic routing to pure digital circuit (especially low frequency signal and low density of circuit) would not be a problem. But when you try to use the routing software provides automatic routing tools do analog, mixed signal or high speed circuit wiring, there may be some problems, but can cause very serious circuit performance problems.

On mixed-signal circuit wiring, various devices after careful consideration before manually placing the parts to the Board and will separate digital and analog devices.

About wiring has many things to consider, but the more troubling issue is grounding. If the path is determined by the upper ground, each unit of grounding all through the layer of wire connected to the ground. On the lower deck of each device, is determined by the Board on the right side of the upper cross hole connected to the ground loop. Users check the cabling, you see the immediate red flag indicates that there is more than oneground loop. In addition, the lower layer of the ground loop be a horizontal divider signal lines. The ground structure of merit lies Simulator (MCP3202; 12-bitAD converter and MCP4125; 2.5V reference voltage) is concentrated in the circuit board on the right. This arrangement ensures that digital ground signals from these travels under simulated chip.

Use manual wiring, to comply with the following design guidelines to ensure good results:

● The earthing design into a ground as current return path.

● Analog ground and digital ground.

● If you cannot avoid signal alignment and grounded on the same layer, signal lines and ground line designed mutually perpendicular to lower signal cable for grounding current loop interference.

● Analog circuits in the circuit, digital circuit system next to the closest to the power supply. To reduce digital switching I/δ δ t on the impact of analog circuits.

But it should be noted that these two double plate in the middle of the Board has a ground. This is designed to allow engineers to do troubleshooting can quickly see the wiring, this way often appears in the device manufacturer for demonstration and evaluation board. But more typically in the upper layer of the Board on the ground in order to reduce the electromagnetic interference (EMI).
Ground current return path has the non-processing current return path should be the basic issues to be considered are:

(1) if the only use of the line, as far as possible, local cable widened pull line; but if you consider only pull line as PCB's grounding wire, cord should be as much as possible. The thumb is very good standard, but also you must know the Earth wire minimum width is a line from that point to the end of effective copper foil width, 「introduction end 」 is defined as the power connection from the farthest.

(2) avoid formation of closed ground-loop.

(3) if there is no ground, you can use the star join pattern.
r>Star-connection

If you cannot design into ground, current returns the path available 「introduction star 」 wiring in order to deal with
In this way, each unit of Earth current separate return to power. Users will find the figure five in not all devices have their own return path. U1 and U2 share return path, allowing this presupposes the following design elements of the required attention.

Keep the device through the simulation of digital circuits.

Digital circuit switching and circuit during will form a significant current but its time is very short. This phenomenon is due to ground loop of equivalent inductance and resistance. Ground or ground lead inductance, will produce V = I/δ δ L t pressure drop, L is the ground or ground equivalent inductance, δ I come from a digital device currents of change and δ t is the current change of the time. Calculation of ground or ground equivalent resistance part caused by voltage variation is V = RI, R is the ground or ground equivalent resistance, I is a digital device's current change. This ground or ground voltage changes will impact simulation device input and grounding between normal signal.

Do not enable high speed current through low-speed devices

High speed circuit ground return signal on the ground changes are similar to the above effect, decide the interference effect of the formula is: butt ground or ground equivalent inductance L, V = δ δ I/t, and the docking of the ground or ground equivalent resistance, V = RI. When the digital circuit or high speed circuit ground or ground across Simulator pull line, causing simulation device input and ground signal changes. Regardless of what technology is used, you must design makes ground return path's equivalent resistance and inductance is minimal. If you use the ground, cut off the ground may increase or decrease the circuit performance, need to be used with care.

Fully analog and digital mode of ground space.
Sometimes theeffects of continuous ground is being separated from the ground.
Exact simulation and connector closer, but it and digital circuit and from the power supply circuit switchCurrent isolation. This is a way to effectively make the earth return path separator.
Conclusions of the

Discussion and wiring-related technology, two issues will be discussed: first, as if the management does not use double panel or ground, but still need to reduce the noise in circuit? and how you want to designed to meet the needs of the circuit ground? general solution to inform management, if you want to achieve reliable circuit performance, the ground was necessary. Use ground's main rationale is the grounding impedance low, and reduces a level of EMI. However, if due to cost constraints and let users unable to reach the desired, this article provides a number of recommendations, such as the star network, and the correct current return path will be slightly reduced circuit noise.