Grounding design in printed circuit board design

pcb One of the most difficult problems in system design is grounding design. Although its concept is relatively simple, its implementation is very complex. Unfortunately, there is no simple way to ensure good results with detailed steps, but if some details are handled improperly, it may lead to headache.

For linear systems, the ground is the reference point of the signal. Unfortunately, in the unipolar power supply system, it is also occupied by acts as the loop of power supply current. If the grounding strategy is not applied properly, it may seriously damage the performance of high-precision linear system.

Grounding is all analog pcb An important problem in design, it is also important to ground correctly in the circuit based on printed circuit board. Fortunately, there are some high-quality grounding principles inherent in the printed circuit board environment, especially the use of grounding layers. This factor is one of the significant advantages of analog printed circuit board design based on printed circuit board.

Other aspects of managing grounding include controlling decentralized grounding and signal return voltage that may lead to performance degradation. These voltages may be caused by external signal coupling and common current, or by excessive IR voltage drop in the ground wire. Correct wiring, wiring size, differential signal processing and grounding isolation technology enable us to control this parasitic voltage.

In fact, high quality grounding problems must affect mixed signals pcb The overall layout principle of the design.

Current signal processing systems usually need mixed signal equipment, such as ADC, DAC and fast digital signal processor. Because analog signals with wide dynamic range need to be processed, high-performance ADC and DAC must be used. In the harsh digital environment, maintaining wide dynamic range and low noise is closely related to the use of good high-speed circuit printed circuit board design technology, including appropriate signal wiring, decoupling and grounding.

In the past, high-precision and low-speed circuits were considered to be different from the so-called high-speed circuits. For ADC and DAC, the sampling (or update) frequency is usually used as the speed standard. However, the following two examples show that, in fact, most of today's signal processing technologies are really high-speed, so they must be regarded as such devices to maintain high performance. This is true for DSP, ADC and DAC.

All sampling ADCs (ADSCs with built-in sample and hold circuits) suitable for signal processing applications operate on high-speed clocks with fast rise and fall times (usually nanoseconds), even if the throughput seems to be low. For example, a medium speed 12 bit proximity (SAR) ADC can operate on a 10MHz internal clock with a rate of only 500ksps.

σ-δ ADC has high sampling rate and needs high-speed clock. High resolution with throughput ranging from 10Hz to 7.5khz. The so-called low-frequency industrial measurement ADC (such as ad77xx Series) can also work at clock frequency above 5MHz to provide 24 bit resolution.

More complex, mixed signal integrated circuits have analog and digital ports, so how to use appropriate grounding technology becomes more complex. In addition, the digital current of some mixed signal integrated circuits is relatively low, while the digital current of other mixed signal integrated circuits is relatively high. In many cases, these two integrated circuits require different processing to achieve optimal grounding.

Digital and analog PCB design engineers tend to look at mixed signal equipment from different perspectives. The purpose of this paper is to explain the general grounding principle applicable to most mixed signal equipment without understanding the details of internal circuits.