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Technique RF
Caractéristiques et contrôle de l'impédance des PCB à haute fréquence
Technique RF
Caractéristiques et contrôle de l'impédance des PCB à haute fréquence

Caractéristiques et contrôle de l'impédance des PCB à haute fréquence

2021-11-29
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Author:iPCBer

1. AC Impedance  AC impedance
AC resistance (Resistance; R), capacitive reactance (CapaciTIve Reactance; Xc), and inductance (InducTIve Reactance; XL) are combined into AC "resistance", referred to as "impedance" (Impedance, representing symbol Z) . The formula is Z=√(R2+(XL-XC)2). This word is related to the signal in high-speed or high-frequency transmission lines (Signal; this word still has other synonyms such as Pulse, Onde carrée, Step Wave, Attendez..). "Charac terisTIc Impedance" (Charac terisTIc Impedance) , Its representative symbol is Zo) is completely different from the former, and its formula is Zo=√(L/C). The AC in the original word refers to AlternaTIng Current, which is the "current of polarity exchange". That is, the current that changes with time, Abréviation AC. This AC symbol is often used for power supplies that change polarity (Polarity Switching) many times per second, Sa forme d'onde est généralement sinusoïdale, square wave, or triangle wave.

2. Characteristic Impedance
It means that when there is an electronic "signal" waveform in the conductor, the ratio of its voltage to current is called "Impedance". Because the "Resistance" that has been mixed with other factors (such as capacitive reactance, inductive reactance, etc.) in an AC circuit or at high frequencies is no longer just a simple direct current "Ohmic Resistance" (Ohmic Resistance), Par conséquent, il ne doit plus être appelé "résistance" dans le circuit., but should be called "impedance". Cependant,, when it comes to the actual use of "Impedance Impedance" AC, it will inevitably cause confusion. For the sake of distinction, the electronic signal has to be called "Characteristic Impedance". When the signal in the circuit board line propagates, Le facteur qui affecte son "impédance caractéristique" est la section transversale de la ligne., the thickness of the green material between the line and the ground layer, Et sa constante diélectrique. At present, there are many boards with high frequency and high transmission speed, and the "characteristic impedance" must be controlled within a certain range. Dans la fabrication de circuits imprimés, the above three important parameters and other cooperation conditions must be carefully considered.

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3. Frequency
Refers to various periodic motions, in terms of the number of repetitions per unit time. Electric frequency is usually in units of "Herz" (Herz, the number of repetitions per second or number of cycles). The "signal" in the circuit board circuit is transmitted in a fluctuating manner, La haute fréquence est donc une condition nécessaire au fonctionnement à grande vitesse.. At high frequencies, La constante diélectrique des tôles minces est critique. For example, for high-frequency microwave communication boards above 3 GHz, FR-4 with a dielectric constant of 4.5 doit être remplacé par seulement 2.6 to reduce the signal Dissipation and delay.

4. Impedance Match impedance matching
If a signal (Signal) is being transmitted in the electronic circuit, it is hoped that it can be transmitted to the receiving end (Load) smoothly from the source of the power source with the least energy loss. And it is completely absorbed by the receiving end without any reflection. Afin d'atteindre cette bonne diffusion ou diffusion, the impedance (ZL) in the circuit must be equal to the impedance (Zo) inside the "transmitting end", which is called "impedance matching".

5. Radio Frequency Interference (RFI) radio frequency interference
It is an unexpected and undesirable interference, including the appearance of some undesirable transients (Transients) signals, Interférer avec le fonctionnement des équipements de communication électronique ou d'autres machines électroniques et affecter leur fonctionnement normal. For example, in the early TVs that were not protected against RFI, when a foot-pedal motorcycle was started nearby, the sparks (Spark) electromagnetic waves emitted by the spark plugs would cause temporary chaos in the picture after being transmitted to the TV. Si la paroi intérieure du boîtier en plastique de la télévision est traitée avec un revêtement chimique contenant du cuivre ou du nickel, a shielding layer can be used to guide the electromagnetic waveguide to the "grounding layer" to reduce RFI interference. Pour certains ateliers de soudage "haute fréquence", it is also necessary to ground their buildings with metal meshes to avoid the interference of the high-frequency electromagnetic waves emitted from the surrounding electronic appliances. Operators near the airport channel may even cause interference to the aircraft landing radar instruments, which poses a great threat to flight safety and must be strictly guarded.

6. Reflection
In common sense, Cela signifie que le miroir reflète la lumière incidente. However, Lorsque le signal à grande vitesse se propage dans la carte mère de l'ordinateur, it means that the "signal" is sent by the Driver through the signal line and broadcast on the Receiver. Si les trois valeurs d'impédance correspondent, the energy of the signal can reach the Receiver smoothly. En cas de problème de qualité de la ligne de signal, Cela fait que la valeur d'impédance de la propriété dépasse la limite, Cela provoquera un retour partiel de l'énergie du signal au conducteur., also known as "reflection".

7. Rise Time
This word is an important property of square wave logic signal (Signal) or pulse (Pulse). The "clock" (clock pulse) system composed of the ordinate as the voltage (such as 5V in the early days and 3.Maintenant, c'est 3V., and possibly 2.5V in the future), and the abscissa as the time; the generation of square waves in its propagation In theory, Il doit passer verticalement d'un état bas à un état élevé., but in fact it rises on a certain slope. Le temps nécessaire pour élever la pente de 10% à 90% de hauteur est appelé temps de montée, L'Unit é commune est de 10 - 9 secondes, abbreviated as NS, Traduit en nanoseconde.

8. Ultra High Frequency (UHF)
Refers to the "ultra ultrashort wave" with a frequency between 300MHz and 3GHz or a wavelength between 1 m and 10 cm, Ça s'appelle UHF.. Such as TV, Téléphone de voiture, big brother phone, etc. belong to this range, La carte de circuit fr - 4 utilisée peut encore accomplir la tâche. As for microwave electronic products with higher frequencies, PTFE PCB are required (see the special article of the 50th issue of the Circuit Board Information Magazine for details). EMI Electromagnetic Interference; electromagnetic interference RF Radio Frequency; radio waves, radio frequency RFI Radio-Frequency Interference; radio frequency interference SHF Super High Frequency; The big brother of wireless or satellite communication) UHF Ultra-High Frequency; Ultra-high frequency electromagnetic waves refer to radio waves with a frequency between 300 and 3,000 MHz, or "ultra ultra short waves" with a wavelength between 1 and 10 dm (10 to 100 cm). Ils sont couramment utilisés dans les téléviseurs d'affichage d'images HD. VHF Very High Frequency; Very high frequency electromagnetic waves (ie ultrashort waves) refer to radio waves with a frequency between 30 and 300 MHz, Longueur d'onde entre 1 et 10 mètres, used for broadcasting and television.