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PCB Reverse Engineering

High frequency material pcb general board and reverse engineering pcb characteristics impedance control introduce

 1, reverse engineering pcb AC Impedance
Alternating current "resistance", which is referred to as "impedance" (Impedance, symbol Z), which is composed of resistance (R), Capacitive Reactance (Xc), and Inductive Reactance (XL) The The formula is = √ (R2 + (XL-XC) 2). The word "Charac teristic Impedance" ("Charac teristic Impedance") is the same as the signal in the high-speed or high-frequency transmission line (Signal; there are other synonyms such as pulse, square wave, Step Wave, etc.) , The representative symbol Zo) is completely different from the former, the formula is Zo = √ (L / C). And AC in the original word refers to Alternating Current, which is the "polarity exchange current". That is, with the time of the current, referred to as communication. This AC symbol is often used to convert polarity (Polarity Switching) many times per second power, the waveform is often sine wave, square wave or triangular wave and so on.
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2, reverse engineering pcb Characteristic Impedance 
Refers to when the conductor in the electronic "signal" waveform propagation, the voltage to the current ratio is called "impedance Impedance". As the "circuit" of the AC circuit or the "resistance", it is no longer just the "ohmic resistance" of the simple direct current, so that the "resistance" In the circuit should not be called "resistance", but should be called "impedance". But to really use the "Impedance impedance" of the AC situation, will inevitably lead to confusion, in order to distinguish, had to electronic signal as "characteristic impedance." When the signal in the circuit board is propagated, the factors affecting its "characteristic impedance" are the cross-sectional area of ​​the line, the thickness of the green material between the line and the ground layer, and the dielectric constant. At present, there are many high-frequency high transmission speed of the board, has been asked "characteristic impedance" to be controlled within a certain range, the board in the manufacturing process, we must seriously consider the three important parameters and other conditions.
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3, reverse engineering pcb Frequency frequency
Refers to a variety of cyclical movement, in the unit time to repeat the number of terms. The frequency is usually in units of "he" (Herz, that is, the number of cycles per second or the number of weeks). Circuit board line in the "signal", is a way to transmission, it is necessary to high-speed high-frequency first. At high frequencies, the dielectric constant of the sheet is critical, such as high-frequency microwave communication boards above 3 GHz, the FR-4 with a constant of 4.5 must be replaced with a 2.6 PTFE sheet to reduce the signal Dissipation and delay.
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4, reverse engineering pcb Impedance Match impedance matching
In the electronic circuit if the signal (Signal) in the transmission, hope from the power source (Source), in the case of the least energy loss, can be successfully transmitted to the receiver (Load). And is completely absorbed by the receiving end without any reflection. To achieve this good transmission or transmission, the impedance (ZL) in the circuit must be equal to the impedance (Zo) inside the "end", called "impedance matching".
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5, reverse engineering pcb Radio Frequency Interference (RFI) RF interference
Is an unintentional interference, including the emergence of some bad temporary state (Transients) signal, will interfere with the operation of electronic communications equipment or other electronic equipment and affect its normal function. Such as the early did not do RFI prevention of the TV, when the foot near the start of a motorcycle, because of its spark plug Spark (Spark) electromagnetic waves, incoming TV will cause a brief picture of the confusion. If the Shielding layer is treated with chemical copper or nickel-containing paints on the inner wall of the TV shell, the incoming electromagnetic wave can be directed to the "ground plane" to reduce RFI interference. As for some "high frequency" welding workshop, also need to be its building to the metal network grounding, to avoid the scattered high-frequency electromagnetic waves on the surrounding electronic and electrical interference. In the vicinity of the airport waterway operators, even when the aircraft will drop even on the radar instrument interference, a great threat to Feian, must be strictly guard against.
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6, reverse engineering pcb Reflection
General knowledge refers to the mirror will be reflected by the incident light that. However, in the computer motherboard in the high-speed signal transmission, it refers to the "signal" issued by the driver line by the Receiver Fu broadcast, if the impedance value between the three can match, the signal can reach the success of Receiver Receiver Once the signal line quality problems, resulting in its "characteristic impedance" value exceeds the limit, will result in part of the signal energy back to Driver, also known as "reflection."
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7, reverse engineering pcb Rise Time
This word is an important property of a square-wave logic signal or a pulse. (Clock pulse) system consisting of the abscissa as the voltage (such as the early 5V and the current 3.3V, and the future possible 2.5V), the abscissa for the time; the generation of the square wave in its propagation , In theory, should rise from the low vertical to reach the "high state", but in fact it is a slope to rise. The rise of the slope of the 10% height to 90% of the height of the time consumed, known as the Rise Time, commonly used units for the 10-9 seconds Nono-Second, referred to as NS, translated as Nie seconds.
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8, reverse engineering pcb Ultra High Frequency (UHF) UHF
Refers to the frequency between 300MHz ~ 3GHz, or wavelength of 1 m ~ 10 cm of the "very short wave", known as UHF. Such as TV, car phone, big brother phone, etc. are all within this range, the use of the circuit board FR-4 is still able to achieve the mission. As for the higher frequency of microwave electronic products, you need to use the Teflon plate. (Ie, the frequency of 3 ~ 30GHz between the microwave; wavelength of 1 ~ 10cm, can be used for remote (RF) radio frequency, radio frequency interference Wireless high brother or satellite communications) UHF Ultra-High Frequency; UHF frequency of electromagnetic waves refers to the frequency of 300 ~ 3,000MHz radio waves, or wavelength of 1 ~ 10dm (10 ~ 100cm) "very short wave" In the high-definition TV. VHF Very High Frequency (ie, ultrashort wave) refers to the frequency of 30 ~ 300MHz between the radio waves, the wavelength between 1 ~ 10m, for broadcasting and television.


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