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The method to increase the anti - interference capability of film capacitance is selected
Jan 08, 2019

1.Reduce the distortion in signal transmission:
The microcontroller is mainly manufactured by high-speed CMOS technology. Static input current signal input at about 1 ma, around ten pf in the input capacitance, high input impedance, high speed CMOS circuit outputs are fairly on load capacity, namely the considerable output value, the output end of a door through a very long lead to the high input, the input impedance reflection problem is very serious, it will cause the signal distortion, increasing the system noise. When Tpd > Tr becomes a transmission line problem, signal reflection, impedance matching and other issues must be considered. Zhixu electronics believes that the delay time of the signal on the PCB is related to the characteristic impedance of the lead, that is, the dielectric constant of the PCB material. Roughly speaking, a signal travels between one-third and one-half the speed of light on a printed circuit board lead. The Tr (standard delay time) for commonly used logic telephone elements in a microcontroller system is between 3 and 18ns.


When the rise time of the signal is faster than the delay time of the signal, it should be processed according to fast electronics. Pu film capacitor manufacturers think that at this time to consider the transmission line impedance matching, for a printed circuit board on the integrated block between the signal transmission, to avoid the Td > Trd situation, the larger the printed circuit board system speed is not too fast.


2. Choose microcontroller with low frequency:
The microcontroller with low external clock frequency can effectively reduce the noise and improve the anti-interference ability of the system. Square waves and sine waves of the same frequency have much more high frequency components than sine waves. Although the amplitude of the high-frequency component of the square wave is smaller than that of the fundamental wave, the higher the frequency is, the easier it is to emit as a noise source. The most influential high-frequency noise generated by the microcontroller is about 3 times of the clock frequency.

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