Characteristics of capacitors - "pass AC and block DC"
Capacitors can be used to pass AC signals while isolating DC signals. This is because capacitors have the properties of low impedance (passing) to AC signals and high impedance (blocking) to DC signals.
At low frequencies, the impedance of the capacitor is high and hardly allows current to pass, thereby isolating the DC signal. At high frequencies, the impedance of the capacitor is low, allowing AC signals to pass through.
This feature can be used to implement the filtering function of AC signals . When a capacitor is connected in series with a load resistor, an RC low-pass filter can be formed .
It should be noted that due to the characteristics of the capacitor in the frequency domain, for high-frequency signals, the impedance of the capacitor will become very small, allowing high-frequency signals to pass. Therefore, when designing a filter circuit, it is necessary to select an appropriate capacitor value based on the required cutoff frequency.
1. First-order low-pass filter circuit
The formula is as follows:
2. First-order high-pass filter circuit
The formula is as follows:
Supplement: For the RC low-pass filter, the calculation formula of the cutoff frequency is :
fc = 1 / (2πRC)
Among them, fc represents the cut-off frequency, R represents the resistance of the resistor, and C represents the capacitance of the capacitor.
3. Hysteresis comparator
The circuit is as follows:
4. Square wave generator
T=2*R48*C7*ln( 1+2*(R47/R49) )
Simulation results:
5. RC sine wave generator
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reference:
https://zhuanlan.zhihu.com/p/350139503
https://blog.csdn.net/zwc475793240/article/details/122432824
https://zhuanlan.zhihu.com/p/61252436
https://zhuanlan.zhihu.com/p/367671862
https://blog.csdn.net/Cherish1ove/article/details/115492199
https://blog.csdn.net/little_grapes/article/details/120589574