The so-called 50 ohm is a unified test standard. Different input and output impedances of a device are different, so a standard load, the so-called matching load, is needed.
The filter is not all 50 ohm ports, but also has the function of impedance transformation. The so-called matching to 50 ohms means that the in-band and out-of-band filters basically have reflections.
If the filter is designed with a 50 ohm port, the in-band input impedance of the filter is 50 ohms. For example, the input and output ports of microstrip parallel coupled bandpass filters are generally connected by 50 ohm microstrip lines, which are mainly used to connect upper and lower devices and do not play the role of impedance transformation. That is to say, without it, the input and output impedance from the filter port is theoretically 50 ohms (in-band, of course), and these two microstrip lines only play the role of transmitting energy. If the input and output impedance of the filter itself is not 50 ohms, the energy will be reflected when passing through this microstrip line with a characteristic impedance of 50 ohms.
Finally, say two points:
1. There will be reflection where the impedance is discontinuous;
2. The so-called impedance from a certain point refers to the effect of various reflections superimposed on this port, so what we do is to present the port we need as the impedance we need at different frequency points by various means.
Ask an expert, why should the input and output impedance of the filter be 50 ohms?
Not all filters require an impedance of 50 Ω, only high-frequency filters and cable transmission systems have this requirement, because high-frequency cables are mostly 50 Ω impedance, and impedance mismatch cannot be transmitted.
First filtering or impedance matching
Look at your signal. If the signal is to be input to other places, it is usually filtered first and then impedance matched.
If the signal is taken from other places, it is impedance matching first and then filtering.
Actually, it depends on where your interface is. The nearest interface is impedance matching.
Introduction of matched filtering
Matched filtering is one of the best filtering methods. When the input signal has a special waveform, its output signal-to-noise ratio reaches the maximum.
When designing a circuit, when capacitors and resistors are needed, when filtering is needed,
The applications of capacitors in circuits include filtering, coupling, oscillation, bypass, resonance and timing. Capacitors are used when the circuit has these requirements.
The applications of resistors in circuits include voltage division, current limiting and impedance matching. Resistors should be used when the circuit needs these applications.
The function of filtering is to remove the pulsating components in the DC power supply, and the DC power supply of electronic circuits should be filtered. Removing other clutter in AC power supply is also filtering. This kind of AC filtering is used in more sophisticated electronic circuits or electronic circuits that will produce electromagnetic interference.
In transistor amplifier circuit, DC negative feedback can be used to stabilize the operating point of transistor. Negative feedback can be used to improve the distortion in the amplifier circuit. Positive feedback can be used to form an oscillation at the top of the amplifier.
How to determine the capacitance resistance of the filter
If the product value of RC has been determined, then you only need to choose the value of resistor R, and then you can calculate the value of capacitor C. ..
When choosing the value of resistor R, we should follow certain principles, such as: if the resistance in series in the circuit is large, it generally plays a role of pressure relief, while if the resistance is small, it plays a role of current limiting. Do you filter out the pressure or limit the flow?
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How to get 50 ohm filter input and output impedance?
The so-called 50 ohm is a unified test standard. Different input and output impedances of a device are different, so a standard load, the so-called matching load, is needed.
The filter is not all 50 ohm ports, but also has the function of impedance transformation. The so-called matching to 50 ohms means that the in-band and out-of-band filters basically have reflections.
If the filter is designed with a 50 ohm port, the in-band input impedance of the filter is 50 ohms. For example, the input and output ports of microstrip parallel coupled bandpass filters are generally connected by 50 ohm microstrip lines, which are mainly used to connect upper and lower devices and do not play the role of impedance transformation. That is to say, without it, the input and output impedance from the filter port is theoretically 50 ohms (in-band, of course), and these two microstrip lines only play the role of transmitting energy. If the input and output impedance of the filter itself is not 50 ohms, the energy will be reflected when it passes through this microstrip line with a characteristic impedance of 50 ohms.
Finally, say two points:
1. There will be reflection where the impedance is discontinuous;
2. The so-called impedance from a certain point refers to the effect of various reflections superimposed on this port, so what we do is to present the port we need as the impedance we need at different frequency points by various means.
Why does the impedance to ground become zero after the normal circuit is connected to the filter? 130.
You have to post the filter circuit before asking. Don't let people guess.
In addition, is DC resistance or AC impedance measured?
How many capacitors ng does the filter 1 kHz match?
Only the capacity is different, everything else is the same. Capacitance 103: there is a capacitance of 0.0 1μF 104: there is a capacitance of 0. 1μF, which is usually referred to as a capacitor for short, and the letter c indicates the definition. 1: A capacitor, as its name implies, is a' charged container' for holding. K stands for 10% error. That is, the actual capacitance is between 0.09 and 0.11μ f, so I just want to know if I can apply for a patent for what I do. Is there innovation? Generally, low-frequency filtering consists of RC, active and operational amplifiers. As long as you are different, it is possible. 1, the impedance of the inductor is proportional to the frequency, and the impedance of the capacitor is inversely proportional to the frequency. Therefore, inductance can block the passage of high frequency, and capacitance can block the passage of low frequency. By combining them properly, various frequency signals can be filtered. For example, in a rectifier circuit, AC ripple can be filtered by connecting a capacitor in parallel with the load or an inductor in series with the load. 2. Capacitive filtering belongs to voltage filtering, which directly stores the pulsating voltage to smooth the output voltage, which is high and close to the peak value of AC voltage; Suitable for small current, the smaller the current, the better the filtering effect. 3. Inductive filtering belongs to current filtering. The output current is smoothed by electromagnetic induction generated by current, and the output voltage is low, which is lower than the effective value of AC voltage; Suitable for large current, the larger the current, the better the filtering effect. Many characteristics of capacitance and inductance are just the opposite. Generally speaking, the function of electrolytic capacitor is to filter out low-frequency signals in current, but even low-frequency signals have several orders of magnitude. Therefore, in order to adapt to the use of different frequencies, electrolytic capacitors are also divided into high-frequency capacitors and low-frequency capacitors (high frequency is relative here). 5. The low-frequency filtering capacitor is mainly used for mains power filtering or transformer rectification, and its working frequency is 50Hz, which is consistent with the power supply; High-frequency filter capacitor mainly works in the filtering after rectification of switching power supply, and its working frequency is from several thousand Hz to tens of thousands Hz. When the low-frequency filter capacitor is used in high-frequency circuit, due to the poor high-frequency characteristics of the low-frequency filter capacitor, the internal resistance is large and the equivalent inductance is high during high-frequency charge and discharge. Therefore, in use, due to the frequent polarization of electrolyte, a lot of heat will be generated. However, higher temperature will vaporize the electrolyte inside the capacitor, increase the pressure inside the capacitor, and eventually lead to the bulging and bursting of the capacitor. 6. The size of the power supply filter capacitor is usually designed like this. The former stage uses 4.7u to filter out the low frequency, and the second stage uses 0. 1u to filter out the high frequency. The capacitance of 4.7uF is used to reduce output pulsation and low-frequency interference, and the capacitance of 0. 1uF is used to reduce high-frequency interference caused by instantaneous change of load current. Generally, the bigger the former, the better. The difference between the two capacitors is about 100 times. 7. Power supply filtering and switching power supply depend on ESR (equivalent series resistance of capacitor), and the selection of high-frequency capacitor is best at its self-resonant frequency. The large capacitance is to prevent surge, and the mechanism is like a large reservoir with stronger flood control ability; Small capacitors filter high-frequency interference, and any device can be equivalent to a series-parallel circuit of resistors, inductors and capacitors, so there is self-resonance. Only at this self-resonant frequency, the equivalent resistance is the smallest, so the filtering is the best. 8. The equivalent model of the capacitor is that the inductor L, the resistor R and the capacitor C are connected in series, where the inductor L is reached by the capacitor lead, the resistor R represents the active power loss of the capacitor and the capacitor C, so it can be equivalent to a series LC loop to find its resonance frequency. The condition of series resonance is WL= 1/WC, W=2*PI*f, and thus the formula F = 1 is obtained. The minimum reactance at the center frequency of series LC circuit is pure resistance, so the center frequency plays a filtering role. The lead inductance varies with its thickness, and the inductance of grounding capacitor is generally around 1MM, depending on the frequency to be grounded. Parameters to be considered in the design of capacitive filter: resonance frequency of ESRESL withstand voltage.