[introduction]Input impedance, output impedance, it is so important that these two parameters are done not have it seems that, but the fact is not such. Next my views say below.
Input impedance, output impedance, it is so important that these two parameters are done not have it seems that, but the fact is not such. Next my views say below.
The coupling capacitance in frequency has from 0.1uF-220uF, is this sick? It is to use as keep apart dc, how cannot be united?
Understand this problem actually very simple, we see signal is how to be transmitted understood easily. Here analyses a method with respect to what tell a circuit, perhaps saying is thinking means.
Circuit analyses a method
We see all sorts of complex circuit via regular meeting, if be a novice, the likelihood was cheated. Change actually numerous for sheet of Jian Fei Chang Jian:
Need to divide circuit only piece, output signal at the same time, receive signal at the same time additionally. Call those who output signal to output module for the moment, receive those who receive signal to make receive module.
If we make clear what this Hunan signal produced to change in transmission process, that understood with respect to what.
Output module to left, we know what the signal of output is normally, frequency is in what limits, additionally an important parameter outputs impedance namely, so circuit model is below this
This see very easily, output impedance Zout is very important, it measured the output ability of this module. If output module is a power source, so Zout is power source internal resistance, sure very small. Otherwise, if Zout=100 Ω , receive a 10 Ω load, the voltage that result load shares has power source voltage only very one of not returning go to, can that still make power supply?
So, general to output module, yue Xiaoyue of this output impedance is good.
The circuit that receives signal is too much, gaudy. Some signal input IC chip, some signal receive MOS above the canal drive switch, some receives a horn, wait a lot of kinds a lot of a moment.
We no matter what is it after all, express with a Zin, input impedance namely. Should know very easily, this input impedance has profit quite greatly.
Our extreme a bit, if input impedance infinity, namely open circuit, so no matter the outputs signal module output impedance in front is how old, signal can very good reception, as the signal of output. And toward little extreme a bit, if input infinitesimal, for 0, be ground connection short circuit actually, that still sends the signal of a ball.
We receive input and output rise, namely below this.
As a whole, the meeting when we see signal transmit produces what change, it is good to need to become this model in equivalent of circuit of brains lieutenant general only.
So first-class effect, be much simpler? Use Ohm’s law, sink receives received signal to come out. Of course, establish ties among circuit sometimes have resistance, capacitance, or inductance, we need an inter to add these parts of an apparatus only can.
Citing 1: Put away piece frequency coupling capacitance comes citing.
This is typical circuit of some frequency Codec, what pin of frequency input MIC establishs ties is 0.1uF capacitance, is this electric capacity so small OK?
We are analysed according to the method in front.
Frequency of collect of Mi head Mic, output imitate signal, so it is in front the output module in saying model, how much is its output impedance?
We look for a book of Mi head norms to look casually, saying is 2.2K Ω , the output impedance of general Mi head also is about the same.
If pursue, chip norms book also supplied the in-house circuit of Mi head, it is a circuit of FET canal enlarge actually. If learn well (the importance that learns well by the university) , the output impedance that knows this FET is in charge of enlarge circuit is that RL, manufacturer this RL is 2.2K Ω , so it tags output impedance is 2.2K Ω .
And the resistor that what the Codec circuit that go out sticks to use before us is 1K Ω , so actual output impedance is 1K Ω , we use 1K Ω .
We look again receive module.
Receiving module is Codec chip, how much is the input impedance that pin is it? We examine norms, inputting impedance is 20K Ω or 80K Ω (concern with configuration) , we take adverse cost, namely the least value, 20K Ω
Have among output module and input module lie between straight capacitance, we increase this electric capacity. So, circuit is changed brief after be over, be such.
Actually, this is a RC connect filter high, end frequency is 1/2 π (Zin+Zout)C.
Now Zin+Zout =20K Ω + 1K Ω , c=0.1uF, so 3dB ends frequency is 75.8Hz. We know, sound frequency limits of the person is 300Hz-3.4Khz, can judge so, the transmission with this frequency OK and very good signal went, that is to say the volume of capacitance 0.1uF is enough, if increase 1uF, end frequency turns into 7.58Hz, also do not have a problem. Nevertheless 1uF capacitance should compare 0.1uF capacitance to want for certain some more expensive, choose 0.1uF more economy.
There still is an earphone to output port in this Codec graph, of series connection is the capacitance of 220uF, why to receive so big?
To this circuit, it is chip outputs signal to send earphone. Outputting module is chip, receiving module is earphone
We see chip of output module Codec first, examine norms book, impedance of output of chip correspondence pin is 16 Ω . Seeing sink — earphone, the impedance of earphone has 16 Ω , 32 Ω , 64 Ω . We are taken the poorest (go against signal to receive) , namely 16 Ω , after circuit simplifies, circuit catchs up with the face is same, I was not drawn
Also be connect filter high, end frequency is 1/2 π (Zin+Zout)C. Now Zin+Zout=16+16=32 Ω , c=220uF, so 3dB ends frequency is 22.6Hz. Same, the 300Hz-3.4Khz of voice can pass the past very well. If we choose 10uF capacitance, so end frequency turned into 497.6Hz, apparent, low frequency by attenuation, frequency cannot very good transmission, appear lack fidelity.
Reckon somebody can ask, 220uF is too big, do I choose 22uF to be no good all right? 22uF is taken, up to frequency it is 226Hz, also be besides sound frequency 300Hz of the person, should OK.
This I want to say to see my apply, seeing the voice that you put is what frequency paragraph. Microphone pickup is the person’s sound commonly, in 200Hz-3.4K limits. But sound reproduction does not have the person’s voice only certainly, the sound of person ear is 20Hz-20Khz, so lowest can arrive at 20Hz. If your demand is high, must lowermost frequency also cannot damply, need the electric capacity of 220uF so.
If be to hear a sound, low frequency breaks not lack fidelity be indifferent toing, you do a 22uF to also go, even 10uF is patchy also, it is low frequency heft was weakened.
Besides the example of this frequency, we see another case again.
Citing 2: MOS provides the analysis of resistor of grid series connection
Analysing what the face says in front of the method is same, receiving module is MOS canal, the input resistance that MOS provides can regard as infinity, but parasitism electric capacity is larger, so it serves as when receiving module, parasitism capacitance station inputs the body of impedance, its input the impedance that impedance is capacitance, for 1/jwC.
I put this to here, basically be to want to explain actually a bit. Input impedance, output impedance, it two be answer impedance, include resistance not just, still include capacitance and inductance.
Labor passes before this circuit, said no longer, want to see the word of next concrete analysises, can nod below this link
[the meaning of resonance of LC series connection]
A lot of chip also can give out the parasitism capacitance size of relevant port, we want to consider according to actual condition. The example of the frequency that cites in front, because frequency is inferior, and the parasitism capacitance of relevant port also is controlled with respect to 10pF, this influence is quite small, nature is so negligible drop capacitance.
The purpose with main article does not depend on discussing the issue of capacitance of coupling of a frequency, the key depends on analysing a method.
If you come up against a new circuit, when knowing how to do it, might as well try according to this method. In brains build a model simply, era enters output impedance, input impedance. Afterthought alls alone what the signal that processes is, its included what frequency weight (Fourier alternates) . Perhaps the answer came out, need not someone else tells you.
Additional, we should know now, why manufacturer can give out input impedance, outputted impedance parameter. When studying modular report, why to want to calculate that input impedance, output impedance. Because they are useful.
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