What exactly is input impedance and output impedance??

how does input impedance and output impedance affect design parameters and component selection?? What does it practically convey??

the input impedance is the total sum of resistance inductance and capacitance seen by the source , it is calculated using thevin or norton methods

it is a variabe withe frequency and time

regards

Hi,

For further understading:

Impedance, in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals. Impedance is expressed as the ratio of the voltage impressed across a pair of terminals to the current flow between those terminals. When a circuit is supplied with steady direct current, the impedance equals the total resistance of the circuit. The resistance depends upon the number of electrons that are free to become part of the current and upon the difficulty that the electrons have in moving through the circuit. When a circuit is supplied with alternating current, the impedance is affected by the inductance and capacitance in the circuit. When supplied with alternating current, elements of the circuit that contain inductance or capacitance build up voltages that act in opposition to the flow of current. This opposition is called reactance, and it must be combined with the resistance to find the impedance. The reactance produced by inductance is proportional to the frequency of the alternating current. The reactance produced by capacitance is inversely proportional to the frequency of the alternating current. In order for a source of electricity that has an internal impedance to transfer maximum power to a device that also has an impedance, the two impedances must be matched. For example, in the simple case of pure resistances, the resistance of the source must also equal the resistance of the device. Impedance matching is important in any electrical or electronic system in which power transfer must be maximized

The input and aouput impedance its a very important parameter in a analog circuit design. It value can determinate the maximun or minumun transfer of power, noise, etc. In the otrher hand, at cascade systems, this parameters can vary the transfer fuction of the intere system.

simply put- output impedance is the impedance seen from the output node after removing all independent current and voltage sources and similarly we can define input impedance as the impedance seen from the input node

i/p impedance is the impedance seen by the source
and o/p impedance is the impedance seen by the load

this can be found by measuring change in voltage with change in current across
load for o/p impedance
and across source for i/p impedance

y should input impedance be ideally infinite and output impedance be low.. as in op-amps ..?? or y should it be vice versa??

Hi,
input impedance be ideally infinite and output impedance be low.. as in op-amps ..?? or y should it be vice versa??

because reliably we want to pass signal from input to output. for more detail refer to any two port network analysis book.
Vice versa will be in Current mirror, because we need constant current source so we go for high output resistance.

Re:

Input Impedance is the impedance of a circuit as seen from the source end after replacing all the current and voltage ( independent ) ..Means Replace the ideal voltage source by a short circuit ( Zero Impedance ) and replace the ideal current source by an open ciruit ( infinite impedance ) and leaving the dependent voltage and current sources as it is..
Same is the case with the output impedance,except that it is the impedance seen from the load end

Added after 8 minutes:

y should input impedance be ideally infinite and output impedance be low.. as in op-amps ..?? or y should it be vice versa??

One issue is that of attenuation..
We desire that the signal that we pass to a circuit should be going into the circtui in full and that it should not be attenuated ..So, the circuit components( R,C ) should be chosen such that no attenuation occurs.
.So ,, in the input, as R comes in parallel, that should be as high as possible and so ideally we take it as infinite
When u take the case of output resistance, the R comes in series and so it should be as low as possible..Ideally, we take this as zero...

BUT , THIS IS THE CASE ONLY WITH VOLTAGE AMPLIFIERS..

In other amplifier configurations these vary..
Refer any standard book and u will find more info on them

yeap it does affect design because u need to take consideration how much load current is required and how much voltage is requierd to turn on the device which depends on the input and output impedances.........

For any practical circuit do have small resistance/impedance

In order the circuit to work properly, the source (input impedance) should
match with destination (output impedance) that is to say should have equal
value, then maximum power will be transferred, then no standing wave will
present on the circuit, circuit will work efficiently

I hope this may be helpful

Infinite input impedance means that the opamp draws no current, which means that all of the current goes to the load.

Zero output impedance means that there is no voltage drop within the opamp, which means that all of your signal is delivered to the load.

Hope this helps

Input impedance of the ckt determines how much i can take from the power supply. and o/p impedace determines how much voltage it deliver to other device connected to it.