Is the input impedance of a circuit defined...
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SSLtech
Well-known member
No.
For several reasons.
Firstly, resistance is DC only. Capacitance and inductance have an effect. Transformers reflect what comes after them (as best they can; again frequency-dependant) and semiconductors make all things more complicated.
And that's just inputs.
Outputs can have series current-limit resistances and still have less effective impedance, due to negative feedback.
There's much -*much*more to it than that, but there's a couple of very quick examples why it's not that simple.
Keith
For several reasons.
Firstly, resistance is DC only. Capacitance and inductance have an effect. Transformers reflect what comes after them (as best they can; again frequency-dependant) and semiconductors make all things more complicated.
And that's just inputs.
Outputs can have series current-limit resistances and still have less effective impedance, due to negative feedback.
There's much -*much*more to it than that, but there's a couple of very quick examples why it's not that simple.
Keith
[quote author="syn"]Resistance is DC related and impedance AC?
Thanks[/quote]
Basically, yes.
When you deal with AC signals, other components start to act a bit like resistors (reactance).
This varies with frequency though, so it is complex.
Search on the internet for impedance, and look at some very basic filters - eg. a series RC filter to help you understand what happens.
Thanks[/quote]
Basically, yes.
When you deal with AC signals, other components start to act a bit like resistors (reactance).
This varies with frequency though, so it is complex.
Search on the internet for impedance, and look at some very basic filters - eg. a series RC filter to help you understand what happens.
