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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
hello all. I get task to simulate LRCD frequency difference detector circuit. and i wonder can i use simple voltage divider formula ? U=Uin(X1/(X1+X2)) ?( X1 X2 frequency dependent resistor ) But this model lead me to major problem: How i can calculate X1 ( lets say it's inductor, so it would be X1=2*pi*f*L ) if i have two frequencies ? (U=Asin(w1)Asin(w2)) and will it work if i take diode as resistor R=U/I=F(U)/G(I) where F is voltage characteristics, and G is current characteristics of diode
ok, i found out that sin(w1) is responsible for Amplitude, and sin(w2) for frequency. now only problem left is calculate resistance of diode
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Sulaiman wrote ...
I don't get what you're attempting, could you give an example of what input(s) you're considering and what output(s) it should produce?
i have input V=sin(w1t)sin(w2t); in output i should get f=(w1+w2)/2 and show spectrograph and other part of the task how LCRD system reacts for short pulses of square wave (i need do get response at the end of circuit) all should be made by using MatLab
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I recognise V=sin(w1t)sin(w2t) as amplitude modulation, When 'detected' you get sum and difference frequencies w =(w1 + w2) and w = (w1 - w2) but I've not come across w = (w1 + w2)/2.
Please post the solution when you get it as it would interest me.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
simulation in multisim show that i will get middle frequency of two incoming waves.(just like title of the task says) if i use w1=500 w2=502 i get in output w=501 same results with bigger difference (500+510 >> 505) All equations already written, now just need to write diode as resistor dependent of voltage. But that is tricky part, because i need to calculate voltage on diode ( and that is hard, because diode himself is responsible off voltage drop, and that drop depends of voltage across terminals of diode) any ideas how to do that ?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You will need to use some kind of iterative solver.
In other words, the diode voltage drop depends on the current, which depends on the voltage drop, so you start by guessing one of the two variables. Then you can calculate the other one, and use Kirchhoff's circuit laws to see if your guess fits with the rest of the circuit, this gives you an error which you can use to drive your guess in the right direction. When the error reaches some small value you stop and move on to the next time step.
This is (grossly simplified) how the transient simulation engine works in Spice, Multisim etc. Matlab should have several kinds of solvers built in.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Can some one check if i did it right ? (all should be ok, except i can change + to -) But after solving this problem with matlab, i get very small output ( and multisim show normal output) i get V=10e-10
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LCRD circuit
