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How to build a negative resistor??

 
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Alles Gute



Joined: 04 Dec 2003
Posts: 142
Helped: 5
Post23 Dec 2004 22:27   How to build a negative resistor??
In the analog filter design. Sometimes we need a negative resistor. Then how to build a nagative resistor? Use feedback? how?
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zorro



Joined: 06 Sep 2001
Posts: 327
Helped: 36
Post23 Dec 2004 22:43   How to build a negative resistor??
Hi Alles,

You can use a Negative Inmitance Converter (NIC). Look for it in network theory literature. It is an active device with one operational amplifier and 2 resistors that converts an impedance Z (not necessarily resistive) into -k*Z. It uses feedback, of course.
Regards

Z
(with a NIC I become -Z, ha...)
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arsenal



Joined: 17 Oct 2004
Posts: 134
Helped: 11
Post23 Dec 2004 23:27   How to build a negative resistor??
i think if u realize the filter in sc mode then sc inverting connected circuit acting as a negtive res should be used
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v_naren
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Post25 Dec 2004 8:03   Re: How to build a negative resistor??
there u go
Smile

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srivatsan



Joined: 04 Aug 2004
Posts: 183
Helped: 4
Post02 Jan 2005 0:37   Re: How to build a negative resistor??
I did not know that you can build negative resistance with MOSFETs. probably thats the best answer.

- this is what i got:

Usually, my way has been to have an OpAmp, with its inverting node connected to both the output node of the OpAmp (feedback resistance R3) and the input current (Iin) and the non-inverting node is connected to both the output node of the OpAmp through R2 resistor and to the ground via R1 resistor. the Output is given by:

Vout = -R3*R1*Iin/R2.

Vout is between the inverting node and the ground.
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zorro



Joined: 06 Sep 2001
Posts: 327
Helped: 36
Post02 Jan 2005 6:15   How to build a negative resistor??
What srivatsan described is a NIC.
For any Z1 in the place of R1:
Zin=-(R3/R2)*Z1

-Z
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v_naren
Guest
Post02 Jan 2005 6:41   Re: How to build a negative resistor??
well since the question is for a negative resistor I think the cross-coupled mos pair is simple enough.
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