I just watched an interesting video about negative feedback and I have a couple questions. The first one I have is what would happen if you were to replace a feedback resistor with a negative feedback element? I don't know how to model circuits or I would try to myself.
IF you were to put a negative resistance element in series with an equivalent resistor would they act like a short in circuit?
How can negative resistance be used in audio? Are there any practical applications?
IF you were to put a negative resistance element in series with an equivalent resistor would they act like a short in circuit?
How can negative resistance be used in audio? Are there any practical applications?
negative resistance supplies power to what it is connected to - so practical "negative resistance" circuits use amplifying devices and require a external power source
they can only be made to approximate the negative resistance function over a restricted range of I, V and frequency
mixed negative and positive feedback can be used to create occasionally useful audio frequency negative resistance circuits
(partially) canceling the series resistance of a coil of wire - speaker voice coil, or transformer primary is sometimes helpful
there was a fad for FDNR frequency dependent negative resistance in active filter design
they can only be made to approximate the negative resistance function over a restricted range of I, V and frequency
mixed negative and positive feedback can be used to create occasionally useful audio frequency negative resistance circuits
(partially) canceling the series resistance of a coil of wire - speaker voice coil, or transformer primary is sometimes helpful
there was a fad for FDNR frequency dependent negative resistance in active filter design
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Hi,
There are no linear negative resistance devices so basically it won't work.
There is no such thing as real negative resistance device, only devices
that drop resistance with a negative slope over a voltage range,
so an effective short is impossible passively.
However its very easy to rearrange the feedback using linear elements
to give a very linear negative output impedance, it has lots of uses.
rgds, sreten.
There are no linear negative resistance devices so basically it won't work.
There is no such thing as real negative resistance device, only devices
that drop resistance with a negative slope over a voltage range,
so an effective short is impossible passively.
However its very easy to rearrange the feedback using linear elements
to give a very linear negative output impedance, it has lots of uses.
rgds, sreten.
In the video I posted there is what looks like a relatively linear negative resistance shown @ 11:53 on the O-scope. Is this not linear? Couldn't something like this be used only in the linear region?
when you say there is not such thing as a negative resistance device, only active devices that behave in a negative resistance fashion. Does that really matter in circuit? What about tunneling diodes? I know they aren't linear but wouldn't they be a partially negative resistance device?
This is all new to me and I am still trying to wrap my head around it and think of uses.
If you were to replace the feedback resistor with an active device that demonstrated negative resistance, would you have a stable circuit or would you have an oscillator?
It is a funny coincidence that we just recently discussed some use of negative resistance in another thread:
http://www.diyaudio.com/forums/multi-way/255492-if-transient-perfect-only-were-easy.html
It was about a patent by a big multinational company showing something that will definitely NOT work.
Within the thread it was also pointed at the dangers of blindly believing into simulation results. If you simulate circuits using negative resistance(s), especially filters, always run a transient simulation besides the frequency response !
Regards
Charles
http://www.diyaudio.com/forums/multi-way/255492-if-transient-perfect-only-were-easy.html
It was about a patent by a big multinational company showing something that will definitely NOT work.
Within the thread it was also pointed at the dangers of blindly believing into simulation results. If you simulate circuits using negative resistance(s), especially filters, always run a transient simulation besides the frequency response !
Regards
Charles
I used resistors having a negative value as virtual components to simplify simulations when studying configurations à la Stahl.
Of course, in reality, such virtual components need to be synthesize by an elaborate circuit.
Rgs.
Tunnel diodes etc. provide a limited somewhat non-linear negative resistance. They were popular about 40-50 years ago but they have a tendency to oscillate at UHF or microwave frequencies - which is what they were sometimes used for. Best avoided for audio.
Plenty enough fun can be had by using ordinary components in clever circuits.
Plenty enough fun can be had by using ordinary components in clever circuits.
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