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How would the temperature affect current flow in the resistor?

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sys_eng

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How would temperature affect current flow in resistor?

Would temp increases current flow in resistor?

Some say for conductor , increasing temp will increase resistance and for insulator , increasing temp will decrease resistance.

So, resistor is more of a insulator, right? Increased temp will decrease resistance and therefore more current flow.

But the resistance formula shows increasing temp would reduce electron mobility therefore increase resistance.

I am hearing two conflict views
 

Re: How would temperature affect current flow in resistor?

It depends on the resistor material; some have a positive temperature coefficient, some have a negative one.
 

Re: How would temperature affect current flow in resistor?

barry said:
It depends on the resistor material; some have a positive temperature coefficient, some have a negative one.
Click to expand...
Let say it's on chip resistor, transistor and the resistor made of diffusion with heavier doping.
 

Re: How would temperature affect current flow in resistor?

sys_eng said:
Let say it's on chip resistor, transistor and the resistor made of diffusion with heavier doping.
Click to expand...

Read my answer again: IT DEPENDS ON THE MATERIAL
 

Re: How would temperature affect current flow in resistor?

A resistor is more of a conductor than a dielectric.

In most materials, resistivity goes up with temperature increase (Al, Cu, W, doped poly-Si, ...).
The reason for that is increased scattering and decreased mobility of carriers (electrons / holes).
Resistivity may go down with temperature, for example, if carrier concentration goes up (for example, in a semiconductor with deep donors or acceptors that are not fully ionized - their ionization ratio increases with temperature, hence carrier concentration goes up and resistance goes down).

Max
 

Re: How would temperature affect current flow in resistor?

sys_eng said:
Let say it's on chip resistor, transistor and the resistor made of diffusion with heavier doping.
Click to expand...

In such case it is basically a semiconductor and the temp co-efficient will be negative.

In other words, higher temp will cause more excitations from the valence band to the conduction band and the conductivity will increase or the resistance will decrease.

In these matters, the semiconductor acts like an insulator (as far as conduction is considered)
 

Re: How would temperature affect current flow in resistor?

No.
Unless we are talking about some extreme conditions (like very deep impurities - like In in Si, or extremely high or low temperatures) - in doped semiconductor, the dominant effect would be decrease of carrier mobility with increasing temperature.
So, temperature coefficient in doped semiconductor (acting as a resistor) is positive, i.e. resistance increases with temperature.
Resistivity of semiconductors (bulk doped semiconductor) is many orders of magnitude lower than that of insulators, that's why different names - insulator, conductor, semiconductor.
 

Re: How would temperature affect current flow in resistor?

timof said:
No.
Unless we are talking about some extreme conditions (like very deep impurities - like In in Si, or extremely high or low temperatures) - in doped semiconductor, the dominant effect would be decrease of carrier mobility with increasing temperature.
So, temperature coefficient in doped semiconductor (acting as a resistor) is positive, i.e. resistance increases with temperature.
Resistivity of semiconductors (bulk doped semiconductor) is many orders of magnitude lower than that of insulators, that's why different names - insulator, conductor, semiconductor.
Click to expand...

Is this it? mobility goes down as temp goes up therefore resistance increase as temp increases. Positive TC.
resistance.jpg


Can you understand this one. ISI has a positive temp coefficient because negative temp cofficients of Up and Rs.
I can underand Up goes down as temp increase but why Rs goes down as temp increases?

fully.jpg
 
Last edited:

are resistance Rs and RT on chip or external resistors?

Rs=10K and RT=40K

That's huge for onchip resistance! The values look like external resistors but the diagram look like on chip integrated resistance. It looks fully integrated!

Which one is it? on chip or external?


Can you understand this one. ISI has a positive temp coefficient because negative temp cofficients of Up and Rs.
I can understand Up goes down as temp increase but why Rs goes down as temp increases?

fully.jpg
 

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Re: How would temperature affect current flow in resistor?

I don't know why Rs has negative temperature coefficients, one should read that article to understand that.
 

Re: are resistance Rs and RT on chip or external resistors?

Tens of kΩ are not huge resistances. On ICs we have an access to a number of different kind of resistors. Well resistors and high resistive un-salicided poly's provide sheet resistance in order of kΩ/sq.
The temperature coefficient depends on many thing (i.e. doping) so it could be both positive and negative for resistors used in IC. Not only metal materials are used as conductors.
 

Re: How would temperature affect current flow in resistor?

Although the article (C. Yoo and J. Park, A new compact temperature-compensated CMOS current reference, ELECTRONICS LETTERS 6th December 2007) , claims a negative temperature coefficient of Rs, it doesn't tell anything about the utilized technology. The authors may be wrong in this point.
 

Re: How would temperature affect current flow in resistor?

Dominik Przyborowski said:
Tens of kΩ are not huge resistances. On ICs we have an access to a number of different kind of resistors. Well resistors and high resistive un-salicided poly's provide sheet resistance in order of kΩ/sq.
The temperature coefficient depends on many thing (i.e. doping) so it could be both positive and negative for resistors used in IC. Not only metal materials are used as conductors.
Click to expand...
Kill ohm/square, that in micron square unit?
 

Re: How would temperature affect current flow in resistor?

ohm/sq is dimensionless, simply the resistance of a structure of same length and width.
 

Re: How would temperature affect current flow in resistor?

FvM said:
ohm/sq is dimensionless, simply the resistance of a structure of same length and width.
Click to expand...

let'ssay,for argument sake, the spec is 10kohm/sq.
IfI can realize it in 10 kohm /micron square versus 10 kohm/milimeter square, then of course I choose micron square. It's smaller.right?
Both are squares, but I choose the smaller one
 

Re: How would temperature affect current flow in resistor?

sys_eng - since resistance is given by the formula:

R=rsh * L / W

where rsh is sheet resistance in Ohm/square), L is length, and W is width -

for the same ratio L/W (L/W=1 for square) - it does not matter if L and W are expressed in meters, or centimeters, or microns, or angstroms...

Resistance of a square (assuming a 1D current flow, i.e. two opposite edges are each equipotential) is the same, whether that is 1 um x 1 um, or 1 meter x 1 meter, etc.

This gives a very convenient way of estimating resistance form the layout - you just need to count the number of squares (and multiply by sheet resistance).
 

Re: How would temperature affect current flow in resistor?

FvM said:
Although the article (C. Yoo and J. Park, A new compact temperature-compensated CMOS current reference, ELECTRONICS LETTERS 6th December 2007) , claims a negative temperature coefficient of Rs, it doesn't tell anything about the utilized technology. The authors may be wrong in this point.
Click to expand...
For argument sake, ?lets say the article is correct. What's the percentage change in resistance per C degree temp change typically?

Does the temp affect RS or Pmos transistor M3 more that make ISI current increases as temp increase?
 

Re: How would temperature affect current flow in resistor?

sys_eng said:
For argument sake, ?lets say the article is correct. What's the percentage change in resistance per C degree temp change typically?
Click to expand...

For pure metals, the temp coefficient is almost constant: a google search shows the value is close to 0.003 to 0.004 /C (http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1)

It can be very different for alloys and semiconductors. For intrinsic semiconductors, you need to look up their band structures.
 

Re: How would temperature affect current flow in resistor?

c_mitra said:
For pure metals, the temp coefficient is almost constant: a google search shows the value is close to 0.003 to re0.004 /C (http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1)

It can be very different for alloys and semiconductors. For intrinsic semiconductors, you need to look up their band structures.
Click to expand...

RS, RT resistors are semiconductor resistors.
Anyone knows the purpose of them? I think they are for sensing temp changes.
 

Re: How would temperature affect current flow in resistor?

The answers on all your questions are available in many textbooks. Below is a table from the most principle one (A. Hastings "Art of analog Layout")
res_tc.png

Those are an example values. E.g. a well resistor could have highly negative TC due to heavier doping.

//edit
For Rs purpose look for "constant-gm biasing" circuits. Again, to find in any textbook.
 
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