What's the function of this circuit???

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newhand

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In the circuit,the input "VREF" is a bandgap voltage which generates from a bandgap circuit.
"BP1" is a bias voltage and its bias current is propotional to VREF.

Now i only know the circuit has something to do with the modulation of temperature coefficient.
What I can't understand is that there is a resistor which connect between the input of the emitter-coupled pair,what's it's function???
 

Well, the image is not clear, but this is a trick used sometimes to avoid that the differential input of an amplifier gets too high when the amplifier goes out of its linear regio, i.e. it saturates. The resistor forces a relatively small voltage so that the amplifier can recover faster from the saturation state.
 

I don't think it has something effect to TC, what you said
"its bias current is propotional to VREF." means

Ibias = vref / Rpod ??
 

not clearly ,hope u to interpret ur question clearly!
 

I don't think it has something effect to TC, what you said
"its bias current is propotional to VREF." means

Ibias = vref / Rpod ??
Click to expand...
Yes ,Ibias=vref/Rpod.
I guess the "OUT" will sink some current which will be relevant to Temperature.
And the strange structure similar to diffrential pair seems to decide how much current will be sank.
Cause we can see that the two terminal of the strange structure has something to do with temperature coefficient,
but details still not known...
 

If It is to sink current, the current should be

Ibias + (Ic / VT) * (Ibias - Ic) * R

and

Ic = (Vref-VBE)/R

So the resistor between two input terminal is to sense the current diffrence between Ibias and Ic

U can get more information to know about it , for example , the output is current or voltage?
 

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    newhand

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Hi hardings:
Thanks,now I know the out pin will sink some current.It seems that the circuit works as u said.But I don't understand why the voltage drop of the resistor
is (Ibias - Ic) * R,could u please expain more clearly ,
or give me some reference book about it???
 

That is the KCL at the right input of the differential pair.

Can u tell me the output connect to a resistor or drain of mosfet or others ?

I think if the circuit is to get ZTC current , it is too expansive with so mang element.
 

hi,hardings:
The circuit is not used for getting a ZTC current.As I know ,its function is to get a current whose temperature coefficient is between 0.1mA/°C and 0.13mA/°C.
The complete circuit is in the attachment.
In the circuit ,the M1's drain current will be mirrored with scale of 1:600,but I didn't draw the parts for mirroring which i will get the current I want .Because of the scale of 1:600,So the temperature coefficient of M1's drain current should be between 0.1mA/600/°C and 0.13mA/600/°C.
Now I am still simulating this circuit and seem to get a result I want.But I am still puzzled about the details of the circuit as u said that it seemed too complicated,
 

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