need your help in temperature sensor

[psthanh]

I must to design a temperature sensor based on Cmos technology using PTAT core with output 1uA/K can use the power supply from 3.3 V to 5 V But i don't know about electronic, i work on electrical. Could you please help my with the ideal. So many Thanks.

 

[tyanata]

This is basic circuit of Ptat temperature sensor.

Vptat=(k*T/q)*LN(N), where N is ratio of emmitter areas of two bipolar tansistors.

I thing you make mistake whe define sensor sensetivity in uA/K, it is right to be V/K.

 

[psthanh]

Thank you very much.
For the basic circuit the output is very small for example N=8 the VT = T*0.1792mV/K

i don't know how to make it larger.
Thanks again.

 

[tyanata]

There is two ways to increase Vptat:

1. Just increase Bipolar transistor ratio
2. See voltage PTAT2 at figure bellow:

PTAT2=PTAT*M

Where M can be current mirror ratio W(M5)/W(M3), or resistor value ratio R2/R1.
Advantage of this approach that it saves area in lay-out, but drawback is that it is more unaccurate, because of offsets and all possible parasitic effects.

 

[psthanh]

Thanks sir.
May i ask one more question. because the AD590 have current output 1uA/K
and the power supply can be from 4 to 30 but when it change from 5 to 10 the output only error 1uA.

 

[tyanata]

I didn't understand the question, but if you asking how Ptat voltage can be transfered to Ptat current. Just put resistor R1 in first stage to be with low TC and obtained current will have characteristic almost proportional to T, [uA/k].

I=Vptat/(R1nom*(1+TC1*dT+TC2*dT*dT), if TC2=0 and TC1≈0
I=Vptat/R1 so curren becomes Ptat current. Now simpli mirror this current and use it.

 

[psthanh]

thank sir. i will try to simulate it tonight.