How does this circuit work?

[holddreams]

(1)How does this circuit work?T1---T6 seem to be a start-up circuit.

(2)What's the function of T1,T2?
Can they be substituted by NMOS?

(3)Can this circuit avoid the existence of degeneration bias points?

 

[Btrend]

1. it's Iptat generator (part of bandgap core) , not a start-up, but it need a star-up circuit to kick it on
2. ur graph seems not completed yet.

 

[snoop835]

YES, I agree with Btrend. Its a PTAT current reference used in bandgap circuit. The significant attribute of this circuit is that the output current is independent of resistor R1 current. The current throught the NPN transistors are forced to equal each other by active load mirror (T3-T6). Be careful of the mismatch between mirror devices. IT10 = IPTAT

 

[holddreams]

Thanks.

Then what's the function of T8?

 

[sunking]

cascode.
for high out res.

 

[Humungus]

T8 is just a cascode for T7 to improve the output resistance.

 

[snoop835]

Improving output resistance, hence improving PSRR of the circuit.

 

[holddreams]

The output(out1 ,out2) of the startup circuit is connected to the PTAT,
How does it work?

 

[sunking]

upload the fully schematic

 

[GDF]

YES, I agree with Btrend. Its a PTAT current reference used in bandgap circuit. The significant attribute of this circuit is that the output current is independent of resistor R1 current. The current throught the NPN transistors are forced to equal each other by active load mirror (T3-T6). Be careful of the mismatch between mirror devices. IT10 = IPTAT

Why the output current is "independent" of R1?