what is the type of feedback in this circuit? help!!!

[carlson]

This is a part of a bandgap circuit! It seems to be a feedback circuit. But I don't know the machnism of this feeback and the type. Please give me your views! thanks a lot!!!

 

[sharas]

As I understand, the feedback is serial input - parallel output. The drain voltage of the NMOS on the first stage is also the gate voltage of the upper PMOS of the second stage - therefore it determines the current in the second stage (current is a function of Vgs).
Now, The current in the second stage determines the voltage drop across the resistor, whic is the Vsource of the NMOS in the first stage. The current in the first stage depends on Vgs of the NMOS, so now the drain voltage of the NMOS changes accordingly - and this is your feedback.

 

[andy2000a]

output feedback current -> series
input use Resistor cascode with Mos --> series

this is series - series

after feedbackup
Input/output impednace both will increase

 

[carlson]

Thanks for your discussions.And what's the benefits of this circuit? whtat's the objective of the feedback?

 

[timer]

hi carlson,
could you put up the whole ckt. with the bandgap
thanks
bye

 

[surianova]

Below is how negative feedback work

1. You inject a AC signal current across the resistor, the AC voltage across resistor will be increase, V=IR.

2. Then the drain voltage of NMOS will be increased.

3. Then drain voltage of PMOS ( top right) will be reduced.

4. Then the AC voltage across resistor will be reduced. This show a invert sign of input current, it is a negative feedback.

 

[carlson]

This is the main part of the bandgap voltage reference.I have 3 questions.

1. how can we know the curren flowing the M9 and M10? I think we should know this current if we calculate the voltage of the "vref" .

2. why do it use the feedback?

3. why is the number of diode D2 three ?

 

[carlson]

if you can help me analysis this circuit ,i will appreciate very much!