4analog
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Hi, I have a question on the bandgap refence. I am refering to the the bandgap reference where the Opamp is used to match the two nodes X & Y and bias the current sources that set the current in both the legs , where v(X) = VBE1 and V(Y) = dVBE + VBE2.
(Razavi, Pg:391, Fig:11.18)
The current is mirrored to generate the PTAT current and then the Vref is obtained by using another Resistor ( R3) and BJT #3, such that Vref = Iptat* R3 + VBE3 .
My question is, why cant we just use the node voltage V(y) as Vref instead of mirroring the PTAT current and using another resitor,BJT ..?
If we can tap the voltage V(Y), then what about the voltage V(X)..? SInce the Opamp forces, both X and Y to be the same, is V(X) also a bandgap voltage..?
Thanks.
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