# bandgap reference

#### Nancy@21

##### Newbie level 4
Hi,
I want to study this bandgap reference circuit. Please suggest.

1. The vbgt expression will be as follows( derivation.jpg).
2. Is it a low voltage folded bandgap reference circuit.

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• bandgap.png
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• derivation.jpg
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#### Nancy@21

##### Newbie level 4
Thank you. the attached paper is useful. Is it a low voltage folded bandgap reference circuit.
Is the derivation of vbgt is correct?

#### Nancy@21

##### Newbie level 4
Is it a low voltage folded bandgap reference circuit.

#### arthorios

##### Junior Member level 3
It should be correct assuming the resistances connected to nodes vn and vp are the same, i.e. IMP2=IMP4.

Is it a low voltage folded bandgap reference circuit.
I don't know what you mean with folded in this circuit. This is considered a "sub-bandgap voltage reference" since it is below the usual 1.25V bandgap voltage. Because of that, it can also operate at power supplies <1V (which can be considered "low voltage").

#### Nancy@21

##### Newbie level 4
Thank you. I study this reference paper and see this derivation again.

#### deep_sea

##### Full Member level 1
Thank you. the attached paper is useful. Is it a low voltage folded bandgap reference circuit.
Is the derivation of vbgt is correct?
The short version of expression is that you add a PTAT current to a CTAT current to get a zero to absolute temperature (ZAT) current.
PTAT comes from $\Delta$ VEB /R1 = VT ln / R1.
CTAT voltage VEB is divided by (R2 + (R4||R5) to give a CTAT current.
Both currents are added in IMP4 (ZTAT current).
IMP4 is copied into IMP6 and flows in R3 to produce a ZTAT output voltage as given by the expression you have derived.

#### Nancy@21

##### Newbie level 4
The short version of expression is that you add a PTAT current to a CTAT current to get a zero to absolute temperature (ZAT) current.
PTAT comes from $\Delta$ VEB /R1 = VT ln / R1.
CTAT voltage VEB is divided by (R2 + (R4||R5) to give a CTAT current.
Both currents are added in IMP4 (ZTAT current).
IMP4 is copied into IMP6 and flows in R3 to produce a ZTAT output voltage as given by the expression you have derived.
Thanks very much for the detailed description. I study it and if needed further I will discusses.