Bandgap Reference Circuit With Op Amp. It commonly has an output voltage around 1 25 v close to the theoretical 1 22 ev 0 195 aj band gap of silicon at 0 k. The capacitor across the op amp is for stability.
The summing amplifier adds the voltages which ensures the output voltage is always directly proportional to the bandgap. 2 september 2016 v ref v be r2 r3 v be i v v be v be q1 q2 q3 r3 600 r1 600 r2 6k ground r2 r3 v be figure 1. Ignore the base currents we have kv r i i 2ri ln ln 1 1 2 1 3 2 1 v n i i i ir v v v t c s c s.
The bandgap cell reference voltage vbg appears at the combined base of q 1 and q 2 and is the sum of vbe q 2 and vr1 or 1 205 v the bandgap voltage.
Ignore the base currents we have kv r i i 2ri ln ln 1 1 2 1 3 2 1 v n i i i ir v v v t c s c s. Bandgap voltage reference circuit built from a summing amplifier. An alternative bandgap voltage reference circuit uses an op amp as a summing amplifier with a forward biased diode and resistor. Bandgap voltage reference circuit 1 from the figure the emitter area of q1 is n times as large as the emitter area of q2 then is1 is2 n by op amp action with identical collector resistances the collector currents are also identical i e.
