Why we use BJT in bandgap reference?
Most BGR use bipolar junction transistors (BJT) to easily reduce the temperature dependence, due to temperature coefficients, other common practice is the use of operational amplifiers (OP-AMP).
Why PNP transistor is used in BGR?
A npn transistor has electrons as majority charge carriers whereas the pnp transistor has holes as majority charge carrier. The mobility of electrons is better than mobility of holes. So a npn transistor is faster in operation than a pnp transistor. As mobility of electrons are greater than holes.
Why are BJT transistors used instead of diodes?
I’m just asking what is the main reason to use BJT transistors as pn or np junctions for bandgap voltage reference instead of using just pn or np diodes also available on CMOS technologies. Diode-connected BJTs behave more like ideal diodes than diodes. In particular the ideality factor η is 1.0 rather than somewhere closer to 1.5 or 2 for diodes.
Can a ESD diode be used as a bandgap?
It usually has a terrible beta but for use as a diode this does not matter. I’m sure you could use an ESD diode as the basis for a bandgap but in the end the structure of the diode will be very similar to that Vertical PNP.
What is the principle of the bandgap voltage reference?
The principle of the bandgap voltage reference is to balance the negative temperature coefficient (NTC) of a pn junction with the positive temperature coefficient (PTC) of the thermal voltage, Vt = kT/q. For some reason, someone decided to call them PTAT/CTAT wasn’t aware that PTC/NTC was already common long before bandgaps.
What is the primary effect of bipolar bandgap references?
The primary effect in bipolar bandgap references is the variation of resistors in the circuit. Absolute value of these resistors is controlled to 20% or even 50% by process parameters. This problem can get more acute when different types of semiconductor resistor are used for curvature compensation.