Why BJT is used in bandgap reference?

Why BJT is used 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).

How does a bandgap voltage reference work?

A bandgap voltage reference is a temperature independent voltage reference circuit widely used in integrated circuits. It produces a fixed (constant) voltage regardless of power supply variations, temperature changes, or circuit loading from a device. This circuit concept was first published by David Hilbiber in 1964.

Why PNP transistor is used in BGR?

NPN is most suitable for negative ground system. Common Emitter configuration is most widely used transistor configuration. with PNP transistor, +ve supply line becomes common point (circuit ground) of input & output signal, which is not so convenient for design, testing and maintenance.

Why is transistor used with diode?

When switching speed is important: if you need to switch the diodes fast, a transistor hooked up as diode usually performs better in high speed switching and in high frequency applications; because transistors are designed for high frequency and diodes are typically not optimized for high frequency applications.

Can we use diode instead of transistor?

No, two diodes connected back to back cannot be used as a transistor. A PN diode will have equal doping on both sides, but for a transistor, the base must have the least doping level and the emitter must be highly doped. Joining two diodes will make the base size larger than the emitter and the collector.

What is the objective of the band gap reference circuit?

Bandgap ref. Objective of reference generation is to establish a dc voltage or current that is independent of the dupply and process and has a well defined behavior temperature. In most of the applications ,the required temperature dependence assumes one of the 3 forms.

What is voltage reference Why is it needed?

A voltage reference is a precision device specifically designed to maintain a constant output voltage, even as parameters such as ambient temperature or supply voltage change. The precision of a voltage reference enables its use in several differ- ent types of applications beyond a data converter.

Why do we use NPN transistor instead of PNP?

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. mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that’s why they are preferred..

Why is NPN transistor preferred over PNP transistors?

The majority charge carriers in an NPN transistor are electrons and the majority carriers in a PNP transistor are holes. The electrons have better mobility than holes. Therefore, NPN transistors are preferred over PNP transistors.

What’s the difference between a transistor and a diode?

The main difference between diode and transistor is that transistor is a three terminal device which passes current from high resistance region to low resistance region while the diode is a two-terminal device which current in only one direction from the anode to the cathode.

Why diode is used in transistor?

Put simply, a diode is a two-terminal semiconductor device and a transistor is a three-terminal semiconductor device. A diode can allow the flow of current in one direction while blocking the flow of current in the other direction.

What is the ideality factor of a diode-connected BJT?

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. The exact reasons for this are a bit involved. See this paper, for example.

Why do we use bipolar transistors as diodes?

It is a common practice in precision analog electronics to use Bipolar transistors as diodes. The purpose is to obtain a very low leakage diode. For example, a 3904 type transistor will have <1pA of reverse leakage using the Base Emitter junction. However, it turns into a zener diode at around 6.8V.

Can I use an ESD diode 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 function of a rubber diode in a circuit?

“Rubber diode”. If we apply not the whole collector-emitter voltage to the base-emitter junction but a part of it, VBE will be multiplied (like in the non-inverting amplifier). The “transistor diode” will act as a “transistor Zener diode” with any desired voltage. This network is widely used as a bias circuit in op-amp and power amplifiers.