What is bandgap and why is it important in analog design?

Hi,

My knowledge in analog design is very limited. Thus, can someone please tell me what is a bandgap? why is it so important in Analog Design (mix signal)?

Highly appreciated

Thanx in advance,
-no_mad

dtmos band gap reference

bandgap generate output that is independent of temperature. It is very
important in analog design as a reference voltage. For example, in voltage
regulator design, common mode feedback , you need a reference voltage constant
across temperature.

bandgap voltage reference 1.205

The bandgap in very important in A/D and D/A.

bandgap voltage 1.205

accuracy of the data converters depends on the precision reference voltage.,
bandgap reference voltage is temperature and process independent.,
thus it will be used in A/D and D/A converters.

recombination third body conserve momentum

Normally, the band-gap we say means the band-gap voltage of silicon, and it equates 1.205V, furthermore it has very low temperature coefficient.
In analog design, we often use Band-gap voltage to generate voltage reference. So for Band-gap voltage reference, the very low temperature coefficient is its most keypoint, certainly also contain its precision characteristic.

silicon band-gap temperature coefficient

huojinsi said:

Normally, the band-gap we say means the band-gap voltage of silicon, and it equates 1.205V, furthermore it has very low temperature coefficient.
In analog design, we often use Band-gap voltage to generate voltage reference. So for Band-gap voltage reference, the very low temperature coefficient is its most keypoint, certainly also contain its precision characteristic.

Click to expand...

Hi Houjinsi,
i agree that the bandgap voltage of silicon is around 1.2V. But how is it related to the reference voltage circuit. I have seen some bandgap references having a different output voltage other than 1.205V. can u please explain. any material regarding this would be welcome.

thanx in advance
chethan

what is bandgap

Chetan, for achieving a voltage reference with a low temperature coefficient you need to add a CTAT(Complementary to absolute temperature) voltage with a PTAT(Proportional to absolute temperature) voltage. The CTAT voltage usually is the forward bias voltage across a p-n diode; this voltage at 0ºK is almost equal to the bandgap voltage of the material at 0ºK (silicon≈1.2V); then the output voltage of the bandgap reference is almost the bandgap voltage at 0ºK. See the figure that i uploaded.

A bandgap reference circuit can generate other voltages:
You can scale the output voltage with resistors.
You can use DTMOS devices.
You can use other material with a different bandgap voltage at 0ºK (Ge≈0.6V) for making your circuit.

bandgap pvt independent

bandgap is essential in most analog applications.A good bandgap provides very stable voltage reference with PVT independent.

complementary to absolute temperature -patent

jc2 said:

You can use DTMOS devices.

Click to expand...

hello jc2,
i was hoping more info about DTMOS devices.
thnx and regards,
a.safwat

what is bandgap?

In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is often spelled "bandgap".
There is virtually no bandgap in most metals, but a very large one in an insulator (dielectric). In a semiconductor, the bandgap is small. Technically, the bandgap is the energy it takes to move electrons from the valence band to the conduction band.
A bandgap reference voltage is just a voltage reference based on this property.

rgds,
M

what is band gap

In semiconductor physics, a direct bandgap means that the minimum of the conduction band lies directly above the maximum of the valence band in momentum space. In a direct bandgap semiconductor, electrons at the conduction-band minimum can combine directly with holes at the valence band maximum, while conserving momentum. The energy of the recombination across the bandgap will be emitted in the form of a photon of light. This is radiative recombination, also called spontaneous emission. In indirect bandgap semiconductors such as crystalline silicon, the momentum of the conduction band minimum and valence band maximum are not the same, so a direct transition across the bandgap does not conserve momentum and is forbidden. Recombination occurs with the mediation of a third body, such as a phonon or a crystallographic defect, which allows for conservation of momentum. These recombinations will often release the bandgap energy as phonons, instead of photons, and thus do not emit light. As such, light emission from indirect semiconductors is very inefficient and weak.

What is bandgap?

bandgap reference circuit can generate other voltages

Re: What is bandgap?

safwatonline this paper presents a bandgap circuit that use DTMOST devices