What are the specifications of opamp design for bandgap?

• Feb 25, 2005

• #1

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avinash

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bandgap opamp stability

while designing opamp for first order bandgap,what are the specifications of the opamp we should keep in mind other than high gain.

 

• Feb 25, 2005

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ccw27

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low offset voltage opamp design

High Gain at all temperature condition and also need to check stability

 

• Feb 25, 2005

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lastdance

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Re: opamp design for bandgap

i suggest u pick up a basic analog book and read the chapter on bandgap design. almost any well known analog design book will help.

 

• Feb 25, 2005

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bastos4321

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Re: opamp design for bandgap

Take care of the offset voltage of the amplifier, since this offset will directly reflet in the bandgap voltage.

Bastos

 

• Feb 25, 2005

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kwkam

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opamp design for bandgap

I suggest you check the unity gain bandwidth. If the feedback is not fast enough. The bandgap will oscillate.

 

• Feb 26, 2005

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ambreesh

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Re: opamp design for bandgap

Need a low offset for the amplifier. As offset TC would also effect the total TC of the BGR. You need high gain for the amplifier as you need to reduse the gain error as fionally attain same currents in both the branches. Their is no doubt thst the system must be stable.
An BGR must have good line regulation and PSRR. The choise of amplifier topology is critical. The output of the amplifier goes to gate of PMOS transistors that are pumping current. To make the power supply ripple common mode, your amplifiermust pass the complete power supply rippel to its output. Thus you see the ripple at both gate and source of the PMOS.
Your amplifier must have good CMRR.
Hope it helps

 

• Mar 2, 2005

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cliffj

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Re: opamp design for bandgap

low input offset and also low offset drift. The stability issue, since the paristic capacitance from PMOS current mirror is going to locate a new position of your pole.(especially for two stage opamp with miller compensation)

 

• Sep 30, 2005

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nuiscet

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opamp design for bandgap

The gain of amplifier is not the most important , the most important factore is the offset voltage of the amplifier which can greatly affect your bandgap reference.

 

• Sep 30, 2005

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schwang1970

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Re: opamp design for bandgap

bandwidth and offset voltage and DC gain.

 

• Oct 1, 2005

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nandu_r

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Re: opamp design for bandgap

Also should consider noise, and psrr spec

 

• Oct 1, 2005

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zenisle

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opamp design for bandgap

I suggest you get some example of bandgap, it is a quick method.

 

• Nov 10, 2005

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jinxingsun

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opamp design for bandgap

offset voltage ,slew rate and stability

 

• Nov 26, 2005

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leonlin

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Re: opamp design for bandgap

Take care of the offset voltage of the amplifier

 

• Nov 26, 2005

• #14

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bsrivastava

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Re: opamp design for bandgap

ICMR of the op-amp should be close to the cutin voltage of the p-n junction diode.

 

• Nov 27, 2005

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Re: opamp design for bandgap

The offset is very important to the OPA,it badly affect the reference voltage

 

• Nov 27, 2005

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tanghua_0407

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opamp design for bandgap

The offset is very important to the OPA,it badly affect the reference voltage

 

• Nov 29, 2005

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Re: opamp design for bandgap

The OPAMP ensure that two nodes have the same voltage in a bandgap voltage reference; this nodes are conected to the OPAMP inputs

How does the OPAMP ensure that these two nodes have the same DC voltage? (=0.7 Volts).............. by its simetry?.
I understand that in AC the two inputs can have the same voltage, by its feedback and its high gain; but
why in DC?

Thanks

 

• Dec 6, 2005

• #18

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Re: opamp design for bandgap

the input offset

 

• Dec 7, 2005

• #19

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Chethan

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Re: opamp design for bandgap

sina25 wrote
The OPAMP ensure that two nodes have the same voltage in a bandgap voltage reference; this nodes are conected to the OPAMP inputs

How does the OPAMP ensure that these two nodes have the same DC voltage? (=0.7 Volts).............. by its simetry?.
I understand that in AC the two inputs can have the same voltage, by its feedback and its high gain; but
why in DC?

Thanks
----------------------------------------------------------------------------------------------
If both the inputs to an opamp in a BGR is 0.7V then my ICMR(min) has to be less than 0.7V. I am designing the same with a 5V process and 0.756V VTh , is it possible for me to acheive that small ICMR(min) value. I am trying with a NMOS type input differential pair as the first stage of the opamp.

Thanx with advance ................

 

• Mar 14, 2006

• #20

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derknand

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opamp design for bandgap

It's impossible.The Vth of the input nmos will increase for the V between S and B.And u still need a Vds.So I suggest u used pmos input OA.