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Generating the bias voltage of an op-amp

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firsttimedesigning

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So I am trying generate the bias voltage of an op-amp. So far the only circuit I know that can be used to generate the bias voltage is bandgap reference. But bandgap reference can only generate a voltage that is around 1.4V. I need a bias voltage that is higher than 1.4V...What circuit should I use?
 

resistor layout bandgap

you can use LDO.

the output voltage will be :

vout=(1+r1/r2)*vreg.

so you can get the voltage by adjusting the r1 and

r2.
 

designing band gap reference generator

yeah but when i fabricate the chip, the resistance will vary within 20%...a 4k resistor might only have 3.2k resistance. the result wont be very accurate...i need something that can generate a very accurate bias voltage...something that only have error within 0.1%...
 

only pmos beta multiplier

you are wrong.
r1/r2 means the accuracy depends on the relative accuracy of the resistors.

so you can get the result you want.
 

bandgap bias

i dont get it...let's say i want r1/r2 to be 2....i set r1 to be 4k and r2 to be 2k...
but the actual resistance of r1 is 3.2k and r2 is 2.4k....then the ratio is not 2...rather it is 1.3333....how is that going to give me the result that i want?
 

bandgap reference opamp

if you implement the resistor in silicon IC.
the varation of the resistance will be the same.

if r1 increase 20%, the r2 will increase 20% too.

the relative accuracy of resistor can give 0.1% requirement if you design and layout it carefully.
 
how to generate 2.5 v bandgap reference

use current mirror to copy the current from the band gap to another resistor
 

bandgap reference voltage with op-amp

You can match 2 resistors better than 1% if you use common-centroid layout.
Please "reference the art of analog layout" book, chap.7 about common-centroid layout.
 
brokaw bandgap with compensation or beta

thanks for replying...i got it now..ok i will use LDO....thx a lot
 

Bandgap Reference

why u are using a bandgap bias the opamp?
 

Bandgap Reference

the bandgap circuit can get 2.5v.
 

Re: Bandgap Reference

thx for replying...
to Qutang...bandgap reference is the only circuit that i know...are there temperature and power supply independent circuits that i can use to bias the op-amp?
 

Re: Bandgap Reference

can any explain how to design a LDO? i just dont get it....
 

Bandgap Reference

Why don't you just gain up the bandgap voltage? It's commonly done. Check out the brokaw circuit.
 

Re: Bandgap Reference

use a close loop buffer or charge pump if it has a clock.
 

Bandgap Reference

If for biasing opamp, you don't need "absolute value" of bias voltages, current mirror is a better way to generate your bias voltages for opamps. Razavi's book Ch.6 and Ch.9 have detail explainings.
 

Bandgap Reference

what about beta multiplier
 

Re: Bandgap Reference

Why need LDO ?
It doesn't make any sense to use LDO as bias boltage generator,
as you know, LDO need large cap compensation.
I think you mis-understood what the LDO is

Bandgap, with an op-amp and feedback resistor divider will have a gain >1, so
you can get any voltage by resistor divider ratio.
 

Re: Bandgap Reference

firsttimedesigning said:
So I am trying generate the bias voltage of an op-amp. So far the only circuit I know that can be used to generate the bias voltage is bandgap reference. But bandgap reference can only generate a voltage that is around 1.4V. I need a bias voltage that is higher than 1.4V...What circuit should I use?
Click to expand...

If you are trying to bias opamp, you don't need bandgap. Just use current mirrors. Otherwise, how are you going to generate the bias for the opamp used in bandgap?
 

Bandgap Reference

use the resistor network!
 

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