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Another question about Bandgap--- the start up circuit.

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benchen

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I found the start up circuit for a bandgap is difficult to work well at different Vcc supply. For example, 2.7v and 3.6V. When the Vcc is high, the start up circuit can not shut up completely and when the Vcc is low, the startup circuit can not bias the bandgap core circuit to a wanted level.
How to handle this problem when the Vcc changes? Can you show me some other start up circuits?
 

connect those two line to the bandgap output
 

1. VCC High -> Not rpoperly shutting down ->M13 gate voltage high in normal operation -> VGS of PMOS M21 low or strong PMOS -> so make M21 further weak

2. VCC Low -> Not able to bias properly-> The gate voltage of M13 is low. But M21 can't be made stronger. So try making M13 stronger.

This should solve the problem.

If the problem is not solved yet, it should be because your supply variation is very large. Then you may have to try a different startup architecture.

Thanks
 
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    woai

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go for the bekar book for startup circuit
 

your start up circuit is dependant on the supply voltage. don't use the amplifier like M14 and M21. Just use switches.
 

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