How to verify the start-up circuit in a bandgap??

[Sam81]

start up circuit

Hi,

I'm designing a bandgap and use a classic start-up circuit, but I have problem of how to make sure if it works. Without the start-up circuit, the bandgap still start to work after the supply voltage ramps up. So how to simulate the practical situation? Thank you so much.

 

[malizevzek]

bandgap startup

Transient simulation + Monte Carlo + Process Corners

 

[Vamsi Mocherla]

Oh, its very simple, charge the nodes to zero, the nodes the start-up circuit has to charge. PMOS gates will get a VDD level and NMOS gates will get a VSS level. The problem with the normal sim is that it estimates the iniital conditions and arrive at the final value because there is a positive feedback inherently in the bandgap cirucit.

You can do the above test with and without a start-up circuit and I am sure that you will see the difference

 

[name_n16]

hi,
use .ic statement to initialize the node and no need for startup circuit ....
you can simulate start-up circuit separately too.... advantage of using .ic is that it will allow you to do estimation of total noise in the Bandgap ref ckt. else with start-up it may pop error as start-up will have to have pulse source...

regards
nandish

 

[a_cube_e]

Try to ramp your supply fast and slow ramp for your bandgap without startup and do the same thing on bangap with start-up. You will find that with start-up circuit, the bandagap will work in two conditions.