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Bandgap start-up at low temperature

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Ayman Essam

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Hi
I've designed the BGR with Core OTA works with high gain, high phase margin, and high PSR.
When I transient-test the BGR, at LOW TEMPERATURE, the BGR doesn't give the output voltage.
Any help about it ?
 

Start from 0 without the startup circuit. You do have an
explicit startup circuit, right? Attach a DC current source
instead. Initial value zero. Get your failing DC solution and
do a DC sweep of the current. Find where it causes the
bandgap to "snap in". What's the voltage at the injection
point, what's the current? How does this compare to what
the startup circuit is doing when attached?
 

Thank you for your reply, but I hardly understand your tracing methodology, would you please elaborate a bit more?
dick_freebird said:
Start from 0 without the startup circuit. You do have an
explicit startup circuit, right? Attach a DC current source
instead. Initial value zero. Get your failing DC solution and
do a DC sweep of the current. Find where it causes the
bandgap to "snap in". What's the voltage at the injection
point, what's the current? How does this compare to what
the startup circuit is doing when attached?
Click to expand...
 

Presuming you have a startup circuit, you want to determine why
it's failing. This might have to do with the "foot-race" between the
boot-stack and the bandgap core's operating voltage needed to get
to the point of adequate regenerative gain, via whatever current
steering network (or switches) you may have employed.

But a common omission is to have no startup circuit at all, these
often being omitted from papers (but seldom from successful products).

All I'm telling you to do, is look at the difference between "what it
takes" and "what it gets".
 

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