how to troubleshoot start-up issue in bandgap

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selvaraja

Joined: 01 Jun 2004
Posts: 224
Helped: 3

04 Aug 2008 3:53 how to troubleshoot start-up issue in bandgap

hi guys.,

how to troubleshoot start-up issue in bandgap. any relevant document or journal will help full.thank in advance.

renwl

Joined: 26 Apr 2004
Posts: 455
Helped: 23
Location: shanghai,china

04 Aug 2008 12:41 how to troubleshoot start-up issue in bandgap

.tran analysis can solve it.

A_U_J

Joined: 09 Apr 2007
Posts: 42
Helped: 9

04 Aug 2008 19:02 how to troubleshoot start-up issue in bandgap

Hi,
Are you having the issue in simulation(pre tapeout) or in Silicon ?I think bandgap is a self biased circuit and hence the circuit will either operate as desired (with required current mirroring + bg voltage generation etc) or will not startup.
So in general , a startup circuit is added in bandgap so that it does start up.
Now assuming you have a startup circuit and you have a problem with simulation, you can check which transistors have the problem.
As "renwl" said, you can use a .tran statement and run transient simulations. I would suggest you to ru a DC simulation too..

selvaraja

Joined: 01 Jun 2004
Posts: 224
Helped: 3

05 Aug 2008 7:16 Re: how to troubleshoot start-up issue in bandgap

my bandgap in Silicon showing out of 20 board fabricated 15 boards showing 1.63 volt and 5 boards showing 200mV.

A_U_J

Joined: 09 Apr 2007
Posts: 42
Helped: 9

05 Aug 2008 18:40 how to troubleshoot start-up issue in bandgap

I think the problem may be with your startup circuit..I am not sure how to debug in Silicon.. since some boards are working and some dont may be you can experiment with changing the power supply voltage in the unworking boards...

ashish_chauhan

Joined: 02 Sep 2007
Posts: 262
Helped: 39

06 Aug 2008 6:28 Re: how to troubleshoot start-up issue in bandgap

Hi
On the boards that are not working just try to switch on and off the power supply.

Many times this thig works when its an issue with bandgap.

else if u are not having a buffered output of bgr then try to give a pulse at the output itself... this can also help.

rfsystem

Joined: 25 Feb 2002
Posts: 858
Helped: 96

12 Aug 2008 20:29 Re: how to troubleshoot start-up issue in bandgap

Simulate the supply ramping with a transient simulation. Use either a positive and a negative offset on your error amplifier. If only one polarity works you get the issue. Startup in CMOS bandgap set the operating point at a value where the PTAT generate enough voltage to overcome offsets.

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electronrancher

Joined: 24 Mar 2002
Posts: 505
Helped: 34

19 Aug 2008 21:37 how to troubleshoot start-up issue in bandgap

Also, simulate with worst-case conditions such as -40C and slow mosfets.

Your input supply ramp in transient sim should be very slow, on the order of hundreds of ms.

Using these techniques, you can find why your startup circuit fails to operate on the simulator. In silicon it is hard to check physically since the capacitance and/or leakage of a probe needle will often "kick" the circuit into starting. A picoprobe can probably do it, but the work of probing is much more taxing than just making it fail in sim.