[SI-LIST] Re: How to measure the On Die decupling capacitor value ?

Measuring w/o bias is prone to a number of errors.  There are techniques 
for measuring with bias applied, and those should be used. 

In any event with deep submicron circuits I recommend you stay at or 
below -20dB.  You should also make sure that you are using a DC block 
appropriate to the task.

Steve
Eddy wrote:
> A few notes:
> * When measuring the VDD to VSS capacitance without 
> bias, be aware that all the on-chip circuitry connected to the power 
> lines will also present a significant capacitance. Of course it depends 
> upon the size of the circuit but there could be a few hundred pF from 
> the circuit itself. However, you are most likely not interested in 
> measuring the capacitance with 1% accuracy but rather want to know 
> approximately how much is there (20~50% accuracy). For this purpose the 
> measurement without bias is good. To be effective, the decoupling 
> capacitance needs to be a lot bigger than the circuit capacitance 
> anyway.
> * When measuring capacitance you are injecting a test signal.
>  Make sure this test signal does not affect the circuits other than the 
> capacitance. When measuring without bias you want to stay below 0.4Vpp 
> to not open any diodes in the circuit
>  that will affect the test result. This could for example be a reason 
> for an unstable reading. Most network analyzers will default test with 
> 0dBm signal level,
>  which would be too much. Lower the signal level to at least -10dBm. 
> Theoretically the capacitance value should not be dependent upon signal 
> level so you could try at different levels and determine for yourself 
> how low your test signal level needs to be for a stable result.
> *
>  The fact that the chip needs on-chip power supply decoupling means that
>  there are signals inside the chip that might interfere with the power 
> lines. When you apply bias the circuit becomes "alive" and signals from 
> the chip might interfere with your capacitance test signals. This may be
>  another reason for an unstable test result. If possible put the chip in
>  a sleep mode or 
> powered down mode so there can be no other signals than your test signal
>  on the power lines. When powering up only an I/O power pin it might be 
> OK but
>  there can still be diodes between the I/O power line and other power 
> lines so you could still be partly powering other circuits.
> * Capacitance meters
>  can have a bias setting but usually this is not strong enough to power a
>  chip. Make sure that when you set for example Bias=1.8V that the DC 
> voltage on your chip is actually going up to 1.8V.
> * To minimize the 
> influence from bond wires and other leadframe parasitic inductance you 
> can use a low test frequency like 10MHz or perhaps as low as 1MHz. The 
> lower the test frequency, the smaller the error in your capacitance test
>  from parasitic inductance.
> * When one node for your test probe or test signal is the ground plane
>  then you can use S11. The VSS of your chip is most likely connected to 
> the ground plane. When you need to do a differential test between two 
> nodes then I would recommend S12 (or S21). Most network analyzers have 
> built in functionality to convert S parameters to impedance.
> * Before
>  hooking up your test system and test methods
>  to the chip, first verify with a known capacitor that your method is 
> working OK. Take for example a 1000pF (1nF) capacitor and verify that 
> your equipment is indeed measuring something close to 1000pF. It can 
> save you a lot of trouble and a lot of time to first make sure that your
>  test method is OK.
> I hope these notes will help you getting good test results for the on-chip 
> decoupling capacitance. ;-)
>
> Eddy van Keulen
> Sr Applications Eng. Mgr.
> PhaseLink Corp.
> San Jose, CA - USA
>
>
> --- On Fri, 9/10/10, yardala <yardala@xxxxxxxxx> wrote:
>
> From: yardala <yardala@xxxxxxxxx>
> Subject: [SI-LIST] How to measure the On Die decupling capacitor value ?
> To: si-list@xxxxxxxxxxxxx
> Date: Friday, September 10, 2010, 7:15 PM
>
> Hi, All
> Can I measure the value of On Die Decoupling capacitor use only capacitor
> meter
> probing at  pin Vdd and Vss ?
>
> When I use meter to measure the value of core logic are few nH and unstable,
> the value of I/O power are several hundred pF.
>
> Does these value make sense ? does it good enough , or any other methods are
> suggest ?
>
> Does the bonding wire effect the capacitor value ?
>
> Thanks!
>
> Yardala
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
>                 http://www.si-list.net
>
> List archives are viewable at:     
>         http://www.freelists.org/archives/si-list
>  
> Old (prior to June 6, 2001) list archives are viewable at:
>          http://www.qsl.net/wb6tpu
>   
>
>
>
>
>       
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
>                 http://www.si-list.net
>
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
>  
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>   
>
>
>   


-- 
Steve Weir
IPBLOX, LLC 
150 N. Center St. #211
Reno, NV  89501 
www.ipblox.com

(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: