The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Mixed-Signal Design >> how can i add a test pad in the ADC circuit?
https://designers-guide.org/forum/YaBB.pl?num=1129547278

Message started by tuza2000 on Oct 17^th, 2005, 4:07am

Title: how can i add a test pad in the ADC circuit?
Post by tuza2000 on Oct 17^th, 2005, 4:07am

i have finish a ADC layout,and i want to add a test pad in the layout,i dont know is it necessary add a buffer between the test point and the pad?
and if need,how ?

thanks

Title: Re: how can i add a test pad in the ADC circuit?
Post by Paul on Oct 19^th, 2005, 12:29am

Hi,

you will have to provide more information to get a serious answer. It depends on the type of node you want to test (especially its impedance level) and the type of measurement equipment you want to connect (active probe, 50 Ohm load, etc).

If you need to add a buffer, you will not be able to avoid layout modifications, except if you can put your buffer off-chip.

Paul

Title: Re: how can i add a test pad in the ADC circuit?
Post by tuza2000 on Oct 19^th, 2005, 9:56pm

i want to add the test point on the comparator output,but i worry about the digital part interfere the analog part so i add the test point on the digital correction part,and i have modify the layout ,i will test the chip use probe with 50ohm.
i add four inv between the test and pad.
their size are nmos:2u pmos:5u
nmos:4u pmos:10
nmos:8u pmos:20
nmos:16u pmos:40
in order to drive the probe so i use the size at the last step of the buffer.

regards!

Title: Re: how can i add a test pad in the ADC circuit?
Post by ywguo on Oct 20^th, 2005, 10:00pm

Hello, tuza2000,

Can the inverters drive a probe with 50 Ohm? Now that you want to test digital signals at digital correction part, why do you use the probes with 50 Ohm input impedence?

You'd better test the signals using a probe with capacitive load.

Best regards,
Yawei