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chip-on-board questions about mixed signal

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darkk

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Dear folks,

I am designing a mixed-signal circuit. The analog output is at 500 MHz and digital at around 200 MHz. In the bench test, I try to use chip-on-board. You can see the diagram in the attached picture. I will bond-wire the pads on the chip to the pads on the board, (i.e. no package for the chip). Since I just used probe station before, I'm not familiar with this kinda setup. So here I come up with a couple of questions:

1. Do I need to add the output buffer to drive the loads from the pads of on the chip and on the board?

2. If the buffer is needed, I guess that the 50 Ohms matching should be done at the output of the buffer. Am I right?

3. The same questions for digital part: output buffer and 50 Ohms matching?

Thanks for you guru's response!

-darkk
 

I don't know what loads u need to drive. But in ur case the requirements are same as for chip in package. U must take a great care with ESD protection, SSO and substrate noise. Include resistance and inductance of bond wires in ur test bench. If it's ur case, 50 Ohm matching is only requred for transmission line or coaxial cable usage at the inputs or outputs (depending on termination strategy).
 

Thanks to DenisMark for the reply! Actually, there's no specified requirement for loading.
For digital part, I will plan to use the open drain buffer on chip and a termination res of 50 Ohms on board. The oscilloscope probe will be connected to the pad on board to capture the signal. Certainly, the ESD is also taken care of later.

But still I am not sure what kina buffer is good for analog output, so any suggestions will be highly appreciated.
 

why not bypass cap added at the power pins? eg 2.2uf or 4.7 uf.
 

Areky_qin said:
why not bypass cap added at the power pins? eg 2.2uf or 4.7 uf.

The bypass cap. is a must but not my concern here.
I just concerned about the I/O buffer design for analog and digital output, esp. considering the effect from die pads and board pads.
Any suggestions?
 

if u only consider the coupling between the analog and digital ,I think this will be helped for you, of cource this only come from the chip, not consider the board.





Coupling effects in Mixed analog-digital ICs

maybe help.

best regards
 

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