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Measure on-wafer circuits

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wuwoze

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Hi, I am using probe card, Agilent SMU, and oscilloscope to measure the ring oscillator and other circuit outputs on wafer. But somehow the oscilloscope could not get anything.

Would it be because the low impedance of the probe card?

Thank you.
 

As the osc. has its own capacitance, I am afraid your ring oscil. output cannot drive its load.
 

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    wuwoze

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Thank you for your reply.

OK. How can I measure the signal straight from wafer? The probe card could have some circuits built into it. If it is high impedance, would it work?

Thank you.
 

wuwoze said:
OK. How can I measure the signal straight from wafer?
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You need to have a buffer between the ring oscillator signal and the probe tip. Most designers build the buffer on-chip, but you can try doing it off-chip.
 

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    wuwoze

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Thank you for your reply.

The ring oscillator frequency is divided down to 10MHz. There is small buffer between the divider and output pad.

So I have to find an off-chip buffer to drive the oscilloscope? Is there anything that I can purchase and fit into the probe card?

Thank you very much.
 

wuwoze said:
So I have to find an off-chip buffer to drive the oscilloscope? Is there anything that I can purchase and fit into the probe card?
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This all depends on the type of probe card you're using. First, you need to solve the design problem: what sort of buffer needs to be inserted between the on-wafer buffer, and the probe tip. Once you know what kind of performance you need, then you can begin looking for a part which meets your performance requirements (including the requirement of fitting on the probe card).

Good luck.
 

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