testing continuity through capacitors

[nkaufma]

I'm touching a few probes down on a wafer to test for continuity. I currently use a DC power supply which lights up LED's when the end is touched to the wafer. However, some lines may have an inline capacitor from 10pf to 100pf. The resistance needs to be around 15 ohms, which by calculations I would need a 100mhz to 1ghz power supply. Any ideas on a power supply like this or am I looking at this the hard way.

[bodgy]

Are you sure you're not confusing DC signals that light the LEDs with AC?<p>I'm not sure why you have brought reactance into your problem. It is true that you will get a signal delay, due to the capacitors taking time to charge and if you are checking waveforms or propagation times this will need to be taken into account.<p>Colin

[nkaufma]

A DC signal won't make it through an inline cap, or at least not enough current to light the LED. I'm grounding the wafer, putting a positive bias through the signal line which has a LED at the top, when the probe touches the wafer, the circuit it complete and the LED lights. The reason for reactance is using a high frequency power supply instead of a DC Power supply. Do you know of any circuit available to operate at 1ghz?

[russlk]

You don't want continuity thru the capacitor. If you want to know that the cap is there, use an inexpensive cap meter (Dec. N&V page 65).

[josmith]

Or you could just tell us what you are actually trying to acomplish.

[cato]

I think its quite clear what he's trying to accomplish. He wants to check the internal connections of an IC as far as he can. Some of the pins are either AC coupled or have bypass caps to ground. He wants to test that they are there or that the connections between the components are there. <p>A signal generator, series resitor and an oscilloscope are what I would use. The scope would be used to measure the voltage drop across the resistor. The higher the drop, the more current is flowing in the circuit under test.<p>The alternative is to build an oscillator to replace the signal generator and a voltage sensing circuit/comparator/blinkly light circuit to replace the scope......or you could just put the IC in its target circuit and see if it works