what "Inputs ac-grounded" mean?

[chang830]

Hi,
In some product, the 1st stage is the differtial amp stage. In measuring some spec,the test condition need "Inputs ac-grounded with Ci=1uF", would anyone pls. tell me what it exactly mean?

Thanks

 

[dsp_]

Hi chang830,
AC-grounded simply means that the impedance against ground gets lower with higher frequencies(lowpass).
For example you can drive your diff. input single ended, if you ac-ground one input and measure the voltage drop on a resistor on the other one.

HTH
dsp_

 

[chang830]

Hi chang830,
AC-grounded simply means that the impedance against ground gets lower with higher frequencies(lowpass).
For example you can drive your diff. input single ended, if you ac-ground one input and measure the voltage drop on a resistor on the other one.

HTH
dsp_

hi dsp_,
Thanks for the reply. Now ,I understand what the AC-grounded mean. But the second part of your reply"For example you can drive your diff. input single ended, if you ac-ground one input and measure the voltage drop on a resistor on the other one." made me more puzzled, would u pls. clarify it a bit more?

Also, do u think the "Inputs ac-grounded with Ci=1uF" means the diff input connect a Ci=2uF to ground,respectively? Or it means a Ci=2uF connected the two diff input directly? For the two caes, the cap value has two times difference.

Thanks