highpass roll-off

[zesla]

Hi,

the datasheet of LM3875 says that Ci Is:
""Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
fc = 1/(2π Ri Ci)""

What is the meaning of the blue one?

Thanks

 

[crutschow]

It means that the gain will decrease as the frequency is reduced below the -3dB point of fc.

The circuit has a gain of 1 at DC and increases to a maximum gain of 21 at a frequency above fc. The gain would be -3dB (14.87) at fc.

Edit: Attached is a simulation of the circuit frequency response (fc = 7.2Hz).