An amplifier module has a 10Hz low pass filter.
When I obtain the gain vs frequency graph by applying different freq. signals to the inputs I get a consistent plot for the gain. I use a function generator and between 0.001Hz and 100Hz I get very consistent decrease in Bode plot.
But if I apply a constant DC offset to the amplifier inputs, the gain I obtain is lower than the gain at 1Hz. The difference is around 1dB. The 1Hz gain is 1dB more than the DC gain.
If I also apply 0.001Hz the gain is less comparing to 1Hz.
But if I apply 25mV DC input, the gain is less comparing to 1Hz and 0.001Hz. I would expect max gain at DC inout but it is not.
When I measure DC gain I even tried to take offsets for input and output and subtract them but still it is lower than the gain at 1Hz.
Is it possible DC gain is less than the gain at 1Hz or this is due to measurement error?