Hi,

I want to use AD8304 to design a device to accurately measure optical power from a photodiode , so I have to caculate the theory errors of the output of AD8304 first. But apart from the log conformance error,I didn't find anything else to do this. No data about typical input bias current or gain errors . In Ti's

LOG114 datasheet, there is a method to caculate the total output errors,not just a log conformance error in dB.By the way, how to transform 0.1 dB log conformance error into Vlog output error in percent?

Thanks,

Eason

Hi Eason,

The log conformance error that we show, for example in TPC 2, is equivalent to Ti's "Total Error".

0.1 dB of error will be 1mV of error. The math is: 0.1 dB = (Vlog_ideal - Vlog_actual)/ 10mV/dB

Vlog_error = Vlog_ideal - Vlog_actual = 0.1 dB * 10 mV/dB = 1mV

percent error would be: Error_percent = ( Vlog_ideal - Vlog_actual )/ Vlog_ideal *100, although I don't know how useful this will be because given the same voltage error on the output, 1mV, the percentage error will change depending on what the ideal output log voltage is. In other words, the bigger Vlog is, the percentage error will be smaller. Vice versa, the smaller Vlog is, the percentage error will be bigger, given the same absolute voltage error on the output.

With decibels, 1mV will always be 0.1 dB of error no matter where you are in the dynamic range of the part.

Hope this helps,

Joel