LOG114: miscellaneous questions

Hirano-san,

Please see my responses to your questions.

Q1

Any capacitor should be connected between pin#16(Vref) and GND?

If yes how much [F] is recommended?

•  No added capacitance is required from pin 16 to ground.

Q2

The frequency response spec described in page #4 and #6 and the four frequency response plots described in page #9 are taken with a photo diode?

If yes, how much is the photo diode capacitance?

If no, could you show the test circuit used to take the data, pleae?

• The LOG114 was developed over 15 years ago and there isn't much information remaining from its development and characterization. It doesn't seem likely that a photodiode was used to generate the different current levels used for the frequency response plots. The datasheet Electrical Characteristics would have indicated that if that were the case and the photodiode characteristics. A photodiode would have required a precisely controlled light source to be able to produce the current levels over 8 decades and that would be very difficult to achieve. The Electrical Characteristics table under Conditions indicates "IAC = 10% of IDC value, IREF = 1µA." Therefore, the dc current level had 10 % amplitude modulation (AM). All indicators are the input current was provided by a professional, commercially produced current source instrument. 

I don't have a simple current source circuit that I can provide because of the 8-decade ultra-wide current range required, and amplitude modulation capability. I suggest having a look at professionally produced current source products that are designed for such purposes.

www.tek.com/.../keithley-ultra-sensitive-current-sources-seri

Kikusui in Japan may have a suitable precision current generator product as well.

Regards, Thomas

Precision Amplifiers Applications Engineering