ADA4530-1Recommended for New Designs
The ADA4530-1 is a femtoampere (10−15 A) level input bias current operational amplifier suitable for use as an electrometer that also includes an integrated...
Datasheet ADA4530-1 on Analog.com
I am somewhat surprised that you do not have the low frequency response data as I would have expected that to be central to the original development of the ADA4530-1. I am developing very high gain transimpedance amplifiers (100Tohm) for application in mass spectrometers, in particular for measurement of geochronological times i.e. billions of years (see e.g. argon-argon dating in Wikipedia). The response time of these amplifiers has to be much faster than you would expect from such high value feedback resistors (the ions disappear quite quickly in the spectrometer vacuum) so a number of special techniques have been developed to improve the response time to a few seconds. Part of the theoretical analysis of the circuits requires the knowledge of the zero-frequency gain and of the open-loop corner frequency, and hence the request I have made. The ADA4530 looks particularly attractive as the input amplifier for its very low bias current, which is the limiting factor in the ultimate signai-to-noise ratio, and for the built-in guard driving amplifier. The bandwidth of the system is of the order of 10mHz to 1Hz so well within the presumed open-loop bandwidth of the 4530. To obtain even better precision the 4530 is followed within the loop by a ~X10 non-inverting stage (OP37) so achieving dynamic stability does present some difficulty in achieving a suitable open-loop frequency response. A major reason for trying to achieve such high gain transimpedance amplifiers is of course to be able to measure the tiny atto or femtoamp ion currents to determine the isotopic ratios of say Argon (you do not get much Argon in a piece of meteorite or moon rock). The general argument is that increasing the feedback resistor by say 10X increases the signal gain by the same ratio but the noise, which is primarily the Johnson noise of the feedback resistor, only increases by root 10 so the S/N ratio increases by root 10. The ultimate limit is reached when the shot noise of the amplifier bias current becomes greater than the Johnson noise. To obtain the best performance the amplifiers are housed in an evacuated and temperature controlled housing to avoid surface contamination of the feedback resistor and their significant temperature coefficients. These high value resistors leave much to be desired.
I hope this gives you enough information as to our application and that you will be able to provide us with the requested information. If you would like any further information please let me know.
I am somewhat surprised that you do not have the low frequency response data as I would have expected that to be central to the original development of the ADA4530-1. I am developing very high gain transimpedance amplifiers (100Tohm) for application in mass spectrometers, in particular for measurement of geochronological times i.e. billions of years (see e.g. argon-argon dating in Wikipedia). The response time of these amplifiers has to be much faster than you would expect from such high value feedback resistors (the ions disappear quite quickly in the spectrometer vacuum) so a number of special techniques have been developed to improve the response time to a few seconds. Part of the theoretical analysis of the circuits requires the knowledge of the zero-frequency gain and of the open-loop corner frequency, and hence the request I have made. The ADA4530 looks particularly attractive as the input amplifier for its very low bias current, which is the limiting factor in the ultimate signai-to-noise ratio, and for the built-in guard driving amplifier. The bandwidth of the system is of the order of 10mHz to 1Hz so well within the presumed open-loop bandwidth of the 4530. To obtain even better precision the 4530 is followed within the loop by a ~X10 non-inverting stage (OP37) so achieving dynamic stability does present some difficulty in achieving a suitable open-loop frequency response. A major reason for trying to achieve such high gain transimpedance amplifiers is of course to be able to measure the tiny atto or femtoamp ion currents to determine the isotopic ratios of say Argon (you do not get much Argon in a piece of meteorite or moon rock). The general argument is that increasing the feedback resistor by say 10X increases the signal gain by the same ratio but the noise, which is primarily the Johnson noise of the feedback resistor, only increases by root 10 so the S/N ratio increases by root 10. The ultimate limit is reached when the shot noise of the amplifier bias current becomes greater than the Johnson noise. To obtain the best performance the amplifiers are housed in an evacuated and temperature controlled housing to avoid surface contamination of the feedback resistor and their significant temperature coefficients. These high value resistors leave much to be desired.
I hope this gives you enough information as to our application and that you will be able to provide us with the requested information. If you would like any further information please let me know.
