This sensor circuit for currents of the order of nanoamperes was found in an American documentation from the 1980s. The components are from that time.
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...
We found this circuit in an old American documentation, from 1971, but the component used is still...
This circuit is from a 1991 publication, but it can be assembled with more modern components. We...