抄録
For the study of intracellular potential recording, authors made an atempt to devise a two stage d. c. pre-amplifier with negative capacitance circuit using selected N-channel J-FET (Junction-Field Effect Transistor, Toshiba 2 SK 13) whose gate current was within a range of 10-12A at 25°C. In the 1st stage amplifier, the differential circuit of the source-follower principle was adopted. In the 2 nd stage amplifier, the differential circuit of the drain-follower principle was employed with the J-FET. Negative capacitance was applied to the input through a 10 pF capacitor connected with the one stage a. c. amplifier having variable gain of 2-3 times.
The pre-amplifier was stable in operation and worked linearly in a range of ±1.0 V of input voltage (the gain was 5x). This satisfactorily amplified the applied square pulse of 1.0 msec duration as the original form in practical use. The noise voltage was about 0.3 mV under just compensation when the input resistance was 100mΩ. This device is a compact, light and shock-proof one and is suitable for electrophysiological recording from superfine microelectrodes. The power source is very easily simplified because of low consumption of electric power, thus this can take the place of tube pre-amplifier and is better than the MOS-FET pre-amplifier in several features especially in a very low noise.
