| 摘要 |
Outer offset voltages for electrical amplifiers with high input impedance are difficult to obtain with preservation of the high impedance both for the resistive and capacitive part. One solution of the problem is to connect photo diodes (1) in series to the input of the amplifier (5) and illuminate these with the light from a lamp (9), which intensity varies with the voltage (10) of the lamp. A resistor (11) is connected in parallel with the photo diodes. From the connector (15) for the input voltage, AC voltages are fed directly to the input of the amplifier (5) by a bypassing capacitor (19). Due to the small dimensions of the diodes (1), capacitor (19) and resistor (11) the leakage capacitance will be very small. Further amplifiers (6, 7 and 8) can be given outer offset voltages by means of the light from the same lamp. By means of small shields (23, 24) photo diodes in different amplifiers can be shaded making the outer offset voltages individually adjustable. |
