| 摘要 |
PURPOSE:To obtain an FET current switching circuit having a small input signal amplitude required for switching by using a diode pair whose cathodes are connected to switch the current and driving an FET whose source is connected to the cathodes of the diodes. CONSTITUTION:A semiconductor laser 61 is used as a load, the cathodes of the switching diode pairs 51, 52 are connected in common and to a constant current source 3. Constant current sources 71, 72 are connected to each source as the bias for FETs 1, 2. Through the constitution above, when (potential V11 at a terminal 10) - (potential V12 at a terminal 12) is a value or over, a current I0 of the constant current source 3 is almost switched, the current I0 flows to the FET 1 and the signal current to the FET 2 is zero. Conversely when the voltage V11 is smaller than the voltage V12, the current I0 flows to the FET 2 and no signal current flows to t FET 1. In this case, since the gate- source voltage of an FET is larger when the current increase and smaller when decreases, the potential difference fed to the diode pairs is smaller than the potential difference of the input signal so as to decrease the input signal amplitude required to switch the current. |
