| 摘要 |
PURPOSE:To extract an output to a signal input of wide range with excellent linearity by connecting an NPN-PNP composite transistor (TR) circuit in series with a switching control circuit obtaining a switching control signal. CONSTITUTION:A collector of an NPN TRQ1, an emitter of a PNP TRQ2, an emitter of the Q1 and a base of the Q2 are connected respectively in common. In taking a current of a constant current source as I0, a current to a TRQ3 constituting the switching control circuit SW as I1, a current to an output terminal as I2 and a current of a resistor R1 as I3, the relation of I1=I0 is established when the Q3 and Q4 of the switching control circuit SW are turned on and off respectively, and when the drop voltage of the TRs Q1, Q2 is nearly equal, a voltage Vi to a terminal IN is expressed as Vi=-R1.I3. Since the current gain of the Q1 is large, the sum of the I1, I2, I3 should be zero and the relation of I2=I3-I1 is obtained. Thus, the relation of I2=(-Vi/R1)-I1=(-Vi/R1)-I0 is obtained and it is known that an output current I2 proportional to the input voltage Vi is obtained. Thus, the relation of proportion between the input and output is obtained accurately over a wider range than a conventional method and a level shift circuit giving an input voltage is not required. |
