| 摘要 |
PURPOSE:To reduce considerably the input current of an amplifier and reduce the offset voltage also by using PNP-type and NPN-type bipolar transistors to constitute the differential amplifier and connecting commonly their corresponding bases. CONSTITUTION:Transistors Q1 and Q2 are PNP-type transistors to constitute a differential amplifier, and transistors Q2 and Q4 are NPN-type transistors to constitute a differential amplifier. Next, input terminal 1 of the circuit is connected to one end of resistance R1, which has the other end grounded, and bases of transistors Q1 and Q3. Then, emitters of transistors Q1 and Q2 are connected to the collector of transistor Q6, and bases of transistors Q5 and Q6 are connected through resistance R2. Currents flowed to bases of transistors Q1 and Q3 are denoted as I1B and I3B, and -I1B=I3B is set to cancel both base currents. As a result, the input current to the amplifier becomes 0 approximately and can be made into DC, and the amplifier has gm smaller than the DC amplifier using FETs, so that noise may be small, and the offset voltage may be reduced. |
