| 摘要 |
PURPOSE:To obtain the symmetrical circuit for a variable AC resistor generating no distortion by a method wherein, among the p-n-p junction groups constituting a ladder circuit with a resistor, a p-n junction and a n-p junction, a bias current is supplied to the point where a resistor, a p-n junction and an n-p junction groups are short-circuited with a conductor. CONSTITUTION:The differential amplifier, wherein p-n-p transistors 1 and 2 are provided, has a symmetrical circuit 9 to be used for formation of a variable AC resistor, between emitter terminals. Q3 and Q4 are invertedly connected to p-n-p elements Q1 and Q2 in antiseries form to the signal current between terminals 7 and 8 through the intermediaries of R1 and R2. The emitter junction of the Q1 is shunted by the emitter base junction of the R1 and Q3, and the Q2 is also shunted by the series circuit of the R2 and the p-n junction in the same manner as above. A ladder circuit is formed by performing the same procedures. A control current Ir is supplied from the junction point 10 located between the emitter bases of the final stage, and a bias current I is supplied from the junction point of each collector. According to this constitution, a signal current can be increased, a linear variable resistance can be obtained even when the rate of the control current Ir is reduced, and the distortion in a signal and modulation can also be reduced greatly. |
