| 摘要 |
<p>PURPOSE:To freely set a DC characteristic without affecting on another AC feedback loop, by adding the feedback loop to obtain a constant current characteristic on the feedback loop to decide a constant resistance characteristic, and passing an added output through an LPF. CONSTITUTION:The normal output Q of the balancing amplifier A1 of a gain of 1 is connected to a chip terminal 1 via a resistor RF, and the inverted output O' is connected similarly to a ring terminal 2 via the resistor RF. A telephone line with a line resistor RL is connected between the terminals 1 and 2. And the inverted output O' is connected to a first input of a voltage discriminator 3 with two voltage follower inputs, and a second input is connected to a constant voltage source Vref. In such a case, it is assumed that the voltage discriminator outputs a low value out of the two inputs. And an output multiplying a differential voltage between the terminals 1 and 2 by 1/2 and the output multiplying the output of the discriminator 3 by betaare inputted to a calculator 6 which performs the addition of them. And the output of a calculated result is passed through the LPF7, and is doubled at an output amplifier 8, then, is fed back to the input of the amplifier A1. In such a way, it results that a constant current has no relation with the RL, and it is possible to obtain a desired constant current characteristic by changing the voltage Vref.</p> |
