| 摘要 |
PURPOSE:To reduce the resistance value of an input resistor to reduce noises even in the constant current system, by providing a means, which controls the current of a magneto-resistance element so that the resistance of this element is constant, for this element, which detects magnetic material components, in respect to a magnetic detecting device which discriminates whether a kind of paper is good or not. CONSTITUTION:A current I is supplied to magneto-resistance elements 31 and 32 and a resistance 33 by a constant current source 1. An integrator 3 is so operated that the resistance of the magneto-resistance element 32 is equal to Rref. For example, when the temperature rises and the value of the magneto-resistance element 32 is smaller than Rref, Vr is reduced to reduce the current I because the potential at a point (a) becomes higher than that at a point (b). Therefore, the internal power consumption of the magneto-resistance element 32 is reduced, and the resistance is increased to become equal to Rref. Thus, since the value of the magneto-resistance element 32 is always Rref, the gain of an amplifier 2 is always constant even if the value of a resistance 42 is reduced. It is possible to omit the resistance 42. |
