National Science Council

Shiao-Long Zhan

Chien-Ping Wu

Chang-Da Tsai

A second-order differential highpass filter constructed according to the present invention includes a difference amplifier and a feedback processing circuit. The difference amplifier includes an operational amplifier OP.sub.1, and four resistors R.sub.3, R.sub.4, R.sub.5 and R.sub.6, wherein R.sub.4 /R.sub.3 =R.sub.6 /R.sub.5. An input voltage V.sub.1 is fed to the inverting terminal (-) of the operational amplifier OP.sub.1 via the resistor R.sub.5. Another input voltage V.sub.2 is fed to the noninverting terminal (+) of the operational amplifier OP.sub.1 via the resistor R.sub.3. The output of the operational amplifier OP.sub.1 is fed back to the inverting terminal (-) of the operational amplifier OP.sub.1 via the resistor R.sub.6. The feedback processing circuit includes an operational amplifier OP.sub.2, two resistors R.sub.1 and R.sub.2, and two serial capacitors C.sub.2 and C.sub.1. The output of the operational amplifier OP.sub.2 is fed back to the inverting terminal (-) of the operational amplifier OP.sub.2 via the two serial capacitors C.sub.1 and C.sub.2, and is connected to the noninverting terminal of the operational amplifier OP.sub.1 via the resistor R.sub.4, and the noninverting (+) terminal of the operational amplifier OP.sub.2 is grounded. The inverting terminal of the operational amplifier OP.sub.2 is connected to the output terminal of the operational amplifier OP.sub.1 via the resistor R.sub.1. The two serial capacitors C.sub.1 and C.sub.2 are connected therebetween to one terminal of the resistor R.sub.2 of which another terminal is grounded.

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Taipei, Taiwan

Shiao-Long Zhan