| 摘要 |
PURPOSE:To obtain a fast scanable analog input circuit which can reduce effect of common mode noises in a boarder frequency band by connecting outputs of two secondary windings of a transformer for a chopper respectively to a positive input and a negative input of a differential amplifier in opposite polarity to each other. CONSTITUTION:An input filter circuit for reducing normal-mode noise comprises a resistance R1 for a filter and a capacitor C1 for a filter and a chopping circuit is made up of a switch S1 for a chopper and two transformers T1A and T1B for choppers. Secondary outputs of the transformers T1A and T1B are inputted respectively into a (+) input and a (-) input of a differential amplifier A2 in opposite polarity to each other, where an output from which common mode noises are cancelled is taken out as digital value through a sample holding amplifier IC2 and an A/D converter IC3. Such a chopper type analog amplifica tion circuit can produce a digital value free from effect of the common mode noises. |
