US 4,303,889 A · Filter circuit

Abstract

A filter circuit comprises an inverting amplifier, a first resistor connected between an input and output of the filter circuit, a second resistor connected between the input of filter circuit and an input of the inverting amplifier, a parallel combination of a third resistor and capacitor which is connected between the input and output of inverting amplifier, and a fourth resistor connected between the output of inverting amplifier and the output of filter circuit. The resistance values R.sub.1 to R.sub.4 of the first to fourth resistors are selected such that R.sub.1 .multidot.R.sub.3 =R.sub.2 .multidot.R.sub.4, with the result that a DC component is blocked. The capacitance value of the capacitor connected in parallel with the third resistor may be small provided that the resistance value of the third resistor is large. The third resistor and capacitor define the low cutoff frequency of the filter circuit.

Claims4

Dependent claims

A filter circuit having an input and an output, comprising:

an inverting amplifier having an input and an output;
a first resistor connected between an input and an output of said filter circuit and having a resistance R.sub.1 ;
a second resistor connected between said input of said filter circuit and said input of said inverting amplifier and having a resistance R.sub.2 ;
a third circuit connected between said input and output of said inverting amplifier, said third circuit comprising a parallel combination of a third resistor having a resistor value R.sub.3 and a capacitor;
and
a fourth resistor connected between said output of said inverting amplifier and said output of said filter circuit and having a resistance R.sub.4 ;
said resistance values R.sub.1 to R.sub.4 of said first to fourth resistors being selected such that
R.sub.1 .multidot.R.sub.3 =R.sub.2 .multidot.R.sub.4.

5 more elements

Dependencies are inferred from the claim text.

Filter circuit

Life of this patent

Filter circuit

Life of this patent

Abstract

Claims4