Design of active R filters using only resistors and operational amplifiers

Abstract

Active filters car1 be designed using only resistors and amplifiers as the circuit elements. The reactance for these filters is obtained from the parasitic capacitances associated wit,h the amplifiers. The resonant frequency and Q of the poles and t.he location of the zeros can be controlled over a wide range by resistor feedback and feedforward circuits.General configuration for t,he first., second-and third-order filter building blocks may be used in cascade to achie\.e any desired filtering funct,ion. The basic building block is constructed from only two amplifiers and three resistors. This circuit simultaneously exhibits low.pass. high-pass, and bandpass lunctione, respectively, a t its three outputs. A simple summing network allows these out,puts to be summed t,o obtain any second. or third-order filter function.I n addition to simplifying tho circuit configuratione, the active H filter technique r e~d t s in filters which may be operated a t much higher frequencies than classical active RC filters. I n fact, experimental results confirm several orders of magnitude improvement in thc high frequency response of such filters.

Brief communication Active-R realization of current-mode highpass filters

“…Many circuits for realizing voltage-mode filters and immittance functions using the operational amplifier (op.-amp.) pole have been published (Soderstrand 1976, Mitra and Aatre 1976, Soliman and Fawzy 1978, Nandi 1978, Ananda Mohan 1980, Saha and Nandi 1980, Schauman et al 1980, Ishida et al 1986, Tsukutani et al 1991, Siddiqi and Ahmed 1991a. However, the circuit for realizing current transfer functions using the op.-amp.…”

Current-mode lowpass and bandpass filters using the operational amplifier pole

“…Many circuits for realizing voltage-mode transfer functions using the op.-amp. pole have been published (Soderstrand 1976, Mitra and Aatre 1976, Nandi 1978, Siddiqi and Ahmed 1991. However, there are few circuits for realizing current-mode transfer functions using the op.-amp.…”

A novel current-mode active-R biquad using differential-input differential-output operational amplifiers

“…The proposed circuit has employed Soderstrand's voltage-mode state variable filter (Soderstrand 1976) as a prototype. It is shown that the circuit can realize low-pass, bandpass, high-pass.…”