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UNIVERSAL ACTIVE FILTER

ABSTRACT

An electronic filter is a device which passes the required frequencies of a signal and rejects the unwanted frequencies of a signal. Filters are of two types depending upon the components used. 1)Passive filter:If only passive components are used it is known as Passive Filter. 2)Active filter:If atleast one active component is used it is known as Active Filter. As in this circuit opamp which is a active component is used,it is known as active filter. As various types of filters such as Low Pass Filter,High Pass Filter,Band Pass Filter and Band Reject Filter are provided in a single circuit and therefore it is called as UNIVERSAL ACTIVE FILTER. Anew active universal filter with one input and four outputs is presented here. This configuration uses four Opamps, two capacitors and eight resistors.

# I. Introduction

The Universal active filter can be configured for a wide range of low-pass, high-pass, band reject and band-pass filters.The Universal Filter is a double pole (= second order) active filter built of 4 op-amps.

We can use a single Universal Filter for following four filters

1)Low pass filter

2)High pass filter

3)Band pass filter and

4)Band reject filter

# III. CIRCUIT DIAGRAM OF AN UNIVERSAL ACTIVE FILTER

The Circuit diagram shows how the functions are connected to multiply two input voltages. Constant terms are omitted for simplicity.

SUBCIRCUIT OF OPAMP:

UNIVERSAL ACTIVE FILTER CIRCUIT:

V(3)- Band reject filter output

V(5)-High pass filter output

V(7)-Band pass filter output

V(9)-Low pass filter output

Each output of the four op-amps provides different filter characteristics:

1)Notch-filter

2)2nd order high-pass filter

3)Band-pass filter

4)2nd order low-pass filter

In the circuit diagram above, it is possible to directly set up the most interesting filter parameters, the frequency and gain of each op-amp.Cut off frequencies and gain values can be varied by changing the values of Resistances and Capacitances.

Gain of each opamp will be= -(Rf/R)

where Rf is the feedback resistance and R is resistance at inverting terminal.

# III. NETLIST(NG SPICE)

SUBCIRCUIT OF OPAMP:

*opamp subckt*

.subckt opamp 1 2 6

Rin 1 2 10Meg

E1 3 0 1 2 100k

R1 3 4 1k

C1 4 0 15u

E2 5 0 4 0 1

R2 5 6 10

.ends

MAIN CODE:

*UAF*

.include OPAMP1.cir

xop1 0 2 3 OPAMP

xop2 0 4 5 OPAMP

xop3 0 6 7 OPAMP

xop4 0 8 9 OPAMP

r2 1 2 1000k

r4 2 3 9k

r3 2 7 10k

r5 3 4 10k

r6 4 5 10k

r7 4 9 10k

r8 5 6 10k

c3 6 7 0.01u

r9 7 8 10k

c4 8 9 0.01u

vin 1 0 dc 0 ac 1

.CONTROL

run

set color1=black

set color0=white

set xbrushwidth=3

AC DEC 10 1 1Meg

plot vdb(3) xlog

*plot {57.29*Vp(3)} xlog

plot vdb(5) xlog

*plot {57.29*Vp(5)} xlog

plot vdb(7) xlog

*plot {57.29*Vp(7)} xlog

plot vdb(9) xlog

*plot {57.29*Vp(9)} xlog

*plot v(5)/v(1)

*plot v(7)/v(1)

*plot v(9)/v(1)

.endc

.end

# VII.EXAMPLES

Examples of UNIVERSAL FILTER are UAF41 and UAF42 IC's

UAF42 is an analog IC that serves as a second order active filter building block that can be used to realize any filter. It can be of three or four OpAmp circuit with two integrators.

UAF42 IC:

The above IC is of 14 pin package with three outputs Low pass,High pass and Band pass filters.

APPLICATIONS:

1) Test equipment

2) Communications equipment

3) Biomedical instrumentation 4) Used in audio systems

1) Universal active filter building block IC's provide a fast and accurate method to design and build analog active filters from the simplest to the most complicated in a quick and simple way.

2) Realization of low pass, band pass, high pass and band reject filters simultaneously.

Compatibility: One input is given and the outputs of four filters can be observed from their respective nodes.

3) We can change the gain and cutoff frequency of a filter as per our requirement.