• Introduction
• Picture of circuit
• Equipment Used
• Devices Used
• Results

        The purpose of this project was to design a low noise amplifier to be used at very low frequencies.

It measures electrical noise in the order of 10^-8 volts.  To construct this device I had to use metal film

resistors, cylindrical metal capacitors, LM741 amplifier, and 2N3904 transistor.  We bought a LM721

amplifier to use in our circuit, but when it arrived we found that it was too physically to small for our

circuit.  We will have to integrate it into the circuit at a later date.  Below are the details of the project.

        Every electrical circuit has some type of noise in it.  This noise becomes undesirable when the signal

to noise ratio becomes low enough to adversely effect the operation of the electrical circuit.  Electrical

devices that cause changes in voltage or current are common sources of noise.  Noise is often described

by how it is coupled in a circuit.  The five basic types of couplings are capacitive, inductive, radio

frequency, common impedance, and conducted.

        Of these five the ones that affect the project are capacitive, inductive, and conducted.  Capacitive

noise is coupled into a circuit by a capacitive effect.  This occurs when a voltage difference between two

conductors is separated by air or other insulating materials.  This sepperation creates a capacitor through

which noise can be coupled.  Inductive noise is coupled into a circuit by an inductive effect and is current

based.  Current flowing through one circuit induces noise current in another circuit.  Conducted noise is

coupled into a circuit by the transmission of noise by wires or other conducting materials.
 

Picture of Circuit

 
 
 
 

• Tektronix TAS 220 Oscilloscope
• B. K. Precision 3010 Function Generator
• Instek Digital Multimeter
• Global Specialties 1302 D.C. Power Supply

        We found that when the circuit was connected it gave us these results.  I found that this circuit is

works well between the frequency of 10 Hertz and 10,000 Hertz.  This is shown in the following table

and graph.  The input voltage for the information shown in this table and graph is 1 milli-volt

peak-to-peak.
 
 

    The transfer function which is shown above can be found by dividing the output voutage by the input

voltage.
 

    When we sent a voltage of 1 milli-volt peak-to-peak we got the following oscilloscope read out.  This

read out shows a complete signal that is not cut off in any way.  It also shows that the output is inverted

from the input.

    When we sent a signal of 2 milli-volts to the circuit we noticed that the output was inverted as before

and also that the signal was cut off at the top and bottom.  This proved that the circuit was only good at

a certain input voltage.

A special thanks goes out to Harish Ananthamurthy for all the help he gave me with this project.
 

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