Introduction

This lab will cover the amplification of a small signal (500 mVpp, 1Hz, 1V DC offset) to the 0-5v range. Amplification will include the use of operational amplifiers and instrument amplifiers

Materials and Methods

A sine wave with 500mV amplitude, 1 Hz frequency, and a 1V DC offset was sampled by the oscilloscope set to DC couple. Due to DC coupling, the signal is shown exactly as it occurs in the circuit (Figure 1). The oscilloscope was then set to AC coupling and the circuit is tested again (Figure 2). 60Hz noise was then added to the circuit through the addition of a 3.3V DC power source. The circuit was tested using both AC and DC coupling (Figure 3 & Figure 4). A low pass filter (c_f=3.4 Hz,Ω=102.2kΩ,F=458nF) was then added to remove the 60Hz noise (Figure 5). A high pass filter (c_f=0.5 Hz,Ω=67.7kΩ,F=4.7μF) was then added to remove the DC offset (Figure 6). A 741 OP AMP was added to the previous filter circuit in order to amplify the  attenuated signal (Figure 7). The circuit from Task 6 was adjust so that the reference voltage is set to 5V and the OP AMP top rail is provided 10V. The circuit was tested using DC couple (Figure 8). A instrument amplifier was added to the original high/low filter circuit and Vo was probed using DC couple (Figure 9).

Results

Task 1:

A sine wave with 500mV amplitude, 1 Hz frequency, and a 1V DC offset was sampled by the oscilloscope set to DC couple. Due to DC coupling, the signal is shown exactly as it occurs in the circuit.

Task 2:

The same sine wave was sampled by the oscilloscope but with AC coupling enabled. Due to AC coupling being enabled, the oscilloscope automatically filtered out the DC offset.

Task 3:

The same signal, from Task 1 and Task 2, was used in this circuit but with the addition of noise with an amplitude of 3.3V and 60Hz frequency. The oscilloscope is individually set to both coupling modes and is used to test the signal output.

Task 4:

A low pass filter is added so that the previously added 60 Hz noise is filtered out. Given a cutoff frequency of 3.4 Hz, a 102.2 k resistor is used for the low pass filter.

Task 5:

A high pass filter is now added, before the low pass filter, to filter out the DC offset. Given a cutoff frequency of 0.5 Hz, a 67.7 k resistor is used for the high pass filter.

Discussion
Several passive and active filtering circuits were shown in this study. It was shown that passive filters cause amplitude attenuation and some types of active filters distort the output signal.