Theory of the experiment - Lab Report Example

Theory of the experiment The main objectives of this experiment were To build a amplifier To evaluate the performance of the built amplifier T learn the functions of its components through testing To improve my knowledge and skills of an amplifier through conducting ‘real’ experiments To strengthen my technical skill An amplifier for example an audio amplifier is used to increase the amplitude of a signal that is small to a level that is useful to the user. While increasing the amplitude, the small signal’s details and characteristics are maintained. This process is known as linearly. Greater linear the more the output signal. There exists many different types of amplifiers. There has been great advancements of amplifier design in the recent past. The following are some types of amplifiers. Class A amplifiers This is the simplest type of audio amplifier. This amplifier contains output transistors that conduct irrespective of its output signal waveform. This amplifier is known to be the most linear. The only disadvantage is that it has low frequency. It is mostly applied in areas where high linearity is needed and have enough power available. Figure 1.0 shows a part of class A amplifier and the associated wave forms (Robert Nicoletti 2013 n.d). Figure 1.0: part of Class A amplifier and its waveform Class B amplifiers The push-pull topology of amplifier is used in class B amplifiers. This amplifier normally contains has a negative and a positive transistor where each transistor conducts during half of the available signal to replicate the input. This gives a chance to idle with no current (zero current). This characteristic increases the efficiency of Class B amplifier as compared to class A amplifier. Figure 1.1 shows a class B amplifier diagram and its input and output waveforms (Robert Nicoletti 2013 n.d). Figure 1.1: a class B amplifier and its input and output waveforms Class B amplifier have an advantage over Class A amplifier in that its frequency is high and it degrades the quality of the audio signal. This is brought about by a cross over point through which two transistors change from ON state being in OFF state. Crossover distortion can occur when the transistor is handling very low signal levels. These amplifiers performs poorly in applications with low power. Class AB Amplifiers This can be said to be a compromise between the Class A amplifiers and the Class B amplifier topologies. These amplifiers combines the sound quality provided by the class A simplifiers and the efficiency provided by the Class B amplifiers. This is achieved by having both transistors biased to have them conduct a signal close to zero. Figure 1.3 shows a class AB amplifier and its associated input and output waveforms. Figurer 1.3: a Class AB amplifier and its associated input and output waveforms. When small signals are applied, both transistors will be active, making the amplifier to function like a Class A amplifier. When a large signal is applied, only one transistor becomes active. This makes the amplifier to operate like a Class B amplifier. Class AB speaker amplifiers gives a high SNR and a low THD+N. they are also about 65% efficient. These amplifiers are used in making portable media players, tablets, cameras, and so on where high fidelity is required. Class D amplifiers These amplifiers use PWM (pulse width modulation) to produce a rail to rail output signal. This signal has a variable duty cycle that is used to approximate the input signal which is analog in nature. These amplifiers are highly efficient and have an efficiency of about 90%. This is so because the output transistors used are fully turned on/off in a normal operating. Use of this approach eliminates the need to use the transistor’s linear region that brings in inefficiency in the other types of amplifiers. Figure 1.4 shows a basic class D amplifier and a possible waveform Figure 1.4: a Class D amplifier and its input and output waveforms Since this class of amplifier has a high efficiency, it finds application in modern portable media like smart phones, MP3 players and so on. Examples of class D amplifiers include MAX98304 and MAX984000. Class G amplifiers These amplifiers operates in a similar manner to class AB amplifiers. The only difference is that they use more than one power supply voltage. This amplifier selects the correct power supply as the signal level is increased. This class of amplifiers is more efficient compared to class AB because maximum supply is used when necessary. Class B amplifiers uses maximum voltage at all times. Figure 1.5 below shows a part of Class G amplifier and its input and output waveform. Figure 1.5: a class G amplifier and its waveforms Class DG Amps This class of amplifiers uses pulse width modulation to produce (PWM) to give a rail to rail output signal. This signal has a variable duty cycle. This means that a class D amp is similar to a class DG amp. However, class DG amp may also use multilevel output stage in order to sense magnitude of output signal. This is shown in the figure 1.6. The class DG amps switches supply rails in order to supply the signal power required in a more efficient manner. For higher efficiency, class DG is incorporated with a class D topology using similar dual-power. Figure 1.6: A class DG amplifier and its input/output waveform. Class H amplifiers This class of amplifiers modulate their power supply to reduce the drop across the output stage. The implementation of this class ranges from usage of multiple digital voltages signals to an analog adjustable supply. Unlike class G, this class does not require multiple supplies of power. Figure 1.7 shows a basic class H circuit and its waveforms Figure 1.7: Class H amplifier and its waveforms NOR Gate oscillators A NOR gate oscillator is a relaxation type of oscillator. The RC circuit used in this oscillator is to slow down the changes on the input pin of the second NOR gate. The output is connected to the input and therefore it contains no stable state. In the waveforms of this oscillator, the capacitor voltages discharges toward zero until a transition voltage of 2.5V is reached. On reaching this point, the voltage reverses and starts charging towards 2.5V. Equipment and components of the experiment Experiment on Design of the amplifier circuit. The following equipment and components were used in designing this circuit. A solder less breadboard DC power supply unit (PSU) Oscilloscope Digital Multi-meter (DMM) Components. Resistors (Ώ): 51k, 2x 5.1, 1k, 82Ώ, Capacitors (nF): 470, 4.7, Transistors: BC109BP Experimental Methods and Procedure The circuit shown on figure 1.9 was built on a breadboard Figure 1.9: an amplifier circuit In the above circuit, all the values were as follows; R1=51k, R2=5.1k, R3=1K, R4=82R, and C1-0.47uF. Vs had a frequency of 1 kHz. ‘a’ and ‘b’ represent two nodes. The value Vs was set to 0V and the voltage at the nodes was measured. The magnitude of Vs was set to 0.1V. The DC and AC components of the signal were measured. R1 was disconnected. The voltage Vb (Total) and Vb (AC). R1 was reconnected. C1 was disconnected and Vs was connected to the node ‘a’. Vb (total) was measured and Vb (AC). C1 was reconnected and R3 increased to 5.1k. The values of Vb (total) and Vb (AC) were measured. The value of R3 was reset to 1k and Vs(AC ) and Vb (AC) were monitored using an oscilloscope. The value of Vs was increased gradually to 0.3V. To explore the effects of the input frequency, the following procedures were followed. The value of Vs was reset to 0.1 V. The input frequency was varied between 10 Hz and 1 MHz and for each frequency, the value of the peak b (AC) was recorded. Design and test of oscillator The main objectives of conducting this lab were Building an oscillator based on NOR gate Evaluating the performance of the oscillator Finding out how to set the oscillating frequency Exploring the relation between sound and frequency To strengthen our practical skills Equipment’s and components Equipment The following equipment was used Solderless breadboard DC power supply unit (PSU) Function generator (AFG) Digital multi-meter Oscilloscope Components Resistors (): 10, 68, 1k, 10k, 2100k, 220k, 620k, 1M, 3.3M, 5.6M, 10M, Capacitors (nF): 10, 100 Transistors and Chips: BC109BP, CD4001BCN, Loud speaker 64 ohms Experimental procedure and methods The circuit shown on figure 2.0 was bult on a solder less bread board For testing the oscillator on figure 2.0, the following was done; The chip was powered by applying 9V DC between pin 14 and pin 7 The waveform of Va, Vb and Vc was recorded. The oscilloscope frequency was measured To interface oscillator with the amplifier, the following was done; The oscillator was linked with the amplifier by connecting the dashed line on figure 2.0 To estimate the power delivered to the to the load, the following was done The loud speaker was replaced with the load resistor R(load)=10R The waveform of the voltage drop across the R(load) and Vload was recorded The top level of Vload, V(top) was measured To check how the power affects the amplitude of the load, the following was done The supply power was reduced from 9V gradually and the corresponding reduction Vtop value was noted To study the effect of component value on the oscillation the following was done; For the values of R=1k, 10k, 620k and 3.3M, the Vc was monitored and the frequency measured To improve the tune, the following was done; The component Reset R=100 from figure 2.0 was renamed as R4 in figure 2.1 The circuit on figure 3.2 was built on a breadboard To get the effects of the effects of the component value on the tune, values R7=620, 5.6M and 10M were used Observations, Data findings, results and discussion Design and test of the amplifier On Biasing the DC voltage using a voltmeter or oscilloscope, the voltage values can be calculated as follows Therefore the V (total) is equal to 724mV this is the value of the Peak AC Therefor the value of the peak DC is 8.60V On disconnecting the value of R1, the value of peak to peak voltage changes to 24mV. From this, it can be observed that this is a very large decrease and therefore R1 plays a very important role in the circuit Changing the value of R1 reduces the voltage and also the peak to peak value. Increasing it increases the value peak to peak value. Input voltage increase to 4.11V. The peak to peak value of the input also increase by 450mV Reconnecting the resistor R1 and replacing C1 with a signal generator Disconnecting C1 means that there is a decrease of 550mV from the original input but the AC peak to peak value remains the same. The output signal varies from a positive to a negative value. Part 3 DESIGN AND TEST OF OSCILLATOR On powering the oscillator with 9V, a saw tooth waveform is observed at the oscilloscope fo the value of Va. Vc produces a square wave with a positive amplitude while Vb produces a square waveform with a negative amplitude Frequency = 618.1Hz, theoretically, the frequency should be 1 kHz. The variation in the values of frequency are brought out by the capacitive element in the chip circuit. The total capacitance value is larger than 10nF. It can be observed that the sound of the speaker does not change. It remains constant. This shows that the oscillator is working properly. The amplifier has an input of mA and the output is in the Am region Estimating the power delivered to the load RL There is a factor of two since this is a peak to peak power How the power affects the system V (top) starts decreasing gradually and so does the speaker. On decreasing the power supply below 3V, no sound comes from the speaker. Table 1.0 below show values for frequency obtained at different voltages Resistance (ohms) Vc (frequency) 1K 40 MHz 10K 5.6MHz 620R 100Hz 3.3 18.8Hz From the table, it is clear that the lower the value the lower the pitch of the speaker. This is as a result of varying values of the resistors. On building the circuit on figure 2.1, the tone of the speaker is heard oscillating. This means that, the larger the resistor value the slower the oscillating time. 64 ohm speaker was used because it allows more power load and is more efficient than the 8 ohm References Robert Nicoletti 2013, Audio Amplifier Basics,select the best topology for your design.n.d Retrieve on april 14th 2013, www.eetimes.com John Bird 2007, Electrical and Electronics Principals And Technology, third edition Newnes Elsivier UK Anil K. Maini 2007, Digital Electronics, Principle, Devices and Application, John Wiley and Son Limited, England Chi-Tsong Chen 2002, Analog and Digital Control System Design, Saunder college publishing Professor Barry Parton 1998, Fundamentals of Digital Electronics, National Instrument Corporation Read More