Analog Devices Circuits - Lab Report Example

Lab Report of Analogue Electronic ABSTRACT Analogue electronics are electronic systems that have a continuously varying signal with a proportional relationship existing between a signal and current or voltage. Transistors, capacitors, resistors, inductors and diodes are the basic components in an analogue circuit board. The Transistor Feedback Circuit boards consist of three circuit blocks that include; Series Feedback, Multistage Amplifier Feedback and the Differential Amplifier Feedback. The first three circuit blocks demonstrate feedback methods while the fourth one is used to demonstrate a differential amplifier. An input signal with defined amplitude is fed into the circuit and it consists of a voltage with a certain value of current transistor. Transistor Feedback Circuit board s carry three forms of feedback. These include; the Series Shunt feedback or the Series feedback, the Multistage Amplifier Feedback consists of multistage series shunt feedback and multistage shunt series feedback, as well as the Differential Amplifier Feedback. The multistage circuit involves two major stages of amplification, using a combination of both shunt and series feedback. Table of Contents INTRODUCTION 3 THEORY 3 Equipment Used For the Experiment 4 EXPERIMENTAL PROCEDURES 4 RESULTS AND DISCUSSION 6 CONCLUSION 8 Works Cited 9 INTRODUCTION Feedback in transistor feedbacks refers to the return of a part of an amplifier’s output signal. There are only two types of feedbacks, the positive and the negative feedbacks. The positive feedback produces a signal that in turn makes the transistor circuit to deliver a larger signal. The feedback is in the form of a signal moving in a negative direction. In the negative feedback, a signal back-passes to a previous stage and reduce the signal amplitude. In both cases, a feedback signal is of greater effect on the troughs and peaks that represent distortions [UAB09]. Differential amplifier is an amplifier with output signals that is proportional to the difference between input signals. The attenuator and a generator buffer are incorporated into the circuit board to reduce the magnitude of the input signal[SWA00]. In this experiment, the key objective was to locate and identify the circuit boards of Transistor Feedbacks. Other objectives of the experiment included; gaining ability in describing effect of series shunt feedback by use of DC and AC gain measurements. To observe the characteristics and operation of the multistage amplifiers, and differential amplifier and to understand how bandwidth is affected by the series negative feedback using feedback circuit [San09]. THEORY The setup of this experiment was based on the four major Transistor Feedback Circuits mentioned above. Most transistors have leads in a single line with plastic cases. They have a current gain of 100, up to 25% of the rated current. This falls to 50 for the following 25% current increase. This further falls to 30 for the following 25% in current gain and 10 at the maximum allowable current. The transistor arrangement is slightly changed to come up with various feedback circuits with new features [Wil86]. The diagram below shows circuits of the Transistor Feedback Circuit. Equipment Used For the Experiment Setting up this experiment required the following lab equipment; F.A.C.E.T base unit, Multimeter, 15v DC power supply, Oscilloscope, Dual trace Generator, Transistor feedback circuit and Transistor feedback Circuit board. EXPERIMENTAL PROCEDURES 1. Series Feedback. The series feedback supply was adjusted to +10Vd.c and R3 set to obtain 5.5Vd.c at the transistor collector Q1 and Ch1 connected to display Vb. Ch2 was connected to display Vo at Q2 output and the generator set for 3Vpk-pk and10khz sine wave at Q1 output.Ch1was then connected to the output Vo and the generator set for 2Vpk-pk, 25 kHz square wave and the scope was set at 5S/div. C2 was removed to add ac gain and the generator set at 2Vpk-pk, 100 kHz square wave at output Vo., scope at 1s/div.C2 was then put back to the circuit and the generator set at 2Vpk-pk, 50Hz square wave at output, and the oscilloscope set for 0.2Ms/div. The procedure was repeated with C2 removed from the circuit to add ac gain and oscilloscope set for 1mS/div.Ch1 was then connected to the input Vi, the generator set at 80mVpk-pk and 80 kHz sin wave. Ch2 was connected to display Vb and the oscilloscope set at 50Mv/div. C2 was then disconnected to introduce a feedback and Vi adjusted to 80mVpk-pk. 2. Multistage amplifier feedback The oscilloscope ch1 was connected between Vo and the ground and the generator set for 100 mV pk-pk, 10 kHz across R11. Ch1 was then connected to the junction of C1 and R1 while Ch2 to the base of Q1. Ch1 was then connected between R11 and the output Vo measured. The generator was then set for 3Vpk-pk and 10 kHz sine wave.R9 CCW was then adjusted to obtain a maximum resistance. The post connecter between R9 and the output was removed and the generator adjusted to VO = 3Vpk-pk.The ohmmeter was then disconnected and two post connectors inserted at R9 to obtain VO=1.5Vpk-pk. R9 was disconnected and post connectors connected above R9, and then CW fully set to minimize resistance. The generator was then set at 10 kHz, 1Vpk-pk sine wave and Av calculated. CM8 was activated to reduce R8 set for 1Vpk-pk at Vo. The generator was again set for 200mVpk-pk, 10 kHz sine wave and R11set fully and connector inserted between R11 and R12 with R11 adjusted to obtain 100mV pk-pk at the output.CM10 was activated to reduce R9 and the generator set for 200mV pk-pk, 10 kHz sine wave at the output. The connector at R11 was inserted and adjustments made to obtain 100mVpk-pk. CM8 was then activated to reduce R9 and the generator set for 200mV pk-pk, 10 kHz sine wave at the output. The connector at R11 was inserted to obtain 100mVpk-pk. 3. A differential amplifier A voltmeter was connected across collectors Q1 and Q2 and R4 adjusted until 0Vdc was obtained. The voltmeter was then connected across R3 and a dc ammeter in series across R5and and AF generator with two post connectors at Q1 base. Ch1 was connected to Q1 base and the generator set for 500mVpk-pk, 1 kHz sine wave at the input. Ch2 was connected to Q2 and both set for 0.5V/div and ch1 triggered. Ch1 was then connected to the Q1 base and the generator set for 500mVpk-pk , 1 kHz sine wave, while Ch2 was connected to the collector Q2 with the input voltage still at 500mVpk-pk. Ch2 and ch1 were set for 0.5 V/div and the differential output voltage measured across Q1 and Q2. Two post connectors were used at R1 with 5V dc at both inputs and the collector voltage recorded and the common mode voltage gain obtained. Ch1 was connected to the AF generator and set for 5Vpk-pk , 1KHz sine wave. Ch1 was then moved the collector Q1, and ch2 to Q2 and the two set at 100mV/div. RESULTS AND DISCUSSION Effect of feedback on AC gain Effect of feedback in bandwidth The negative feedback reduces the amplitude of the output amplifier, and improves the low and high frequency responses. Effect of feedback on impedance Increasing the circuit input impedance reduces the input current and addition of the series feedback increases the input impedance. Shunt - series current gain The resistor Rsh in the circuit provides the input with a shunt feedback while resistor Rsh provides series feedback for the output. Shunt - series output impedance The output impedance of the circuit is high with the output current being essentially constant due to the high impedance. Series - shunt voltage gain Series - Shunt Output Impedance The output impedance of a series-shunt feedback is low and is not related directly to the collector resistance. Differential Feedback Amplifier The collector signal becomes out of phase with the input base signal and is positive when the base is negative and vice versa. Single Ended and Differential Gain of Differential Amplifier Common Mode Gain of Differential Amplifier The dc and ac signals that are common to both inputs are rejected by the differential amplifier. CONCLUSION A feedback amplifier is described based on the way of connection of the feedback network. The series feedback amplifier circuit block develops series and shunt feedback that is parallel to the amplifier input. Addition of series feedback results to increase in impedance of the amplifier. The impedance of a shunt-series network decreases by the value of the collector resistor. Works Cited UAB09: , (A.P.Godse, 2009), SWA00: , (Amos & James, 2000), San09: , (Kal, 2009), Wil86: , (Siebert, 1986), Read More