Lab Report 5 - ECE 342 Lab 5: BJT Amplifiers Stephanie Duy,...

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ECE 342 Lab 5: BJT Amplifiers Stephanie Duy, Robert England Lab Group 4 December 6, 2007 Abstract This report describes the simulation, construction and test of a voltage amplifier built using 2N3904 BJTs. The amplifier uses a BJT constant-current sink to bias a common-emitter voltage amplifier. The amplifier requires ±10 V power supplies. The amplifier itself produces a gain of 25.9 dB at 1 kHz with a lower cutoff frequency of 2.8 Hz. The amplifier has an input resistance of 87.6 kΩ and an output resistance of 9.27 kΩ. The output voltage can range from 0.4688 V to 9.844 V. An optional output voltage buffer addition was also designed; with the buffer, the output resistance was 468 Ω, and the output voltage ranged from -5.312 V to 4.562 V. Component selection and test procedures are described. 1
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Contents 1 Introduction 3 2 Circuit Design 4 2.1 Primary Voltage Amplifier 5 2.2 Current Sink 7 2.3 Voltage Buffer 8 3 Theoretical Analysis 9 3.1 Analysis Without Buffer 9 3.2 Output Resistance Calculation With Buffer 11 4 Simulated Results 12 4.1 Simulation for β 12 4.2 Amplifier Simulation: No Buffer 13 4.3 Amplifier Simulation: With Buffer 17 5 Experimental Results 20 5.1 Voltage Amplifier Without Buffer 21 5.2 Voltage amplifier: With Buffer 23 6 Discussion 25 7 Conclusion 26 2
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1. Introduction This report describes the analysis and test of a voltage amplifier built using 2N3904 transistors. The amplifier was tested with and without a buffer stage attached. Measurements were made to find the gain vs. frequency characteristics of the filter, the input and output resistance of the amplifier, and the dynamic output voltage range. The resulting data was analyzed to examine the quality of the amplifier and the differences produced by attaching the output buffer. Section 2 details the process of designing the voltage amplifier and the buffer stage. Section 3 contains a theoretical analysis of the amplifier with and without the buffer to find the characteristics of the amplifier. Section 4 gives the results of a computer simulation of the voltage amplifier with and without the buffer. Section 5 describes the testing of a physical circuit prototype. Section 6 discusses the results of the experiment. 3
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2. Circuit Design A complete schematic of the voltage amplifier is shown in Figure 1 below. Figure 1: Voltage amplifier There were four required specifications for the circuit: The amplifier must provide a gain of 26 dB. The output dynamic range must be as large as possible. The input impedance should be large. The output impedance should be small. According to the assignment, resistor R C must be between 1 kΩ and 10 kΩ, and capacitor C must be between 10 μF and 100 μF. The data sheet for the 2N3904 specifies β to be between 30 and 300; α is very close to 1 for these values, so α is approximated to 1 for all of this design. The amplifier consists of three separate segments: a primary amplifier, a
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Lab Report 5 - ECE 342 Lab 5: BJT Amplifiers Stephanie Duy,...

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