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Vermont Technical College Electronics I – Laboratory ELT-2051 Lab 07: Transistor Biasing Circuits and Q-point Stability Objectives: • To set an operating point for a transistor using three different bias techniques • To explore amplification of an AC signal • To use MultiSim to verify your experimental data General: In this laboratory, you will be supplied with two NPN transistors with varying ß’s. Prelab: Calculate values of Rb in Figures 1 and 2 assuming ß = 200, VCE = 6V . For Figure 3, calculate R1 and R2 so that their parallel resistance is about 20KΩ or 10% of (ß+1)RE. Also, calculate the critical frequency of the 1uF capacitor in Figure 4. Materials: • 2N3904, 2N4123 NPN TXs (1 high ß, 1 low ß) • (2) 1 k Ohm, 100 k Ohm, assorted resistors • 1uF, 10uF capacitors • Curve Tracer • DC Power Supply • Multimeter • Signal Generator • Oscilloscope • Breadboard Procedure: 1. Use the curve tracer to plot the curves for each of your transistors. From these curves, again using the curve tracer, determine the ßDC for each transistor at the IC currents of 1mA, 3mA, 6mA, and 10mA with VCE = 6V. Of course, be sure to keep track of which transistor goes with which curve. Verify that the ßDC values that you obtain are within the manufacturer’s specifications. Remember– ßDC = hFE ! 2. For each of the three circuits shown in Figures 1-3, using the R values calculated in your prelab, determine the operating points IC and VCE for each of the transistors. Be sure to table your data. In addition, plot ß vs IC for both transistors on a single graph so that the data is meaningful! What conclusions can be reached for the 3 biasing circuits? 3. Lastly – Build Figure 4 and determine the ratio (Gain) of Vout/Vin at 1KHz. Now vary the frequency of Vin to determine at what frequencies this ratio decreases to 0.707 of the value at 1KHz. 4. Use the Bode Plotter feature in MultiSim to verify your data of Part 3. Is the cut-off frequency the same as you measured in the lab? Base Bias: Parameter Calculated Value Simulated Value Measured Value VCE1 (high β) VCE2 (low β) n/a n/a |VCE1 – VCE2| 0 0 IC1 (high β) IC2 (low β) n/a n/a |IC1 – IC2| 0 0 Emitter Bias: Parameter Calculated Value Simulated Value Measured Value VCE1 (high β) VCE2 (low β) n/a n/a |VCE1 – VCE2| 0 0 IC1 (high β) IC2 (low β) n/a n/a |IC1 – IC2| 0 0 Voltage Divider Bias: Parameter Calculated Value Simulated Value Measured Value VCE1 (high β) VCE2 (low β) n/a n/a |VCE1 – VCE2| 0 0 IC1 (high β) IC2 (low β) n/a n/a |IC1 – IC2| 0 0 Laboratory Report: This lab is a semi-formal lab. Be sure to collect all data necessary to make observations and answer questions before you leave the lab. Also, you and your lab partner should discuss the results and outcomes prior to leaving. Take notes, fill in tables and include diagrams as needed. Your report should include: • Data Table • Beta Plot • MultiSim Frequency Response • Comparison of biasing schemes • Comparison of measurements vs. simulations and expectations.Biomedical Signal and Image Processing (4800_420_001) Assigned on September 12th, 2017 Assignment 4 – Noise and Correlation 1. If a signal is measured as 2.5 V and the noise is 28 mV (28 × 10−3 V), what is the SNR in dB? 2. A single sinusoidal signal is found with some noise. If the RMS value of the noise is 0.5 V and the SNR is 10 dB, what is the RMS amplitude of the sinusoid? 3. The file signal_noise.mat contains a variable x that consists of a 1.0-V peak sinusoidal signal buried in noise. What is the SNR for this signal and noise? Assume that the noise RMS is much greater than the signal RMS. Note: “signal_noise.mat” and other files used in these assignments can be downloaded from the content area of Brightspace, within the “Data Files for Exercises” folder. These files can be opened in Matlab by copying into the active folder and double-clicking on the file or using the Matlab load command using the format: load(‘signal_noise.mat’). To discover the variables within the files use the Matlab who command. 4. An 8-bit ADC converter that has an input range of ±5 V is used to convert a signal that ranges between ±2 V. What is the SNR of the input if the input noise equals the quantization noise of the converter? Hint: Refer to Equation below to find the quantization noise: 5. The file filter1.mat contains the spectrum of a fourth-order lowpass filter as variable x in dB. The file also contains the corresponding frequencies of x in variable freq. Plot the spectrum of this filter both as dB versus log frequency and as linear amplitude versus linear frequency. The frequency axis should range between 10 and 400 Hz in both plots. Hint: Use Equation below to convert: Biomedical Signal and Image Processing (4800_420_001) Assigned on September 12th, 2017 6. Generate one cycle of the square wave similar to the one shown below in a 500-point MATLAB array. Determine the RMS value of this waveform. [Hint: When you take the square of the data array, be sure to use a period before the up arrow so that MATLAB does the squaring point-by-point (i.e., x.^2).]. 7. A resistor produces 10 μV noise (i.e., 10 × 10−6 V noise) when the room temperature is 310 K and the bandwidth is 1 kHz (i.e., 1000 Hz). What current noise would be produced by this resistor? 8. A 3-ma current flows through both a diode (i.e., a semiconductor) and a 20,000-Ω (i.e., 20-kΩ) resistor. What is the net current noise, in? Assume a bandwidth of 1 kHz (i.e., 1 × 103 Hz). Which of the two components is responsible for producing the most noise? 9. Determine if the two signals, x and y, in file correl1.mat are correlated by checking the angle between them. 10. Modify the approach used in Practice Problem 3 to find the angle between short signals: Do not attempt to plot these vectors as it would require a 6-dimensional plot!