BEndicott_Week_6_iLab_1.docx - Lab 6 \u2013 Filters and Oscillators By Benjamin Endicott ECT246 Electronic Systems III with Lab Gary House DeVry University

# BEndicott_Week_6_iLab_1.docx - Lab 6 – Filters and...

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Lab 6 – Filters and Oscillators By Benjamin Endicott ECT246 Electronic Systems III with Lab Gary House DeVry University Online June 15, 2014 Part A-Active Filters
A V(dB) f (Hz) f C -3(dB) A V(dB) f (Hz) f C -3(dB) A V(dB) f (Hz) f C1 -3(dB) f C2 A V(dB) f (Hz) f C1 -3(dB) f C2 Low-pass High-pass Bandpass Notch ---BW--- ----BW----- Week six addresses the concept of active filters and oscillators. The low, high, bandpass and notch active filters, their circuits, and operating parameters are covered. The Wein-bridge RC oscillator, its configuration, operation and circuit is discussed. TCO #6: Given an application requiring active filters calculate, simulate and measure filter characteristic of a low-pass, high-pass, band-pass, and notch filter. A. Identify the gain-versus-frequency response of basic filters. a. Draw the frequency response of a low-pass, high-pass, bandpass, and a notch filter. Label each axis, the critical frequency, bandwidth and the 3-dB point. Low High Band (above) Notch (above)
b. What is the “order” of a filter? How is an order created? The term order is used to identify the number of poles (RC circuits). A first order filter contains one pole, a second order filter contains two poles, a third order filter contains three poles and so on. A filter with an order value less than another will execute before that filter. A filter with an order of 1 will always execute before a filter with an order of 2. B. Simulate the frequency response of an active low-pass filter such as a Butterworth filter. a. Given the following circuit, calculate the critical frequency and the closed-loop gain. C f = __34Hz_______ CL A = __5.7_______ fc = 1/2πR1*C1 =1/2π*47kΩ*0.1uF = 34 Hz ACL = Rf1/Rf2 +1 = 47kΩ/10kΩ + 1 = 5.7 R  k V out V in + - +10 V C   F -10 V R f1  k R f  k
b. Download “ECT246_Week_6_Low1.ms” from Doc Sharing, week 6. Run the simulation. Use the Bode Plotter to find the -3-dB point and determine the critical frequency. C f = _34.328Hz__ @ -3 dB ACLdB = 20log(5.7) = 15dB ACLcrit = 15dB-3dB = 12dB c. Compare the calculated value to the simulated results. I calculated 34Hz and simulated 34.328Hz. C. Prototype the active single-pole low-pass filter and measure and sketch its frequency response, compare and contrast the simulated and measured results . a. Prototype the active single-pole low-pass filter in the diagram above using a LM741 op-amp. b. Connect a frequency generator to the input of the filter. Set the frequency generator’s output to a sine wave at 100 mV peak and as close to 0 Hz as possible. c. Connect channel 1 of an oscilloscope to the input and channel 2 to the output of the filter. d. Vary the input frequency according to the chart below and record the input and output voltage in the table. Calculate the other values.
Frequency (Hz) Input Voltage (peak) Output Voltage (peak) Gain out in v v Gain dB 20log out in v v 1 .197 0 0 0 10 .627 16.3 26.0 28.3 100 .614 3.6 5.9 15.4 1k .64 3.5 5.5 14.8 10k .36 10.6 29.5 29.4 100k .31 1075.8 3470.5 70.8 500k 5.8 1600.0 275.9 48.8 Although my circuit is showing some crazy numbers I can see that whenever I increase the frequency the gain is supposed to decrease and it did a couple

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