Download EE 304 Lab: Building and Analyzing 2nd-Order Resonant Filters and more Lab Reports Microelectronic Circuits in PDF only on Docsity! Name: ___________________________ Lab Instructor: _________________ Date Performed: ________________ Date Due: _______________________ Lab Partner(s): ______________________________________________________ © 2008 Simon J. Tritschler. All Rights Reserved. EE 304 Laboratory V Resonant Filters The purpose of this laboratory is to examine 2nd-order resonant filters and their behavior in various AC circuit applications. These filters are sometimes called tuned circuits because the combination of inductance and capacitance results in a specific resonant frequency that is often critical to a given application; to that end, one element is sometimes made variable in order to “tune” the circuit to exactly the desired frequency. In the previous lab, we constructed a first-order low-pass filter using a simple RC network. By augmenting the series resistor of the filter with an inductor, we create a second-order low-pass filter. The capacitive element still functions as before, reducing its capacitive reactance at high-frequencies to cause more shunting action in the lower leg of the voltage divider; but now we additionally have the inductor’s reactance rising at high frequencies, resulting in increased impedance in the voltage divider’s upper leg and enhancing the attenuation capability. Consider the following circuit: + The critical parameters of 2nd-order filters such as these are the resonant frequency and the damping, which determines how the filter behaves at or near this resonant frequency. This damping characteristic can range from highly-damped, typified by a gentle roll-off that resembles the 1st-order filter but with an ultimately sharper slope of attenuation of −12 dB per octave (as opposed to the 1st-order filter’s −6 dB per octave), to a highly-resonant under- damped peak at the characteristic frequency of the circuit which is then followed by the same attenuation slope. We quantify damping with the parameter known as quality factor, or Q. The higher the value of Q, the more resonant the circuit will behave near the corner frequency (f0) of the filter. + VOUT − 1.5 kΩ 100 mH VSOURCE 10 VPK-PK SINE 10 nF 100 kΩ © 2008 Simon J. Tritschler. All Rights Reserved. 1. Build the circuit. Compensate for any parasitic winding resistance of the 100-mH inductor by reducing the value of the series 1.5-kΩ resistor, if necessary. Present a 10-VP-P sine wave to the input terminals and connect your oscilloscope to the output. Viewing the output signal, sweep the frequency of the signal up and down until a resonant peak is found. Record this resonant frequency. f0 = __________ kHz Now measure output voltage at this resonant frequency and compare it to the passband output voltage; that is, output voltage in the (low-frequency) region of flat response. This is equivalent to comparing peak gain to passband gain. VOUT (PEAK) = __________ VPK-PK VOUT (PASSBAND) = __________ VPK-PK Now divide these two numbers to determine the quality factor of the circuit, which is defined as the ratio of center-frequency gain to passband gain in an under-damped low-pass filter circuit. Q = VOUT (PEAK) / VOUT (PASSBAND) = __________ Comments?
