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FPGA Controlled High Performance Amplifier May06--14 Total Harmonic Distortion Test Overview: The Total Harmonic Distortion Test is a LabVIEW automated test designed to verify the amount of distortion of the FPGA controlled amplifier using HP 8662A Function Generator, HP 3585A Spectrum Analyzer and HP 8563E Spectrum Analyzer. As in the Frequency Response Flatness Test, extra caution should be taken to avoid inputting DC voltage into the analyzer. Prior to testing, a LabVIEW program should be developed to automate the test. Proper driver should be downloaded from the Internet. The computer controls the HP 8662A Function Generator through a GPIB bus to output a signal at desired frequency. When the signal is below 40MHz, HP 3585A Spectrum Analyzer should be used to measure the frequency spectrum and the HP 8563E Spectrum Analyzer should be used to measure the distortion for frequency between 40MHz-100MHz. Since we are measuring the third, fifth…. Harmonics of the input signal, proper LabVIEW program should be set up to find peaks at multiples of input frequency f. Then we shall take the log of the following equation result and multiple it by 10 to obtain the total harmonic distortion: where terms H2…..Hn are the power levels of the harmonics and term H1 is the power level of the fundamental (the pure tone). FPGA Controlled High Performance Amplifier May06--14 Total Harmonic Distortion Test Equipment: Function Generator: HP 8662A Function Generator Specs: http://www.spectratest.com/8662A.asp Spectrum Analyzer: HP 8563E Spectrum Analyzer (For 40MHz-100MHz, but this one will burn up with more than 200mV DC. Must be very careful.) Specs: http://www.valuetronics.com/vt/assets/pdfs/hp_8560eseries.PDF Spectrum Analyzer: HP 3585A Spectrum Analyzer Specs: http://www.testbuyer.com/c-52045A080AD5-asd.htm Terms & Definitions: GPIB – General Purpose Interface Board. Same as IEEE 488 IEEE 488 – A communication bus, standard in the test industry. Same as GPIB TEK – Tektronix THD – Total Harmonic Distortion Fundamental frequency—The harmonic component of a complex wave that has the lowest frequency and commonly the greatest amplitude. Harmonics -- Signals that are integer multiples of the fundamental frequency. FPGA Controlled High Performance Amplifier May06--14 Total Harmonic Distortion Test Explanation of tests: By changing resistor values in the circuit, the team should be able to adjust the gain setting of the circuit. There are 4 available gain settings and the frequencies corresponding to these settings are up to 100MHz. The amount of total harmonic distortion generated by an analog circuit is an important measure of the performance of that circuit. There should be as little harmonic as possible generated. 10 log (THD) = 10 log(√ (E2f2 + E3f2 + … + Enf2)/√ (Ef2 + THD is calculated using E2f2 + E3f2 … + Enf2)) THD = percentage of total harmonic distortion Ef = amplitude of fundamental voltage E2f = amplitude of second harmonic Enf = amplitude of nth harmonic voltage Test Setup: FPGA Controlled Amplifier Spectrum Analyzer Signal Input Output Observation GPIB Control LabView Program FPGA Controlled High Performance Amplifier May06--14 Test Specifications: Input Frequency Range Total Harmonic Distortion (dB) DC – 1kHz > 1kHz - 20 kHz > 20kHz – 100kHz > 100kHz – 1MHz > 1MHz – 10MHz > 10MHz – 20MHz > 20MHz – 50MHz > 50MHz – 100MHz < - 105 dB < - 95 dB < -85 dB < - 80 dB < - 70 dB < -65 dB < -50 dB < -40 dB Reference: http://seniord.ece.iastate.edu/may0614/