MEASUREMENT AND CONTORL OF TOTAL HARMONIC DISTORTION IN FREQUENCY RANGE 0,02-10KHZ.

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1 ELECTRONICS 00 September, Sozopol, BLGARIA MEASREMENT AND CONTORL OF TOTAL HARMONIC DISTORTION IN FREQENCY RANGE 0,0-0KHZ. Plame Agelov Agelov Faculty for Computer Sciece, Egieerig ad Natural Studies, Burgas Free iversity, Sa Stefao Street, 800 Burgas, Bulgaria, office phoe: , GSM: , pagelov@bfu.bg The measuremet ad cotrol of the o-liear distortio has always bee a challege with the qualitative reproductio of the audio sigal. There are may methods ad ways to determie the bad sigal level. Some of the methods suggest filter separatio of the useful sigal ad preserve oly the uwoted distortio value. It is impossible to make a qualitative assessmet of the distortio by this method. The preset article deals with the qualitative assessmet of the sigal at the time of its optimal reproductio withi the whole frequecy rage f0 [Hz] 0 [khz].. TASK OF THE ARTICLE Keywords: measurig, harmoic distortio, phase corrector The electric sigals passig through a give amplificatio or correctio chai suffer a uwated chage i their form ad phase. This kig of chage is called oliear distortio. The value of this distortio is characterized by the so-called coefficiet of o-liear distortio equatio.. This coefficiet represets the relatio betwee the geometric sum total of the effective values of all harmoic without the first oe ad the amplitude of the first harmoic.... () KTHD There is aother way to represet mathematically the o-liear distortio coefficiet equatio.. Here we have the relatio betwee the geometric sum total of the effective values of all the harmoics without the first oe ad the effective value of the full sigal () KTHD... Equatio.. represet the relatio betwee the two coefficiets. KTHD () KTHD KTHD With o-liear distortio of the sigal uder % coefficiets K THD ad K THD are equal. The suggested method to measure the o-liear distortio coefficiet is used maily to measure low value distortio. The method gives precisio of up to 0,0%.

2 ELECTRONICS 00 September, Sozopol, BLGARIA The geeral block scheme of the suggested measurig device of o-liear distortio is show o fig.. i Y scope Phase i corector Amp. i corector Power Amplifier X scope Defferetiate i -out Phase out Corector Load Fig.. Bloc schematic The method does ot filter the iput sigal ad has bee kow through Akulpiev s ivetio. A o-liear distortio assessmet with this method is made trough the graphic compariso of the two sigals. To set a similar iterrelatio if is ecessary to itroduce a model sigal ad to separate the o-liear distortio sigal. This is achieved whe we compare two levels of the sigals which are simultaeously trasmitted to a substractor. The substractor i tur seds out the sigals, trasmitted to both its etraces. To get oly a harmoic distortio output sigal i the substractor if is ecessary ad it s both etraces for the sigals to have the same phase ad amplitude. This is easily achieved with model sigals but what would happe if oe of them had o-liear distortio? I this case the device well get oly a o-liear distortio output sigal. Now let s look at the priciple scheme of the device... Graphic measuremet of o-liear distortio. Ge CON i Power Amp CON out Power Amp CON i RP. k C R 9. k R.7 k R Z or 8 / 00W 0-80p SW S C. RP 00 k RP k C7 C..7u / V R9. k R 00 k C 80 R k A way to measure the THD graphically is show o Fig.. The measuremet ad accordig to this scheme is optimal for the frequecy rage f0 [Hz] 0 [khz] i the followig order: - calibratio of the device switch SW is i the suggested positio ad the iput sigal of the geerator is trasmitted simultaeously to chael X ad C R 0 k.7u / V V -V R0 00 k V 8 B 7 TL07 -V power CON SW "X" EO CON R.7 k R.7 k R8 7 k Fig.. Graphical measuremet TDH v.. "Y" EO CON C out 0u R7 7 k V 8 A TL07 -V

3 ELECTRONICS 00 September, Sozopol, BLGARIA chael Y of the electroics oscilloscope. The sigal, trasmitted to chael Y has a chaged phase (group C, R ad the chose capacity C - ). Amplitude correctio is achieved by variable impedace RP (rough regulatio) ad RP (precise regulatio). This the sigal i switch SW goes to the o-ivertig etrace of A. A sigal to this secod etrace is trasmitted by chai R, R 9. Operatio amplifier A i this case fuctios as a substractor i.e. it seds out its defese iput sigals. Calibratio is achieved whe the sigals trasmitted to the two etraces of the substractor are equal i amplitude ad phase. Oly i this case the output voltage to chael Y of the electroic scope will be equal to zero. The the device is calibrated. This method allows for the usage of sigal geerators with lower techical requiremets. They are calibrated the basic of this scheme. - measuremet of the o-liear distortio coefficiet the measuremet is made after we have already calibrated the device ad we tur switch SW to positio two. I this case the iput geerator sigal goes to the etrace of a measured lowfrequecy amplifier. Load impedace Z/8 [Ω] is coect to the output of this amplifier. The output sigal i SW is trasmitted to the secod etrace of substractor A. We agai compesate for the amplitude by RP ad RP without chagig the phase of the sigal. Whe the amplitude is leveled oly the o liear distortio sigals well be see the scope scree. A shortcomig of the suggested scheme is the o-liear phase regulatio i the iput geerator ad the hi-value of variable capacity C. The simulatio results of this kid of phase regulatio are show o Fig.. To avoid this basic shortcomig we correct the scheme i the way show o Fig.. Here the phase correctio group has bee replaced by operatio amplifier which compesates for the amplitude reductio Fig.. Phase correctio v.. Fig.. Phase correctio v.. ad regulates the phase trough cotrolled impedace RP. The simulatio results are show o Fig.. To make this scheme uiversal there is a switch regulatio of the phase i the differet research stages. The amplitude regulatio i its tur is achieved trough a liear regulatio group, which is restricted to the study of output power P out 00 [W] of the ivestigated stage with load impedace Z t [Ω]. I the scheme there is a additioal iversio of the sigal before it is trasmitted to the substractor (differece operatio amplifier). I this way we ca study the fuctioig of both a ivertig ad o-ivertig power amplifier.

4 ELECTRONICS 00 September, Sozopol, BLGARIA Ge CON i Power Amp CON out Power Amp i CON RP 70 k R 00 k RP. k R.7 k SW R Z or 8 / 00W 8 -V A TL07 R V 00 k RP 00 k RP k C7.7u / V S C R 00 k C 0 Fig.. Graphical measuremet TDH v.... Test the project Experimetal result of the measuremet of the total harmoic distortio (THD) of TDA79 with load impedace Z[Ω] ad output power withi the limit of P out 0 [W] 00 [W]. C 80 R7. k R 00 k V 8 A TL07 -V R9 0 k R8 k V -V C.7u / V SW CON power CON R0.7 k R.7 k "X" EO R 7 k C 0u "Y" EO R 7 k 8 CON V out B 7 TL07 -V

5 ELECTRONICS 00 September, Sozopol, BLGARIA. Coclusio: The preset research suggests a practical way to achieve a programmed time delay. A system to suppress the output sigal level has bee itroduced i order to limit the amplitude. This kid of stabilizatio does ot produce a large harmoic distortio i the sigal which makes if suitable for the Hi-Fi soud rage. The eclosed simulatio result show the priciple of work ad what has already bee achieved By the project.. REFERENCES [] Audio limiter - [] Electroic Projects Olie - Surroud Soud Decoder Mk [] Protel 99SE (trial versio) [] D.Clayto, B.Newby. Operatio amplifiers publishig by Techique i 997.