Parametric filter with programmability for data acquisition

Pa ame ic Fil e wi h P og ammabili y o Da a Acquisi ion He minio Ma ínez-Ga cía, and Enca na Ga cía-Vílchez Eas e n Ba celona School o Enginee ing (EEBE) Depa men o Elec onics Enginee ing Technical Uni e si y o Ca alonia (UPC). Ba celonaTech C/ Com e d’U gell, nº 187. 08036 - Ba celona. SPAIN [email p o ec ed] Abs ac —Audio il e ing sys ems a e used in comme cial applica ions in ol ing equalize s. Howe e , some o he opologies used can be modi ied o be used in audio signal ea men applica ions. Pa ame ic il e opologies allow he use o modi y independen ly he cen al equency o he il e , he bandwid h and he gain. Using a mic op ocesso and p og ammable componen s will allow he use o modi y he pa ame e s o he il e and o acqui e he il e ed signal so i can be p ocessed in o he s ages. To imp o e he unc ionali y o he sys em, a se e will be implemen ed o p ocess he da a sen by he use , will be sen a e wa ds o he mic ocon olle . Finally, he esul s ob ained will be h own back o he use . I. INTRODUCTION A il e is a ci cui which pe o ms signal p ocessing unc ions, like noise- educ ion o enhancing speci ic equencies. In his way, a pa ame ic il e is an analog ci cui able o modi y a signal acco ding o some pa ame e s, which a e cen al F equency, Gain and Bandwid h. Mos ly used in equaliza ion, his kind o il e s a e wo h o implemen when i is desi ed o enhance o supp ess a gi en equency. To de elop he p ojec (see Fig. 1), ou band-pass pa ame ic il e s ha e been implemen ed. Th ee o hem ac as a main modi ie o he inpu signal, and he las one wo ks wi h he mic op ocesso as a da a acquisi ion sys em. These il e s ha e been modi ied o allow he mic op ocesso change hei pa ame e s. Figu e 1. Basic block diag am o he p ojec de eloped. The da a acqui ed by he mic op ocesso will be sen o he compu e , in o de o upload hem in o a se e p e iously c ea ed. This se e will adap he da a ans e ed o gi e he use some Bode cu es, which will show mo e accu a ely he modi ica ion o he inpu signal. The es o he pape is o ganized as ollows. Sec ion II p o ides some in o ma ion abou he s uc u e o he il e s and he basic equa ions. Sec ion III all he conside a ions aken in o accoun in he inal design o he il e . The simula ions o he il e beha io a e shown in he Sec ion IV. In Sec ion V is p o ided some explana ions abou he connec ions o he il e s o he mic op ocesso , and he da a acquisi ion sys em. Finally, Sec ion VI shows he main clues abou he da a ans e ence be ween he mic op ocesso and he se e . Finally, some concluding ema ks a e d awn in he las sec ion. II. FILTER STRUCTURE AND EQUATIONS The main opology used o implemen he il e is he bi-quad a ic il e opology [1], [3], [4]. This opology is buil a ound wo in eg a o s wi h wo eedback loops ha con ol he cen al equency and he bandwid h. This opology has 3 ou pu s ha p o ide a low-pass il e , a band-pass il e and a high-pass il e . Finally, he gain po en iome e eedbacks he di e ence be ween he inpu and he ou pu in o he en y o he bi-quad a ic il e (see Fig. 2). The bi-quad a ic il e equa ion [2] gi en he alues o he esis ances used is shown in (1). To simpli y he exp ession i has been used he ollowing conside a ions: The ollowing esis ances ake he same alue. R1=R2=R3=R4=R6=R7=RA. Capaci o s ha e he same alues: C1=C2=C. The ollowing po en iome e s ake he same alues: P3 =P4=PA. The ollowing po en iome e s ha e he same alues: P2=P5=PB . (1) Figu e 2. Schema ic o he il e in Pspice® O CAD®. F om (1) i can be ob ained he cen al equency and he quali y ac o . The inal ans e unc ion ob ained is showed in (2). As i can be seen on (3), (4) and (5) he equa ions ob ained o he gain, he quali y ac o and he cen al equency a e independen , he e o e hey can be modi ied indi idually. (2) (3) (4) (5) III. CONSIDERATIONS OF THE FILTER The inal il e implemen ed equi es some ex a componen s o achie e a p ope pe o mance. I i is p e ended o ha e a equency sweep be ween 10 Hz and 100 kHz ha becomes impossible o be achie ed wi h a single capaci o using he componen s chosen. Using a single capaci o also has p oblems ega ding linea i y. I i is plo ed equa ion (2) wi h a ixed capaci o i can be seen ha he ela ion be ween he equency and he alue o he po en iome e is exponen ial. In e ms o esolu ion means ha o low alues o he po en iome e he a ia ion o he equency be ween wo close alues is oo high (see Fig. 3). TABLE I. CAPACITORS SELECTED FOR THE FINAL DESIGN Capaci o used Maximum equency ob ained 1.5 µF 33.36 Hz 470 nF 112.87 Hz 150 nF 353.67 Hz 47 nF 1128.75 Hz 15 nF 3536.77 Hz 4.7 nF 11287.58 Hz 1.5 nF 35367.76 Hz 470 pF 112875.846 Hz Figu e 3. Va ia ion o he equency o a minimum 10 Hz equency alue o all he possible po en iome e alues in MATLAB®. I i is educed he ange o he po en iome e s i can be a oided he inc emen ob ained o he low esis ance alues o he po en iome e . The inal solu ion o his p oblem only uses he po en iome e om 20 kΩ o 6 kΩ. In his case (see Fig. 4) he e olu ion o he equency is close o being linea . Howe e , when implemen ing his solu ion i is needed o use mul iple capaci o s o be able o wo k in he desi ed equency spec um. The maximum esolu ion o any gi en capaci o does no exceed a minimum esolu ion o 0.3%. This can be p oblema ic a high equency alues because he a ia ion is a pe cen age. Howe e , gi en he opology chosen i canno be changed o a ixed alue esolu ion. I has been conside ed o use he capaci o alues seen in Table 1. To ob ain he desi ed equency alues wo capaci o s a e pu in se ies o ob ain one ha hal es i s ini ial alue and educes he ole ance o he componen . Wi h hese capaci o s i is almos possible o ob ain a linea esponse h ough he whole equency spec um. Finally, o implemen he design, some speci ic componen s mus be used.  To implemen he po en iome e s, digi al po en iome e s a e be used. I has been chosen he AD5293 [7] om Analog De ices®. This componen o e s a e y low ole ance and a 10-bi esolu ion wi h a alue o 20 kΩ.  To choose di e en capaci o s depending on he desi ed equency ange, analog mul iplexe s a e used. I has been chosen he ADG1604 [8] om Analog De ices®. This 4/1 analog mul iplexe has a low esis ance ha minimizes he second o de e ec s. The implemen a ion o he mul iplexe s adds a non-desi ed esis ance alue o he in eg a o s o he bi-quad a ic il e . A high esis ance alue (see Fig. 5). This addi ional esis ance esul s on a high equency cons an gain a e he cen al equency has been eached. Howe e , o low alues o he esis ance, he high equency cons an gain is oo small o be aken in conside a ion, hus he equa ions de ining he second o de e ec s ha e no been included. Figu e 4. Va ia ion o he equency o a minimum 10 Hz equency alue o a a ia ion o he po en iome e be ween 6.0 kΩ and 20 kΩ using Ma Lab®. IV. BEHAVIORAL SIMULATIONS A e ob aining all he equa ions o bo h cases o he il e desc ibed in he Sec ion III, o assu e he unc ionali y o he il e implemen ed, some simula ions ha e been done. Fi s o all, his conside a ion has been aken in o accoun . The i s ype o simula ions s ands o he il e wi h no mul iplexe s, and he second wi h hem, which include a i s o de pole in o he in eg a o s o he band-pass il e equa ion. Secondly, i has been conside ed a a ia ion o he bandwid h, o gi e acknowledgemen abou his pa ame e and how i a ec s he il e . A a ia ion o he main gain o he il e has been done, o show how i modi ies he beha io o he esponse. Nume ical solu ions o he models desc ibed in Sec ion III had been ob ained by using Ma lab®, wi h he compila ion o a code c ea ed o ob ain hem. The sys em is simula ed h ough he whole desi ed equency spec um, om 10 Hz o 100 kHz. The ollowing dynamic beha io s a e obse ed in e ms o he pa ame e s chosen.  Q = 1.4: In his case, he sys em p esen s a wide bandwid h. Due o his, he gain o he ci cui is applied o a la ge equency ange.  Q = 5.0: Fo his alue o he bandwid h, he sys em esponse is na ow han in he o he case. This makes he il e mo e selec i e h ough he equency spec um. Apa om he p e ious conside a ions o simula e he beha io o he il e , ano he one has been aken in o accoun . The addi ion o a mul iplexe o ob ain he desi ed equency spec um adds a i s o de pole due o he swi ching esis ance o he mul iplexo , as i is said be o e. Fo his eason, his pole has been quan i ied wi h simula ions, wi h a alue o esis ance equal o en, o see how i a ec s he esponse o he il e . Finally, ou simula ions ha e been done o acqui e all he necessa y in o ma ion o quan i y he co ec beha io o he sys em. Each ow gi es he compa ison om he sys em Figu e 5. Responses o he il e o di e en beha io s co esponding o he di e en alues o he con ol pa ame e s. The i s column shows he il e wi h mul iplexing, he second one he no mal il e . Top ow: Q=5.0, bo h esponses show a huge selec i i y h ough he equency spec um. The e a e no app eciable di e ences be ween bo h esponses. Bo om ow: Q=1.4, bo h esponses show less selec i i y han in he i s case. The e a e no di e ences be ween esponses. wi hou mul iplexing o he o he one, and he di e ence o he bandwid hs. To end wi h, all o he plo s shows a a ia ion o he gain. V. SYSTEM CONNECTION In his sec ion a e explained he connec ions be ween he il e s and he mic op ocesso [5]. Also he e a e explained he connec ions h ough he CPLD [6] implemen ed, o allow he mic op ocesso change he s a e o he po en iome e s using less bi s. Fi s o all, i mus be aken in o accoun ha he il e s con igu a ion will be in wo modes. The i s mode s ands o a se ies con igu a ion, whe e he ou pu o he i s il e is connec ed o he inpu o he second one, and all in his way. The second mode wo ks as a pa allel con igu a ion o all h ee il e s. Finally, he ou pu o hese modes is connec ed o he las il e , which wo ks as a poin e , o gi e in o ma ion o he mic op ocesso o he signal in he desi ed equency. To use he poin e , he il e is enabled wi h a speci ic alue o hei po en iome e s, which will use a high quali y ac o alue and a pa icula cen al equency. Wi h his, he poin e will gi e he mic op ocesso he alue in his equency, in an accu a ely way due o he high quali y ac o . This alue will be aken by he analog- o-digi al con e e included in he mic op ocesso , s o ing i un il i is sen back o he PC. On he o he hand, he CPLD wo ks as a ans e ence enable o he po en iome e s in he ci cui . As he implemen ed il e has wen y po en iome e s in i s schema ic, is needed a way o change hei alue using he minimum numbe o bi s possible. In his way, a de-mul iplexe has been implemen ed, using i e con ol bi s. Wi h his, he po en iome e s can be enabled jus changing he i e bi s sequence. Finally, he mul iplexe s o he boa d, used o swi ch be ween he capaci o s o ob ain he quo ed equency ange, a e connec ed o he mic op ocesso , which changes he channel used. VI. DATA TRANSFER This sec ion explains how he da a ob ained by he poin e il e and con e ed o bi s h ough he analog- o-digi al con e e o he mic op ocesso is ans e ed o he compu e . Mo eo e , he e is sligh ly explained how will wo k he se e connec ion, which will allow he use s o pe o m hei calculus om home wi h he designed boa d. Fi s ly, he da a acqui ed om he analog- o-digi al con e e is s acked momen a ily in o he memo y o he mic op ocesso . La e , his da a is send using RS-232 p o ocol o a RS-232 o USB con e e . This is done o a oid using he mic op ocesso USB hos . The con e e changes he p o ocol o sending da a, and sends i h ough he USB connec ion o he compu e . Secondly, he da a a i es o i s des iny. Then, i is p ocessed by he compu e , which s acks he alues on o a ile. This ile is loaded o he se e , which con e s he alues o i in o a plo . This plo is shown o he use , including he able o alues o pos e io plo s. Finally, o load he alues o he pa ame e s o he il e , he same way as he shown be o e is done, bu in he e e se o de . Fi s , he use gi es he pa ame e s o he se e . The se e con e s hem in o a da a ile, and sends i o he compu e . When he ile a i es a he compu e , i is modi ied o ob ain he equi ed alues o each componen o he il e , o ob ain he pa ame e s se p e iously by he use . These alues a e sen o he mic op ocesso , which dis ibu es hem o he di e en de ices o he il e boa d. VII. CONCLUSIONS In his pape has shown a pa ame ic il e labo a o y wi h noise gene a o and da a acquisi ion subsys em, emphasizing he mos impo an pa s o i . Fi s ly, his pape shows he adap a ion o he il e o ou design, using he mul iplexe sys em, and gi ing some clues o do i . On he second hand, he simula ions gi e he necessa y in o ma ion o e i y he co ec ope a ion o he sys em implemen ed, in compa ison o he i s il e . Finally, some clues abou he da a acquisi ion and ansmission in all he ci cui a e gi en, like he p o ocols used o he con igu a ion o he ansmissions. To sum up, is impo an o highligh ha he esul s ob ained in his wo k can p o ide some help o acqui e a highe equency ange, and some basic le el abou he da a acquisi ion and ansmission. ACKNOWLEDGMENTS This wo k has been pa ially suppo ed by he Spanish Minis e io de Economía y Compe i i idad by p ojec DPI2013- 47799-C2-2-R. REFERENCES [1] S. F anco, "Diseño con ampli icado es ope acionales y ci cui os in eg ados analógicos", 3 d ed, Mc G aw Hill, 2002, pp. 150–153. [2] K. Oga a, Mode n Con ol Enginee ing, 3 d ed, P en ice-Hall, 1998, pp. 87–91. [3] A. Sed a and K.Smi h, Mic oelec onic Ci cui s, 4 h ed, Ox o d Uni e si y P ess, 1998, pp. 938–944. [4] G. Clay on and S.Winde , Ope a ional Ampli ie s, 5 h ed, Newnes- Bu e wo h, 2003, pp 248–251. [5] Mic ochip Technology Inc, "PIC18F4550 Da a Shee ", Re ision E, 2009. [6] Xilinx Inc, “XC2C64A CoolRunne -II CPLD”, Re ision 2.31, 2008 [7] Analog De ices Inc, "AD5293 Da a Shee ", Re ision D, 2011. [8] Analog De ices Inc, “ADG1604 Da a Shee ”, Re ision A, 2009.