A Low Power and High Bandwidth Gm-C Anti Aliasing Filter for DAB Receivers

Transcription

1 Proceedins of the World Conress on Enineerin 00 Vol II WCE 00, June 30 - July, 00, London, U.K. A Low Power and Hih Bandwidth G-C Anti Aliasin Filter for DAB Receiers Mohaad Mehdi Farhad, Sattar Mirzakuchaki Abstract- This paper describes a low-oltae and low-power G-C low pass filter. The low-pass filter that precedes the A/D conerter is called anti-aliasin filter. In the analo sinal processin, the anti-aliasin filter would be one of the ost iportant circuits in the transceier architecture. This filter is located in the analo front-end circuits of DAB receiers. The 4 th order butterworth G-C low-pass filter usin the proposed transconductore is siulated in a 0.8µ CMOS process. In this project, we hae iniized the power consuption and axiized the cut-off frequency of the anti aliasin filter. The circuit consued 848.7µwatt throuh a power supply with a cut off frequency 80MHZ. Index Ters - Anti Aliasin Filter, Diital audio broadcastin, -c filter, Transconductance. I. INTRODUCTION Nowadays, diital technoloy can increase the quality of sound produced with conentional techniques by 50%, but this increase will not reach 00% until the broadcast is also diital. Broadcastin with analo technoloy suffers sinal deradation probles, accuulatin noise and distortions durin each one of the phases that it oes throuh. On the other hand, diital inforation is easily transportable and storable, also usin up less space. This characteristic allows receiers to act like sall coputer that can process the inforation, and this not only affects the sound but all the data that the radio broadcaster wants to send in order to ie added alue to the serice offered. In contrast to AM and FM radio, the new diital radio broadcast (DRB) serice proides uch better quality of serices to fixed, portable, and ehicular receiers. Diital Audio Broadcastin is a ethod for the diital transission of radio sinals. DAB is the transission technoloy of the future and will replace FM and AM radio in the ediu to lon ter. [3] The DAB receier sales and rowth of the arious diital platfors are shown in Fi. and Fi.. The key features of the diital audio broadcastin syste are suarized: Quality of serice - Superior sound quality - Usability - Perfect reception conditions Wide rane of alue-added serices - Typical audio broadcastin (ain serice) - Public inforation (news, weather reports etc) - Electronic newspapers - Electronic ailbox Uniersal syste lay - Standardization - Unique syste desin - Wide choice of receiers Transission efficiency - Lower transission costs for transitter network proides - Lower transission costs for broadcasters. Fiure.: The DAB Receier Sales since 00 to 007 Manuscript receied March 4, 00. M.M.Farhad is with the Faculty of Enineerin-Departent of Electronic, Islaic Azad Uniersity, Saeh branch, Iran (phone: , e-ail: farhad00@yahoo.co ) S.Mirzakuchaki is with the Electrical Enineerin Departent, Electronic Research Center, Iran Uniersity of Science & Technoloy, Iran (phone: , e-ail: _kuchaki@iust.ac.ir ) Fiure.: Growth of the arious diital platfors In 986, the Eureka-47 diital radio project was launched with the objectie to replace analo FM radio. The ain oal of the project was to construct a syste that deliered frequency efficient and CD-quality broadcastin to both obile and stationary receiers. ISBN: ISSN: (Print); ISSN: (Online) WCE 00

2 Proceedins of the World Conress on Enineerin 00 Vol II WCE 00, June 30 - July, 00, London, U.K. The DAB ethod was deeloped in Europe within the fraework of Eureka project 47 and is currently bein introduced in a lare nuber of countries. [4] The diital radio ondiale (one of the DAB standards) has oted to extend its broadcastin bands at up to 0MHZ. The diital radio ondiale (DRM) standard has been deeloped for operation in the AM band. This standard is able to broadcast oer extreely lon distances with the use of satellites. Thus, the diital technoloy iproes broadcastin and reception qualities, allows the deelopent of new production techniques and offers a reater ariety of serices than analo technoloy. And this benefits both broadcasters and audience. II. THE ROLE OF ANTI-ALIAS FILTER IN THE DAB RECEIVERS Fi.3 shows the block diara of DAB receiers. After deodulation and prior to A/D conersion, additional filterin is required to aoid destructie aliasin fro of-band sinals. The low-pass filter that precedes the A/D conerter is called anti-aliasin filter. This filter is located in the analo front-end circuits of DAB receiers. Fiure.3: The block diara of DAB receiers Aliasin due to unwanted, spurious -of-band sinals is a proble in any applications that use A/D conerters. These sinals, if not filtered properly, can seriously ipact the perforance of a data-conersion syste. In processin analo sinals usin discrete-tie systes, if the input is not band liited or if the nyquist frequency of the input is too hih, prefilterin ay be necessary. Also, een if the sinal is naturally bandliited, wideband additie noise ay fill in the hiher frequency rane, and as a result of saplin, these noise coponents would be aliased into the low-frequency band. The block diara of Fi.4 shows a continuous to discrete (C/D) conersion syste that analo sinal is conerted to diital sinal and anti-alias filter is used in a stae prior to A/D conerters. [5] For this architecture, the priary desin challenes in the analo section are the A/D conerter and its associated antialias filter. The required saplin rate of the ADC is directly dependent on the cobined -of-band attenuation proided by the RF and anti-alias filters. When selectin a filter, the oal is to proide a cut off frequency that reoes unwanted sinals fro the ADC input or at least attenuates the to the point that they will not adersely affect the circuit. The channel filter allows a sinal of the desired band to pass, and attenuates the adjacent channel and the alternate channel interferer. If an ideal frequency response was aailable, the anti aliasin filter would be fairly siple to desin; unfortunately, ideal RF filters are not aailable and the analo circuit requireents increase accordinly. Ideally, the frequency response of the low pass filter would be: H AAF ( j ω ) = 0 π ω < ωc < () T ω > ω c If we wish to aoid aliasin, the input sinal ust be forced to be band liited to frequencies below one-half the desired saplin rate (nyquist saplin theore). [5] III. G-C FILTER In this project, we require sharp-cutoff anti aliasin filters. Such sharp-cutoff analo filters can be realized usin actie networks and interated circuits. Analo interated filters are ainly used before A/D conerters in ixed analo diital systes as anti aliasin filters. Three ain roups of interated analo filters are: OPAMP-C, MOSFET-C and, G-C filters. In coparison to actie-rc filters, G-C filters use OTAs instead of opaps to oercoe effects of opap nonidealities on actie-rc filters. [0] Also, OTAs hae the adantaes of easy tunability and enerally sipler circuitry than ost opaps. G-C filters are applicable in a wide rane of frequencies fro a few hertz in bioedical systes to seeral hundred ea hertz rane in counication systes. Furtherore, transconductance aplifiers hae the followin adantaes: the transconductance aryin with bias oltaes, operatin in a wide frequency rane, hih input ipedance and hih put ipedance. Hence, the -c filter based on OTAs is better than the OPAMP-C and MOSFET-C filters. G-C filters, also naed OTA-C filters or transconductance-c filters are widely used in hih frequency applications. The basic buildin block of a -c filter is an interator inolin a transconductor and a capacitor. A transconductor () is a oltae controlled current source and it is tunable throuh aryin DC bias current. [], [] A -c interator is shown in Fi. 5(a) that the put current ( I ) achiees by: I =.( id ( id )) =.. () id Fiure.4: The position of anti alias filter in the C/D conersion syste ISBN: ISSN: (Print); ISSN: (Online) WCE 00

3 Proceedins of the World Conress on Enineerin 00 Vol II WCE 00, June 30 - July, 00, London, U.K. Fi. 5(b) shows the sybol of the syetric transconductor. V C L = =, (6) I L V V R = = =. (7) I. V Fiure.5 (a): A -c interator (a) Equialent circuit of the resistor Fiure.5 (b): The sybol of the syetric transconductor. IV. The PROPOSED G-C AAF DESIGN The construction of 4 th order G-C filter is based on topoloy of passie RLC network, realization of resistors usin transconductors and eulation of inductors usin G-C yrators. Fi. 6 shows the basic AAF structure which is a 4 th order passie LC ladder filter. Traditional RC-based filters with passie eleents can not be directly applied in soc (systeon-chip) desins due to lare area cost. Transfer function of the 4 th order passie low-pass filter, as shown in Fi. 6, is ien in (3). in R = 4 3 RLLCC S + ( RR C + L ) LC S + PS + QS + ( R + R ) P = L RC + R C ) + RL ( C + ), (4) ( C Q = RR ( C + L + L. (5) + C) (3) (b) Syetrical floatin yrator which is equialent to an inductor Fiure.7: The realization of resistor and inductor The transconductance can be widely tuned by chanin DC bias current. Hih linearity and wide bandwidth are achieed by usin a transconductance () cell, as shown in Fi. 8. The alue can be approxiated as w =. µ. cox.. I d l, (8) w = µ. c ox.. od. l (9) Fiure.6: The 4 th order butterworth passie LC ladder filter Passie inductors and resistors usually occupy lare area on chip which is not acceptable in soc desins. The silicon area and power consuption are two ost iportant factors in the interated circuits. Hence, the passie inductors are replaced with actie inductors, whereas the resistors are replaced with actie eleents. One adantae of the -c filter is that passie coponents like the resistor and inductor can be realized with OTA and capacitor. The realization of resistor and inductor are shown in Fi.7 (a), (b). [], [7] The inductance and resistance alues, as shown in Fi.7, are ien in (6), (7). Fiure.8: The proposed transconductor circuit ( cell) Equation (8) shows that it is possible to control the transconductance alue throuh the tail current. On the other hand, equation (9) shows the proportionality between and the oltae oerdrie. The upper liit of od is related to the liited oltae supply. In low-pass filter desin, the cut off frequency of the filter is proportional to /c, where is the transconductance of the OTA and C is the capacitance. [] ISBN: ISSN: (Print); ISSN: (Online) WCE 00

4 Proceedins of the World Conress on Enineerin 00 Vol II WCE 00, June 30 - July, 00, London, U.K. The relationship between the put current and the input differential oltae can be tuned by IM3 and IM4. With a suitable alue of IM3, we can increase IM4 to increase the oerall transconductance. Thus, we can increase the cut off frequency of anti-aliasin filter. The transconductor is used as an operational transconductance aplifier (OTA) in the desin of the 4 th order butterworth low-pass filter. Fi. 9 shows the fully differential -c biquad filter. Transfer function of -c block diara of this filter, as shown in Fi. 9, is ien in (0), that the ariables of X and Y achiees by (),(). in = c ccl L 4 S + c ( 9. c 4 c ) S XS + YS , (0) Fiure.0: The frequency response of the -c filter with 80MHZ cut off frequency X = c c ( ) c ], () L[ L 3 4c Y = c ( ) ]. () L[ V. SIMULATION RESULTS A CMOS operational transconductance aplifier (OTA) for low-pass and wide tunin rane filter application is proposed in this paper. A 4 th order butterworth low-pass filter ipleented with the OTAs is siulated by TSMC 0.8µ CMOS process. With the use of the OTA as a buildin block in the -c filter architecture, the cut off frequency of the low-pass filter is achieed to 80MHZ. Fi.0 shows the frequency response of the -c anti aliasin filter with a 80MHZ cutoff frequency. The power consuption of the -c filter was 848.7µwatt throuh the supply oltae of. Also, this filter consued.3 watt on a power supply with 00MHZ cut off frequency, as shown in Fi.. This result is better than the recent siilar works with hih power consuption. Fiure.: The frequency response of the -c filter with 00MHZ Cut off frequency Table suarizes the easured results of anti-alias filter in DAB receier. In this paper, we achieed to iniize the power consuption in the diital radio receiers. These results are achieed by aryin the aspect ratio of transistors and by aryin the bias oltaes. The transistor sizes and the alue of capacitors and the bias oltaes for this result are illustrated in table. A coparison of the proposed desin with seeral prior desins is suarized in table 3. Fiure.9: Actie ipleentation of the passie anti aliasin filter ISBN: ISSN: (Print); ISSN: (Online) WCE 00

5 Proceedins of the World Conress on Enineerin 00 Vol II WCE 00, June 30 - July, 00, London, U.K. TABLE I. PERFORMANCE SUMMARY of MEASURED RESULTS Technoloy Filter type Power Supply Power Result consuption Cut-off frequency Result Paraeter Power consuption Cut-off frequency M,, M7,8, M3,4, M9,0, M5,6 M3,3, M37,38, M43,44, M49,50 M3,4, M9,0, M5,6, M,, M7,8 M33,34, M39,40, M45,46, M5,5 M5,6, M,, M7,8,M3,4, M9,30 M35,36, M4,4, M47,48, M53,54 V b,, 3, 4, 5, 6, 7, 8, 9, C C L C, [] [5] [8] [3] This work TABLE II. G-C Filter Paraeters VI. CONCLUSIONS TSMC 0.8µ CMOS 4 th -order low-pass µwatt 80MHz.3 watt 00MHz Value Result Result 0µ/0.3µ 0µ/0.5µ 5µ/0.75µ 0.55V 0.0PF TABLE III. COMPARISON WITH PRIOR DESIGNS Filter type CMOS Cut-off Power PROCESS freq. Consuption 5 th order 50Hzelliptic MHz 0.8W 5 th order 0.35µ 330MHz 43W 3 th order 900KHz -MHz 3.W 3 th order 500KHz -0MHz.W 4 th order µwatt MHz.3 watt 0µ/0.3µ 0µ/0.5µ 5µ/0.75µ 0.58V 0.0PF POWER SUPPLY ±.65.V Baseband circuits in a direct conersion receier can be ipleented with a continuous-tie anti aliasin filter and the A/D conerter. The low-pass filter that precedes the A/D conerter is called anti-aliasin filter. This filter is located in the analo front-end circuits of DAB receiers. In 987, European project Eureka 47 was fored, in order to deelop a new diital radio broadcastin syste. This work presents a CMOS ipleentation of a lowpower 4 th order low-pass -c filter for a ery wide frequency tunin rane, which can operate as the channel selection filter for the audio speech, bio edical and wireless application. The 4 th order butterworth low-pass filter desin is initialized by a standard 4 th order butterworth low-pass LC-ladder prototype. G-C filters are built with transconductance eleents and capacitors, to take adantae of these structures for akin interators at hih frequencies. The anti-aliasin -c filter is siulated in the TSMC 0.8µ CMOS technoloy. In this work, we were able to iniize the power consuption and the nuber of transistors in such circuits. This circuit consists of 54 MOSFET transistors and consues 848.7µwatt on a supply oltae of with 80MHZ cut-off frequency. VII. REFERENCE [] C.C.Wan,C.L.Lee,C.C.Hun, A G-C Anti Aliasin Filter Desin With Diitally Tunable Bandwidth for DVB-T Receiers,, IEEE ICSS005 International Conference On Syste& Sinal, pp ,005. [] C.C.Hun, T.Y.Lo, A Wide Tunin Rane G-C Continuous tie Analo Filter, IEEE Transactions on circuits and systes, pp , 007. [3] T.Y.Lo, C.C.Hun, M.Isail, A Wide Tunin Rane G-C Filter for Multi-Mode Direct-Conersion Wireless Receiers,, IEEE 33th Conf. Solid-State Circuits, pp.0-3, sept.007. [4] D.Chala, A. Kaiser, A.Cathelin and D.Belot, A G-C Low-Pass Filter for Zero-IF Mobile Applications With a Very Wide Tunin Rane, IEEE Journal of Solid-State Circuits, Vol.40, No.7, pp , July 005. [5] M.Gabhir, V.Dhanasekaran, J.S.Martinez, S.Sinencio, Low power Architecture and Circuit Techniques for Hih Boost Wide band G- C Filters, IEEE Journal of Solid-State circuits, May 006. [6] C.C.Hun, K.Halonen, M.Isail, A.Hyoo, V.Porra, A Low- Voltae, Low Power CMOS Fifth-order Elliptic G-C Filter for Base band Mobile, Wireless Counication, IEEE Trans. circuits and systes, ol.7, No.4, pp , Au.997. [7] M.M.Farhad, S.Mirzakuchaki, A G-C Anti Aliasin Filter for Diital Radio Receiers,, 008 nd Inter.conf. On Electrical Enineerin (ICEE' 0), PP.3-7, March 008. [8] Y.K.Moon, H.M.Seo, K.Won, Y.K.Park, M.H.Yoon, J.J.Yoo, S.D.Ki, A CMOS Continuous-Tie G-C Filter and Proraable Gain Aplifier for WPAN Receiers, IEEE, pp , 005. [9] C.Yoo, S.W.Lee, W.Ki, A ±.5-V, 4-MHZ CMOS Continuous- Tie Filter with a Sinle-Interator Based Tunin, IEEE J.on solidstate circuits, ol.33, No., January 998. [0] Y.P.Tsiidis, Interated Continuous-Tie Filter Desin-An Oeriew, IEEE Journal of Solid-State Circuits, ol.9, No.3, March.994. [] Z.Xion, Radio Frequency Low noise and Hih Q interated Filters in Diital CMOS Processes,, Readin: Published by Georia institute of Technoloy, July 004. [] R.L.Geier and E.Sanchez-Sinencio, Actie Filter Desin usin Operational Transconductance Aplifiers: A Tutorial, IEEE Circuits and Deices Maazine, ol., pp.0-3, March 985. [3] Asaad S.Baharib & Roland K.C.Tan, Diital Radio Reolution- The Future is Here! Readin: Published by Radio Asia Conference Broadcast Asia, Sinapore, June 005. [4] F.Kozaernik, Diital Audio Broadcastin-radio now and for the future, Readin: Published by EBU Technical Reiew, autun 995. [5] Alan V.Oppenhei, Ronald W.Schafer and John R.Buck, Discrete- Tie sinal Processin, Readin: International Edition, Second Edition, 00. ISBN: ISSN: (Print); ISSN: (Online) WCE 00