circuit note cn- 0211 circuits from the lab? reference circuits are engineered and tested for quick and easy system integration to help solve todays analog, mixed - signal, and rf design challenges. for more i nformation and/or support , visit www.analog.com/cn0211 . devices connected /referenced adg904 -r wideband 2.5 ghz, 37 db isolation at 1 ghz, cmos, 1.65 v to 2.75 v, 4:1 mux/sp4t if b and - p ass f ilter b ank s witching n etwork for w ireless i nfrastructure rev . 0 circui ts from the lab? circuits from analog devices have been designed and built by analog devices engineers. standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested an d verified in a lab environment at room temperature. however, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. accordingly, in no event shall analog devices be liable for dir ect, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any circuits from the lab circuits. (continued on last page) one technology way, p.o. box 9106, norwood, ma 02062 - 9106, u.s.a. tel : 781.329.4700 www.analog.com fax: 781.461.3113 ? 2011 analog devices, inc. all rights reserved. evaluation and desig n support circuit evaluation boards cn - 0211 circuit evaluation board (eval - cn 0211 - eb1z ) design and integration files schematics, layout files, bill of materials circuit function and benefits the function of th e circuit , shown in figure 1 , is to route an rf signal through an if band - pass filt er bank . the circuit uses three 140 mhz if saw filters with different bandwidt hs and two adg904 - r sp4t cmos rf switches. the adg904 - r switches control which band - pass filter the rf signal will pass through. only one filter is selectable at a ti me. the typical name given to this type of switching is filter bank switching. this application is very common in wireless infrastructure applications , such as cell phone base stations and point - to - point radio rf front ends . selecting if filters wit h d ifferent bandwidth s results in more flexibility in controlli ng the various data rates in these systems . insertion loss versus frequency in the if band must be flat to achieve optimum system performance. the adg904 - r switch is ideally suited for this circuit because it has very flat insertion loss versus frequency . th e insertion loss also remains flat over the supply voltage and temperature range. switch off isolation is an other very important parameter to m aximize the performance of this circuit. the adg904 - r has excellent off isolation of greater than ? 50 db up to 200 mhz. circuit description the circuit consists of two adg904 - r cmos rf switches and three if saw filters connected as show n in figure 1 . the switches have a supply voltage range of 1.65 v to 2.75 v . in this evaluation , a nominal value of 2.5 v is used. the rf inp ut is connected to p in 10 ( rfc ) of the adg904 - r switch , u1. the adg904 - r switch is a sp4t switch where the rfc pin is the common connection to all four switches (rf 1, rf2, rf3 and rf4). pin 4 of u1 ( rf1 ) is connected to the input of the triquint 856592 saw filter. this filter is a single ended filter with a characteristic impedance of 50 ? . it has a center frequency of 140 mhz and a typical 1 db bandwidth of 20.7 mh z. note that lumped element matching is required to achieve the optimum 50 ? termination impedance. the output of the filter is connected to pin 17 ( rf2 ) of the adg904 - r , u2. similarly , the second saw filter (t riquint 856684) is connected to u1 and u2. in this case , the filter is connected to p in 17 ( rf2 ) of u1 and p in 4 ( rf1 ) of u2. the 856684 filter has a center frequency of 140 mhz and a typical 1 db bandwidth of 16.18 mhz. the third saw filter (triquint 856656 ) is connected to p in 7 ( rf3 ) of u1 and p in 14 ( rf4 ) of u2. the 856656 filter has a centre frequency of 140 mhz and a typical 1 db bandwidth of 11.82 mhz it is important to use the pcb land layout pattern recommended by the manufacturer of the saw filters. to achieve the maximum isolation from the input port to the output port, a plated slot was positioned under the filter. improving this isolation enables the full out - of - band attenuation to be achieved and minimizes the in - band ripple. eac h filter is matched to 50 ? on the input port and output port using 0603 size inductor and capacitor lumped elements. this is an important aspect for achieving good performance from the circuit evaluation board. to further improve isolation, the 50 ? transmission lines that connec t the filters to the switches and to the rf edge connectors are designed as coplanar waveguides. the stand alone insertion loss vs. frequency for the 11.82 mhz bandwidth filter is shown in figure 3 . this data was meas ured with the filter on a separate circu it evaluation pcb with the same transmission line design and matching components, but with no switches in the rf path. this response is used as reference data. the insertion loss at 140 mhz was ?9.17 db, which is consistent with the data sheet value of ?9.2 db typical.
cn- 0211 circuit note rev. 0 | page 2 of 6 10 9 8 6 5 4 3 2 1 11 12 7 10 9 8 6 5 4 3 2 1 11 12 7 gnd gnd gnd gnd gnd gnd gnd gnd gnd gnd gnd en vdd rf1 rf3 rfc rf4 rf2 a1 a0 150nh 15nh 82pf 43nh 27nh 43nh 68pf 27pf 36nh 68pf 39pf 36nh 39pf 68pf adg904-r, u1 0.1f 10f vdd rf input a1 a0 a1 a0 rf output en en note: gnd connections for u1 and u2 not shown 856684 saw filter 856656 saw filter 10 9 8 6 5 4 3 2 1 11 12 7 856592 saw filter 150nh a1 gnd gnd gnd gnd en vdd gnd gnd gnd gnd gnd gnd rf4 rf2 a0 rf1 rf3 gnd rfc adg904-r, u2 + 0.1f 10f vdd + 09853-001 figure 1. if band - pass filter bank switching network (simp lified schematic: all connections and decoupling not shown) s a w f i l t e r s ad g 90 4 - r ad g 904 - r 09853-002 figure 2. eval - cn0211 - eb1z c ircuit e valuation b oard.
circuit note cn- 0211 rev. 0 | page 3 of 6 figure 4 shows test results from the circuit evaluation pcb when the adg904r switches are selecting the 856656 saw filter. the resp onse compares well to the stand alone response , which is also included in the plot for reference. due to the loss of the two adg904 - r switches in series , the insertion loss of the filter has increased by 1 db. r ipple in the pass band is of importance in wireless infrastructure applications. the ripple across the band is 0.47 db from the minimum to maximum pea k within the pass band of 135.5 mhz to 144.5 mhz. this level is well within the data sheet specification for ripple , which is 0.8 db max. the high off isolation of the switches is critical in this application to minimize leakage from one filter channel to the next. poor switch off isolation would increase the in - band insertion loss and ripple of the filter . n o evidence of this is visible in these test results. figure 5 and f igure 6 show t he 856592 and 856684 saw filter channel test results , respectively. the results shown include the loss from the two adg904 - r switches in series . this loss is approximately 1.0 db. both filter cha nnels show good flat insertion loss , plus high out - of - band attenuation levels . the results shown are wi t hin the manufacturers data sheet tolerances and clearly show that the adg904 - r switches are not introdu cing any ripple, mismatch , or a ffecting the flatness of the filters in any way. ?9 0 ? 8 0 ?7 0 ? 6 0 ?5 0 ? 4 0 ?3 0 ?2 0 ?1 0 0 10 5 1 1 5 12 5 13 5 14 5 15 5 16 5 17 5 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) ?7 ?8 ?9 ?10 ?11 ?12 ?13 ?14 130 132 134 136 138 140 142 144 146 148 150 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) 09853-005 figure 3 . standal one 140 mhz (center frequency), 11.82 mhz (1 db bw), 856656 saw filter frequency response, no switches ?9 0 ? 8 0 ?7 0 ? 6 0 ?5 0 ? 4 0 ?3 0 ?2 0 ?1 0 0 10 5 1 1 5 12 5 13 5 14 5 15 5 16 5 17 5 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) sa w fil t er s a w f i l t e r + s w ?7 ?8 ?9 ?10 ?11 ?12 ?13 ?14 130 132 134 136 138 140 142 144 146 148 150 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) sa w fil t er s a w f i l t e r + s w 09853-006 figure 4. 140 mhz (center frequency), 11.82 mhz (1 db bw), 856656 saw filter frequency response measured on evaluation board with and without switches
cn- 0211 circuit note re v. 0 | page 4 of 6 ?8 ?9 ?10 ?11 ?12 ?13 ?14 125 130 135 140 145 150 155 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) 09853-009 ?9 0 ? 8 0 ?7 0 ? 6 0 ?5 0 ? 4 0 ?3 0 ?2 0 ?1 0 0 10 5 1 1 5 12 5 13 5 14 5 15 5 16 5 17 5 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) figure 5. 140 mhz (center frequency) 20.7 mhz (1 db bw) 856592 saw filter frequency response measured on e valuation board with switches ?9 0 ? 8 0 ?7 0 ? 6 0 ?5 0 ? 4 0 ?3 0 ?2 0 ?1 0 0 10 5 1 1 5 12 5 13 5 14 5 15 5 16 5 17 5 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) ?9.0 ?12.0 ?11.5 ?10.5 ?9.5 ?10.0 ?11.0 ?13.0 ?12.5 ?13.5 ?14.0 130 135 140 145 150 m a g n i t ud e ( d b ) f r e q u e nc y ( m h z ) 09853-010 figure 6. 140 mhz (center frequency) 16.18 mhz (1 db bw) 856684 saw filter frequency response measured on e valuation board with switches common variations the abs orptive version of the adg904 switch can also be used in this filter bank switching circuit. the absorptive version contains 50 ? shunt resistors on the rfx port s. this results in a good 50 ? match when the switch is in the off state. this is importan t in some applications w h ere reflected signals in the off channels need to be absorbed. the circuit can be easil y scaled to include more or fewer filter channels. depending on the number of channels, o ther switches from the adg9 xx family may be better to use and offer more flexib ility with layout. the adg936 is a dual spdt switch , the adg918 is a n spdt switch , and the adg901 is a n spst switch . all of th ese switches are available in both absorptive and reflective configurations. circuit evaluation a nd test the circuit is designed to be connected to a vector network analyzer ( vna ) via sma type connectors. the sma connectors on the board are female. to sw itch between each filter channel there are jumper terminals on the board that can be manually changed. note that one of the switch throws in each adg904 - r switch is not used. therefore , when these unused switches are selected , the rf input and rf output po rts are is olated, i.e. , the switches are not connected to a filter .
circuit note cn- 0211 rev. 0 | page 5 of 6 vector network analyzer vdd 2.5v gnd j4 u6 u5 u4 j5 j12 adg904-r u1 adg904-r u2 eval-cn0211-eb1z 09853-0 1 1 figure 7 . test setup functional block diagram equipment needed ? vector network analy z er , hewlett packard 8753e with hewlett packar d 85033d 3.5 mm c alibration k it , or equivalent. ? e va l - cn0211 - eb1z circuit evaluation board ? power supply (2.5v) ? coaxial rf cab le with 3.5 mm type connectors ? setup and test th e test setup is shown in figure 7 . the vna is connected to the circuit evaluation board through 3 . 5 mm connector type cables. full two port calibration of the vna to the end of the cables will be required before testing of the circuit evaluation board. table 1 sho ws the logic s tates to enable each individual filter channel. table 1. truth t able for f ilter p ath s election filter en adg904 - r u1 adg904 - r u2 a0 a1 a0 a1 u6 0 1 0 0 0 u5 0 0 1 1 1 u4 0 0 0 1 0 . learn more cn0211 design suppor t package: www.analog.com/cn0211 - designsupport corrigan, theresa, an - 952 application note, adg9xx wideband cmos switches: frequently asked uestions, analog devices. mt - 101 tutorial, decoupling techniques , analog devices.
cn- 0211 circuit note re v. 0 | page 6 of 6 data sheets and evaluation boards cn - 0211 circuit evaluation board ( e va l - cn0211 - eb 1z ) ad g 904 data sheet ad g 904 evaluation board ad g 901 data sheet ad g 901 evaluation boar d ad g 918 data sheet ad g 918 evaluation board ad g 936 data sheet ad g 936 evaluation board revision history 10/1 1 rev ision 0 : initial version (continued from first page) circuits from the lab circuits are intended only for use with analog devices products and are the intellectual property of analog devices or its licensors. while you may use th e circuits from the lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectua l property by application or use of the circuits from the lab circuits . information furnished by a nalog devices is believed to be accurate and reliable. however, "circuits from the lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of mer chantability, noninfri ngement or fitness for a particular purpose and no responsibility is assumed by analog devices for their use, nor for any infringements of patents or other right s of third parties that may result from their use. analog devices reserves the right to change any circuits from the lab circuits at any time without notice but is under no obligation to do so. ? 2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of t heir respective owners. cn09853 - 0 - 10/11(0)
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