AN-8006 rev. 1.0 1 www.fairchildsemi.com ?005 fairchild semiconductor corporation december 2005 AN-8006 capacitor selection for the fms6410b s-video filter AN-8006 capacitor selection for the fms6410b s-video filter method the fms6410b requires 0.1? input coupling capacitors, but may be ac or dc coupled out. finding video quality ?i.e., low esr, equivalent series resistance, low inductance, low leakage, and constant capacitance over a frequency range from 20hz to 6mhz ?0.1? capacitors presents no problem. surface mount capacitors meeting these requirements are both inexpensive and plentiful. the fms6410b, when ac coupled out, also requires four 220? output coupling capacitors if all outputs are to be used. see figure 1. however, some users may use values up to 1000? to pass ?ilt speci?ations in the two-?ld test. in the past, when wideband signals such as video needed coupling capacitors in the hundreds of ? s, tantalums were the only choice. this presents a problem. the fms6410b was designed for low- cost applications. in the quantities needed, the cost of the tantalums is greater than the cost of the ?ter and the other associated components. there is a solution: modern, surface mount, aluminum electrolytic capacitors designed for use in high-frequency switching power supplies have all the necessary qualities. for a given capacitance and voltage rating these electrolytics are about the same size as the tantalums. they also have low equivalent series resistance, low inductance, and low leakage. since they are intended for use as bypass capacitors in switching power supplies operating up to 1mhz, they have an adequate frequency response as video coupling capacitors. several types from several manufacturers have been investi- gated. some 220? surface mount aluminum electrolytic capac- itors from cornell dubilier, elna, and united chemi-con were indistinguishable from highquality, high-cost tantalums, as can be seen by comparing figures 2 and 4 with figures 3 and 5. it should be pointed out that these are not the only suppliers of usable capacitors. any physically small, surface mount, 220?, 6v to 10v, aluminum electrolytic capacitor with esr less than 1 at 6mhz and with less than 2% capacitance change from 20hz to 6mhz is a candidate for use in fms6410b circuits. many capacitors meet these requirements. with the right capacitors, their cost is no barrier to using the fms6410b. 220f 220f 1f 0.1f 220f 0.1f 0.1f 220f video cables 75 75 75 c* r* 75 75 75 75 75 fms6410b y out cv out cv out on-channel modulator, vcr, and tv c out y in c in 5v + + 5th-order filter 5th-order filter 1 4 8 5 3 7 2 6 * c and r depend on the input impedance of load figure 1. ac coupled s-video and composite video line driver for ntsc
www.fairchildsemi.com 2 AN-8006 rev. 1.0 AN-8006 capacitor selection for the fms6410b s-video filter figure 2. -3db response with tantalum capacitor figure 3. -3db response with aluminum electrolytic capacitor figure 4. wideband response with tantalum capacitor figure 5. wideband response with aluminum electrolytic capacitor 0 1 2 3 4 5 6 7 8 9 amplitude (db) 12345678910 frequency (mhz) 10 0 1 2 3 4 5 6 7 8 9 amplitude (db) 12345678910 frequency (mhz) 10 0 1 2 3 4 5 6 7 8 9 amplitude (db) 12345678910 frequency (mhz) 10 0 1 2 3 4 5 6 7 8 9 amplitude (db) 12345678910 frequency (mhz) 10 0 -10 -20 -30 -40 -50 -60 -70 amplitude (db) 10 100 1k 10k 100k 1m 10m 100m frequency (hz) -80 0 -10 -20 -30 -40 -50 -60 -70 amplitude (db) 10 100 1k 10k 100k 1m 10m 100m frequency (hz) -80
AN-8006 rev. 1.0 3 www.fairchildsemi.com AN-8006 capacitor selection for the fms6410b s-video filter disclaimer fairchild semico n ductor reser v es the right to make cha n ges without further n otice to a n y products herei n to impro v e reliability, fu n ctio n or desig n . fairchild does n ot assume a n y liability arisi n g out of the applicatio n or use of a n y product or circuit described herei n ; n either does it co nv ey a n y lice n se u n der its pate n t rights, n or the rights of others. trademarks the following are registered and u nregistered trademarks fairchild semicond u ctor owns or is a u thorized to u se and is not intended to b e an exha u stive list of all s u ch trademarks. life support policy fairchild?s products are n ot authorized for use as critical compo n e n ts i n life support de v ices or systems without the express writte n appro v al of fairchild semico n ductor corporatio n . as u sed herein: 1. life s u pport devices or systems are devices or systems which, (a) are intended for s u rgical implant into the b ody, or ( b ) s u pport or s u stain life, or (c) whose fail u re to perform when properly u sed in accordance with instr u ctions for u se provided in the la b eling, can b e reasona b ly expected to res u lt in significant inj u ry to the u ser. 2. a critical component is any component of a life s u pport device or system whose fail u re to perform can b e reasona b ly expected to ca u se the fail u re of the life s u pport device or system, or to affect its safety or effectiveness. product status definitions definition of terms datasheet identification product status definition advance information preliminary n o identification n eeded o b solete this datasheet contains the design specifications for prod u ct development. specifications may change in any manner witho u t notice. this datasheet contains preliminary data, and s u pplementary data will b e p ub lished at a later date. fairchild semicond u ctor reserves the right to make changes at any time witho u t notice in order to improve design. this datasheet contains final specifications. fairchild semicond u ctor reserves the right to make changes at any time witho u t notice in order to improve design. this datasheet contains specifications on a prod u ct that has b een discontin u ed b y fairchild semicond u ctor. the datasheet is printed for reference information only. formative or in design first prod u ction f u ll prod u ction n ot in prod u ction isopla n ar? littlefet? microcoupler? microfet? micropak? microwire? msx? msxpro? ocx? ocxpro? optologic ? optopla n ar? pacma n ? pop? power247? poweredge? fast ? fastr? fps? frfet? glo b aloptoisolator? gto? hisec? i 2 c? i-lo ? implieddisconnect? intellimax? rev. i16 acex? activearray? bottomless? b u ild it n ow? coolfet? cross v olt ? dome? ecospark? e 2 cmos? ensigna? fact? fact q u iet series? powersaver? powertrench ? qfet ? qs? qt optoelectronics? q u iet series? rapidconfig u re? rapidconnect? serdes? sile n t switcher ? smart start? spm? stealth? s u perfet? s u persot?-3 s u persot?-6 s u persot?- 8 syncfet? tinylogic ? ti n yopto? tr u translation? uhc? ultrafet ? unifet? v cx? wire? across the b oard. aro u nd the world.? the power franchise ? programma b le active droop?
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