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zxf36l01 issue 3 - january 2002 1 variable q filter description the zxf36l01 is a versatile analog high q bandpass filter. the device contains two sections: 1 variable q bandpass filter. 2 mixer block. the basic filter section requires 2 resistors and 2 capacitors to set the centre frequency. the filter operates up to a frequency of 150khz. two external resistors control filter q factor. the q can be varied up to 50. the mixer is included to extend the frequency range up to 700khz and to permit the centre frequency to be tuned. the local oscillator can be any waveform, making microprocessor control convenient. applications many filter applications including: - ? audio bandpass and notch ? micro controlled frequency ? adaptive filtering ? sonar and ultrasonic systems ? instrumentation features and benefits ? centre frequency up to 700khz ? tuneable centre frequency ? variable q ? low power ? standby mode for improved battery life system diagram part number package part mark ZXF36L01W24 so24w zxf36l01 ordering information part number container increment ZXF36L01W24tc reel 13? 330mm 1000 ZXF36L01W24 tube 31
absolute maximum ratings voltage on any pin 7.0v (relative to vss) operating temperature range 0 to 70c (de-rated for -40 to 85oc) storage temperature -55 to 125c electrical characteristics test co ditions: temperature =25c, v dd = 5.00v, v ss = 0.00v general characteristics parameter conditions min. typical max. units operating current pd =v dd 2.2 3.4 4.5 ma shutdown current pd =v ss 160 300 a iih (pd) vih =5v (wrt v ss )1.0a iil (pd) vil =0v (wrt v ss ) -1.0 a filter characteristics max. operating frequency 150 khz q usable range 0.5 50 centre frequency temperature coefficient q=30, fo = 1khz note 1 10 ppm/c average q temperature coefficient q=30, fo = 1khz note 2 0.1 % /c voltage noise 1 ? 100 khz 20 nv/ hz input impedance 30 50 k ? max. output swing output load 10 k ? 1.6 v pk-pk output sink current 150 a output source current 150 a mixer characteristics max. operating frequency 700 khz maximum signal input 300 mv pk-pk maximum local oscillator input 100 mv pk-pk minimum local oscillator input 5 mv pk-pk local oscillator input impedance 60 ? note 1 centre frequency temperature coefficient is dominated by the external r & c components. on chip drift is negligable. note 2 average q temperature coefficient is dominated by the external r components. zxf36l01 issue 3 - january 2002 2
typical electrical characteristics test co ditions:v dd = 5.00v, v ss = 0.00v zxf36l01 issue 3 - january 2002 3 typicalgainatfovqfactor (fo = 140 khz) 20 25 30 35 40 45 50 10 20 30 40 50 60 70 80 90 100 q factor gai n (db) q factor v frequency 16 18 20 22 24 26 28 30 32 0 20 40 60 80 100 120 140 160 180 200 frequency (khz) qfactor gain at fo describes the peak gain of the notch pass filter. this gain is defined by the value of q factor. components used: 1/8 watt metal film resistors (+/- 50 ppm). ceramic capacitors (+/- 50 ppm). the curve shows q factor over frequency for a fixed loop gain (rf/ri).
zxf36l01 issue 3 - january 2002 4 description of pin functions v dd positive supply connection (5 volts). both pins to be connected. to be decoupled with a 100nf capacitor to v ss . v ss negative supply connection; system ground (0 volts). both pins to be connected. bg bias generator output. to be decoupled with a 100nf capacitor to v ss . bi bias inputs for internal circuitry, both to be connected to bg. (or external supply referenced to v ss ) pd active low. this feature can be used to reduce power consumption for applications that have a standby mode. fi1,fl2 filter input, fi1 or fi2 depending on filter configuration. fo filter output for all configurations. lo local oscillator signal input. mxi mixer signal input. mxo mixer signal output. c1, rc1 phase advance network nodes. values r and c set centre frequency, fo. r2, rc2 phase retard network nodes. values r and c set centre frequency, fo. gp1,2,3 loop gain programming nodes. connection diagram v ss fi1 c1 r2 rc1 rc2 v dd fi2 fo bi gp1 gp3 gp2 mxo v ss mxi lo bi bg n/c n/c n/c pd v dd 1
zxf36l01 issue 3 - january 2002 5 r=10k ? c=100nf rf=19.5k ? ri=10k ? filter configurations and responses notch filter filter ac performance notch filter gain response -35 -30 -25 -20 -15 -10 -5 0 5 10 100 1000 10000 fre q uency (hz) gain (db) notch filter phase response 90 120 150 180 210 240 270 10 100 1000 10000 fre q uency (hz) phase (degrees) f rc qrr o f i = 1 2 (/) where r, ri and rf 10k ? and c 50 pf see ?designing for a value of q? for more details. typical responses for the circuit with component values shown in circuit diagram. output signal input signal v dd fi2 fo v ss fi1 c1 rc1 rc2 gp1 gp2 gp3 r2 bi mxo v ss mxi lo bi bg n/c n/c n/c pd v dd c c rf ri 124 5v 5v 100nf 100nf 100nf r r
zxf36l01 issue 3 - january 2002 6 filter ac performance f rc qrr o fi = 1 2 (/) where r, ri and rf 10k ? and c 50 pf see ?designing for a value of q? for more details. filter configurations and responses (continued) typical responses for the circuit with component values shown in circuit diagram. notch pass filter gain response -5 0 5 10 15 20 25 30 10 100 1000 10000 frequency (hz) gain (db) notch pass filter gain response -5 0 5 10 15 20 25 30 10 100 1000 10000 frequency (hz) gain (db) notch pass filter phase response -270 -240 -210 -180 -150 -120 -90 10 100 1000 10000 fre q uency (hz) phase (degrees) v dd fi2 fo mxi bi bg n/c n/c n/c pd v dd output signal input signal r r c c rf ri 124 5v lo 100nf 100nf 100nf 5v v ss fi1 c1 rc1 rc2 gp1 gp2 gp3 r2 bi mxo v ss r=10k ? c=100nf rf=19.5k ? ri=10k ?
zxf36l01 issue 3 - january 2002 7 filter ac performance notch pass filter 2 gain response -30 -20 -10 0 10 20 30 1 10 100 1000 10000 frequency (hz) gain (db) notch pass filter 2 phase response -120 -90 -60 -30 0 30 60 90 120 1 10 100 1000 10000 frequency (hz) phase (degrees) f rc qrr o fi = 1 2 (/) where r, ri and rf 10k ? and c 50 pf see ?designing for a value of q? for more details. the skirt ?roll off? away from the peak is -20db/decade regardless of chosen q. filter configurations and responses (continued) notch filter (with attenuating skirts) r=10k ? c=100nf rf=19.5k ? ri=10k ? typical responses for the circuit with component values shown in circuit diagram. v dd fi2 fo mxi bi bg n/c n/c n/c pd v dd output signal input signal r r c c rf ri 124 5v lo 100nf 100nf 100nf 5v v ss fi1 c1 rc1 rc2 gp1 gp2 gp3 r2 bi mxo v ss
zxf36l01 issue 3 - january 2002 8 designing for a value of q as menti oned on the configuration pages, there is a proportional, but non-linear relationship between the ratio of rf and ri, and q. these resistors define the gain of an inverting amplifier that determines the peak value gain and therefore the q of the filter,q is defined as: q f db bandwidth o = ? 3 this value of required gain is critical. as the maximum value of q is approached, too much gain will cause the filter to oscillate at the centre frequency, fo. a small reduction of gain will cause the value of q to fall significantly. therefore, for high values of q or tight tolerances of lower values of q, the resistor ratio must be trimmed as shown. frequency dependant effects must be accounted for in determining the appropriate gain. as the frequency increases because of internal phase shift effects the effective circuit gain reduces and thus q factor reduces. the frequency effect is not a problem for circuits where the fo remains constant, as the phase shifts are accounted for permanently. for designs where q is high and fo is to be ?swept?, care must be taken that a gain appropriate at the highest frequency does not cause oscillation at the lowest. below are some typical values of gain required for several example conditions: example1 fo = 48khz, r = 10k ? , c = 320pf q=60, rf/ri = 36.6k ? / 18 k ? => 2.033 example2 fo = 140khz, r = 10k ? , c = 100pf q=15, rf/ri = 37k ? / 18k ? => 2.055 it can be seen from these examples that the higher q example actually has a lower inverting amplifier gain. as mentioned before, the frequency will affect the value of gain. the q factor v frequency graph illustrates this effect. these examples show that the gain required is nominally 2. for the specified range of q: 0.5 to 50 (values up to 250 are obtainable), the gain values vary from 1.9 to 2.5 correspondingly. due to internal gain errors, when the absolute value of q is increased, the device to device variation in q will also increase. pin 11 pin 9 22k 2k 10k pin 10 this diagram shows the exponential relationship between gain and q factor. (fo = 140 khz) suggestion for gain setting component values.
filtering higher frequencies using the mixer frequencies above 150 khz cannot be filtered directly; the mixer enables the notch pass filter to function up to 700khz. the signal to be filtered is mixed with another frequency (local oscillator), chosen so that the difference (intermediate) frequency equals the filter?s centre frequency, fo. the local oscillator signal waveform can be of any shape (sine, square, etc.) but must be approximately 50% duty cycle. example input frequency = 300 khz, local oscillator (lo) frequency = 250 khz, output (if) frequency = 50 khz. if the bandwidth of the 50 khz filter were 1 khz, the filter?s q factor would be: 50/1 = 50. the bandwidth of the filter is still 1 khz when 300 khz is applied to the mixer?s input, but now the q factor is: 300/1 = 300. the mixer provides a q factor improvement equal to the ratio of the input frequency and the intermediate frequency. the effective centre frequency can also be externally controlled by changing the lo frequency. this allows frequency tuning, trimming or sweeping while employing fixed resistors and capacitors for the filter. as the lo signal can be a square wave, this allows ?fo? to be controlled using a microcontroller or microprocessor. mixer configuration with notch pass filter (with attenuating skirts) the mixer can only be used with this filter configuration, as the other types have 0db stop bands. the mixer output ?mxo? becomes the input of the filter. as the gain of the notch filter changes with q, the output of the mixer must be attenuated by some factor (vr atten ). this will prevent the filter from being overdriven and allows the user to set the required output level. note: as the local oscillator input, lo has a low input impedance (60 ? ), it will often be necessary to increase it for driving circuitry. as the input voltage required is low (around 5 mv pk-pk min.), a series resistor ?r mixer ? can be inserted. a value of 1 k ? per 100mv (pk) oscillator signal input will be suitable. zxf36l01 issue 3 - january 2002 9 5v output signal input signal v dd fi2 fo mxi lo bi bg n/c n/c n/c pd v dd r r c c rf ri 124 5v oscillator input (lo) r mixer 100nf 100nf 100nf 100nf vr atten v ss fi1 c1 rc1 rc2 gp1 gp2 gp3 r2 bi mxo v ss
application note an assembled evaluation pcb is available from zetex plc, part code: zxf36l01-evb. it provides a fast and easy way of testing the filter configurations mentioned in this datasheet. this board is configured for 10khz operation. zxf36l01 issue 3 - january 2002 10 jumper settings notch filter notch pass filter with 0db stopband notch pass filter 2 with attenuating skirts mixer configuration with notch pass filter 2 input is fi2 feedback fo to fi1 input is fi1 feedback fi2 to fi1 input is fi1 no external feedback input is mxi mixed signal mxo to fi1 no external feedback 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 j6 1 2 3 j6 1 2 3 normal operation power down power gnd c4 100n zxf36l01 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 v dd fi2 fo mxi lo bi bg nc nc nc pd v dd v ss fi1 bi mxo v ss r i 10k r f 22k vr1 2k input output osc. input +5v input gnd output gnd r 10k c 1.5nf r mix 1k c1 100n c2 100n c3 100n c5 100n j1 - j5 j6 1 2 3 osc. gnd vr2 100k r 10k c 1.5nf 1 2 3 4 5 c1 rc1 rc2 gp1 gp2 gp3 r2
zxf36l01 issue 3 - january 2002 11 evaluation an evaluation board (zxf36l01-evb) is available to assist with in-system or stand-alone performance evaluation. the board can be set, by simple jumper links, to perform any of the filter characteristic responses. the mixer can be selected in conjunction with the notch pass filter 2 functions. evaluation boards can be purchased from our catalogue distributors. digi-key north america (www.digikey.com) tel:1-800344-4539 europe - farnell (www.farnell.com) tel:44-113-263-6311
zetex plc fields new road chadderton oldham, ol9 8np united kingdom telephone (44) 161 622 4422 fax: (44) 161 622 4420 zetex gmbh streitfeldstra?e 19 d-81673 mnchen germany telefon: (49) 89 45 49 49 0 fax: (49) 89 45 49 49 49 zetex inc 700 veterans memorial hwy hauppauge, ny11788 usa telephone: (631) 360 2222 fax: (631) 360 8222 zetex (asia) ltd 3701-04 metroplaza, tower 1 hing fong road kwai fong hong kong telephone: (852) 26100 611 fax: (852) 24250 494 these offices are supported by agents and distributors in major countries world-wide. this publication is issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. the company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. for the latest product information, log on to www.zetex.com ? zetex plc 2001 zxf36l01 12 issue 3 - january 2002 package outline dim millimetres inches min max min max a 15.20 15.40 0.598 0.606 b 1.27 ? 0.05 ? c 0.66 ? 0.026 ? d 0.36 0.46 0.014 0.018 e 7.40 7.60 0.291 0.299 f 2.44 2.64 0.096 0.104 g 0.10 0.30 0.004 0.012 h 0707 i 0.23 0.28 0.009 0.011 j 10.11 10.51 0.398 0.414 k 0808 l 0.51 1.01 0.02 0.04 r 0.63 0.89 0.025 0.035 a 7bsc 7bsc package dimension soic 24 lead

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