ZXF6L0 VAIABLE Q FILTE DESIPTION The ZXF6L0 is a versatile analog high Q bandpass filter. The device contains two sections: 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 0kHz. Two external resistors control filter Q Factor. The Q can be varied up to 0. 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. APPLIATIONS Many filter applications including: - Audio bandpass and notch Micro controlled frequency Adaptive filtering Sonar and Ultrasonic Systems Instrumentation FEATUES AND BENEFITS entre Frequency up to 700kHz Tuneable centre frequency Variable Q Low power Standby mode for improved battery life ODEING INFOMATION PAT NUMBE PAKAGE PAT MAK ZXF6L0W24 SO24W ZXF6L0 PAT NUMBE ONTAINE INEMENT SYSTEM DIAGAM ZXF6L0W24T eel 000 0mm ZXF6L0W24 Tube
ZXF6L0 ABSOLUTE MAXIMUM ATINGS Voltage on any pin 7.0V (relative to Vss) Operating temperature range 0 to 70 (de-rated for -40 to 8º) Storage temperature - to 2 ELETIAL HAATEISTIS Test oνditions: Temperature =2, =.00V, = 0.00V GENEAL HAATEISTIS Parameter onditions Min. Typical Max. Units Operating current PD= 2.2.4 4. ma Shutdown current PD = 60 00 µa IIH (PD) VIH = (WT ).0 µa IIL (PD) VIL =0V (WT ) -.0 µa FILTE HAATEISTIS Max. operating frequency 0 khz Q usable range 0. 0 entre frequency temperature Q=0, fo = khz 0 ppm/ coefficient Note Average Q temperature Q=0, fo = khz 0. % / coefficient Note 2 Voltage noise 00 khz 20 nv/ Hz Input impedance 0 0 kω Max. output swing Output load 0 kω.6 V pk-pk Output sink current 0 µa Output source current 0 µa MIXE HAATEISTIS Max. operating frequency 700 khz Maximum signal input 00 mv pk-pk Maximum Local Oscillator input 00 mv pk-pk Minimum Local Oscillator input mv pk-pk Local Oscillator input Impedance 60 Ω NOTE entre frequency temperature coefficient is dominated by the external & components. On chip drift is negligable. Note 2 Average Q temperature coefficient is dominated by the external components. 2
ZXF6L0 TYPIAL ELETIAL HAATEISTIS Test oνditions: =.00V, = 0.00V 0 4 TypicalGainatFoVQFactor (Fo = 40 KHz) Gain at fo describes the peak gain of the notch pass filter. This gain is defined by the value of Q Factor. 40 Gain (db) 0 2 20 0 20 0 40 0 60 70 80 90 00 Q Factor 2 0 28 Q Factor V Frequency The curve shows Q Factor over frequency for a fixed loop gain (f/i). 26 QFactor 24 22 20 8 6 0 20 40 60 80 00 20 40 60 80 200 Frequency (khz) omponents used: /8 watt metal film resistors (+/- 0 ppm). eramic capacitors (+/- 0 ppm).
ZXF6L0 DESIPTION OF PIN FUNTIONS Positive supply connection ( volts). Both pins to be connected. To be decoupled with a capacitor to. BG PD FI,Fl2 FO LO MXI MXO Negative supply connection; system ground (0 volts). Both pins to be connected. Bias Generator output. To be decoupled with a capacitor to. Bias inputs for internal circuitry, both to be connected to BG. (or external supply referenced to ) Active low. This feature can be used to reduce power consumption for applications that have a standby mode. Filter input, FI or FI2 depending on filter configuration. Filter output for all configurations. Local Oscillator signal input. Mixer signal input. Mixer signal output., Phase advance network nodes. Values and set centre frequency, fo. 2, 2 Phase retard network nodes. Values and set centre frequency, fo. GP,2, Loop gain programming nodes. ONNETION DIAGAM FI 2 MXO 2 GP GP2 GP FI2 FO MXI LO BG PD 4
ZXF6L0 FILTE ONFIGUATIONS AND ESPONSES Notch Filter =0kΩ = f=9.kω i=0kω i f 24 FI FI2 FO MXI 2 LO MXO BG 2 GP GP2 GP PD Input Signal Output Signal Filter A Performance Notch Filter Gain esponse Gain (db) 0 - -0 - -20-2 -0 fo = 2π Q ( f / i) Where, i and f 0kΩ and 0 pf See Designing for a Value of Q for more details. - 0 00 000 0000 Frequency (Hz) 270 240 Notch Filter Phase esponse Typical responses for the circuit with component values shown in circuit diagram. Phase (Degrees) 20 80 0 20 90 0 00 000 0000 Frequency (Hz)
ZXF6L0 FILTE ONFIGUATIONS AND ESPONSES (continued) Input Signal =0kΩ = f=9.kω i=0kω i f FI FI2 FO MXI 24 2 MXO 2 GP GP2 GP LO BG PD Output Signal Filter A Performance 0 2 20 Gain (db) 0 0 Notch Pass Filter Gain esponse fo = 2π Q ( f / i) Where, i and f 0kΩ and 0 pf See Designing for a Value of Q for more details. - 0 00 000 0000 Frequency (Hz) -90 Notch Pass Filter Phase esponse Typical responses for the circuit with component values shown in circuit diagram. -20 Phase (Degrees) -0-80 -20-240 -270 0 00 000 0000 Frequency (Hz) 6
ZXF6L0 FILTE ONFIGUATIONS AND ESPONSES (continued) Notch Filter (with attenuating skirts) =0kΩ = f=9.kω i=0kω Input Signal i f FI FI2 FO MXI 24 2 MXO 2 GP GP2 GP LO BG PD Output Signal Filter A Performance 0 20 Notch Pass Filter 2 Gain esponse fo = 2π Q ( f / i) Gain (db) 0 0-0 -20-0 0 00 000 0000 Frequency (Hz) Where, i and f 0kΩ and 0 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. Phase (Degrees) 20 90 60 0 0-0 -60-90 Notch Pass Filter 2 Phase esponse Typical responses for the circuit with component values shown in circuit diagram. -20 0 00 000 0000 Frequency (Hz) 7
ZXF6L0 DESIGNING FO A VALUE OF Q As mentioned on the configuration pages, there is a proportional, but non-linear relationship between the ratio of f and i, and Q. 0k 2k 22k Pin 9 Pin 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: fo Q = db Bandwidth 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. Pin 0 Below Suggestion are some for gain typical setting values component of gain required values. for several example conditions: Example fo = 48kHz, = 0kΩ, = 20pF Q=60, f/i = 6.6kΩ / 8 kω => 2.0 Example2 fo = 40kHz, = 0kΩ, = 00pF Q=, f/i = 7kΩ / 8kΩ => 2.0 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. to 0 (values up to 20 are obtainable), the gain values vary from.9 to 2. correspondingly. Due to internal gain errors, when the absolute value of Q is increased, the device to device variation in Q will also increase. This diagram shows the exponential relationship between gain and Q Factor. (fo = 40 khz) 8
ZXF6L0 FILTEING HIGHE FEQUENIES USING THE MIXE Frequencies above 0 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 0% duty cycle. Example Input frequency = 00 khz, Local Oscillator (LO) frequency = 20 khz, Output (IF) Frequency = 0 khz. If the bandwidth of the 0 khz filter were khz, the filter s Q factor would be: 0/ = 0. The bandwidth of the filter is still khz when 00 khz is applied to the mixer s input, but now the Q factor is: 00/ = 00. 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. MIXE ONFIGUATION WITH NOTH PASS FILTE (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 (V 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 Ω), it will often be necessary to increase it for driving circuitry. As the input voltage required is low (around mv pk-pk min.), a series resistor Mixer can be inserted. A value of kω per 00mV (pk) oscillator signal input will be suitable. V Atten i f 24 FI FI2 FO MXI 2 LO MXO BG 2 GP GP2 GP PD Mixer Output Signal Input Signal Oscillator Input (LO) 9
ZXF6L0 Application Note An assembled evaluation PB is available from Zetex Plc, part code: ZXF6L0-EVB. It provides a fast and easy way of testing the filter configurations mentioned in this datasheet. This board is configured for 0kHz operation. INPUT INPUT GND 00n J - J 2 4.nF 0k ZXF6L0 24 2 FI FI2 2 FO 22 4 MXI 2 2 00n + OUTPUT OUTPUT GND V2 00k 0k.nF 2 6 7 MXO LO 20 9 BG 8 00n MIX k OS. INPUT OS. GND I 0k V 2k F 22k 8 2 9 GP 0 GP2 GP 2 N 7 N 6 N PD 4 00n 4 00n 2 J6 POWE GND JUMPE SETTINGS NOTH FILTE 2 4 INPUT IS FI2 FEEDBAK FO TO FI NOTH PASS FILTE WITH 0dB STOPBAND NOTH PASS FILTE 2 WITH ATTENUATING SKITS MIXE ONFIGUATION WITH NOTH PASS FILTE 2 2 4 2 4 2 4 INPUT IS FI FEEDBAK FI2 TO FI INPUT IS FI NO EXTENAL FEEDBAK INPUT IS MXI MIXED SIGNAL MXO TO FI NO EXTENAL FEEDBAK NOMAL OPEATION 2 J6 POWE DOWN 2 J6 0
ZXF6L0 Evaluation An evaluation board (ZXF6L0-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:-80044-49 Europe - Farnell (www.farnell.com) Tel:44--26-6
ZXF6L0 PAKAGE DIMENSION DIM Millimetres Inches Min Max Min Max A.20.40 0.98 0.606 B.27 0.0 0.66 0.026 D 0.6 0.46 0.04 0.08 E 7.40 7.60 0.29 0.299 F 2.44 2.64 0.096 0.04 G 0.0 0.0 0.004 0.02 H 0 7 0 7 I 0.2 0.28 0.009 0.0 J 0. 0. 0.98 0.44 K 0 8 0 8 L 0..0 0.02 0.04 0.6 0.89 0.02 0.0 a 7 BS 7 BS PAKAGE OUTLINE SOI 24 LEAD Zetex plc 200 Zetex plc Fields New oad hadderton Oldham, OL9 8NP United Kingdom Telephone (44) 6 622 4422 Fax: (44) 6 622 4420 Zetex GmbH Streitfeldstraße 9 D-867 München Germany Telefon: (49) 89 4 49 49 0 Fax: (49) 89 4 49 49 49 Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY788 USA Telephone: (6) 60 2222 Fax: (6) 60 8222 Zetex (Asia) Ltd 70-04 Metroplaza, Tower Hing Fong oad Kwai Fong Hong Kong Telephone: (82) 2600 6 Fax: (82) 2420 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 ompany 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 ompany 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 2