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| ZXF36L01 VARIABLE Q FILTER DESCRIPTION APPLICATIONS The ZXF36L01 is a versatile analog high Q bandpass Many filter applications including: filter. The device contains two sections: * Audio bandpass and notch 1 Variable Q bandpass filter. * Micro controlled frequency 2 Mixer block. * Adaptive filtering The basic filter section requires 2 resistors and 2 * Sonar and Ultrasonic Systems capacitors to set the centre frequency. The filter * Instrumentation operates up to a frequency of 200kHz. Two external resistors control filter Q Factor. The Q can be varied up to 50. FEATURES AND BENEFITS The mixer is included to extend the frequency range up * to 1MHz and to permit the centre frequency to be tuned. * The local oscillator can be any waveform, making * microprocessor control convenient. * * Centre Frequency up to 1MHz Tuneable centre frequency Variable Q Low power Standby mode for improved battery life ORDERING INFORMATION PART NUMBER ZXF36L01W24 PACKAGE SO24W PART MARK ZXF36L01 SYSTEM DIAGRAM ISSUE 1- FEBRUARY 2000 1 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 ABSOLUTE MAXIMUM RATINGS Voltage on any pin Operating temperature range Storage temperature 7.0V (relative to Vss) 0 to 70C (de-rated for -40 to 85C) -55 to 125C ELECTRICAL CHARACTERISTICS Test Conditions: Temperature =25C, VDD = 5.00V, VSS = 0.00V GENERAL CHARACTERISTICS Parameter Operating current Shutdown current IIH (PD) IIL (PD) Conditions PD= V DD PD = V SS VIH =5V (WRT V SS ) VIL =0V (WRT V SS ) Min. 2.2 Typical 3.4 160 Max. 4.5 300 1.0 Units mA A A A -1.0 FILTER CHARACTERISTICS Max. operating frequency Q usable range Centre frequency temperature coefficient Average Q temperature coefficient Voltage noise Input impedance Max. output swing Output sink current Output source current Output load 10 k Q=30, Q=30, fo = 1kHz fo = 1kHz 0.5 2000 0.7 20 30 1.6 150 150 50 200 50 ppm/C % /C nV/Hz k V pk-pk A A kHz 1 - 100 kHz MIXER CHARACTERISTICS Max. operating frequency Maximum signal input Maximum Local Oscillator input Minimum Local Oscillator input Local Oscillator input Impedance 1.0 300 100 5 60 MHz mV pk-pk mV pk-pk mV pk-pk ISSUE 2 - JANUARY 2000 2 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 TYPICAL ELECTRICAL CHARACTERISTICS Test Conditions:VDD = 5.00V, VSS = 0.00V Typical Gain at Fo V Q Factor 50 (Fo = 140 KHz) Gain at fo describes the peak gain of the notch pass filter. This gain is defined by the value of Q Factor. 45 40 Gain(dB) 35 30 25 20 10 20 30 40 50 60 70 80 90 100 Q Factor Q Factor V Frequency 32 30 28 26 The curve shows Q Factor over frequency for a fixed loop gain (Rf/Ri). QFactor 24 22 20 18 16 0 20 40 60 80 100 120 140 160 180 200 Frequency (kHz) Q Factor V Temperature 45 40 Components used: 1/8 watt metal film resistors (+/- 50 ppm). Ceramic capacitors (+/- 50 ppm). Fo = 1 KHz Fo = 100 KHz 35 30 Fo = 10 KHz QFactor 25 20 15 10 5 0 -60 -40 -20 0 20 40 60 80 100 Temperature (C) ISSUE 1- FEBRUARY 2000 3 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 DESCRIPTION OF PIN FUNCTIONS VDD VSS BG BI PD FI1,Fl2 FO LO MXI MXO C1, RC1 R2, RC2 GP1,2,3 Positive supply connection (5 volts). Both pins to be connected. To be decoupled with a 100nF capacitor to VSS. Negative supply connection; system ground (0 volts). Both pins to be connected. Bias Generator output. To be decoupled with a 100nF capacitor to VSS. Bias inputs for internal circuitry, both to be connected to BG. (or external supply referenced to VSS) Active low. This feature can be used to reduce power consumption for applications that have a standby mode. Filter input, FI1 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 R and C set centre frequency, fo. Phase retard network nodes. Values R and C set centre frequency, fo. Loop gain programming nodes. CONNECTION DIAGRAM 1 V SS FI1 C1 RC1 R2 BI MXO RC2 GP1 GP2 GP3 V SS V DD FI2 FO MXI LO BI BG N/C N/C N/C PD V DD ISSUE 1 - FEBRUARY 2000 4 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES Notch Filter 5V 1 C V SS FI1 C1 RC1 R2 BI MXO RC2 GP1 GP2 GP3 V SS V DD FI2 FO MXI LO BI BG N/C N/C N/C PD V DD 24 100nF Input Signal Output Signal R Connect to BG (Pin18) C R Pin 6 (BI) 100nF R=10k C=100nF Rf=19.5k Ri=10k Ri 5V 100nF Rf Filter AC Performance Notch Filter Gain Response 5 0 -5 Gain (dB) -10 -15 -20 -25 -30 -35 10 100 Frequency (Hz) 1000 10000 1 2RC Q (Rf / Ri ) fo = Where R, Ri and Rf 10k and C 50 pF See "Designing for a Value of Q" for more details. Notch Filter Phase Response 270 240 Phase (Degrees) T y p i ca l r e sp o n se s f o r t h e ci r cu i t w i t h component values shown in circuit diagram. 210 180 150 120 90 10 100 1000 Frequency (Hz) 10000 ISSUE 1- FEBRUARY 2000 5 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES (continued) Notch Pass Filter (with 0dB Stop Band) 5V 100nF Input Signal C 1 V SS FI1 C1 RC1 R2 BI MXO RC2 GP1 GP2 GP3 V SS V DD FI2 FO MXI LO BI BG N/C N/C N/C PD V DD 24 Output Signal R R C Pin 6 (BI) 100nF R=10k C=100nF Rf=19.5k Ri=10k Ri 5V 100nF Rf Filter AC Performance Notch Pass Filter Gain Response 30 25 20 Gain (dB) 15 10 5 0 -5 10 100 Frequency (Hz) 1000 10000 1 2RC Q (Rf / Ri) fo = Where R, Ri and Rf 10k and C 50 pF See "Designing for a Value of Q" for more details. Notch Pass Filter Phase Response -90 -120 T y p i ca l r e sp o n se s f o r t h e ci r cu i t w i t h component values shown in circuit diagram. Phase (Degrees) -150 -180 -210 -240 -270 10 100 Frequency (Hz) 1000 10000 ISSUE 1 - FEBRUARY 2000 6 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES (continued) Notch Filter (with attenuating skirts) 5V 100nF Input Signal C 1 V SS FI1 C1 RC1 R2 BI MXO RC2 GP1 GP2 GP3 V SS V DD FI2 FO MXI LO BI BG N/C N/C N/C PD V DD 24 Output Signal R R C Pin 6 (BI) 100nF R=10k C=100nF Rf=19.5k Ri=10k Ri 5V 100nF Rf Filter AC Performance Notch Pass Filter 2 Gain Response 30 20 10 Gain (dB) 0 -10 -20 -30 1 10 100 Frequency (Hz) 1000 10000 1 2RC Q (Rf / Ri) fo = 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. Notch Pass Filter 2 Phase Response 120 90 Phase (Degrees) 60 30 0 -30 -60 -90 -120 1 10 100 Frequency (Hz) 1000 10000 T y p i ca l r e sp o n se s f o r t h e ci r cu i t w i t h component values shown in circuit diagram. ISSUE 1- FEBRUARY 2000 7 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 DESIGNING FOR A VALUE OF Q As mentioned 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: 10k Pin 9 2k 22k Pin 11 Pin 10 Suggestion for gain setting component values. Below are some typical values of gain required for several example conditions: Example1 fo = 48kHz, Q=60, Example2 fo = 140kHz, Q=15, R = 10k, C = 100pF Rf/Ri = 37k / 18k => 2.055 R = 10k, C = 320pF Rf/Ri = 36.6k / 18 k => 2.033 Q= fO -3dB 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. 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. This diagram shows the exponential relationship between gain and Q Factor. (fo = 140 kHz) ISSUE 1 - FEBRUARY 2000 8 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 FILTERING HIGHER FREQUENCIES USING THE MIXER Frequencies above 200 kHz cannot be filtered directly; the mixer enables the notch pass filter to function up to 1 MHz. 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. 5V Connect to BG (Pin18) VR Atten C 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 (VRAtten). 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 `RMixer' can be inserted. A value of 1 k per 100mV (pk) oscillator signal input will be suitable. 1 V SS FI1 C1 RC1 R2 BI MXO RC2 GP1 GP2 GP3 V SS V DD FI2 FO MXI LO BI BG N/C N/C N/C PD V DD 24 Output Signal Input Signal Oscillator Input (LO) Pin 6 (BI) 100nF 100nF R Mixer 100nF R Connect to BG (Pin18) R C Ri 5V 100nF Rf ISSUE 1- FEBRUARY 2000 9 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 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. J1 - J5 1 C1 100n INPUT INPUT GND 2 3 4 5 C R 1.5nF 10k VR2 100k ZXF36L01 1 VSS 2 FI1 3 C1 4 RC1 5 R2 R C 10k 1.5nF 6 BI 7 MXO 8 RC2 RI 10k VR1 2k RF 22k 9 GP1 10 GP2 11 GP3 12 VSS V DD 24 FI2 23 FO 22 MXI 21 LO 20 BI 19 BG 18 NC 17 NC 16 1 NC 15 PD 14 V DD 13 C4 100n 2 J6 3 POWER GND TO PIN 6 (BI) C3 100n C5 100n R MIX 1k OUTPUT OUTPUT GND OSC. INPUT OSC. GND C2 100n +5V TO PIN 18 (BG) JUMPER SETTINGS 1 2 NOTCH FILTER 3 4 5 1 INPUT IS FI2 FEEDBACK FO TO FI1 NOTCH PASS FILTER WITH 0dB STOPBAND 2 3 4 5 1 INPUT IS FI1 FEEDBACK FI2 TO FI1 NOTCH PASS FILTER 2 2 WITH ATTENUATING 3 SKIRTS 4 5 1 INPUT IS FI1 NO EXTERNAL FEEDBACK MIXER CONFIGURATION WITH NOTCH PASS FILTER 2 2 3 4 5 1 INPUT IS MXI MIXED SIGNAL MXO TO FI1 NO EXTERNAL FEEDBACK NORMAL OPERATION 2 J6 3 1 POWER DOWN 2 J6 3 ISSUE 1 - FEBRUARY 2000 10 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 ISSUE 1- FEBRUARY 2000 11 This Material Copyrighted By Its Respective Manufacturer ZXF36L01 ISSUE 1 - FEBRUARY 2000 This Material Copyrighted By Its Respective Manufacturer |
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