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 SYSTEM DIAGRAM ISSUE 1- FEBRUARY 2000 1 PART NUMBER PACKAGE PART MARK ZXF36L01W24 SO24W ZXF36L01 ZXF36L01 ABSOLUTE MAXIMUM RATINGS Voltage on any pin Operating temperature range Storage temperature 7.0V (relative to Vss) 0 to 70°C (de-rated for -40 to 85ºC) -55 to 125°C ELECTRICAL CHARACTERISTICS Test Conditions: Temperature =25°C, VDD = 5.00V, VSS = 0.00V GENERAL CHARACTERISTICS Parameter Conditions Operating current PD= V DD Shutdown current PD = V SS IIH (PD) VIH =5V (WRT V SS ) IIL (PD) VIL =0V (WRT V SS ) Min. Typical Max. 2.2 3.4 4.5 mA 160 300 µA 1.0 -1.0 Units µA µA FILTER CHARACTERISTICS Max. operating frequency 200 Q usable range 0.5 kHz 50 Centre frequency temperature coefficient Q=30, fo = 1kHz 2000 ppm/°C Average Q temperature coefficient Q=30, fo = 1kHz 0.7 % /°C Voltage noise 1 – 100 kHz 20 nV/√Hz Input impedance Max. output swing 30 Output load ≥10 kΩ 50 kΩ 1.6 V pk-pk Output sink current 150 µA Output source current 150 µA MIXER CHARACTERISTICS Max. operating frequency 1.0 MHz 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 Ω ISSUE 2 - JANUARY 2000 2 ZXF36L01 TYPICAL ELECTRICAL CHARACTERISTICS Test Conditions:VDD = 5.00V, VSS = 0.00V (Fo = 140 KHz) Typical Gain at Fo V Q Factor Gain at fo describes the peak gain of the notch pass filter. This gain is defined by the value of Q Factor. 50 45 Gain(dB) 40 35 30 25 20 10 20 30 40 50 60 70 80 90 100 Q Factor Q Factor V Frequency The curve shows Q Factor over frequency for a fixed loop gain (Rf/Ri). 32 30 28 QFactor 26 24 22 20 18 16 0 20 40 60 80 100 120 140 160 180 200 Frequency (kHz) Q Factor V Temperature Components used: 1/8 watt metal film resistors (+/- 50 ppm). Ceramic capacitors (+/- 50 ppm). 45 40 Fo = 1 KHz 35 Fo = 100 KHz QFactor 30 Fo = 10 KHz 25 20 15 10 5 0 -60 -40 -20 0 20 40 60 80 Temperature (°C) ISSUE 1- FEBRUARY 2000 3 100 ZXF36L01 DESCRIPTION OF PIN FUNCTIONS VDD Positive supply connection (5 volts). Both pins to be connected. To be decoupled with a 100nF capacitor to VSS. VSS Negative supply connection; system ground (0 volts). Both pins to be connected. BG Bias Generator output. To be decoupled with a 100nF capacitor to VSS. BI Bias inputs for internal circuitry, both to be connected to BG. (or external supply referenced to VSS) 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 1 V SS FI1 C1 RC1 R2 BI V DD FI2 FO MXI LO RC2 GP1 GP2 BI BG N/C N/C N/C GP3 V SS PD V DD MXO ISSUE 1 - FEBRUARY 2000 4 ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES Notch Filter 5V 1 C FI1 V DD FI2 C1 FO V SS Connect to BG (Pin18) R R=10kΩ Ri C=100nF Rf=19.5kΩ Rf Ri=10kΩ Input Signal Output Signal LO R2 BI MXO C 100nF MXI RC1 R 24 RC2 GP1 GP2 BI BG N/C N/C N/C GP3 V SS PD V DD Pin 6 (BI) 100nF 5V 100nF Filter AC Performance Notch Filter Gain Response 1 2πRC Q ∝ (Rf / Ri ) 5 fo = 0 Gain (dB) -5 -10 Where R, Ri and Rf ≥10kΩ and C ≥ 50 pF -15 -20 See “Designing for a Value of Q” for more details. -25 -30 -35 10 100 1000 10000 Frequency (Hz) Notch Filter Phase Response 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. 270 Phase (Degrees) 240 210 180 150 120 90 10 100 1000 Frequency (Hz) 10000 ISSUE 1- FEBRUARY 2000 5 ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES (continued) Notch Pass Filter (with 0dB Stop Band) 5V 1 100nF Input Signal C V SS FI1 V DD FI2 C1 FO MXI RC1 R R C R=10kΩ C=100nF Rf=19.5kΩ Ri Rf Ri=10kΩ R2 BI LO BI MXO BG N/C N/C N/C PD RC2 GP1 GP2 GP3 V SS 24 Output Signal Pin 6 (BI) 100nF 5V V DD 100nF Filter AC Performance Notch Pass Filter Gain Response 1 2πRC Q ∝ (Rf / Ri) fo = 30 25 Gain (dB) 20 Where R, Ri and Rf ≥10kΩ and C ≥ 50 pF 15 See “Designing for a Value of Q” for more details. 10 5 0 -5 10 100 1000 10000 Frequency (Hz) 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. Notch Pass Filter Phase Response -90 Phase (Degrees) -120 -150 -180 -210 -240 -270 10 100 1000 10000 Frequency (Hz) ISSUE 1 - FEBRUARY 2000 6 ZXF36L01 FILTER CONFIGURATIONS AND RESPONSES (continued) Notch Filter (with attenuating skirts) 5V 1 100nF Input Signal C V SS V DD FI1 FI2 FO C1 R2 BI R RC2 GP1 GP2 R=10kΩ Ri C=100nF Rf=19.5kΩ Ri=10kΩ 100nF N/C N/C PD GP3 V SS Rf Pin 6 (BI) BG N/C MXO C Output Signal MXI LO BI RC1 R 24 5V V DD 100nF Filter AC Performance Notch Pass Filter 2 Gain Response 1 2πRC Q ∝ (Rf / Ri) fo = 30 20 Gain (dB) 10 Where R, Ri and Rf ≥10kΩ and C ≥ 50 pF 0 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. -10 -20 -30 1 10 100 1000 10000 Frequency (Hz) Notch Pass Filter 2 Phase Response 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. 120 Phase (Degrees) 90 60 30 0 -30 -60 -90 -120 1 10 100 1000 10000 Frequency (Hz) ISSUE 1- FEBRUARY 2000 7 ZXF36L01 DESIGNING FOR A VALUE OF Q 10k 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: Q= fO −3dB Bandwidth 2k 22k Pin 9 Pin 11 Pin 10 Suggestion for gain setting component values. Below are some typical values of gain required for several example conditions: 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. Example1 fo = 48kHz, Q=60, R = 10kΩ, C = 320pF Rf/Ri = 36.6kΩ / 18 kΩ => 2.033 Example2 fo = 140kHz, Q=15, R = 10kΩ, C = 100pF Rf/Ri = 37kΩ / 18kΩ => 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. This diagram shows the exponential relationship between gain and Q Factor. (fo = 140 kHz) ISSUE 1 - FEBRUARY 2000 8 ZXF36L01 FILTERING HIGHER FREQUENCIES USING THE MIXER MIXER CONFIGURATION WITH NOTCH PASS FILTER (with attenuating skirts) 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. 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 Ω), 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 kΩ per 100mV (pk) oscillator signal input will be suitable. 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 1 V SS V DD FI2 FI1 C1 C FO MXI RC1 R Connect to BG (Pin18) C Ri Rf 100nF 100nF LO R2 BI R 24 MXO BI BG RC2 GP1 GP2 N/C N/C N/C GP3 V SS PD V DD R Mixer 100nF 5V 100nF ISSUE 1- FEBRUARY 2000 9 Output Signal Input Signal Oscillator Input (LO) Pin 6 (BI) 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 2 ZXF36L01 3 INPUT 4 INPUT GND 5 C R 1.5nF 10k VR2 100k TO PIN 18 (BG) R C 10k 1.5nF RI 10k VR1 2k RF 22k 1 VSS V DD 24 2 FI1 FI2 23 3 C1 FO 22 4 RC1 MXI 21 5 R2 LO 20 6 BI BI 19 7 MXO BG 18 8 RC2 NC 17 9 GP1 NC 16 10 GP2 NC 15 C2 100n +5V OUTPUT OUTPUT GND TO PIN 6 (BI) C5 100n R MIX 1k OSC. INPUT OSC. GND C3 100n 1 11 GP3 PD 14 12 VSS V DD 13 2 J6 C4 100n 3 POWER GND JUMPER SETTINGS 1 2 NOTCH FILTER INPUT IS FI2 FEEDBACK FO TO FI1 3 4 5 1 NOTCH PASS FILTER WITH 0dB STOPBAND 2 INPUT IS FI1 FEEDBACK FI2 TO FI1 3 4 5 1 NOTCH PASS FILTER 2 2 WITH ATTENUATING 3 SKIRTS 4 INPUT IS FI1 NO EXTERNAL FEEDBACK 5 1 MIXER CONFIGURATION WITH NOTCH PASS FILTER 2 INPUT IS MXI MIXED SIGNAL MXO TO FI1 NO EXTERNAL FEEDBACK 2 3 4 5 1 NORMAL OPERATION 2 J6 3 1 POWER DOWN 2 J6 3 ISSUE 1 - FEBRUARY 2000 10 ZXF36L01 ISSUE 1- FEBRUARY 2000 11 ZXF36L01 ISSUE 1 - FEBRUARY 2000