ETC ZXF36L01W24TR

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
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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)
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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
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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
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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
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ZXF36L01
ISSUE 1- FEBRUARY 2000
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ZXF36L01
ISSUE 1 - FEBRUARY 2000