Datasheet ZXF36L01W24, ZXF36L01W24TC Datasheet (Zetex)

VARIABLE Q FILTER

ZXF36L01

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 includedto extend thefrequency range up
to 700kHz and to permit the centre frequency to be
tuned. The local oscillator can be any waveform,
making microprocessor control convenient.

SYSTEM DIAGRAM

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

ORDERING INFORMATION

PART NUMBER PACKAGE PART

ZXF36L01W24 SO24W ZXF36L01

PART NUMBER CONTAINER INCREMENT

ZXF36L01W24TC Reel 13”

330mm

ZXF36L01W24 Tube 31

MARK

1000

ISSUE 3 - JANUARY 2002

1

ZXF36L01

ABSOLUTE MAXIMUM RATINGS

Voltage on any pin 7.0V (relative to Vss)
Operating temperature range 0 to 70°C (de-rated for -40 to 85ºC)
Storage temperature -55 to 125°C

ELECTRICAL CHARACTERISTICS

Test Coνditions: Temperature =25°C, V

GENERAL CHARACTERISTICS
Parameter Conditions Min. Typical Max. Units

Operating current PD=V
Shutdown current PD
IIH (PD)
IIL (PD)

FILTER CHARACTERISTICS

Max. operating frequency 150 kHz
Q usable range 0.5 50
Centre frequency temperature

coefficient
Average Q temperature

coefficient
Voltage noise 1 – 100 kHz 20
Input impedance 30 50
Max. output swing
Output sink current 150
Output source current 150

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

=V
VIH =5V (WRT VSS)1.0µA
VIL =0V (WRT VSS) -1.0 µA

Q=30, fo = 1kHz
Note 1

Q=30, fo = 1kHz
Note 2

Output load ≥10 kΩ

= 5.00V, VSS= 0.00V

DD

DD

SS

2.2 3.4 4.5 mA
160 300 µA

10 ppm/°C

0.1 % /°C

nV/√ Hz
kΩ

1.6 V pk-pk

µA
µA

Ω

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.

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ZXF36L01

TYPICAL ELECTRICAL CHARACTERISTICS

Test Coνditions:V

TypicalGainatFoVQFactor

50

45

40

35

Gai n (d B)

30

25

20

10 20 30 40 50 60 70 80 90 100

Q Factor

(Fo = 140 KHz)

= 5.00V, VSS= 0.00V

DD

Q Factor V Frequency

32

30

28

26

24

QFactor

22

20

18

16

0 20 40 60 80 100 120 140 160 180 200

Frequency (kHz)

Gain at fo describes the peak gain of
the notch pass filter. This gain is
defined by the value of Q Factor.

The curve shows Q Factor over
frequency for a fixed loop gain
(Rf/Ri).

ISSUE 3 - JANUARY 2002

Components used: 1/8 watt metal
film resistors (+/- 50 ppm). Ceramic
capacitors (+/- 50 ppm).

3

ZXF36L01

DESCRIPTION OF PIN FUNCTIONS

V

DD

V

SS

BG Bias Generator output. To be decoupled with a 100nF capacitor to V

BI Bias inputs for internal circuitry, both to be connected to BG.

PD

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

Positive supply connection (5 volts). Both pins to be connected.
To be decoupled with a 100nF capacitor to V

SS

.

Negative supply connection; system ground (0 volts). Both pins to be connected.

SS

(or external supply referenced to V

Active low. This feature can be used to reduce power consumption for applications that
have a standby mode.

SS

)

.

V

1

SS

FI1
C1

RC1
R2

BI
MXO

RC2
GP1
GP2
GP3
V

SS

V

FI2

MXI

BG
N/C
N/C
N/C

V

DD

FO

LO
BI

PD

DD

ISSUE 3 - JANUARY 2002

4

FILTER CONFIGURATIONS AND RESPONSES

q

q

Notch Filter

V

FI2

MXI

BG
N/C
N/C
N/C

V

DD

FO

LO
BI

PD

DD

R=10kΩ

C=100nF

Rf=19.5kΩ

Ri=10kΩ

V

124

SS

FI1

C

R

C

C1
RC1

R2

R

BI
MXO
RC2
GP1

Ri

GP2
GP3

Rf

V

SS

Filter AC Performance

Notch Filter Gain Response

5

0

-5

-10

-15

Gain (dB)

-20

-25

-30

-35
10 100 1000 10000

Fre

uency (Hz)

5V

100nF

5V

100nF

ZXF36L01

100nF

Input Signal

Output Signal

1

f

o

=

2π

RC

f

∝

(/)

QRR

Where R, Ri and Rf ≥10kΩ and C ≥ 50 pF

See “Designing for a Value of Q” for more
details.

i

Notch Filter Phase Response

270

240

210

180

150

Phase ( Degrees)

120

90

10 100 1000 10000

ISSUE 3 - JANUARY 2002

Fre

Typical responses for the circuit with
component values shown in circuit diagram.

uency (Hz)

5

ZXF36L01

q

FILTER CONFIGURATIONS AND RESPONSES (continued)

5V

Input Signal

100nF

C

R

R

C

R=10kΩ

C=100nF

Ri

Rf

Rf=19.5kΩ

Ri=10kΩ

Filter AC Performance

Notch Pass Filter Gain Response

Notch Pass Filter Gain Response

30

30

25

25

20

20

15

15

10

10

Gain (dB)

Gain (dB)

5

5

0

0

-5

-5
10 100 1000 10000

10 100 1000 10000

Frequency (H z)

Frequency (H z)

124

V

SS

FI1
C1
RC1

R2

BI
MXO
RC2
GP1
GP2
GP3
V

SS

V

FI2

MXI

LO

BG
N/C
N/C
N/C

V

DD

FO

PD

Output Signal

BI

100nF

5V

DD

100nF

f

o

=

QRR

Where R, Ri and Rf ≥10kΩ and C ≥ 50 pF

See “Designing for a Value of Q” for more
details.

1

2π

RC

fi

∝

(/)

Notch Pass Filter Phase Response

-90

-120

-150

-180

-210

Phase (Degrees )

-240

-270
10 100 1000 10000

Fre

uency (Hz)

Typical responses for the circuit with
component values shown in circuit diagram.

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6

FILTER CONFIGURATIONS AND RESPONSES (continued)

Notch Filter (with attenuating skirts)

5V

V

FI2

MXI

LO

N/C
N/C
N/C

V

FO

BG

DD

BI

PD

DD

5V

R=10kΩ

C=100nF

Input Signal

100nF

124

V

SS

C

R

C

FI1
C1
RC1
R2

R

BI
MXO
RC2
GP1

Ri

GP2
GP3

Rf

V

SS

Rf=19.5kΩ

Ri=10kΩ

Filter AC Performance

Notch Pass Filter 2 Gain Response

30

20

10

0

Gain (dB)

-10

-20

-30
1 10 100 1000 10000

Frequency (Hz)

Notch Pass Filter 2 Phase Response

120

90

60

30

0

-30

Phas e (Degrees)

-60

-90

-120
1 10 100 1000 10000

Frequency (Hz)

f

o

=

QRR

Where R, Ri and Rf ≥10kΩ 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.

Typical responses for the circuit with
component values shown in circuit diagram.

Output Signal

100nF

100nF

1

2π

RC

fi

∝

(/)

ZXF36L01

ISSUE 3 - JANUARY 2002

7

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 determinesthe peak value gainand therefore the Q
of the filter,Q is defined as:

f

Q

=

−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 gainreduces andthus Q Factorreduces.

The frequency effect is not a problem for circuits where
the fo remains constant, as the phase shifts are
accounted forpermanently. For designs where Q ishigh
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.

O

dB Bandwidth

2k

10k

22k

Pin 11Pin 9

Pin 10

Suggestion for gain setting component values.

Below are some typical values of gain required for
several example conditions:

Example1

fo = 48kHz, R = 10kΩ, C = 320pF

Example2

fo = 140kHz, R = 10kΩ, C = 100pF

It can be seen from these examples that the higher Q
example actually has a lower invertingamplifier 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 to250 areobtainable), thegain valuesvary
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.

Q=60, Rf/Ri = 36.6kΩ / 18 kΩ => 2.033

Q=15, Rf/Ri = 37kΩ / 18kΩ => 2.055

This diagram shows the exponential relationship between gain and Q Factor. (fo = 140 kHz)

ISSUE 3 - JANUARY 2002

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ZXF36L01

FILTERING HIGHER FREQUENCIES USING
THE MIXER

Frequencies above 150 kHz cannot be filtered directly;
the mixerenables thenotch pass filter tofunction 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 bandwidthof the50 kHzfilter 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 frequencyand 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 canbe a squarewave, 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
will prevent the filter from being overdriven and allows the

Atten

). This

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 ‘R

’ can be

Mixer

inserted. A value of 1 kΩ per 100mV (pk) oscillator signal
input will be suitable.

R

C

ISSUE 3 - JANUARY 2002

5V

V

124

SS

VR

Atten

C

R

Ri

Rf

FI1
C1
RC1
R2

BI
MXO

RC2

GP1
GP2
GP3

V

SS

V

FI2

MXI

LO
BI

BG
N/C
N/C
N/C

V

DD

FO

PD

100nF

R

Mixer

100nF

5V

DD

100nF

Output Signal
Input Signal

100nF

Oscillator Input (LO)

9

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. This board is configured for 10kHz operation.

J1 - J5

1

C1

2

INPUT

100n

3
4
5

VR2

100k

10k

VR1

2k

R

R

10k

1.5nF

I

C

R

22k

C

1.5nF

R

10k

F

1

2

3

4

5

6

7

8

9

10

11

12

ZXF36L01

V

SS

FI1

C1

RC1

R2

BI

MXO

RC2

GP1

GP2

GP3

V

SS

V

FI2

FO

MXI

LO

BG

NC

NC

NC

PD

V

C2

DD

24

23

22

21

20

BI

19

18

17

16

15

14

13

DD

100n

C4

100n

C3

100n

C5

100n

R

MIX

1k

J612

3

+5VINPUT GND

OUTPUT

OUTPUT GND

OSC. INPUT

OSC. GND

POWER GND

JUMPER SETTINGS

NOTCH FILTER

NOTCH PASS FILTER

WITH 0dB STOPBAND

NOTCH PASS FILTER 2

WI TH AT TEN UATI NG

SKIRTS

MIXER CONFIGURATION

WITH NOTCH

PASS FI LTE R 2

NORMAL OPERATION

POWER DOWN

1

2

INPUT IS FI2

3

FEEDBACK FO TO FI1

4

5

1

2

INPUT IS FI1

3

FEEDBACK FI2 TO FI1

4

5

1

2

INPUT IS FI1

3

NO EXTERNAL FEEDBACK

4

5

1

2

INPUT IS MXI

3

MIXED SIGNAL MXO TO FI1

4

NO EXTERNAL FEEDBACK

5

J612

3

J612

3

ISSUE 3 - JANUARY 2002

10

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 beselected inconjunction with the notchpass filter2 functions.

Evaluation boards can be purchased from our catalogue distributors.

Digi-Key North America (www.digikey.com)
Tel:[phone]

Europe - Farnell (www.farnell.com)
Tel:[phone]

ZXF36L01

ISSUE 3 - JANUARY 2002

11

ZXF36L01

PACKAGE DIMENSION

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 0°7°0°7°
I 0.23 0.28 0.009 0.011
J 10.11 10.51 0.398 0.414
K 0°8°0°8°
L 0.51 1.01 0.02 0.04
R 0.63 0.89 0.025 0.035
a 7°BSC 7°BSC

PACKAGE OUTLINE

SOIC 24 LEAD

© Zetex plc 2001

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