AF151-1CJ ,DUAL UNIVERSAL ACTIVE FILTERFeatures
I Independent Q, frequency and gain adjustment
I Very low sensitivity to external co ..
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AF151-1CJ
DUAL UNIVERSAL ACTIVE FILTER
National
Semiconductor
AF151 Dual Universal Active Filter
General Description
The AF151 consists of 2 general purpose stale variable ac-
tive filters in a single package. By using only 4 external re-
sistors for each section, various second order functions may
be formed. Low pass, high pass and band pass functions
are avaiiable simultaneously at separate outputs. In addi-
tion, there are 2 uncommitted operational amplifiers which
are available for buffering or for forming all pass and notch
functions. Arty of the classical rtlttar configurations, such as
Butterworth, Bessel, Cauer and Chebyshev can be easily
formed.
Features
I: Independent o, frequency and gain adjustment
II Very low sensitivity to external component variation
" Separate low pass, high pass and band pass outputs
tt Operation to 10 kHz
II 0 range to 500
a Wide power supply rango-h5V to *18i/
n Accuracy-f 1%
" Fourth order functions in one package
Circuit Diagrams
W" BAND PASS
10k 1000 pr OUTPUT
3 1 22 s
21 HIGH PASS Low PASS 7
OUTPUT OUTPUT
100k = TL"." s 24 12 20
‘N. l T T
=' v’ f IC
TLlK/10113-1
21t, BAND PASS
10k , OUTPUT
15 t3 to 18
" " 17
9 MG! PASS Low PASS 19
OUTPUT ouwur
100k = =
TL/KM0tt3-2
Order Number AF151-1CJ or AF151-20J
See NS Package Number HY24A
Absolute Maximum Ratings
" MllharrdAerotrpaee ttptteWrd devlcoa are required,
Output Short-Circuit Duration (Note Il
Infinite
please contact the National Semiconductor Sales Operating Temperature -25'C to +85%
OfmttVDItttrlttutttra for availability and specifications. Storage T e mperatu r a -2S'C to + 100°C
Supply Voltage i ttN Lead Temperature (Soldering, 10 sec.) 300°C
Power Dissipation 900 mW/Package
Differential Input Voltage i 36V
Electrical Characteristics (Complete Active Filter)
Specifications apply for vs = i15V and over --2tPC to +85°C unless otherwise specified.
(Specifications apply for each section.)
Parameter Conditions Mln Typ Max Unns
Frequency Range to M 0 S 50,000 10k Hz
0 Range to X 0 3 50,000 500 Hz/Hz
fo Accuracy
AF151-1C fe X Q g 10,000, TA = 25''C $2.5 %
AF151-ZC to X tl K 10,000, TA = 25°C Al.0
fo Temperature Coefficient l 50 t 150 ppml°C
0 Accuracy fc x Q S 10,000, TA = 25% 17.5 %
Q Temperature CoeWtient i 300 i 750 ppmPC
Power Supply Current Vs == * 15V 2.5 4.5 mA
Electrical Characteristics (Internal Op Amp) (Note 2)
Parameter Conditions Min Typ Max Units
Input Offset Voltage Rs s 10 kn 1.0 6.0 mV
Input Offset Current 4 50 nA
Input Bias Current 30 200 nA
Input Resistance 2.5 Mn
Large Signal Voltage Gain RL l 2k, VOUT = t10V 25 160 V/mV
OutputVoltage Swing RL = 10 kn + 12 i 14 V
BL = 2 kn :10 * 13
Input Voltage Range l 12 V
Common-Mode Rejection Ratio Rs s 10 kn 70 90 dB
Supply Voltage Rejection Ratio Rs 3 10 en 77 96 dB
Output Short-Circuit Current 25 mA
Slew Rate (Unity Gain) 0.6 V/ws
Small Signal Bandwidth 1 MHz
Phase Margin 60 Degrees
Note P. Any ot the amplifiers can be shorted to ground indefinitely. however. more than one should not be simultaneously shorted as the maximum junction
temperature wilt be exceeded.
Note 2: Specifications apply [or vs = t15V, TA = 25°C.
l-Sl-zIV
Applications Information
The AF151 consists of 2 identical filter sections and 2 un-
committed op amps. The op amps may be used for buffering
inputs and outputs, summing amplifiers (for notch filter gen-
eration), adjusting gain through the filter sections, additional
passive networks to create higher order filters, or simply
used elsewhere in the user's system.
The design equations given apply to both sections; howev-
er. for clarity, only the pin designations for Section 1 will be
shown in the examples and discussion.
See the AF100 datasheet tor additional information on this
type of filter.
The design equations assume that the user has knowledge
of the frequency and t2 values for the particular design to be
synthesized. If this is not the case, various references and
texts are available to help the user in determining these
parameters. A bibliography of recommended texts can also
be found in the AF100 datasheet.
CIRCUIT DESCRIPTION AND OPERATION
A schematic of one section of the AF151 is shown in Figure
f. Amplifier A1 is a summing amplifier with inputs from inte-
grater A2 to the non-inverting input and integrator A3 to the
inverting input. Amplifier A4 is an uncommitted amplifier.
By adding external resistors the circuit can be used to gen-
erate the second order system.
3352 + a2sfat
s2 + bzs f bl
The denominator coefficients determine the complex pole
pair location and the quality of the poles where
(no = Jb_1 = the radian center frequency
T(s) --
Q = 'r'),-' = the quality of the complex pole pair
'-------- u.-- ------- -....- --q....q.Q. o...--.-----
it the output is taken from the output of M, numerator coef-
ficients a, and att equal zero, and the transfer function be-
comes:
T(s) = (High Pass)
s2+:"-1e+o,,2
If the output is taken from the output of M, numerator coef-
ficients at and 83 equal zero and the transfer function be-
comes:
T(s) = (Band Pass)
s2+11s's+au2
If the output is taken from the output of M, numerator coef-
ficitmts as and a2 equal zero and the transfer function be-
comes:
T(s) = (Low Pass)
$2+E°s+002
Using proper input and output connections the circuit can
also be used to generate the transfer functions for a notch
and all pass filter.
In the transfer function for a notch function ag becomes
zero, a1 equals toz? and as equals t. The transfer function
becomes:
T(s) = w ooa2 (Notch)
s2 + y.Lo s + 2
Q ttto
In the all pass transfer function a1 = too2, a2 = -oo/Q
and 83 = 1. The transfer function becomes:
sd - b. S + woz
T(s) = (All Pass)
s2+rcfds+ah,2
LOW PASS AMP IN-
1000 pF
100k t
T. AMP OUT
AMP lN+
TLIK/10113-3
FIGURE 1. AF151 Schematlc (Section "
Applications Information (Continued)
FREQUENCY CALCULATIONS
For operation above 200 Hz, the frequency of each section
of the AF151 is set by 2 equal valued resistors. These resis-
tors couple the output of the first op amp (pin 2) to the input
of the second op amp (pin I) and the output of the second
op amp (pin 23) to the input of the third op amp (pin 22).
The value for Rf is given by:
50.3 X 6
=An (1)
For operation below 200 Hz, "T" tuning should be used as
shown in Figure 3.
For this conriguration,
== _._T_ (2)
Rf - 2RT
where RT or Rs can be chosen arbitrarily, once Rt is found
from Equation 1.
0 CALCULATIONS
To set the Q of each section of the AF151, one resistor is
required. The value of the 0 setting resistor depends on the
input connection (inverting or non-inverting) and the input
resistance. Because the input resistance does affect the Q,
it is often desirable to use one of the uncommitted op amps
to provide a buffer between the signal source impedance
and the input resistor used to set the a
To determine which connection is required for a particular
a, arbitrarily select a value of Rm (Figure 4) and calculate
QMIN according to Equation 3.
3.48 (3)
If the 0 required for the circuit is greater than Own, use
Equation 4 to calculate the value of Ra and the connection
shown in Figure 4.
QMIN =
Ra 3480 -I - Lot ( l
If the Q required for the circuit is less than thm, use Equa-
tion 5 to calculate the value of Ro and the connection
shown in Figure tr.
Q 0.3162(1+1_05)_11 (5)
Q RIN .
Both connections shown in Figures 4 and 5 are "non-invert-
ing" relative to the phase relationship between the input
signal and the low pass output.
For any o, Equation 6 may be used with the "inverting"
connection shown in Figure 6.
Ra = -"T_"iir4t'''" (6)
3.160(1.1+ r1,t,-',,4;) - 1
1 2 22 23
RT ttr ilt Rt
ie '23
il, tts tts
Tbnot0113-4
FIGURE 2. Frequency Tuning = =
TL/K/10113-5
FIGURE 3. "T" Tuning for Low Frequency
o-MN-- o
tte, 21 . ms: mst
TUK/10113-7
= FIGURE s. Connectlon for O < them
TUKM0tt3-6
FIGURE 4. Connection for Q > them
tr-M/b-- -
tto 21
C'"" .
TL/KI10113-8
FIGURE 6. Connection for Any Q, Inverting
Applications Information (Continued)
NOTCH TUNING
When the low pass output and the high pass output are
summed together. the result is a notch (Figure 7).
TL/K/IUI13-9
FIGURE r. Notch Filter
The relationship between RLp. RHp. to and tz, the location of
the notch, is given by Equation 7.
fe ) 2 R LP
R - - 7
P (l, 10 ( )
Again, it is advantageous to use one of the uncommitted op
amps to perform this summing function to prevent loading of
this stage or the resistors Ru, and RHp from affecting the Q
of subsequent stages. Resistor R can be used to set the
gain of the filter section.
GAIN CALCULATIONS
The following list of equations will be helpful in calculating
the relationship between the external components and vari-
ous important parameters. The following definitions are
AL - Gain from input to low pass output at DC
AH - Gain from input to high pass output at high frequency
As - Gain from input to band pass output at center fre-
quency
For Figure 4:
For Figure 6:
A = - -
A = - -
1_05( L05)
AB - ll + 1.0.5
For Figure 7:
At low frequency, when fo < i2, the gain to the output of the
summing op amp is:
HIN Rm)
+ - + -
(1 105 Ha
At high frequency, when fo > tz, the gain to the output of the
summing op amp is:
1.1 (r'b)
RIN RIN)
+ -...- -
(1 105 + no
At the notch, ideally the gain is zero (0).
TUNING TIPS
In applications where 2% to 3% accuracy is not sufficient to
provide the required filter response, the AF151 stages can
be tuned by adding trim pots or trim resistors in series or
parallel with one of the frequency determining resistors and
the Q determining resistor.
When tuning a filter section, no matter what output contigu-
ration is to be used in the circuit, measurements are made
between the input and the band pass output.
Before any tuning is attempted, the low pass output should
be checked to see that the output is not clipping. At the
center frequency of the section, the low pass output is
10 dB higher than the band pass output and 20 dB higher
than the high pass. This should be kept in mind because if
clipping occurs, the results obtained when tuning will be in-
correct.
Frequency Tuning
By adjusting resistor Rt, center frequency of a section can
be adiusted. Adjusting center frequency by phase is the
most accurate but tuning for maximum gain is also correct.
Q Tuning
The Q is tuned by adjusting the Ro resistor. To tune the Q
correctly, the signal source must have an output impedance
very much lower than the input resistance of the filter since
the input resistance affects the Q. The input must be driven
through the same resistance the circuit will “see" to obtain
precise adjustment.
Applications Information (Continued)
The lower 3 dB (45") frequency, fL, and the upper 3 dB (45°)
frequency, tu, can be calculated by the following equations:
fH_(§6+ Co +1)X(fo)
'L‘(\/(E) +1‘E)X(‘°)
where to = center frequency
When adjusting the Q, set the signal source to either m or fc
and adjust for 45'C phase change or a 3 dB gain change.
Notch Tuning
If a circuit has a jw axis zero pair, the notch can be tuned by
adjusting the ratio of the summing resistors (low pass/high
pass summing).
in either case, the signal is connected to the input and the
proper resistor is adjusted for a null at the output.
TUNING PROCEDURE
Center Frequency Tuning
Set oscillator to center frequency desired for the tiiter sec-
tion, adiust amplitude and check that ciipping does not oc-
cur at the low pass output.
Adjust the Rt resistor until the phase shift between input and
band pass output is 180" or ty', depending upon the connec-
0 Tuning
Set oscillator to upper or lower 45° frequency (see tuning
tips) and tune the t2 resistor until the phase shift is 135'
Since the a required for the design (0 = 40), is greater
than thm, the circuit of Figure 4 or Figure 6 may be used.
Arbitrarily we shall select the circuit of Figure 4.
(c) From Equation 4, Ro is found to be
R 105 105
105 105
3.48 -1--- 3.48 OI-I----,
Q Hm ( )(4 ) a M 105
or Ro = 7250
(d) Calculate the center frequency gain for Figure 4.
_ (1 + It25 19?)
Ro Rm - (1 + 137.9 + 0.333)
B ( Rm Rm) (1 + 3.0 + 414)
1 + - + -
105 Ra
A3 T-= 0.333 V/V
Since the gain at to is 0.333 WV, a gain of 10 V/V can be
obtained by using the uncommitted operational amplifier
with a gain of 30.03 as shown in Figure 8.
(upper 45' frequency) or 225' (lower 45'' frequency).
Zero Tuning (Notch Tuning)
Set the oscillator output to the zero frequency and tune one
of the summing resistors tor a null at the output of the sum-
ming amplifier.
Gain Adluet
Set the oscillator to any desired frequency and the gain can
be adjusted by measuring the output of the summing ampli-
for and adjusting the feedback resistance.
DESIGN EXAMPLE
Assume 2 band pass filters are required to separate FSK
f1= 800Hz,Q = 40
f2 = 1000 Hz,t2 = 50
The gain through each filter is to be 10 WV (20 dB).
Since the design is similar for both sections. only the first
section design will be shown for the example.
(a) From Equation 1
- 50.33 x 105 - 50.33 x 106
f to 800
Rt = 62.9k
(b) Checking QMIN from Equation 3, arbitrarily let
RIN = 300k.
105 105
1 + ra 3 x 105
== ___.'L“. - __ =
atm 3.48 3.48 th383
61.9k 50,3k
ougut t; IG It IO 11 mm"
ttree . 1011:;
l 1:293“ mu ,
7 . Ar151 . "
INPUT . 21 It INPUT
300k s 300k
n 72m 22 23 20 " 1: 57m
- $2.$k ‘V 50.3k
TL/K/10113-1D
FIGURE 8. Dual Band Pass Filter
ii l, 12M1a I13 I14
TL/K/10113-11
FIGURE 9. Telephone Multlfrequency (MF)
Band Pass Fllter
Applications Information (Continued)
FREQ BW h, f1 01 & 02 f2 RFt RF2 R0
700 75 698.4 665.6 17 732.8 75.62k 68.68k 1.749k
900 75 898.7 865.8 21.8 932.9 58.13k 53.95k 1.354k
1100 75 1098.8 1065.7 26.7 1 132.9 47.23k 44.43k 1 .100k
1300 75 1298.9 1265.8 31 .6 1332.9 39.76k 37.76k 926.2ft
1500 75 1499.0 1465.8 36.4 1532.9 34.34k 32.83k 802.1 n
1700 75 1699.1 1665.9 41.3 1733.0 30.21 k 29.04k 705.60
"i Hz 900111 1100112 1300Hz 1500111 17001-11
AFHO AF110 AFI10
AF151 AFISI AF151 AF151 AF151 AF151
700 Hz $00 Hz 1100Hz 1300 Hz 1500 Hz 1700 Hz
A=6dB A=6dB A=6dB A=6d9 A=6dB A=tidit
FIGURE 10. MF Tone Recelver
TLfKf10113-12
Applications Information (Continued)
57.4311 40.1111
1212423 I22 fr, '10
INPUT 301 k 2,
21.0211 8 AF151
Cutoff 1270 Hz
Stop Band Edge 2025 Hz
Band Pass Ripple 1.5 dB g" 57.43k 4tht1k 14.1311 171.51:
Rejection 59 dB
1., 876.3 Hz tea 1254.8 Hg
01 1.75 02 8.21 -
111 3201.7 Hz fe, 2113.3 Hz -
m 356.9 Hz
TL/K/10113-13
FIGURE 11. Low Pass Low Speed Asynchronous FSK Modem Filter
24.56k 17.151:
Cutoff 2025 Hz
Stag Band Edge 1270 Hz -
Band Pass Ripple 1.5 dB 10.61k 100k
Reiectitm 59 dB 24.45k
fel 2049.611: 1.2 2934.8 Hz
01 8.21 a2 1.75
1,1 1216.9 Hz tze 803.3 Hz =
tn 7206 Hz
TL/k/ttMi"
FIGURE 12. High Pass Low Speed Asynchronous FSK Modem Filter
Applications Information (Continued)
Standard Resistance Values are obtained from the Decade Table by multiplying by multiples of 10. As an example, 1.33 can
represent 1.33n, 1330, 1.33 kn, 13.3 kn, 133 kn, 1.33 Mn.
Standard 5% and 2% Resistance Values
n n n n n n n n n n n Mn
10 27 68 180 470 1,200 3,300 8,200 22,000 56,000 150,000 0.24 0.62
1 1 30 75 200 510 1,300 3,600 9,100 24,000 62,000 160,000 0.27 0.68
12 33 82 220 560 1,500 3,900 10,000 27,000 68,000 180,000 0.30 0.75
13 36 91 240 620 1,600 4,300 1 1,000 30,000 75,000 200,000 0.33 0.82
15 39 100 270 680 1,800 4,700 12,000 33,000 82,000 220,000 0.36 0.91
16 43 1 10 300 750 2,000 5,100 13,000 36,000 91 .000 0.39 1.0
18 47 120 330 820 2,200 5,600 15,000 39,000 100,000 0.43 1.1
20 51 130 360 910 2,400 6,200 16,000 43,000 110,000 0.47 1.2
22 56 150 390 1,000 2,700 6,800 18,000 47,000 120,000 0.51 1.3
24 62 160 430 1,100 3,000 7,500 20,000 51,000 130,000 0.56 1.5
Decade Table Determlnlng IAM, and 1% Standard Resistance Values
n n n n n n n ft n n n Mn
1.00 1.21 1.47 1.78 2.15 2.61 3.16 3.83 4.64 5.62 6.81 8.25
1.02 1.24 1.50 1.82 2.21 2.67 3.24 3.92 4.75 5.76 6.98 8.45
1.05 1.27 1.54 1.87 2.26 2.74 3.32 4.02 4.87 5.90 7.15 8.66
1.07 1.30 1.58 1.91 2.32 2.80 3.40 4.12 4.99 6.04 7.32 . 8.87
1.10 1.33 1.62 1.96 2.37 2.87 3.48 4.22 5.11 6.19 7.50 9.09
1.13 1.37 1.65 2.00 2.43 2.94 3.57 4.32 5.23 6.34 7.68 9.31
1.15 1.40 1.69 2.05 2.49 3.01 3.65 4.42 5.36 6.49 7.87 9.53
1.18 1.43 1.74 2.10 2.55 3.09 3.74 4.53 5.49 6.65 8.06 9.76
This datasheet has been :
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Datasheets for electronic components.
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This file is the datasheet for the following electronic components:
AF151-1CJ - product/af151-1cj?HQS=TI-nuIl-nu|I-dscatalog-df-pf-nuII-wwe
AF151-2CJ - product/af151-20j?HQS=T|-nuIl-nu|I-dscatalog-df-pf-nuII-wwe
AF151 - product/af151?HQS=T|—nu||—nu|I-dscataIog-df-pf-null-wwe
