AN-797
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/461-3113 • www.analog.com
Quad Precision Op Amp Evaluation Board
by Giampaolo Marino and Steve Ranta
INTRODUCTION
The EVAL-PRAOPAMP- 4R/4RU is an evaluation board
which accommodates quad op amps in SOIC and TSSOP
packages. It is meant to provide the user with multiple
choices and extensive flexibility for different applications circuits and configurations.
Using the superposition principle, we write
This board is not intended to be used with high frequency
components or high speed amplifiers. However, it provides
the user with many combinations for various circuit
types including active filters, instrumentation amplifiers,
composite amplifier, and external frequency compensation circuits. For examples of application circuits refer to
ADI amplifier data sheets under the applications section.
This application note will present different implementations of filter design using quad amplifiers.
Since A2 and A3 are integrators, we have:
VHP = ( –R6 / R4) V1 – (R4 / R JUMP ) VLP +
1 + (R4 / R6 ) + (R4 / R JUMP ) /
VBP
1 + (R JUMP1 / R5 )
VBP = ( –1/ R8 C6s) VHP and VLP = ( –1/ R13 C8) VBP
After extended simplifications we have the following
expressions:
ωo =
(R4 / R JUMP ) / (R8 C6 R13 C8)
and
(
) /
(1 + R JUMP1 / R5 ) R4 R8 C6 /R JUMP R13 C8
Q =
(1 + R4 / R6 + R4 /R JUMP )
HOHP = –R4 / R6 , HOBP = (1 + R JUMP1 / R5 ) /
STATE VARIABLE FILTER (INVERTING)
The SV filter uses two integrators and a summing amplifier
to provide second-order low-pass, band-pass, and highpass responses. A fourth op amp can be used to combine
the existing responses and synthesize the notch or the
all-pass responses.
(1 + R6 / R JUMP + R6 / R4) , HOLP = –R JUMP / R6
From the above expressions we observe that Q depends
on the resistor ratio RJUMP1/R5. We therefore expect Q
to be much less sensitive to resistance tolerances and
drift. Indeed, with proper component selection and
circuit construction, the SV filter can easily yield dependable Qs in the range of hundreds. For best results, it is
advisable to use metal film resistors and polystyrene or
polycarbonate capacitors, and properly bypass the op
amp supplies.
This filter circuit can be easily constructed using the
quad EVAL_PRAOPAMP board and following the schematic in Figure 1.
RJUMP*
R6
R4
C6
R8
VCC
–VINA
2
V+
3
R5
V–
VEE
C8
R13
VCC
A1
6
1
VHP = VOUTA
RJUMP1*
V+
5
A2
V–
VCC
9
7
VBP = VOUTB
VEE
V+
10
A3
V–
8
VLP = VOUTC
VEE
*RJUMP AND RJUMP1 IS AN EXTERNAL COMPONENT, NOT PROVIDED ON THE APPLICATION BOARD.
Figure 1. State Variable Filter (Inverting)
REV. 0
AN-797
The SV filter is usually implemented with R4 = R6 = RJUMP,
R8 = R13 = R and C6 = C8 = C. So, the above expressions
simplify to
ω o = 1/ RC
THE BIQUAD FILTER
This particular filter implementation consists of two
integrators. The third op amp is a unity gain inverting
amplifier whose sole purpose is to provide polarity reversal.
Q = 1/ 3 (1 + R JUMP1 / R5 )
HOHP = –1 HOBP = Q
Unlike the SV filter, the biquad yields only two significant
responses; however, since all its op amps are operated in
the inverting mode, the circuit is immune from commonmode limitations.
HOLP = –1
The filter is tuned as follows:
1. Adjust R6 for desired magnitude of the response
of interest.
2. Adjust R8 or R13 to tune o.
3. Adjust the ratio RJUMP1/R5 to tune Q.
From the circuit above we have:
HOBP = –R4 / R6
ω o = 1/
STATE VARIABLE FILTER (NONINVERTING)
Another popular type of state variable filter can be
formed by just moving the input signal from the
inverting to the noninverting side of A1, resulting in the
noninverting state variable filter. See Figure 2.
(R8 R JUMP C6 C4)
HOBP = –R4 / R6
ω o = 1/ RC
(R8 R JUMP C6 )
HOLP = R / R6
Q = R4 / R
This filter is tuned as follows:
1. Adjust R8 or RJUMP to tune o.
2. Adjust R4 to tune Q.
3. Adjust R6 for desired values HOBP or of HOLP.
R4 = R6; R8 = R13 ; R5 = RJUMP ; C6 = C8
It can be shown that:
HOHP = 1/ Q
Q = R4 C4 /
The biquad filter is usually implemented with R8 = RJUMP = R
C4 = C6 = C, after which the above expressions simplify as:
By properly choosing the following components:
ω o = 1/ R8 C6
HOLP = R JUMP / R6
Q = 1 + R JUMP1 / R3
HOBP = –1 HOLP = 1/ Q
R6
R4
JUMP –VINA TO VOUTC
C6
R8
VCC
2
A1
V+
6
1
VEE
R5
+VINA
VCC
V–
3
C8
R13
VHP = VOUTA
V+
5
VCC
A2
9
7
V–
VBP = VOUTB
V+
10
VEE
RJUMP*
A3
8
V–
VLP = VOUTC
VEE
R3
*RJUMP IS AN EXTERNAL COMPONENT, NOT PROVIDED ON THE APPLICATION BOARD.
Figure 2. State Variable Filter (Noninverting)
RJUMP*
R4
C4
C6
R8
VCC
R6
2
V+
–VINA
3
A1
V–
VEE
R13
R16
VCC
6
1
VHP = VOUTA
V+
5
A2
V–
VCC
9
7
VBP = VOUTB
VEE
V+
10
A3
8
V–
VLP = VOUTC
VEE
*RJUMP IS AN EXTERNAL COMPONENT, NOT PROVIDED ON THE APPLICATION BOARD.
Figure 3. Biquad Filter
–2–
REV. 0
AN-797
C4
R4
VCC
R6
–IN A
R1*
C1
G1
RT1
2
G1
R7*
1
R5*
+IN A
3
C2
RT2
G2
G2
R3
C3
VOUTA
RL1
R2*
VEE
0
C6
R11
R8
–IN B
RT3
6
G3
7
R9*
+IN B
R12*
5
VOUTB
RL2
RT4
G4
R10
C5
0
C8
R16
R13
–IN C
RT5
9
G5
8
R14*
+IN C
R17*
10
VOUTC
RL3
RT6
G6
R15
C7
0
C10
R21
R18
–IN D
RT7
13
G7
14
R19*
+IN D
12
R22*
VOUTD
RL4
RT8
G8
R20
C9
0
Figure 4. Quad Precision Op Amp Evaluation Board Electrical Schematic
REV. 0
–3–
AN05566–0–12/05(0)
AN-797
Figure 5. Quad Precision Op Amp Evaluation Board Layout Patterns
© 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
–4–
REV. 0
0
