DEMO MANUAL DC338A
Universal Lowpass Filter Board
LTC1563 Active RC
Lowpass Filter
DESCRIPTIO
Demonstration board DC338 features the LTC
®
1563
family of universal lowpass filter building blocks. The
LTC1563-2 and LTC1563-3 form a family of easy-to-use
active RC lowpass filters with rail-to-rail input and output
operation and low DC offset. The parts are suitable for use
in systems with resolutions of up to 16-bits.
Demonstration board DC338A-A has the LTC1563-2
installed. The LTC1563-2 with six
equal valued resistors
gives a unity-gain Butterworth response.
Demonstration board DC338A-B has the LTC1563-3
installed. The LTC1563-3 with six
equal valued resistors
gives a unity-gain Bessel response.
The value of the six resistors sets the cutoff frequency for
either filter and is calculated by this simple formula:
R = 10k • (256kHz/f
C
); where f
C
is the desired cutoff
frequency
TYPICAL PERFORMANCE CHARACTERISTICS AND BOARD PHOTO
Frequency Response
10
0
–10
–20
GAIN (dB)
R = 10k
f
C
= 256kHz
R = 10M
f
C
= 256Hz
–30
–40
–50
–60
–70
DC338A
–80
100
1k
100k
10k
FREQUENCY (Hz)
1M
1563 TA02
U
U W
U
By simply using
different valued resistors,
filters with gain
and other response types are achieved. A specific gain
(H
O
), f
O
and Q requirement is met with a unique set of three
resistors. To design these filters use Linear Technology’s
FilterCAD
TM
filter design software. FilterCAD is a powerful,
yet easy to use, program available free of charge from the
LTC website (www.linear-tech.com). It is also available on
CD-ROM.
This board is intended for use in evaluating simple, all pole
lowpass filters using the LTC1563 family of parts. The
filter complexity ranges from 4th to 6th order. The refer-
ence designators on the board correspond directly with
the schematics produced with Linear Technology’s
FilterCAD filter design program. With FilterCAD, the
design of filters is a simple process. With the LTC1563 and
this demonstration board, filter evaluation and integration
are also simple.
, LTC and LT are registered trademarks of Linear Technology Corporation.
FilterCAD is a trademark of Linear Technology Corporation.
Demo Board
1
DEMO MANUAL DC338A
Universal Lowpass Filter Board
PACKAGE A D SCHE ATIC DIAGRA SM
Universal Lowpass Filter
V
+
1
JP1
3
HIGH
SPEED
1
1
R
A1
R
B1
(R11)
2
3
5 4 3 2
C11
OPT
R31
4
5
R21
6
7
C1
0.1µF
2
V
–
J2
V
–
C2
10µF
8
3 DUAL
SUPPLY
JP2
SINGLE
1 SUPPLY
C3
0.1µF
TP1
J3
GND
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTORS ARE OPTIONAL AND IN 0805 PACKAGE.
2. ALL CAPACITORS ARE IN 0805 PACKAGE.
3. INSTALL SHUNTS ON JP1-JP3 PIN 2 AND PIN 3.
4. THERE ARE TWO TYPES OF ASSEMBLIES. LTC1563-2 AND LTC1563-3.
C12
OPT
U1
LTC1563-X
LP
SA
NC
INVA
NC
LPA
AGND
V
–
V
+
LPB
NC
INVB
NC
SB
NC
EN
16
15
14
13
12
11
10
9
ACTIVE
3
V
–
R
A2
R
B2
(R12)
DC338A SD
LOW 2
–
V POWER
J1
V
IN
Figure 1. Demo Board Schematic
PARTS LIST
REFERENCE
DESIGNATOR
C1, C3, C4
C2, C5
C11, C12
JP1-JP3
J1, J5
J2-J4
RB1, RA1, RB2,
RA2, R21, R22,
R23, R31, R32
TP1
U1(-A Assembly)
U1(-B Assembly)
QUANTITY
3
2
0
3
3
2
3
0
PART NUMBER
0805YG104ZAT1A
1206ZG106ZAT1A
TBD
3801S-3G2
CCIJ-230G
112404
575-4
DESCRIPTION
0.1µF 16V 80% Y5V Capacitor
10µF 10V 80% Y5V Capacitor
Capacitor (Optional)
1× 3-Pin 1 Row 0.100cc JMP
0.100cc Shunt
BNC Connector
Banana Jack Standard Conn
Resistor (Optional)
VENDOR
AVX
AVX
TBD
Comm Con
Comm Con
Connex
Keystone
TBD
TELEPHONE
(843) 946-0362
(843) 946-0362
(626) 301-4200
(626) 301-4200
(805) 378-6464
(718) 956-8900
1
1
1
2501-2
LTC1563-2
LTC1563-3
1-Pin Terminal Turrent TP
LTC1563-2 SSOP16GN
LTC1563-3 SSOP16GN
2
W
R32
W
U
V
+
C4
0.1µF
C5
10µF
1
R22
2 3 4 5
LP 1
SA 2
NC 3
INVA 4
J4
V
+
J5
V
OUT
LTC1563CGN
TOP VIEW
16 V
+
15 LPB
14 NC
13 INVB
12 NC
11 SB
10 NC
9
EN
2 SHDN
JP3
V
+
1
NC 5
LPA 6
AGND 7
V
–
8
GN PACKAGE
16-LEAD PLASTIC SSOP
Mill-Max
LTC
LTC
(516) 922-6000
(408) 432-1900
(408) 432-1900
DEMO MANUAL DC338A
Universal Lowpass Filter Board
QUICK START GUIDE
1. Design the filter using FilterCAD V3.0 (or later). When
the design is complete, the schematic’s reference
designators match those used on this board.
2. Solder the resistors to the board. The board is
designed for 0805 sized surface mount resistors
although other sizes can be used with some care.
3. Check the JP1 jumper setting. If the FilterCAD
schematic shows Pin 1 of the LTC1563 connected to
V
+
, make certain that JP1 is in the HIGH SPEED
position. If the FilterCAD schematic shows Pin 1 of
the LTC1563 connected to V
–
, JP1 is placed in the
LOW POWER position.
4. Connect jumper JP2 in the DUAL SUPPLY position
for split supplies (V
+
, V
–
and GND ). Connect JP2 in
the SINGLE SUPPLY position for single-supply
operation (V
+
and GND ).
5. Set jumper JP3 to the ACTIVE position to enable the
LTC1563 for normal operation. This jumper should
be placed in the SHUTDOWN position only if you want
to test the part’s shutdown function.
6. Connect the power supply to the V
+
, V
–
and GND
banana jacks. For single-supply operation, connect
the V
–
and GND banana jacks together.
7. Apply the input signal to the V
IN
BNC connector.
8. Connect the V
OUT
BNC connector to your monitoring
device (oscilloscope, network analyzer, etc). Make
certain that the loading is not excessive. The output of
LTC1563 is connected directly to the V
OUT
BNC.
There is no buffering on this board. The LTC1563
cannot drive a 50Ω load. It may also oscillate when
connected to a large capacitive load. Driving any
significant length of cable is to be avoided. Consult
the LTC1563 data sheet for more details on output
loading issues.
OPERATIO
LT1563 Functional Description
The LTC1563-2/LTC1563-3 are a family of easy-to-use,
4th order lowpass filters with rail-to-rail operation. The
LTC1563-2, with a single resistor value, gives a unity-gain
filter approximating a Butterworth response. The
LTC1563-3, with a single resistor value, gives a unity-gain
filter approximating a Bessel (linear phase) response. The
proprietary architecture of these parts allows for a simple
unity-gain resistor calculation:
R = 10k(256kHz/f
C
)
where f
C
is the desired cutoff frequency. For many appli-
cations, this formula is all that is needed to design a filter.
For example, a 50kHz filter requires a 51.2k resistor. In
practice, a 51.1k resistor would be used as this is the
closest E96, 1% value available.
The LTC1563-X is constructed with two independent 2nd
order sections. The output of the first section (section A)
U
is fed into the second section (section B). Note that
section A and section B are similar but not identical. The
parts are designed to be simple and easy to use.
By using different valued resistors, gain, other transfer
functions and higher cutoff frequencies are achieved. For
these applications, the resistor value calculation is more
difficult. For best results, design these filters using FilterCAD
Version 3.0 (or later).
Using TEE Networks
Figure 2 illustrates the use of an input TEE network to form
an additional pole. The R1 input resistor is split into two
parts with an additional capacitor connected to ground in
between the resistors. This TEE network forms a single
real pole. RB1should be much larger than RA1 to minimize
the interaction of this pole with the 2nd order section. This
circuit is useful in forming dual 3rd order filters and 5th
order filters with a single LTC1563 part. By cascading two
parts, 7th order and 9th order filters are achieved.
3
DEMO MANUAL DC338A
Universal Lowpass Filter Board
OPERATIO
A TEE network can be used in both sections of the part to
make a 6th order filter. This 6th order filter does not
conform exactly to the textbook responses. Textbook 6th
order responses (Butterworth, Bessel, Chebyshev etc.) all
have three complex pole pairs. This filter has two complex
pole pairs and two real poles. The textbook response
always has one section with a low Q value between 0.5 and
0.6. Replacing this low Q section with two real poles (two
real poles are the same mathematically as a complex pole
pair with a Q of 0.5) and tweaking the Q of the other two
complex pole pair sections results in a filter that is indis-
tinguishable from the textbook filter.
R2
RA1
RB1
C11
S
INV
C1
LP
R3
1/2 LTC1563
RA1
≈
f
P
=
2π •
RB1
10
DC338A F01
Figure 2. Input TEE Network
INPUT CONFIGURATION FOR EACH SECTION
The LTC1563 consists of two independent 2nd order
sections. Each section of the board is designed such that
the input can be set up in one of three configurations. The
input section has three positions: RA1, RB1(R11) and C11
for section A and RA2, RB2(R12) and C12 for section B.
The connection and labeling of section A is shown below.
RA1
RB1 (R11)
C11
AC COUPLING
CAP
R11
OPEN
“A POSITION”
4
U
Note that the RB1 resistor is double labeled as RB1(R11).
This is done to conform with the schematic that FilterCAD
provides. If the section is 3rd order, using a TEE network,
the two resistors are labeled as RA1 and RB1 (RA2 and
RB2 for section B) by FilterCAD. If the section is a standard
2nd order, the one resistor is labeled R11 (R12 for section
B) by FilterCAD.
1. Standard 2nd Order Configuration
In this configuration the input consists of a single resistor.
Place the resistor in the board’s “B” position. Place a 0Ω
resistor in the “A” position. Leave the capacitor position
open.
0Ω
R11
OPEN
“A POSITION”
“B POSITION”
DC338A S2
2. 3rd Order Section with Input “TEE” Network
–
C2
+
AGND
In this configuration use all three positions exactly as
labeled. The reference designators match FilterCAD
exactly.
RA1
RB1
C11
“A POSITION”
“B POSITION”
DC338A S3
(
1
RA1 • RB1
RA1 + RB1
)
C11
3. AC-Coupled 2nd Order Section
In this configuration connect the AC coupling capacitor in
the “A” position on the board. Place the resistor in the “B”
position. Leave the capacitor position (C11 or C12) open.
“A POSITION”
“B POSITION”
DC338A S4
“B POSITION”
DC338A S1
DEMO MANUAL DC338A
Universal Lowpass Filter Board
OPERATIO
Cutoff Frequency (f
C
) and Gain limitations
The LTC1563-X has both a maximum f
C
limit and a
minimum f
C
limit. The maximum f
C
limit is set by the speed
of the LTC1563-X’s op amps. At the maximum f
C
, the gain
is also limited to unity.
A minimum f
C
is dictated by the practical limitation of
reliably obtaining large valued, precision resistors. As the
desired f
C
decreases, the resistor value required increases.
When f
C
is 256Hz, the resistors are 10M. Obtaining a
reliable, precise 10M resistance between two points on a
printed circuit board is somewhat difficult. For example, a
10M resistor with 200M of stray, layout related resistance
in parallel, yields a net effective resistance of 9.52M and an
error of – 5%. Note that the gain is also limited to unity at
the minimum f
C
.
At intermediate f
C
, the gain is limited by one of the two
factors discussed above. For best results, design filters
with gain using FilterCAD.
FilterCAD calculates the resistor values using an accurate
and complex algorithm to account for parasitics and op
amp limitations. Using FilterCAD will always yield the best
possible design. By using the FilterCAD design tool you
can also achieve filters with cutoff frequencies beyond
256kHz. Cutoff frequencies up to 360kHz are attainable.
Contact Linear Technology for a copy of the FilterCAD
software. FilterCAD can also be downloaded from our
website at www.linear-tech.com.
U
Output Loading: Resistive and Capacitive
The op amps of the LTC1563-X have a rail-to-rail output
stage. To obtain maximum performance, the output load-
ing effects must be considered. Output loading issues can
be divided into resistive effects and capacitive effects.
Resistive loading affects the maximum output signal swing
and signal distortion. If the output load is excessive, the
output swing is reduced and distortion is increased. All of
the output voltage swing testing on the LTC1563-X is done
with R22 = 100k and a 10k load resistor. For best undistorted
output swing, the output load resistance should be greater
than 10k.
Capacitive loading on the output reduces the stability of
the op amp. If the capacitive loading is sufficiently high,
the stability margin is decreased to the point of oscillation
at the output. Capacitive loading should be kept below
30pF. Good, tight layout techniques should be maintained
at all times. These parts should not drive long traces and
must never drive a long coaxial cable.
When probing the
LTC1563-X, always use a 10x probe. Never use a 1x probe.
A standard 10x probe has a capacitance of 10pF to 15pF
while a 1x probe’s capacitance can be as high as 150pF.
The use of a 1x probe will probably cause oscillation.
For larger capacitive loads, a series isolation resistor can
be used between the part and the capacitive load. If the
load is too great, a buffer must be used.
NOTE:
The output of the LTC1563 is connected directly to the V
OUT
BNC. There is no buffering on
this board.
5
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