LTC1068 Series
17
1068fc
APPLICATIONS INFORMATION
A Surface Mount Printed Circuit Layout
A very compact surface mount printed circuit layout can
be designed with 0603 size surface mount resistors,
capacitors and a 28-pin SSOP of the LTC1068 product
family. An example of a printed circuit layout is shown
in the following figures for an 8th order elliptic bandpass
filter. The total board area of this 8th order filter is 1" by
0.8". No attempt was made to design the smallest possible
printed circuit layout.
70kHz Elliptic Bandpass Filtter, f
CENTER
= f
CLK
/25 (Maximum f
CENTER
is 80kHz, V
S
= ±5V)
Gain vs Frequency
INV B
INV C
281
HPB/NB
HPC/NC
272
SB
NC
NC
SC
245
R21 4.99k
R22 4.99k
BPB BPC
263
R31 24.9k
R32 107k
LPA LPD
209
R43 43.2k
R44 17.4k
BPA BPD
1910
R33 59k
R34 63.4k
HPA/NA
HPD/ND
1811
INV A
INV D
17
16
15
12
13
14
R23 4.99k
R24 7.5k
LPB
LPC
25
4
R41 20.5k
R51
4.99k
R
H2
11.3k
R11 29.4k
V
IN
R64 10k
R62 56.2k
R
H1
28k
R
H3
15.4k
V
OUT
AGND
V
–
236
V
+
227
SA
SD
NC
NC
CLK
218
5V
–5V
1.75MHz
1068 TA04
U1
LTC1068-25
C1
0.1µF
C2
0.1µF
R54
4.99k
R52
4.99k
R
L3
45.3K
R61 11.3k
R
L2
23.2k
FREQUENCY (kHz)
20
GAIN (dB)
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
40
60
70
1068 TA05
30 50
80
90
100
FilterCAD Custom Inputs for f
C
= 70kHz
2nd ORDER SECTION f
0
(kHz) Q f
N
(kHz) TYPE MODE
B 67.7624 5.7236 58.3011 HPN 2b
C 67.0851 20.5500 81.6810 LPN 1bn
A 73.9324 15.1339 81.0295 LPN 2n
D 73.3547 16.3491 BP 2b
