LTC1264-7
O U
W U
I FOR ATIO
PPLICATI
S
A
Table 9. Maximum V vs V and Clock
IN
S
Aliasing
POWER SUPPLY
±7.5V
MAXIMUM f
MAXIMUM V
IN
CLK
Aliasing is an inherent phenomenon of sampled data
systems and it occurs when input frequencies close to the
sampling frequency are applied. For the LTC1264-7 case
at 50:1, an input signal whose frequency is in the range of
fCLK ±10%, will be aliased back into the filter’s passband.
If, for instance, an LTC1264-7 operating with a 100kHz
clock and 2kHz cutoff frequency receives a 95kHz 10mV
input signal, a 5kHz 56µVRMS alias signal will appear at its
output. When the LTC1264-7 operates with a clock-to-
cutoff frequency of 25:1, aliasing occurs at twice the clock
frequency. Table 10 shows details.
5.0MHz
4.5MHz
4.0MHz
≥ 3.5MHz
3.0MHz
≥ 3.0MHz
2.0MHz
1.6V
2.0V
2.5V
1.6V
(f ≥ 160kHz)
RMS IN
RMS IN
(f ≥ 160kHz)
(f ≥ 160kHz)
RMS IN
(f ≥ 500kHz)
RMS IN
±5V
1.6V
(f ≥ 100kHz)
RMS IN
0.7V
(f ≥ 500kHz)
RMS IN
Single 5V
0.5V (f ≥ 400kHz)
RMS IN
Transient Response
Table 10. Aliasing (f = 100kHz)
CLK
INPUT FREQUENCY
OUTPUT LEVEL
OUTPUT FREQUENCY
(Aliased Frequency
(V = 1V
,
(Relative to Input,
IN
RMS
f
= f ± f
)
0dB = 1V
(dB)
)
f
= ABS [f ± f ])
IN CLK OUT
RMS
OUT
CLK IN
(kHz)
(kHz)
25:1, f
= 4kHz
CUTOFF
175 (or 225)
180 (or 220)
185 (or 215)
190 (or 210)
–76
– 69
– 62
– 43
25
20
15
10
10µs/DIV
195 (or 205)
– 7
5
INPUT = 10kHz ± 3V
f
CLK = 2.5MHz
50:1, f
= 2kHz
CUTOFF
RATIO = 25:1
75 (or 125)
80 (or 120)
85 (or 115)
90 (or 110)
95 (or 105)
99 (or 101)
–96
– 90
– 82
– 72
– 45
0
25
20
15
10
5
Figure 5
1
t
s
OUTPUT
INPUT
90%
50%
10%
Table 11. Transient Response of LTC Lowpass Filters
DELAY
TIME*
(SEC)
RISE SETTLING OVER-
TIME** TIME*** SHOOT
t
d
LOWPASS FILTER
(SEC)
(SEC)
(%)
0.5
0
LTC1064-3 Bessel
LTC1164-5 Bessel
LTC1164-6 Bessel
0.50/f
0.43/f
0.43/f
0.34/f
0.34/f
0.34/f
0.80/f
0.85/f
1.15/f
C
C
C
C
C
C
C
C
C
1
t
r
LTC1264-7 Linear Phase
LTC1164-7 Linear Phase
LTC1064-7 Linear Phase
1.15/f
1.20/f
1.20/f
0.36/f
0.39/f
0.39/f
2.05/f
2.20/f
2.20/f
5
5
5
C
C
C
C
C
C
C
C
C
0.36
CUTOFF
RISE TIME (t ) =
5%
2
r
f
LTC1164-5 Butterworth
0.80/f
0.48/f
2.40/f
11
C
C
C
SETTLING TIME (t ) =
s
(TO 1% of OUTPUT)
5%
f
LTC1164-6 Elliptic
LTC1064-4 Elliptic
LTC1064-1 Elliptic
0.85/f
0.90/f
0.85/f
0.54/f
0.54/f
0.54/f
4.30/f
4.50/f
6.50/f
18
20
20
CUTOFF
C
C
C
C
C
C
C
C
C
1.15
CUTOFF
TIME DELAY (t ) = GROUP DELAY ≈
(TO 50% OF OUTPUT)
d
1164-7 F06
f
* To 50% ± 5%, ** 10% to 90% ±5%, *** To 1% ± 0.5%
Figure 6
12647fa
13