LTC1164-7 Linear Technology, LTC1164-7 Datasheet - Page 11

• Manufacturer Part Number: LTC1164-7
• Description: Low Power/ Linear Phase 8th Order Lowpass Filter
• Manufacturer: Linear Technology

A
Transient Response
Aliasing
Aliasing is an inherent phenomenon of sampled data
systems and it occurs when input frequencies close to the
sampling frequency are applied. For the LTC1164-7 case
at 100:1, an input signal whose frequency is in the range
of f
PPLICATI
CLK
INPUT
INPUT = 1kHz 3V
f
f
V
3%, will be aliased back into the filter’s passband.
CLK
C
S
= 10kHz
= 7.5V
RISE TIME (t
SETTLING TIME (t
(TO 1% of OUTPUT)
TIME DELAY (t
(TO 50% OF OUTPUT)
= 500kHz
10%
90%
50%
O
r
) =
U
d
) = GROUP DELAY
t d
f
CUTOFF
S
0.39
s
) =
Figure 5.
t s
Figure 6.
f
CUTOFF
I FOR ATIO
100 s/DIV
±5%
2.2
t r
U
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
±5%
f
CUTOFF
1.2
W
1164-7 F05
OUTPUT
1164-7 F06
U
Table 11. Aliasing (f
INPUT FREQUENCY
50:1, f
190 (or 210)
195 (or 205)
196 (or 204)
197(or 203)
198 (or 202)
199.5 (or 200.5)
100:1, f
97 (or 103)
97.5 (or 102.5)
98 (or 102)
98.5 (or 101.5)
99 (or 101)
99.5 (or 100.5)
If, for instance, an LTC1164-7 operating with a 100kHz
clock and 1kHz cutoff frequency receives a 98kHz 10mV
input signal, a 2kHz, 143 V
its output. When the LTC1164-7 operates with a clock-to-
cutoff frequency of 50:1, aliasing occurs at twice the clock
frequency. Table 11 shows details.
f
IN
(V
= f
IN
CUTOFF
(kHz)
CLK
= 1V
CUTOFF
V
f
f
(f
CLK
C
S
CLK
= 20kHz
RMS
= 7.5V
f
= 1MHz
OUT
/f
= 2kHz
= 1kHz
C
,
) = 50:1
)
CLK
Figure 7. Eye Diagram
(Relative to Input,
= 100kHz )
OUTPUT LEVEL
0dB = 1V
– 51.9
– 36.3
– 18.4
– 53.2
– 36.9
– 19.6
–76.1
–74.2
(dB)
– 3.0
– 0.2
– 5.2
– 0.7
5 s/DIV
RMS
RMS
alias signal will appear at
)
LTC1164-7
f
OUTPUT FREQUENCY
OUT
(Aliased Frequency
= ABS [f
1164-7 F07
(kHz)
10.0
5.0
4.0
3.0
2.0
0.5
3.0
2.5
2.0
1.5
1.0
0.5
CLK
11
f
IN
])