LT10647FB_15 Datasheet, PDF (12/16 Pages) Linear Technology – Linear Phase, 8th Order Lowpass Filter

LTC1064-7
APPLICATI S I FOR ATIO
Speed Limitations
To avoid op amp slew rate limiting at maximum clock
frequencies, the signal amplitude should be kept below a
specified level as shown in Table 9.
Transient Response
Table 9. Maximum V_IN vs V_S and Clock
POWER SUPPLY
±7.5V
± 5V
Single 5V
MAXIMUM f_CLK
5.0MHz
4.5MHz
4.0MHz
≥ 3.5MHz
3.5MHz
≥ 3.0MHz
2.0MHz
MAXIMUM V_IN
1.8V_RMS (f_IN > 80kHz)
2.3V_RMS (f_IN > 80kHz)
2.7V_RMS (f_IN > 80kHz)
1.4V_RMS (f_IN > 500kHz)
1.6V_RMS (f_IN > 80kHz)
0.7V_RMS (f_IN > 400kHz)
0.5V_RMS (f_IN > 250kHz)
Table 10. Transient Response of LTC Lowpass Filters
LOWPASS FILTER
DELAY
TIME*
(SEC)
RISE SETTLING
TIME** TIME***
(SEC) (SEC)
LTC1064-3 Bessel
0.50/f_C 0.34/f_C 0.80/f_C
LTC1164-5 Bessel
0.43/f_C 0.34/f_C 0.85/f_C
LTC1164-6 Bessel
0.43/f_C 0.34/f_C 1.15/f_C
LTC1264-7 Linear Phase 1.15/f_C 0.36/f_C 2.05/f_C
LTC1164-7 Linear Phase 1.20/f_C 0.39/f_C 2.2/f_C
LTC1064-7 Linear Phase 1.20/f_C 0.39/f_C 2.2/f_C
LTC1164-5 Butterworth
0.80/f_C 0.48/f_C 2.4/f_C
LTC1164-6 Elliptic
0.85/f_C 0.54/f_C 4.3/f_C
LTC1064-4 Elliptic
0.90/f_C 0.54/f_C 4.5/f_C
LTC1064-1 Elliptic
0.85/f_C 0.54/f_C 6.5/f_C
* To 50% ±5%, ** 10% to 90% ±5%, *** To 1% ±0.5%
OVER-
SHOOT
(%)
0.5
0
1
5
5
5
11
18
20
20
Table 11. Aliasing (f_CLK = 100kHz)
INPUT FREQUENCY
(V_IN = 1V_RMS,
f_IN = f_CLK ± f_OUT)
(kHz)
OUTPUT LEVEL
(Relative to Input,
0dB = 1V_RMS)
(dB)
50:1, f_CUTOFF = 2kHz
190 (or 210)
195 (or 205)
196 (or 204)
197 (or 203)
198 (or 202)
199.5 (or 200.5)
– 76.1
– 51.9
– 36.3
– 18.4
– 3.0
– 0.2
100:1, f_CUTOFF = 1kHz
97 (or 103)
97.5 (or 102.5)
98 (or 102)
98.5 (or 101.5)
99 (or 101)
–74.2
– 53.2
– 36.9
– 19.6
– 5.2
99.5 (or 100.5)
– 0.7
OUTPUT FREQUENCY
(Aliased Frequency
f_OUT = ABS [f_CLK ± f_IN])
(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
12
50µs/DIV
V_S = ± 7.5V, f_IN = 2kHz ± 3V
f_CLK = 1MHz, RATIO = 50:1
Figure 5.
ts
INPUT
90%
1064-7 F05
OUTPUT
50%
td
10%
tr
RISE
TIME
(t_r)
=
0.39
f_CUTOFF
±5%
SETTLING
(TO 1% of
TIME (t_s)
OUTPUT)
=
2.2
f_CUTOFF
±5%
DELAY TIME (t_d) = GROUP
(TO 50% OF OUTPUT)
DELAY
≈
1.2
f_CUTOFF
1064-7 F06
Figure 6.
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 LTC1064-7 case
at 100:1, an input signal whose frequency is in the range
of f_CLK ±3%, will be aliased back into the filter’s passband.
If, for instance, an LTC1064-7 operating with a 100kHz
clock and 1kHz cutoff frequency receives a 98kHz, 10mV
input signal, a 2kHz, 143µV_RMS alias signal will appear at
its output. When the LTC1064-7 operates with a clock-to-
cutoff frequency of 50:1, aliasing occurs at twice the clock
frequency. Table 11 shows details.
10647fb