Datasheet
LTC1063
11
1063fa
V
IN
V
OUT
1063 F10
C
V
–
V
+
R
0.1µF
1
2
3
4
8
7
6
5
LTC1063
0.1µF
f
CLK
20 102πRC
≤ ≤
1 f
CLK
f
CLK
Aliasing
Aliasing is an inherent phenomenon of sampled data filters
and it primarily occurs when the frequency of an input
signal approaches the sampling frequency. For the
LTC1063, an input signal whose frequency is in the range
of f
CLK
±6% will generate an alias signal into the filter’s
passband and stopband. Table 4 shows details.
Example: LTC1063, f
CLK
= 20kHz, f
C
= 200kHz,
f
IN
= (19.6kHz, 100mV
RMS
)
f
ALIAS
= (400Hz, 3.16mV
RMS
)
An input RC can be used to attenuate incoming signals
close to the filter clock frequency (Figure 10). A Butterworth
passband response will be maintained if the value of the
input resistor follows Table 1.
Table 4. Aliasing Data
INPUT FREQUENCY OUTPUT FREQUENCY
0.9995f
CLK
0.0005 f
CLK
0dB
0.995 f
CLK
0.005 f
CLK
0dB
0.99 f
CLK
0.01 f
CLK
–3 dB
0.9875f
CLK
0.0125 f
CLK
–10.2 dB
0.985 f
CLK
0.015 f
CLK
– 17.7 dB
0.9825f
CLK
0.0175 f
CLK
– 24.3 dB
0.98 f
CLK
0.02 f
CLK
–30 dB
0.975 f
CLK
0.025 f
CLK
–40 dB
0.97 f
CLK
0.03 f
CLK
–48 dB
0.965 f
CLK
0.035 f
CLK
– 54.5 dB
0.96 f
CLK
0.04 f
CLK
– 60.4 dB
0.955 f
CLK
0.045 f
CLK
– 65.5 dB
0.95 f
CLK
0.05 f
CLK
– 70.16 dB
0.94 f
CLK
0.06 f
CLK
– 78.25 dB
0.93 f
CLK
0.07 f
CLK
– 85.3 dB
0.9 f
CLK
0.1 f
CLK
–100.3 dB
Figure 10. Adding an Input Anti-Aliasing RC
noise ratio at a given distortion level. The wideband noise
(µV
RMS
) is nearly independent of the value of the clock
frequency and excludes the clock feedthrough. The
LTC1063’s typical wideband noise is 95µV
RMS
. Figure 9
shows the same scope photo as Figure 8 but with a more
sensitive vertical scale: The clock feedthrough is imbed-
ded in the filter’s wideband noise. The peak-to-peak
wideband noise of the filter can be clearly seen; it is
approximately 500µV
P-P
. Note that 500µV
P-P
equals the
95µV
RMS
wideband noise of the part, multiplied by a crest
factor or 5.25.
OUTPUT AMPLITUDE
REFERENCED TO
INPUT SIGNAL
2µs/DIV
1063 F08
f
CLK
= 100kHz, f
C
= 1kHz, V
S
= ±5V, 1MHz SCOPE BW
5mV/DIV
0.5mV/DIV
2µs/DIV
1063 F09
f
CLK
= 100kHz, f
C
= 1kHz, V
S
= ±5V, 1MHz SCOPE BW
Figure 8. LTC1063 Output Clock Feedthrough + Noise
Figure 9. LTC1063 Output Clock Feedthrough + Noise
APPLICATIO S I FOR ATIO
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