LTC1063CSW datasheet(11/16 Pages) AD

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LTC1063

1063fa

VIN

VOUT

1063 F10

V–

V+

0.1

µF

LTC1063

0.1

µF

fCLK

πRC

≤

fCLK

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 fCLK ±6% will generate an alias signal into the filter’s

passband and stopband. Table 4 shows details.

Example:

LTC1063, fCLK = 20kHz, fC = 200kHz,

fIN = (19.6kHz, 100mVRMS)

fALIAS = (400Hz, 3.16mVRMS)

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

0.9995fCLK

0.0005 fCLK

0dB

0.995 fCLK

0.005 fCLK

0dB

0.99

fCLK

0.01

fCLK

–3

0.9875fCLK

0.0125 fCLK

–10.2 dB

0.985 fCLK

0.015 fCLK

– 17.7 dB

0.9825fCLK

0.0175 fCLK

– 24.3 dB

0.98

fCLK

0.02

fCLK

–30

0.975 fCLK

0.025 fCLK

–40

0.97

fCLK

0.03

fCLK

–48

0.965 fCLK

0.035 fCLK

– 54.5 dB

0.96

fCLK

0.04

fCLK

– 60.4 dB

0.955 fCLK

0.045 fCLK

– 65.5 dB

0.95

fCLK

0.05

fCLK

– 70.16 dB

0.94

fCLK

0.06

fCLK

– 78.25 dB

0.93

fCLK

0.07

fCLK

– 85.3 dB

0.9

fCLK

0.1

fCLK

– 100.3 dB

Figure 10. Adding an Input Anti-Aliasing RC

noise ratio at a given distortion level. The wideband noise

(

µVRMS) is nearly independent of the value of the clock

frequency and excludes the clock feedthrough. The

LTC1063’s typical wideband noise is 95

µVRMS. 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 500

µVP-P. Note that 500µVP-P equals the

µVRMS wideband noise of the part, multiplied by a crest

factor or 5.25.

OUTPUT AMPLITUDE

REFERENCED TO

INPUT SIGNAL

µs/DIV

1063 F08

fCLK = 100kHz, fC = 1kHz, VS = ±5V, 1MHz SCOPE BW

µs/DIV

1063 F09

fCLK = 100kHz, fC = 1kHz, VS = ±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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