LTC1264-7 datasheet(13/16 Pages) AD

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LTC1264-7

12647fa

APPLICATI

I FOR ATIO

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 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 56

µVRMS 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.

Table 10. Aliasing (fCLK = 100kHz)

INPUT FREQUENCY

OUTPUT LEVEL

OUTPUT FREQUENCY

(VIN = 1VRMS,

(Relative to Input,

(Aliased Frequency

fIN = fCLK ± fOUT)

0dB = 1VRMS)fOUT = ABS [fCLK ± fIN])

(kHz)

(dB)

(kHz)

25:1, fCUTOFF = 4kHz

175 (or 225)

–76

180 (or 220)

– 69

185 (or 215)

– 62

190 (or 210)

– 43

195 (or 205)

– 7

50:1, fCUTOFF = 2kHz

75 (or 125)

–96

80 (or 120)

– 90

85 (or 115)

– 82

90 (or 110)

– 72

95 (or 105)

– 45

99 (or 101)

Table 9. Maximum VIN vs VS and Clock

POWER SUPPLY

MAXIMUM fCLK

MAXIMUM VIN

±7.5V

5.0MHz

1.6VRMS (fIN ≥ 160kHz)

4.5MHz

2.0VRMS (fIN ≥ 160kHz)

4.0MHz

2.5VRMS (fIN ≥ 160kHz)

≥ 3.5MHz

1.6VRMS (fIN ≥ 500kHz)

±5V

3.0MHz

1.6VRMS (fIN ≥ 100kHz)

≥ 3.0MHz

0.7VRMS (fIN ≥ 500kHz)

Single 5V

2.0MHz

0.5VRMS (fIN ≥ 400kHz)

Transient Response

INPUT = 10kHz

± 3V

fCLK = 2.5MHz

RATIO = 25:1

INPUT

90%

50%

10%

OUTPUT

1164-7 F06

RISE TIME (tr) =

±5%

0.36

fCUTOFF

SETTLING TIME (ts) =

±5%

(TO 1% of OUTPUT)

fCUTOFF

TIME DELAY (td) = GROUP DELAY ≈

(TO 50% OF OUTPUT)

1.15

fCUTOFF

Figure 6

Table 11. Transient Response of LTC Lowpass Filters

DELAY

RISE

SETTLING OVER-

TIME*

TIME**

TIME***

SHOOT

LOWPASS FILTER

(SEC)

(%)

LTC1064-3 Bessel

0.50/fC

0.34/fC

0.80/fC

0.5

LTC1164-5 Bessel

0.43/fC

0.34/fC

0.85/fC

LTC1164-6 Bessel

0.43/fC

0.34/fC

1.15/fC

LTC1264-7 Linear Phase

1.15/fC

0.36/fC

2.05/fC

LTC1164-7 Linear Phase

1.20/fC

0.39/fC

2.20/fC

LTC1064-7 Linear Phase

1.20/fC

0.39/fC

2.20/fC

LTC1164-5 Butterworth

0.80/fC

0.48/fC

2.40/fC

LTC1164-6 Elliptic

0.85/fC

0.54/fC

4.30/fC

LTC1064-4 Elliptic

0.90/fC

0.54/fC

4.50/fC

LTC1064-1 Elliptic

0.85/fC

0.54/fC

6.50/fC

* To 50%

±5%, ** 10% to 90% ±5%, *** To 1% ±0.5%

µs/DIV

Figure 5

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