Direct-Conversion Tuner IC

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7

Power-Supply Sequencing

The MAX2108 has several +5V supply pins. Configure

the supply layout in a star format, with a bypass capac-

itor that dominates the rise time of the supply at the

center of the star to ensure that all pins see approxi-

mately the same voltage during power-up.

Filters in Direct-Conversion Tuners

Typically, a 5th- or 7th-order L-C lowpass filter is used

for anti-aliasing the ADCs following the MAX2108.

Table 1 offers suggested component values for these

lowpass filters. Figures 1 and 2 describe typical filtering

requirements.

Table 1. Suggested Component Values for Discrete Lowpass Filters

0.1dB Chebyshev,

60

0.1dB Chebyshev,

40

FILTER TYPE

ADC

SAMPLING

RATE

(Msps)

50

50

(

Ω)

11

20

C1

(pF)

620

910

L1

(nH)

41

60

C2

(pF)

910

1500

L2

(nH)

50

75

C3

(pF)

1000

1500

L3

(nH)

41

60

C4

(pF)

20

20

(k

Ω)

50

15

680

39

820

33

Short

Open

20

0.1dB Chebyshev,

90

50

9

390

28

620

34

680

28

20

0.1dB Chebyshev,