Rainbow Electronics MAX2108 - Manual (Page 7)

MAX2108
Direct-Conversion Tuner IC
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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,
f C = 30MHz
60
0.1dB Chebyshev,
f C = 20MHz
40
FILTER TYPE
ADC
SAMPLING
RATE
(Msps)
50
50
R S
(
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
R L
(k
Ω
)
50 15 680 39 820 33 Short Open 20
0.1dB Chebyshev,
f C = 20MHz
90
50 9 390 28 620 34 680 28 20
0.1dB Chebyshev,
f C = 45MHz