Rainbow Electronics MAX2105 User Manual
Page 15
MAX2102/MAX2105
Direct-Conversion Tuner ICs for
Digital DBS Applications
______________________________________________________________________________________
15
MHz
DESIRED
CHANNEL
(20Msps)
dBc
AT SIGNAL
POINT NO. 2
0
0
10
PASSBAND FILTER REQUIREMENTS:
(1) <20% OF BAUD PERIOD DELAY RIPPLE
(2) <0.1dB GAIN RIPPLE
TRANSITION BAND FILTER REQUIREMENTS:
< 2dB GAIN RIPPLE
FILTER CUTOFF
12
20
28
40
MHz
17.16
-30
ADC SAMPLING
TRANSPONDER SPACING = 29.16 MHz
LOWPASS FILTER RESPONSE
DESIRED
CHANNEL
(20Msps)
UNDESIRED ADJACENT CHANNEL
TRANSPONDER BW = 24MHz
dBc
AT SIGNAL
POINT NO. 1
0
0
10
DATA NYQUIST
NYQUIST FOR ADC
α
= 0.2
12
20
29.16
40 41.16
17.16
-30
ADC SAMPLING
MHz
DESIRED
CHANNEL
(20Msps)
ADJ
CHANNEL
FOLDOVER
dBc
AT SIGNAL
POINT NO.3
0
0
10
ADC NYQUIST
12
20
40
17.16
-30
ADC SAMPLING
MHz
DESIRED
CHANNEL
(20Msps)
DIGITAL MATCHED FILTER
dBc
AT SIGNAL
POINT NO.4
0
10 12
40
-30
ADC SAMPLING
Figure 5. Lowpass Filtering Example.
Note:
Data Rate = 40Mbps, Transponder BW = 24MHz, Transponder Spacing = 29.16MHz,
Nyquist Filter:
α
= 0.2