Rainbow Electronics MAX2105 - 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