Rainbow Electronics MAX2108 - Manual (Page 9)

MAX2108
Direct-Conversion Tuner IC
_______________________________________________________________________________________ 9
MHz
DESIRED
CHANNEL
(20Msps)
dBc
AT POINT
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 POINT
0
1
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 POINT
0
0 10
ADC NYQUIST
12 20 40 17.16
-30
ADC SAMPLING
MHz
DESIRED
CHANNEL
(20Msps)
FOR POINTS 1, 2, 3, 4, REFER TO FIGURE 1
DIGITAL MATCHED FILTER
dBc
AT POINT
0 10 12 40
-30
ADC SAMPLING
2
3
4
Figure 2. Lowpass Filtering Example