AD6636CBCZ Analog Devices Inc, AD6636CBCZ Datasheet - Page 30

• Manufacturer Part Number: AD6636CBCZ
• Description: IC DIGITAL DWNCONV 4CH 256CSPBGA
• Manufacturer: Analog Devices Inc
• Series: AD6636r

Specifications of AD6636CBCZ

• Rf Type: Cellular, CDMA2000, EDGE, GPRS, GSM
• Number Of Mixers: 1
• Secondary Attributes: Down Converter
• Current - Supply: 450mA
• Voltage - Supply: 3 V ~ 3.6 V
• Package / Case: 256-CSPBGA
• Brief Features: 4/6 Independent Wideband Processing Channel, Quadrature Correction & DC Correction For Complex Input
• Supply Voltage Range: 1.7V To 1.9V
• Operating Temperature Range: -40°C To +85°C
• Ic Function: Digital Down Converter (DDC)
• Rohs Compliant: Yes
• Pin Count: 256
• Screening Level: Industrial
• Package Type: CSPBGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency: -
• Gain: -
• Noise Figure: -
• Lead Free Status / Rohs Status: Compliant

AD6636
CIC Rejection
Table 14 illustrates the amount of bandwidth as a percentage of
the data rate into the CIC stage, which can be protected with
various decimation rates and alias rejection specifications. The
maximum input rate into the CIC is 150 MHz (the same as the
maximum input port data rate). The data may be scaled to any
other allowable sample rate.
Table 14 can be used to decide the minimum decimation
required in the CIC stage to preserve a certain bandwidth. The
CIC5 stage can protect a much wider bandwidth to any given
rejection, when a decimation ratio lower than that identified in
the table is used. The table helps to calculate an upper boundary
on decimation, M
Table 14. SSB CIC5 Alias Rejection Table (f
M
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Example Calculations
Goal: Implement a filter with an input sample rate of 100 MHz
requiring 100 dB of alias rejection for a ± 1.4 MHz pass band.
CIC
5
−60 dB
8.078
6.367
5.022
4.107
3.463
2.989
2.627
2.342
2.113
1.924
1.765
1.631
1.516
1.416
1.328
1.25
1.181
1.119
1.064
1.013
0.967
0.925
0.887
0.852
0.819
0.789
0.761
0.734
0.71
0.687
0.666
CIC
−70 dB
6.393
5.11
4.057
3.326
2.808
2.425
2.133
1.902
1.716
1.563
1.435
1.326
1.232
1.151
1.079
1.016
0.96
0.91
0.865
0.824
0.786
0.752
0.721
0.692
0.666
0.641
0.618
0.597
0.577
0.559
0.541
, given the desired filter characteristics.
−80 dB
5.066
4.107
3.271
2.687
2.27
1.962
1.726
1.54
1.39
1.266
1.162
1.074
0.998
0.932
0.874
0.823
0.778
0.737
0.701
0.667
0.637
0.61
0.584
0.561
0.54
0.52
0.501
0.484
0.468
0.453
0.439
−90 dB
4.008
3.297
2.636
2.17
1.836
1.588
1.397
1.247
1.125
1.025
0.941
0.87
0.809
0.755
0.708
0.667
0.63
0.597
0.568
0.541
0.516
0.494
0.474
0.455
0.437
0.421
0.406
0.392
0.379
0.367
0.355
in
= 1)
−100 dB
3.183
2.642
2.121
1.748
1.48
1.281
1.128
1.007
0.909
0.828
0.76
0.703
0.653
0.61
0.572
0.539
0.509
0.483
0.459
0.437
0.417
0.399
0.383
0.367
0.353
0.34
0.328
0.317
0.306
0.297
0.287
Rev. A | Page 30 of 80
Solution: First determine the percentage of the sample rate that
is represented by the pass band.
In the −100 dB column in Table 14, find the value greater than
or equal to the pass-band percentage of the clock rate. Then
find the corresponding rate decimation factor (M
M
1.48%, which is slightly larger than the 1.4% calculated.
Therefore, for this example, the maximum bound on the CIC
decimation rate is 6. A higher M
than the 100 dB required.
FIR HALF-BAND BLOCK
The output of the CIC filter is pipelined into the FIR HB (half-
band) block. Each channel has two sets of cascading fixed-
coefficient FIR and fixed-coefficient half-band filters. The half-
band filters decimate by 2. Each of these filters (FIR1, HB1,
FIR2, HB2) are described in the following sections.
3-Tap Fixed-Coefficient Filter (FIR1)
The 3-tap FIR filter is useful in certain filter configurations in
which extra alias protection is needed for the decimating HB1
filter. It is a simple sum-of-products FIR filter with three filter
taps and 2-bit fixed coefficients. Note that this filter does not
decimate. The coefficients of this symmetric filter are {1, 2, 1}.
The normalized coefficients used in the implementation are
{0.25, 0.5, 0.25}.
The user can either use or bypass this filter. Writing Logic 0 to
the FIR1 enable bit in the FIR-HB control register bypasses this
fixed-coefficient filter. The filter is useful in certain filter
configurations only and bypassing it for other applications
results in power savings.
CIC
–100.00
–16.67
–25.00
–33.33
–41.67
–50.00
–58.33
–66.67
–75.00
–83.33
–91.67
–8.33
of 6, the frequency that has −100 dB of alias rejection is
BW
Figure 31. FIR1 Filter Response to the Input Rate of the Filter
0
fraction
0
0.1
=
100
FRACTION OF FIR1 INPUT SAMPLE RATE
0.2
×
100
1.4
0.3
MHz
MHz
0.34
FIR1 RESPONSE
0.4
=
0.5
CIC
1.4
means less alias rejection
0.6
0.66
0.7
0.8
CIC
0.9
). For an
–81