AFE8201PFBR BURR-BROWN [Burr-Brown Corporation], AFE8201PFBR Datasheet - Page 12

• Manufacturer Part Number: AFE8201PFBR
• Description: IF Analog-to-Digital Converter with Digital Downconverter
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

AFE8201
SBWS016A − OCTOBER 2003 − REVISED JANUARY 2005
The SYNC pin can be used to externally control the phase of mixer. While the SYNC pin is high, the phase
accumulator is held to a constant value PHASE, essentially holding t to zero in the I and Q equations. When the SYNC
pin is brought low, the phase accumulator is incremented by the value FREQ once per MCLK cycle.
Note that the mixer can be bypassed by setting FREQ and PHASE to 0 and using only the Q (real) output.
CIC FILTER
The first stage of decimation filtering is provided by a 5th-order CIC filter. The operation of the CIC filter is controlled
by the unsigned variable DEC_RATE, SCALE, and SHIFT which are mapped into control registers as illustrated in
Figure 15. The valid range for DEC_RATE is from 8 to 1024.
The inherent dc gain of the CIC filter is DEC_RATE
this very high gain before the signal is output to the next stage of decimation filter. The combined effect of DEC_RATE,
SHIFT, and SCALE produces an overall dc gain for the CIC filter of:
In general, SHIFT and SCALE should be chosen to make GAIN as close to 1 as possible. For example, if DEC_RATE
is 20, setting SHIFT to 22 and scale to 41 will result in a GAIN of 0.9775.
12
0
0
0
0
0
0
Register Address
Register Address
Register Address
Register Address
Register Address
Register Address
0
0
0
0
0
0
0
0
0
1
1
1
0
1
1
0
0
1
1
0
1
0
1
0
MSB
15
15
15
15
15
15
Don’t Care
14
14
14
14
14
14
Don’t Care
13
13
13
13
13
13
Figure 15. CIC Filter Control Registers
Figure 14. Mixer Control Registers
12
12
12
12
12
12
Gain + DEC_RATE
11
11
11
11
11
11
10
10
10
10
10
10
5
. The control variables SHIFT and SCALE are used to reduce
9
9
9
9
9
9
SCALE
PHASE[31:16]
FREQ[31:16]
PHASE[15:0]
FREQ[15:0]
8
8
8
8
8
8
5
Scale 32
2
7
7
7
7
7
7
shift
6
6
6
6
6
6
DEC_RATE
5
5
5
5
5
5
4
4
4
4
4
4
3
3
3
3
3
3
SHIFT
2
2
2
2
2
2
1
1
1
1
1
1
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LSB
0
0
0
0
0
0
(8)