AK2401 Datasheet, PDF (48/103 Pages) Asahi Kasei Microsystems – Direct Conversion Transceiver

[AK2401]
13.8.3. Programmable FIR Filter
The AK2401 has a programmable FIR filter that can be set a coefficient arbitrary. This FIR filter is
disposed in channel filter block (Figure 30), and enabled by setting DFIL_PROG bit to “1” <Address
0x22> instead of F0~F9 fixed channel filters that are set by DFIL_SEL[3:0] bits.
Figure 30 shows a block diagram of the programmable FIR filter block. This filter is composed by delay
block, coefficient selection block, MAC (Multiplier & Accumulator) block and bit adjustment blocks.
The table in Figure 30 shows bit length of each numbered point in the diagram. For example, bit length
(1.21) indicates 1 bit to left and 21 bits to the right, in total 22 bits configuration. All internal calculations
are executed by 2’s complement expression.
Delay Part
①
Input
Z^-1
Z^-1
Z^-1
・
・
・
Z^-1
Coefficient Select Part
Coefficient
Register
・・・
No.
Location
① Input
② Coefficient
③ Multiplier Output
④ Rounding Output
⑤ Accumulator Output
⑥ Output
Bit Length
(1.21)
(1.15)
(1.36)
(1.21)
(6.21)
(1.23)
②
③
Multiplier
④
ROUND
15bit
MAC Part
Adjust Part
⑤
Saturation
⑥
Bit Shift
Output
Accumulator
Figure 30. Programmable FIR Filter Block
■ Coefficient Limits
Coefficient limits are shown here.
Bit Number
Bit
Input Range
Dec
Hex
Maximum Total Coefficient Value
Dec
Absolute Maximum Total Coefficient Value Dec
Note:
* 19. Do not set “8000” (hex). It is a prohibited setting.
16
+32767 ~ -32767
7FFFh ~ 8001h (* 19)
524288
1048576
The input maximum tap number is controlled by DFIL_SEL[3:0] bits <Address 0x22> as below.
DFIL_SEL[3:0]
Maximum Tap Number
0h ~ 1h
64 (TAP0 ~ TAP63)
4h ~ Fh
75 (TAP0 ~ TAP74)
If the coefficient accuracy is less than 16 bits, input “0” to the LSB side to make the input data 16-bit. It is
necessary to keep the accuracy when rounding the data as shown in Figure 30. Setting examples are
shown in the next page.
017003093-E-00
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2017/3