AD6654/PCB Analog Devices Inc, AD6654/PCB Datasheet - Page 79

• Manufacturer Part Number: AD6654/PCB
• Description: BOARD EVALUATION FOR AD6654
• Manufacturer: Analog Devices Inc

Specifications of AD6654/PCB

• Module/board Type: Evaluation Board
• For Use With/related Products: AD6554
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

CIC Decimation <4:0>
This 5-bit word specifies the CIC filter decimation value
minus 1. A value of 0x00 is a decimation of 1 (bypass), and
0x1F is a decimation of 32. Writing a value of 0 in this register
bypasses CIC filtering, but does not bypass the CIC scaling
operation.
CIC Scale Factor <4:0>
This 5-bit word specifies the CIC filter scale factor used to
compensate for the gain provided by the CIC filter. The
recommended value is given by the following equation:
where:
M
in the CIC decimation register).
ceil operation gives the closest integer greater than or equal to
the argument.
The valid range for this register is decimal 0 to 20.
FIR-HB Control <3:0>
<3>: FIR1 Enable Bit. When this bit is set, the FIR1 fixed
coefficient filter is enabled. When cleared, FIR1 is bypassed.
<2>: HB1 Enable Bit. When this bit is set, the HB1 half-band
filter is enabled. When cleared, HB1 is bypassed.
<1>: FIR2 Enable Bit. When this bit is set, the FIR2 fixed
coefficient filter is enabled. When cleared, FIR2 is bypassed.
<0>: HB2 Enable Bit. When this bit is set, the HB2 half-band
filter is enabled. When cleared, HB2 is bypassed.
MRCF Control Register <12:0>
<12:10>: MRCF Data Select Bits. These bits are used to select
the input source for the MRCF filter. Each MRCF filter can be
driven by output from the HB2 filter of any channel independ-
ently. Table 35 shows the selections available.
Table 35. MRCF Data Select Bits
MRCF Data Select<2:0>
000
001
010
011
1x0
1x1
<9>: Interpolating Half-Band Enable Bit. When this bit is set,
the interpolating half-band filter, driven by the output of the
CRCF block, is enabled. When cleared, the interpolating half-
band filter is bypassed, and its output is the same as its input.
The interpolating half-band filter doubles the data rate.
CIC
is the decimation rate of the CIC (one more than the value
CIC
Scale
Register
=
ceil
MRCF Input Source
MRCF input taken from Channel 0
MRCF input taken from Channel 1
MRCF input taken from Channel 2
MRCF input taken from Channel 3
MRCF input taken from Channel 4
MRCF input taken from Channel 5
5 (
×
log
2
(
M
CIC
))
−
5
Rev. 0 | Page 79 of 88
<8>: This bit is open.
<7>: Half-Rate Bit. When this bit is set, the MRCF filter
operates using half the PLL clock rate. This is used for power
savings when there is sufficient time to complete MRCF
filtering using only half the PLL clock rate. When this bit is
cleared, the MRCF filter operates at the full PLL clock rate. See
the Mono-Rate RAM Coefficient Filter (MRCF) section.
<6:4>: MRCF Number of Taps Bits. This 3-bit word should be
written with one less than the number of taps that are calculated
by the MRCF filter. The filter length is given by the decimal
value of this register plus 1. A value of 0 represents a 1-tap filter
and maximum value of 7 represents an 8-tap filter.
<3:2>: MRCF Scale Factor Bits. The output of the MRCF filter is
scaled according to the value of these bits. Table 36 describes
the attenuation corresponding to each setting.
Table 36. MRCF Scale Factor
MRCF Scale<1:0>
00
01
10
11
<1>: This bit is open.
<0>: MRCF Bypass Bit. When this bit is set, the MRCF filter is
bypassed and, therefore, the output of the MRCF is the same as
its input. When this bit is cleared, the MRCF has normal
operation as programmed by its control register.
MRCF COEFFICIENT MEMORY
The MRCF coefficient memory consists of eight coefficients,
each six bits wide. The memory extends from Address 0x80 to
Address 0x87. The coefficients should be written in twos
complement format.
DRCF Control Register <11:0>
<11>: DRCF Bypass Bit. When this bit is set, the DRCF filter is
bypassed and, therefore, its output is the same as its input.
When this bit is cleared, the DRCF has normal operation as
programmed by the rest of this control register.
<10>: Symmetry Bit. When this bit is set, it indicates that the
DRCF is implementing a symmetrical filter and only half the
impulse response needs to be written into the DRCF coefficient
RAM. When this bit is cleared, the filter is asymmetrical and
complete impulse response of the filter should be written to the
coefficient RAM. When this filter is symmetrical, it can imple-
ment up to 128 filter taps.
<9:8>: DRCF Multiply Accumulate Scale Bits. The output of the
DRCF filter is scaled according to the value of these bits.
Table 37 lists the attenuation corresponding to each setting.
Scale Factor
18.06 dB attenuation (left-shift 3 bits)
12.04 dB attenuation (left-shift 2 bits)
6.02 dB attenuation (left-shift 1 bit)
No scaling (0 dB)
AD6654