SM5846AP_06 Datasheet, PDF (20/36 Pages) Nippon Precision Circuits Inc – Multi-function Digital Filter

SM5846AP
Attenuation setting
The data stored in the D-ATT attenuation register,
accessed through the microprocessor interface,
determines the attenuation setting of the digital
attenuator. The D-ATT register data format is shown
below.
bit1 bit2 bit3 bit4 bit5 bit6 bit7 bit8
"0" a1 a2 a3 a4 a5 a6 a7
MSB
LSB
DATT attenation data (7bit)
Register information
The attenuation setting is given by the following
equations.
Attenuation = 0 [dB]
(DATT = 0)
Attenuation = 20log₁₀ ^{127 − DATT} [dB] (0 < DATT < 127)
128
Attenuation = −∞
(DATT = 127)
The attenuation for a selection of values is given in
the following table.
DATT register
value
Microprocess
or command
[hex]
0
00H
1
01H
2
02H
↓
↓
63
3FH
64
40H
↓
↓
125
7DH
126
7EH
127
7FH
Attenuation
[dB]
0
−0.137
−0.206
↓
−6.021
−6.157
↓
−36.12
−42.14
−∞
Relative gain
× 1.0
× 0.984375
× 0.9765625
↓
× 0.5
× 0.4921875
↓
× 0.015625
× 0.0078125
×0
Digital attenuator operation
The attenuation register is reset to 0 (attenuation = 0
dB) after a system reset signal.
When data is written to the attenuation register,
through the microprocessor interface, the attenuation
changes from the current value to the new value at
the speed shown in the following table.
Operating speed
Speed of
attenuation change
Normal-speed
sampling
8/fs per step change
High-speed sampling
16/fs per step
change
Time from min. to
max. attenuation
1016/fs (23.0ms at
44.1kHz)
2032/fs (23.0ms at
88.2kHz)
Soft muting operation
Soft muting ON/OFF is controlled by the MUTE
flag, accessed through the microprocessor interface.
MUTE
HIGH
LOW
Muting
Notes
OFF _{The MUTE flag is set HIGH (default) after a}
ON ^{system reset.}
When muting is ON, the attenuation ramps down to
−∞ at the speed shown in the table. Similarly when
muting is OFF, the attenuation level returns to the
original value at the same speed.
If the contents of the DATT attenuation register are
changed while muting is ON (attenuation = −∞),
only the register contents are replaced. If muting is
subsequently turned OFF, the attenuation value
changes to the new value at the same speed as shown
in the table.
SEIKO NPC CORPORATION —20