adau1373 Analog Devices, Inc., adau1373 Datasheet - Page 61

• Manufacturer Part Number: adau1373
• Description: Low Power Codec With Speaker And Headphone Amplifier Adau1373
• Manufacturer: Analog Devices, Inc.

PROGRAMMABLE SEVEN-BAND EQUALIZER
The programmable seven-band equalizer is composed of five
biquad filters (Band 1 to Band 5) and two first-order IIR filters
(Band 6 and Band 7). See Figure 112 for a system block diagram.
The EQ shares Register 0x80 through Register 0xBD with the
MDRC. All the filter coefficients are programmable via the
corresponding registers. The filter bank can also be configured
as some other filters, including de-emphasis and notch filter,
when all five midfrequency bands are not needed.
Table 22. Register 0x80 to Register 0xBD EQ Coefficients
Register
Address
0x80
0x81
0x82
0x83
0x84
0x85
...
0xBC
0xBD
To operate as a seven-band equalizer, the two first-order IIR filters
are usually configured as one low-pass shelving filter and one
high-pass shelving filter, and the biquad filters are configured as
peak filters.
The first-order IIR filter cutoff frequency and gain are adjustable
using the filter coefficient registers. In addition, the five biquad
filters have adjustable gain, the center frequency for the peak
filters, or cutoff frequency for shelving filters. For a frequency
band that is <200 Hz, the low-pass shelving filter is
recommended instead of a peak filter.
The biquad common peaking filter transfer function for Band 1
through Band 5 is as follows:
The shelving filter transfer function for Band 6 and Band 7 is
H
H
(
(
z
z
)
)
=
=
Bit Name
EQ1_COEF0_HI[15:8]
EQ1_COEF0_LO[7:0]
EQ1_COEF1_HI[15:8]
EQ1_COEF1_LO[7:0]
EQ1_COEF2_HI[15:8]
EQ1_COEF2_LO[7:0]
...
EQ7_COEF2_HI[15:8]
EQ7_COEF2_LO[7:0]
p0
p0
1
1
−
−
+
+
d1
d1
p1
p1
×
×
×
×
z
z
z
−
BIQUAD1
−
z
1
1
−
−
1
1
−
+
d2
p2
×
×
z
z
−
2
−
Descripton
EQ Band 1, Coefficient 0 MSB
EQ Band 1, Coefficient 0 LSB
EQ Band 1, Coefficient 1 MSB
EQ Band 1, Coefficient 1 LSB
EQ Band 1, Coefficient 2 MSB
EQ Band 1, Coefficient 2 LSB
...
EQ Band 7, Coefficient 2 MSB
EQ Band 7, Coefficient 2 LSB
2
BIQUAD2
Figure 112. Seven-Band Equalizer Block Diagram
BIQUAD3
SEVEN-BAND EQUALIZER
Rev. 0 | Page 61 of 296
BIQUAD4
The filter coefficients can be calculated using the previous two
equations or by using the GUI provided. See the Register
Map—EQ Coefficients section for register addresses.
Register 0xBE and Register 0xBF are used for EQ control. The
EQ_FORMAT bit (Register 0xBE, Bit 2) defines the coefficient
bit format. The default setting is 0, and the corresponding format
is Q3.13. In this default mode, the supported coefficients range
from −4 ~ +4. For equalization, this range means that the cutoff/
center frequencies can vary from 40 Hz to 12 kHz when the input
sampling rate is 48 kHz, and peak gain varies from −18 dB to
+18 dB. When Register 0xBE, Bit 2 = 1, the EQ format changes
to Q4.12 to achieve a larger coefficient range (from −8 ~ +8).
This mode enables larger gain boost or cut range.
On-the-fly coefficient updates are supported. If the filter bank
coefficients are updated in this mode, the EQ_UPD bit (Bit 1,
Register 0xBE) should be set to 1 after the I
finishes. This setting updates the filter coefficients for the filter
desired. The coefficient update procedure takes about 0.05 ms.
The EQ_UPDING bit (Bit 4, Register 0xBE) is a read-only bit
that represents the coefficient update status. This bit should be
read to check the status of the coefficient update process. When
the EQ_UPDING bit is set to 1, the update is in process; when
the EQ_UPDING bit is set to 0, the update is complete.
If the system clock is lost during the updating period, the update
procedure cannot be completed and, in such a case, it is recom-
mended that the EQ_UPD_CLR bit (Bit 3, Register 0xBE) be set
to 1 to cancel the update.
Register 0x80 to Register 0xBD make up the EQ coefficient address.
These addresses are also used by other registers. Therefore, when
the EQ coefficient read/write access is required, the write/read
enable bit, EQ_WR_EN (Register 0xBE, Bit 0), should be set to 1.
Register 0xBF is used for EQ enable/disable control. To save power,
the filter bank can be disabled, and all of the seven bands can be
bypassed. Bit EQEN and Bit EQBP7 to Bit EQBP1 in Register 0xBF
can be used to enable or disable the desired EQ band.
BIQUAD5
ORDER
FIRST-
IIR 1
ORDER
FIRST-
IIR 1
2
C coefficient write
ADAU1373