AD1954 Analog Devices, AD1954 Datasheet - Page 33

• Manufacturer Part Number: AD1954
• Description: SigmaDSP Digital Audio Processor
• Manufacturer: Analog Devices

The AD1954 should be used with an external third-order filter
on each output channel. The circuit shown in Figure 21 combines
a third-order filter and a single-ended-to-differential converter
in the same circuit. The values used in the main channel are for
a 100 kHz Bessel filter, and those used in the subwoofer channel
(Figure 22) result in a 10 kHz Bessel filter. The lower frequency
filter is used on the subwoofer output because there is no digital
interpolation filter used in the subwoofer signal-path. When
calculating the resistor values for the filter, it is important to
take into account the output resistance of the AD1954, which is
nominally 60 Ω. For best distortion performance, 1% resistors
should be used. The reason for this is that the single-ended
performance of the AD1954 is about 80 dB. The degree to
which the single-ended distortion cancels in the final output is
determined by the common-mode rejection of the external
analog filter, which in turn depends on the tolerance of the
components used in the filter.
The SUB output of the AD1954 has a lower drive strength than
the left and right output pins (± 0.25 mA peak versus ± 0.5 mA
peak for the left and right outputs). For this reason, it is best to
use higher resistor values in the external SUB filter.
For best performance, a large (> 10 µf) capacitor should be
connected between the FILTCAP pin and analog ground. This
pin is connected to an internal node in the bias generator, and
by adding an external capacitance to this pin, the thermal noise
of the left/right channels is minimized. The SUB channel is not
affected by this connection.
PRELIMINARY TECHNICAL DATA
– INPUT
+ INPUT
– INPUT
+ INPUT
5.62k
11k
270nF
560nF
2.80k
806
5.62k
2.7nF
3.7k
NPO
NPO
1nF
1.50k
1.00k
3.01k
3.01k
27nF
56nF
499
1.5k
6.8nF
15nF
270pF
NPO
820pF
NPO
6.8nF
150pF
220nF
604
549
2.2nF
AD1954
2.2nF
OUT
OUT