Datasheet


SLES014B − OCTOBER 2001 − REVISED AUGUST 2002
21
www.ti.com
APPLICATION INFORMATION
D/A output filter circuits
Delta-sigma D/A converters utilize noise shaping techniques to improve in-band signal-to-noise ratio (SNR)
performance at the expense of generating increased out-of-band noise above the Nyquist frequency, or f
S
/2.
The out-of-band noise must be low-pass filtered in order to provide optimal converter performance. This is
accomplished by a combination of on-chip and external low-pass filtering.
Figure 30 and Figure 31 show the recommended external low-pass active filter circuits for dual- and
single-supply applications. These circuits are 2nd-order Butterworth filters using the multiple feedback (MFB)
circuit arrangement, which reduces sensitivity to passive component variations over frequency and
temperature. For more information regarding MFB active filter design, see your local Texas Instruments sales
office.
Because the overall system performance is defined by the quality of the D/A converters and their associated
analog output circuitry, high-quality audio op amps are recommended for the active filters. Texas Instruments’
OPA2134 and OPA2353 dual op amps are shown in Figure 30 and Figure 31, and are recommended for use
with the PCM1606.
2
3
1
OPA2134
−
+
V
OUT
R
4
C
2
C
1
R
3
R
2
R
1
V
IN
A
V
[*
R
2
R
1
Figure 30. Dual-Supply Filter Circuit
2
3
1
OPA2134
−
+
V
OUT
R
4
C
2
C
1
R
3
R
2
R
1
V
IN
A
V
[*
R
2
R
1
OPA337
−
+
PCM1606
V
COM
C
2
10 µF
+
To Additional
Low-Pass Filter
Circuits
Figure 31. Single-Supply Filter Circuit