Datasheet

PCM1741
15
SBAS175
ANALOG OUTPUTS
The PCM1741 includes two independent output channels:
V
OUT
L and V
OUT
R. These are unbalanced outputs, each capable
of driving 2.05Vp-p typical into a 5kΩ AC-coupled load. The
internal output amplifiers for V
OUT
L and V
OUT
R are biased to the
DC common-mode (or bipolar zero) voltage, equal to V
CC
/2.
The output amplifiers include an RC continuous-time filter that
helps to reduce the out-of-band noise energy present at the
DAC outputs, due to the noise shaping characteristics of the
PCM1741’s delta-sigma DACs. The frequency response of this
filter is shown in Figure 8. By itself, this filter is not enough to
attenuate the out-of-band noise to an acceptable level for many
applications, therefore, an external low-pass filter is required to
provide sufficient out-of-band noise rejection. Further discus-
sion of DAC post-filter circuits is provided in the Applications
Information section of this data sheet.
V
COM
OUTPUT
One unbuffered common-mode voltage output pin, V
COM
(pin 10), is brought out for decoupling purposes. This pin is
FIGURE 8. Output Filter Frequency Response.
0.1 1 10 100 1K 10K
0
–10
–20
–30
–40
–50
–60
Response (dB)
Frequency (kHz)
ANALOG FILTER PERFORMANCE
(100Hz-10MHz)
nominally biased to a DC voltage level equal to V
CC
/2. This
pin may be used to bias external circuits. Figure 9 shows an
example of using the V
COM
pin for external biasing applica-
tions.
FIGURE 9. Biasing External Circuits Using the V
COM
Pin.
R
1
R
3
R
2
C
1
C
2
V
CC
10µF
(a) Using V
COM
to Bias a Single-Supply Filter Stage
(b) Using a Voltage Follower to Buffer V
COM
when Biasing Multiple Nodes
x = L or R
10µF
Filtered
Output
OPA342
2
3
1
A
V
= –1, where A
V
= –
R
2
R
1
V
OUT
x
V
COM
V
COM
PCM1741
+
+
Buffered
V
COM
V
CC
+
1/2
OPA2342
10µF
PCM1741