8 Analog Interface
8 – 18
8.5.2
Analog Signal Output
The ADSP-21msp58/59’s differential analog output (VOUT
P
– VOUT
N
) is
produced by an on-chip differential amplifier. The differential amplifier
will meet dynamic specifications for loads greater than 2 k
Ω
(R
L
≥
2 k
Ω
)
and has a maximum differential output voltage swing of
±
3.156 V peak-to-
peak (3.17 dBm0). The DAC will drive loads smaller than 2 k
Ω
, but with
degraded dynamic performance. The differential output can can be
ac-coupled directly to a load or dc-coupled to an external amplifier.
Figure 8.7 shows a simple circuit providing a differential output with ac
coupling. The capacitor of this circuit (C
OUT
) is optional; if used, its value
can be chosen as follows:
C
OUT
=
The VOUT
P
– VOUT
N
outputs must be used as differential outputs; do not
use either as a single-ended output. Figure 8.8 shows an example circuit
which can be used to convert the differential output to a single-ended
output. The circuit uses a differential-to-single-ended amplifier, the
Analog Devices SSM-2141.
1
60
π
R
L
Figure 8.7 Example Circuit For Differential Output With AC Coupling
C
OUT
VOUT
P
VOUT
N
R
L
ADSP-21msp5x
C
OUT