adsp-21msp58 Analog Devices, Inc., adsp-21msp58 Datasheet - Page 20

• Manufacturer Part Number: adsp-21msp58
• Description: Dsp Microcomputers
• Manufacturer: Analog Devices, Inc.

ADSP-21msp58/59
Analog Signal Output
The differential analog output (VOUT
by an on-chip differential amplifier which is part of the processor’s
analog interface. The differential amplifier will meet dynamic
specifications for loads greater than 2 k (R
maximum differential output voltage swing of 3.156 V peak-to-
peak (3.17 dBm0). The DAC will drive loads smaller than 2 k ,
but with degraded dynamic performance. The differential out-
put can be ac-coupled directly to a load or dc-coupled to an ex-
ternal amplifier.
Figure 11 shows a simple circuit providing a differential output
with ac coupling. The capacitor of this circuit (C
tional; if used, its value can be chosen as follows:
The VOUT
outputs (do not use either as a single-ended output). Figure 12
shows an example circuit which can be used to convert the dif-
ferential output to a single-ended output. The circuit uses a dif-
ferential-to-single-ended amplifier, the Analog Devices SSM2141.
Voltage Reference Filter Capacitance
Figure 13 shows the recommended reference filter capacitor
connections. The capacitor grounds should be connected to the
same star ground point shown in Figure 10.
Figure 11. Example Circuit for Differential Output with
AC Coupling
10µF
Figure 12. Example Circuit for Single-Ended Output
V
OUT
Figure 13. Voltage Reference Filter Capacitor
GROUND
R
L
STAR
P
and VOUT
GND
5
1
+12V
–12V
A
7
4
C
C
OUT
OUT
0.1µF
0.1µF
0.1µF
SSM2141
C
REF_FILTER
OUT
GND
GND
N
outputs must be used as differential
VOUT
VOUT
A
A
V
REF
ADSP-21msp58/59
P
N
(60 ) R
VOUT
VOUT
ADSP-21msp58/59
1
P
N
BUF
ADSP-21msp58/59
P
, VOUT
L
L
REFERENCE
2 k ) and has a
N
VOLTAGE
OUT
) is produced
) is op-
–20–
APPLICATION EXAMPLES
The ADSP-21msp58/59 is ideal for speech processing applica-
tions where high performance for analog and digital circuitry is
required, but board space is severely limited. The cellular radio
handset is one application. Here the ADSP-21msp58/59 can
digitize the speech, then perform compression algorithms that
sufficiently reduce the bit rate for transmission in a limited radio
bandwidth.
DEFINITION OF SPECIFICATIONS
Absolute Gain
Absolute gain is a measure of converter gain for a known signal.
Absolute gain is measured with a 1.0 kHz sine wave at 0 dBm0.
The absolute gain specification is used as a reference for the
gain tracking error specification.
Gain Tracking Error
Gain tracking error measures changes in converter output for
different signal levels relative to an absolute signal level. The
absolute signal level is 1.0 kHz at 0 dBm0. Gain tracking error
at 0 dBm0 is 0 dB by definition.
SNR + THD
Signal-to-noise ratio plus total harmonic distortion is defined to
be the ratio of the rms value of the measured input signal to the
rms sum of all other spectral components in the frequency range
300 Hz–3400 Hz, including harmonics but excluding dc.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities will create distortion
products at sum and difference frequencies of mfa
m, n = 0, 1, 2, 3, etc. Intermodulation terms are those which
neither m nor n are equal to zero. The second order terms in-
clude (fa + fb) and (fa – fb), while the third order terms include
(2fa + fb), (2fa – fb), (fa + 2fb), and (fa – 2fb).
Idle Channel Noise
Idle channel noise is defined as the total signal energy measured
at the output of the device when the input is grounded (mea-
sured in the frequency range 300 Hz–3400 Hz).
Crosstalk
Crosstalk is defined as the ratio of the rms value of a full-scale
signal appearing on one channel to the rms value of the same
signal that couples onto the adjacent channel. Crosstalk is ex-
pressed in dB.
Power Supply Rejection
Power supply rejection measures the susceptibility of a device to
a signal on the power supply. Power supply rejection is mea-
sured by modulating a signal on the power supply and measur-
ing the signal at the output (relative to 0 dB). Power supply
rejection is defined as the ratio of the rms value of the modula-
tion signal to the rms value of the same signal in the ADC/DAC
channel.
Group Delay
Group delay is defined as the derivative of radian phase with re-
spect to radian frequency,
of the average delay of a system as a function of frequency. A
linear system with a constant group delay has a linear phase re-
sponse. The deviation of group delay away from a constant indi-
cates the degree of nonlinear phase response of the system.
( )/
. Group delay is a measure
nfb where
REV. 0