ADSP-21MSP58BST-104 데이터 시트보기 (PDF) - Analog Devices

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ADSP-21MSP58BST-104

DSP Microcomputers

Analog Devices 

ADSP-21msp58/59

Analog Signal Output

The differential analog output (VOUTP, VOUTN) is produced

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 kΩ (RL ≥ 2 kΩ) 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 kΩ,

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 (COUT) is op-

tional; if used, its value can be chosen as follows:

COUT

=

(60

1

π) RL

COUT

VOUTP

RL

COUT

ADSP-21msp58/59

VOUTN

Figure 11. Example Circuit for Differential Output with

AC Coupling

The VOUTP and VOUTN outputs must be used as differential

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.

VOUT

+12V

0.1µF

7

5

1

4

GNDA

GNDA

SSM2141

0.1µF

–12V

GNDA

ADSP-21msp58/59

VOUTP

VOUTN

Figure 12. Example Circuit for Single-Ended Output

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.

10µF

VREF

REF_FILTER

0.1µF

BUF

VOLTAGE

REFERENCE

ADSP-21msp58/59

STAR

GROUND

Figure 13. Voltage Reference Filter Capacitor

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 ± nfb where

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, ∂φ(ω)/∂ω. Group delay is a measure

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.

–20–

REV. 0

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