MSP58C20

AUDIO-BAND CONVERTER

SPSS015B – DECEMBER 1993 – REVISED JULY 1996

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POST OFFICE BOX 655303

Audio-Band Signal-Processing

Applications

Modulator

Smoothing Filters

Symmetrical Analog Data Paths

Common-Mode Bias Voltage Generation

description

The MSP58C20 is the analog portion of an audio-band sigma-delta analog-to-digital and digital-to-analog

converter and is a companion part to the MSP58C80. The MSP58C20 is designed to operate only with the

MSP58C80, which contains the digital portion of the audio-band converter. The circuit consists of three main

blocks: the analog-to-digital converter (ADC), the digital-to-analog converter (DAC), and internal reference and

bias voltages.

The analog-to-digital conversion chain consists of a continuous-time antialiasing stage, an analog oversampled

modulator, and the modulator bias voltage. The antialiasing stage is a second-order low-pass filter with a cutoff

frequency of typically 190 kHz. The modulator is a sigma-delta feedback loop, which oversamples the signal

at 1.024 MHz and provides second-order noise shaping. It performs the conversion of the differential analog

input signal to a pulse-density-modulated single-bit digital output (ADOUT). When a maximum positive

differential input voltage (i.e., a maximum positive voltage difference of AIP – AIM) is applied at the AIP and AIM

inputs, the resulting code at the ADOUT output is all ones.

The digital-to-analog conversion chain consists of a fast DAC, an analog low-pass filter, and the filter’s bias

voltage. The two input bits (DIGS and DIGL), sampled at 0.512 MHz from a digital modulator on the MSP58C80,

are the inputs of the DAC conversion chain. Based on the values for DIGS (the sign bit) and DIGL (the level bit),

the following table shows the DAC voltage steps that are produced.

DIGS

DIGL

DAC VOLTAGE STEPS

L

L

–1

× Vref

L

H

–2

× Vref

H

L

+1

× Vref

H

H

+2

× Vref

When DIGS = L, the AOM analog output has a more positive voltage than AOP. When DIGL = H, the absolute

value of the voltage difference between AOP and AOM is greater than when DIGL = L. A band-gap voltage

source is used to produce the DAC and ADC reference voltages. These two references are different to avoid

crosstalk between the two converters.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

Copyright

© 1996, Texas Instruments Incorporated

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

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NC

AIP

AIM

PWAD

PWDA

ADOUT

NC

NC

NC

NC

AOP

AOM

DIGS

DIGL

ADCLK

NC

NC

DW PACKAGE

(TOP VIEW)

NC – No internal connection