DSPIC33FJ32GP302THSLASHSP datasheet(265/403 Pages) MICROCHIP

265 / 403 page

 2009 Microchip Technology Inc.

Preliminary

DS70292D-page 265

dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/X04

22.0

AUDIO DIGITAL-TO-ANALOG

CONVERTER (DAC)

The Audio Digital-to-Analog Converter (DAC) module

is a 16-bit Delta-Sigma signal converter designed for

audio applications. It has two output channels, left and

right to support stereo applications. Each DAC output

channel provides three voltage outputs, positive DAC

output, negative DAC output, and the midpoint voltage

output

for

the

dsPIC33FJ64GP804

and

dsPIC33FJ128GP804

devices.

The

dsPIC33FJ64GP802

and

dsPIC33FJ128GP802

devices provide positive DAC output and negative DAC

output voltages.

22.1

Key Features

• 16-bit resolution (14-bit accuracy)

• Second-Order Digital Delta-Sigma Modulator

• 256 X Over-Sampling Ratio

• 128-Tap FIR Current-Steering Analog Recon-

struction Filter

• 100 ksps Maximum Sampling Rate

• User controllable Sample Clock

• Input Frequency 45 kHz max

• Differential Analog Outputs

• Signal-To-Noise: 90 dB

• 4-deep input Buffer

• 16-bit Processor I/O, and DMA interfaces

22.2

DAC Module Operation

The functional block diagram of the Audio DAC module

is shown in Figure 22-1. The Audio DAC module pro-

vides a 4-deep data input FIFO buffer for each output

channel. If the DMA module and/or the processor can-

not provide output data in a timely manner, and the

FIFO becomes empty, the DAC accepts data from the

DAC Default Data register (DACDFLT). This safety fea-

ture is useful for industrial control applications where

the DAC output controls an important processor or

machinery. The DACDFLT register should be initialized

with a “safe” output value. Often the safe output value

is either the midpoint value (0x8000) or a zero value

(0x0000).

The digital interpolator up-samples the input signals,

where the over-sampling ratio is 256x which creates

data points between the user supplied data points.

The interpolator also includes processing by digital

filters to provide “noise shaping” to move the

converter noise above 20 kHz (upper limit of the pass

band). The output of the interpolator drives the Sigma-

Delta modulator. The serial data bit stream from the

Sigma-Delta

modulator

processed

the

reconstruction filter. The differential outputs of the

reconstruction filter are amplified by Op Amps to

provide the required peak-to-peak voltage swing.

22.3

DAC Output Format

The DAC output data stream can be in a two’s comple-

ment signed number format or as an unsigned number

format.

The Audio DAC module features the ability to accept

the 16-bit input data in a two’s complement signed

number format or as an unsigned number format.

The data formatting is controlled by the Data Format

Control (FORM<8>) bit in the DAC1CON register.

The supported formats are:

• 1 = Signed (two’s complement)

• 0 = Unsigned

If the FORM bit is configured for “Unsigned data” then

the user input data yields the following behavior:

• 0xFFFF = most positive output voltage

• 0x8000 = mid point output voltage

• 0x7FFF = a value just below the midpoint

• 0x0000 = minimum output voltage

If the FORM bit is configured for “signed data” then the

user input data yields the following behavior:

• 0x7FFF = most positive output voltage

• 0x0000 = mid point output voltage

• 0xFFFF = value just below the midpoint

• 0x8000 = minimum output voltage

The Audio DAC provides an analog output proportional

to the digital input value. The maximum 100,000 sam-

ples per second (100 ksps) update rate provides good

quality audio reproduction.

Note 1: This data sheet summarizes the features

the

dsPIC33FJ32GP302/304,

dsPIC33FJ64GPX02/X04,

and

dsPIC33FJ128GPX02/X04

families

devices. It is not intended to be a compre-

hensive reference source. To comple-

ment the information in this data sheet,

refer to “Section 33. Audio Digital-to-

Analog Converter (DAC)”, (DS70211) of

the “dsPIC33F/PIC24H Family Reference

Manual”, which is available from the

Microchip website (www.microchip.com).

2: Some registers

and

associated bits

described in this section may not be avail-

able on all devices. Refer to Section 4.0

“Memory Organization” in this data

sheet for device-specific register and bit

information.

Note:

The DAC module is designed specifically

for

audio

applications

and

not

recommended

for

control

type

applications.

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