dspic33fj128mc204 Microchip Technology Inc., dspic33fj128mc204 Datasheet - Page 285

• Manufacturer Part Number: dspic33fj128mc204
• Description: High-performance, 16-bit Digital Signal Controllers
• Manufacturer: Microchip Technology Inc.

23.0
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
dsPIC33FJ128MC804
dsPIC33FJ64MC802
devices provide positive DAC output and negative DAC
output voltages. The positive and negative DAC
outputs are differential about a midpoint voltage of
approximately 0.884 volts to drive the speakers with a
Bridge-Tied Load (BTL) configuration.
23.1
• 16-bit resolution (14-bit accuracy)
• Second-Order Digital Delta-Sigma Modulator
• 256 X Over-Sampling Ratio
• 128-Tap FIR Current-Steering Analog
• 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
23.2
The functional block diagram of the Audio DAC module
is shown in Figure 23-1. The Audio DAC module
provides a 4-deep data input FIFO buffer for each
output channel. If the DMA module and/or the
processor cannot 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 feature is useful for industrial
control applications where the DAC output controls an
important processor or machinery. The DACDFLT
© 2009 Microchip Technology Inc.
Note:
Reconstruction Filter
AUDIO DIGITAL-TO-ANALOG
CONVERTER (DAC)
KEY FEATURES
DAC Module Operation
for
This data sheet summarizes the features
of
dsPIC33FJ64MCX02/X04,
dsPIC33FJ128MCX02/X04
devices. It is not intended to be a
comprehensive
complement the information in this data
sheet, refer to the dsPIC33F Family
Reference Manual, Section 33. “Audio
Digital-to-Analog
(DS70211), which is available from the
Microchip website (www.microchip.com).
the
the
and
dsPIC33FJ64MC804
dsPIC33FJ32MC302/304,
reference
dsPIC33FJ128MC802
devices.
Converter
families
source.
(DAC)”
and
The
and
Preliminary
To
of
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
reconstruction filter. The differential outputs of the
reconstruction filter are amplified by Op Amps to
provide the required 2 volts peak-to-peak voltage
swing into a 1 kOhm load.
23.3
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 (100ksps) update rate provides good
quality audio reproduction.
DAC Output Format
modulator
is
processed
DS70291C-page 283
by
the