AD1847JP Analog Devices Inc, AD1847JP Datasheet - Page 23

• Manufacturer Part Number: AD1847JP
• Manufacturer: Analog Devices Inc

Specifications of AD1847JP

• Single Supply Voltage (typ): 5V
• Single Supply Voltage (min): 4.75V
• Single Supply Voltage (max): 5.25V
• Package Type: PLCC
• Lead Free Status / RoHS Status: Not Compliant

REV. B
DATA FORMAT DEFINITIONS
There are four data formats supported by the AD1847: 16-bit
signed, 8-bit unsigned, 8-bit companded -law, and 8-bit com-
panded A-law. The AD1847 supports these four formats because
each of them have found wide use in important applications.
16-Bit Signed Format
The 16-bit signed format (also called 16-bit twos-complement)
is the standard method of representing 16-bit digital audio. This
format yields 96 dB of dynamic range and is common in con-
sumer compact disk audio players. This format uses the value
– 32768 (8000h) to represent minimum analog amplitude while
32767 (7FFFh) represents maximum analog amplitude. Inter-
mediate values are a linear interpolation between minimum and
maximum amplitude values.
8-Bit Unsigned Format
The 8-bit unsigned format is commonly used in the personal
computer industry. This format delivers 48 dB of dynamic
range. The value 0 (00h) is used to represent minimum analog
amplitude while 255 (FFh) is used to represent maximum ana-
log amplitude. Intermediate values are a linear interpolation be-
tween minimum and maximum amplitude values. The least
significant byte of the 16-bit internal data is truncated to create
the 8-bit output samples.
MAX
MAX
MIN
MIN
00h
8000h
Figure 12. 8-Bit Unsigned Format
Figure 11. 16-Bit Signed Format
DIGITAL VALUE
DIGITAL VALUE
0000h
7Fh
7FFFh
FFh
–23–
8-Bit Companded Formats
The 8-bit companded formats ( -law and A-law) are used in the
telecommunications industry. Both of these formats are used in
ISDN communications and workstations; -law is the standard
for the United States and Japan while A-law is used in Europe.
Companded audio allows either 64 dB or 72 dB of dynamic
range using only 8-bits per sample. This is accomplished using a
nonlinear formula which assigns more digital codes to lower am-
plitude analog signals at the expense of resolution of higher am-
plitude signals. The -law format of the AD1847 conforms to
the Bell System = 255 companding law while the A-law format
conforms to CCITT “A” law models. Figure 13 shows approxi-
mately how both the -law and A-law companding schemes be-
have. Refer to the standards mentioned above for an exact
definition.
APPLICATIONS CIRCUITS
The AD1847 Stereo Codec has been designed to require a mini-
mum of external circuitry. The recommended circuits are shown
in Figures 14 through 22. Analog Devices estimates that the to-
tal cost of all the components shown in these Figures, including
crystals, to be less than $3 in 10,000 quantities.
Industry-standard compact disc “line-levels” are 2 V
around analog ground. (For other audio equipment, “line level”
is much more loosely defined.) The AD1847 SoundPort is a
+5 V only powered device. Line level voltage swings for the
AD1847 are defined to be 1 V
0.707 V
log signals must be attenuated and either centered around the
reference voltage intermediate between 0 V and +5 V or
ac-coupled. The V
nominally 2.25 V. It has limited drive but can be used as a volt-
age datum to an op amp input. Note, however, that dc-coupled
inputs are not recommended, as they provide no performance
benefits with the AD1847 architecture. Furthermore, dc offset
differences between multiple dc-coupled inputs create the po-
tential for “clicks” when changing the input mux selection.
MAX
MIN
rms
00h
2Ah
for a sine wave DAC output. Thus, 2 V
Figure 13. 8-Bit Companded Format
REF
pin will be at this intermediate voltage,
DIGITAL VALUE
FFh
D5h
rms
for a sine wave ADC input and
AD1847
rms
AAh
80h
rms
input ana-
centered
µ-law
A-law