Low Cost SamplePort®
16-Bit Stereo Asynchronous
Sample Rate Converter
a
AD1893
SYSTEM DIAGRAM
FEATURES
Low Cost
LQFP and PDIP Packages
3 V Supply Performance Specified—Very Low Power
Automatically Senses Sample Frequencies—No
Programming Required
Rejects Sample Clock Jitter
Accommodates Dynamically Changing Asynchronous
Sample Clocks
8 kHz to 56 kHz Sample Clock Frequency Range
Approximately 1:2 to 2:1 Ratio Between Sample
Clocks
EXAMPLE
FREQUENCIES:
DAT 48kHz OR
CD 44.1kHz OR
BROADCAST 32kHz
EXAMPLE
FREQUENCIES:
DAT 48kHz OR
CD 44.1kHz OR
BROADCAST 32kHz
AD1893
OUTPUT SAMPLE CLOCK
OUTPUT SERIAL DATA
INPUT SAMPLE CLOCK
INPUT SERIAL DATA
–96 dB THD+N at 1 kHz
96 dB Dynamic Range
Optimal Clock Tracking Control—Slow/Fast Settling
Modes
Linear Phase in All Modes
Automatic Output Mute
Flexible Four-Wire Serial Interfaces with Right-Justified
Mode
The AD1893 uses multirate digital signal processing techniques
to construct an output sample stream from the input sample
stream. The input word width is 4 to 16 bits for the AD1893.
Shorter input words are automatically zero-filled in the LSBs.
The output word width is 24 bits. The user can receive as many
of the output bits as desired. Internal arithmetic is performed
with 22-bit coefficients and 27-bit accumulation. The digital
samples are processed with unity gain.
Power-Down Mode
On-Chip Oscillator
The input and output control signals allow for considerable
flexibility for interfacing to a variety of DSP chips, AES/EBU
receivers and transmitters and for I2S compatible devices. Input
and output data can be independently right- or left- (with or
without a one bit clock delay) justified to the left/right clock
edge. In the right-justified mode, the MSB is delayed 16-bit
clock periods from the left/right clock edge transition. Input and
output data can also be independently justified to the word
clock rising edge. The data justification options are encoded on
two mode pins for both the input port and the output port. The
bit clocks can also be independently configured for rising edge
active or falling edge active operation.
APPLICATIONS
Consumer CD-R, DAT, DCC, MD and 8 mm Video Tape
Recorders Including Portables
Digital Audio Communication/Network Systems
Computer Multimedia Systems
PRODUCT OVERVIEW
The AD1893 SamplePort is a fully digital, stereo Asynchronous
Sample Rate Converter (ASRC) that solves sample rate interfacing
and compatibility problems in digital audio equipment. Concep-
tually, this converter interpolates the input data up to a very high
internal sample rate with a time resolution of 300 ps, then deci-
mates down to the desired output sample rate. The AD1893 is
intended for 16-bit low cost, non-varispeed applications where low
voltage, low power (i.e., battery-powered) operation is required.
Refer to the AD1890/AD1891 data sheet for other products in the
SamplePort family. This device is asynchronous because the fre-
quency and phase relationships between the input and output
sample clocks (both are inputs to the AD1893 ASRC) are arbitrary
and need not be related by a simple integer ratio. There is no need
to explicitly select or program the input and output sample clock
frequencies, as the AD1893 automatically senses the relationship
between the two clocks. The input and output sample clock fre-
quencies can nominally range from 8 kHz to 56 kHz, and the ratio
between them can vary from approximately 1:2 to 2:1.
The AD1893 SamplePort ASRC has on-chip digital coefficients
that correspond to a highly oversampled 0 Hz to 20 kHz low-
pass filter with a flat passband, a very narrow transition band,
and a high degree of stopband attenuation. A subset of these
filter coefficients are dynamically chosen on the basis of the
filtered ratio between the input sample clock (LR_I) and the
output sample clock (LR_O), and these coefficients are then
used in an FIR convolver to perform the sample rate conversion.
Refer to the Theory of Operation section of this data sheet for a
more thorough functional description. The low-pass filter has
been designed so that full 20 kHz bandwidth is maintained
when the input and output sample clock frequencies are as low
as 44.1 kHz. If the output sample rate drops below the input
sample rate, the bandwidth of the input signal is automatically
(continued on Page 4)
SamplePort is a registered trademark of Analog Devices, Inc.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 1998
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