GENERAL DESCRIPTION
(continued from page 1) An extensive SPI port allows click-free parameter updates, along
with read-back capability from any point in the algorithm flow.
The AD1954 contains a program RAM that boots from an internal
program ROM on power-up. Signal processing parameters are
stored in a 256-location parameter RAM, which is initialized on
power-up by an internal boot ROM. New values are written to
the parameter RAM using the SPI port.The values stored in the
parameter RAM control the IIR equalization filters, the dual-
band compressor/limiter, the delay values, and the settings of the
stereo spreading algorithm.
The AD1954 includes ADI’s patented multibit -
DAC architec-
ture.This architecture provides 112 dB SNR and dynamic range
andTHD+N of –100 dB.These specifications allow the AD1954
to be used in applications ranging from low-end boom boxes to
high-end professional mixing/editing systems.
The AD1954 has a very sophisticated SPI port that supports
complete read/write capability of both the program and the para-
meter RAM.Two control registers are also provided to control
the chip serial modes and various other optional features. Hand-
shaking is also included for ease of memory uploads/downloads.
The AD1954 also has a digital output that allows it to be used
purely as a DSP.This digital output can also be used to drive an
external DAC to extend the number of channels beyond the three
that are provided on the chip.
This chip can be used with either its default signal processing
program or with a custom user-designed program. Graphical pro-
gramming tools are available from ADI for custom programming.
The AD1954 contains four independent data capture circuits,
which can be programmed to tap the signal flow of the processor
at any point in the DSP algorithm flow.These captured signals
can be accessed either through a separate serial out pin (i.e., that
can be connected to an external DAC or DSP) or by reading from
the data capture SPI registers.This allows the basic functionality
of the AD1954 to be easily extended.
The AD1954 is comprised of a 26-bit DSP (48 bits with double
precision) for interpolation and audio processing, three multibit
-
modulators, and analog output drive circuitry. Other features
include an on-chip parameter RAM that uses a safe-upload feature
for transparent and simultaneous updates of filter coefficients and
digital de-emphasis filters. Also, on-chip input selectors allow up
to three sources of serial data and master clock to be selected.
The 3-channel configuration is especially useful for 2.1 playback
systems that include two satellite speakers and a subwoofer.
The default program allows for independent equalization and
compression/limiting for the satellite and subwoofer outputs.
Figure 1 shows the block diagram of the device.
The processor core in the AD1954 has been designed from the
ground up for straightforward coding of sophisticated compres-
sion/limiting algorithms.The AD1954 contains two independent
compressor/limiters with rms based amplitude detection and
attack/hold/release controls, together with an arbitrary compression
curve that is loaded by the user into a look-up table that resides
in the parameter RAM.The compressor also features look-ahead
compression that prevents compressor overshoots.
VREF
ZEROFLAG
RESETB
MUTE DE-EMPHASIS
DVDD
AVDD
3
ODVDD
VOLTAGE
3
DATA MEMORY, 512 26
REFERENCE
3
DAC – L
DAC – R
3:1
SERIAL DATA I/O
GROUP
3
3
AUDIO
SERIAL
IN
ANALOG
OUTPUTS
26 22
DSP CORE
DATA
MUX
1
1
2
DAC – SW
AUX SERIAL
DATA INPUT
DATA FORMAT:
3.23 (SINGLE PRECISION)
ANALOG
BIAS GROUP
BIAS
3.45 (DOUBLE PRECISION)
MCLK
GENERATOR
(256 fS/512 fS IN)
256 fS/512 fS OUT
MASTER
CLOCK I/O
GROUP
3:1
1
MCLK
1
MUX
CONTROL
COEFFICIENT
ROM
64 22
PROGRAM
RAM
512 35
PARAMETER
RAM
256 22
REGISTERS
SPI I/O
GROUP
TRAP REG.
SPI PORT
FILTCAP
3
2
(I S, SPI)
SAFELOAD
REGISTERS
DCSOUT
MEMORY CONTROLLERS
DCSOUTTRAP
AGND
3
DGND
2
NOTES
1
CONTROLLEDTHROUGH SPI CONTROL REGISTERS.
2
DAC DOES NOT USE DIGITAL INTERPOLATION.
Figure 1. Block Diagram
REV. A
ADI [ ADI ]
