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AD7725
16-Bit 900 kSPS - ADC with a
Programmable Postprocessor
FEATURES
Programmable Filtering:
Any Characteristic up to 108 Tap FIR and/or IIR
Polynomial Signal Conditioning up to 8
th
Order
Programmable Decimation and Output Word Rate
Flexible Programming Modes:
Boot from DSP or External EPROM
Parallel/Serial Interface
Internal Default Filter for Evaluation
14.4 MHz Max Master Clock Frequency
0 V to +4 V (Single-Ended) or 2 V (Differential) Input
Range
Power Supplies: AV
DD
, DV
DD
: 5 V
5%
On-Chip 2.5 V Voltage Reference
44-Lead MQFP Package
TYPICAL APPLICATIONS
Radar
Sonar
Auxiliary Car Functions
Medical Communications
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD7725 is a complete 16-bit, - analog-to-digital con-
verter with on-chip, user-programmable signal conditioning. The
output of the modulator is processed by three cascaded finite
impulse response (FIR) filters, followed by a fully user-program-
mable postprocessor. The postprocessor provides processing
power of up to 130 million accumulates (MAC) per second. The
user has complete control over the filter response, the filter coeffi-
cients, and the decimation ratio.
The postprocessor permits the signal conditioning characteris-
tics
to be programmed through a parallel or serial interface.
It
is programmed by loading a user-defined filter in the form of a
configuration file. This filter can be loaded from a DSP or an
external serial EPROM. It is generated using a digital filter
design package called Filter Wizard, which is available from the
AD7725 section on the Analog
Devices
website.
Filter Wizard allows the user
t
o design different filter types
and generates the appropriate
configuration file to be down-
loaded to the postprocessor. The
AD7725 also has an internal
default filter for evaluation purposes.
It provides 16-bit performance for input bandwidths up to
350 kHz with an output word rate of 900 kHz maximum. The
input sample rate is set either by the crystal oscillator or an
external clock.
This part has an accurate on-chip 2.5 V reference for the modu-
lator. A reference input/output function allows either the
internal reference or an external system reference to be used as
the reference source for the modulator.
The device is available in a 44-lead MQFP package and is speci-
fied over a –40°C to +85°C temperature range.
2.5V
REFERENCE
POST-
PROCESSOR
DEFAULT FILTER
(ROM)
XTAL
CLOCK
PRESET
FILTER
MOD
CONTROL
LOGIC
UNI
HALF
PWR
STBY
SYNC
S/P
V
IN
(+)
V
IN
(–)
RD/WR
SOE/CS
CFMT/RS
DVAL/INT
SDI/DB0
ERR/DB1
DB2
DB3
RESETCFG/DB4
INT/DB5
FSI/DB6
SCO/DB7
SDO/DB8
SCR/DB13
CFGEND/DB12
DB11
DB10
FSO/DB9
SMODE1/DB15
SMODE0/DB14
XTAL_OFF
XTAL
CLKIN
DV
DD
DGND
REF2
REF1
AV
DD
AGND
AD7725
页面指南
