a
FEATURES
16-Bit Sigma-Delta ADC
64 Oversampling Ratio
Up to 220 kSPS Output Word Rate
Low-Pass, Linear Phase Digital Filter
Inherently Monotonic
On-Chip 2.5 V Voltage Reference
Single Supply +5 V
High Speed Parallel or Serial Interface
16-Bit, 195 kSPS
CMOS, Sigma-Delta ADC
AD7722
FUNCTIONAL BLOCK DIAGRAM
DGND DV
DD
AGND AV
DD
REF1
AD7722
2.5V
REFERENCE
REF2
VIN(+)
VIN(–)
16-BIT A/D CONVERTER
Σ∆
MODULATOR
FIR
FILTER
P/S
CAL
RESET
SYNC
CS
DVAL/RD
CFMT/DRDY
DB0
DB1
DB2
CONTROL
LOGIC
CLOCK
CIRCUITRY
XTAL
CLKIN
UNI
DB15
DB14
DB13
DB12
DB11
DB10
DB9/FSO
GENERAL DESCRIPTION
The AD7722 is a complete low power, 16-bit, sigma-delta
ADC. The part operates from a +5 V supply and accepts a
differential input voltage range of 0 V to +2.5 V or
±
1.25 V
centered around a common-mode bias. The AD7722 provides
16-bit performance for input bandwidths up to 90.625 kHz.
The part provides data at an output word rate of 195.3 kHz.
The analog input is continuously sampled by an analog modula-
tor eliminating the need for external sample-and-hold circuitry.
The modulator output is processed by two Finite Impulse
Response (FIR) digital filters in series. The on-chip filtering
reduces the external antialias requirements to first order, in
most cases. The group delay for the filter is 215.5
µs,
while the
settling time for a step input is 431
µs.
The sample rate, filter
corner frequency, and output word rate are set by an external
clock that is nominally 12.5 MHz.
Use of a single bit DAC in the modulator guarantees excellent
linearity and dc accuracy. Endpoint accuracy is ensured by on-
chip calibration. This calibration procedure minimizes the zero-
scale and full-scale errors.
DB3/
TSI
DB4/ DB5/ DB6/ DB7/ DB8/
DOE SFMT FSI SCO SDO
Conversion data is provided at the output register through a
flexible serial port or a parallel port. This offers 3-wire, high
speed interfacing to digital signal processors. The serial interface
operates in an internal clocking (master) mode, whereby an
internal serial data clock and framing pulse are device outputs.
Additionally, two AD7722s can be configured with the serial
data outputs connected together. Each converter alternately
transmits its conversion data on a shared serial data line.
The part provides an accurate on-chip 2.5 V reference. A
reference input/output function is provided to allow either the
internal reference or an external system reference to be used as
the reference source for the part.
The AD7722 is available in a 44-pin PQFP package and is
specified over the industrial temperature range from –40°C to
+85°C.
REV. 0
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: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1996
AD [ ANALOG DEVICES ]
