a
FEATURES
12.5 MHz Master Clock Frequency
0 V to +2.5 V or 1.25 V Input Range
Single Bit Output Stream
90 dB Dynamic Range
Power Supplies: AVDD, DVDD: +5 V 5%
On-Chip 2.5 V Voltage Reference
28-Lead TSSOP
CMOS Sigma-Delta Modulator
AD7720
FUNCTIONAL BLOCK DIAGRAM
AVDD
AGND
DVDD
DGND
REF1
AD7720
2.5V
REFERENCE
REF2
VIN(+)
VIN(–)
SIGMA-DELTA
MODULATOR
DATA
SCLK
MZERO
GC
CLOCK
CIRCUITRY
XTAL1/MCLK
XTAL2
BIP
CONTROL
LOGIC
DVAL
RESETO
RESET
STBY
GENERAL DESCRIPTION
This device is a 7th order sigma-delta modulator that converts
the analog input signal into a high speed 1-bit data stream. The
part operates from a +5 V supply and accepts a differential input
range of 0 V to +2.5 V or
±
1.25 V centered about a common-
mode bias. The analog input is continuously sampled by the
analog modulator, eliminating the need for external sample and
hold circuitry. The input information is contained in the output
stream as a density of ones. The original information can be
reconstructed with an appropriate digital filter.
The part provides an accurate on-chip 2.5 V reference. A refer-
ence input/output function is provided to allow either the inter-
nal reference or an external system reference to be used as the
reference source for the part.
The device is offered in a 28-lead TSSOP package and designed
to operate 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: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1997
AD [ ANALOG DEVICES ]
