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Family of sigma-delta ADCs offers optimal combination of low noise, low power

Analog Devices today introduced a new family of
sigma-delta analog-to-digital converters (ADCs) that deliver an unprecedented low-noise and low-power solution for applications in industrial and medical instrumentation markets. Unlike traditional precision data-converter solutions, which compromise on either power
or noise, the new ADCs feature both low noise (40 nVrms) and low power
(400 uA), while offering a complete range of analog functions in less
board area. This combination of features is ideal for applications
where noise performance is critical, such as industrial process
control and weigh scales, and space-constrained, low-power
applications, such as portable instrumentation and medical equipment.

Best Balance of Noise and Power in its Class
The AD779x family of analog-to-digital converters, which include the
AD7792 (16-bit), AD7793 (24-bit), AD7794 (24-bit), AD7798 (16-bit) and
AD7799 (24-bit), outperform comparable solutions–which trade low
power for noise or vice versa–by delivering both low noise and low
power. Operating with a 2.7-V to 5.25-V power supply, these converters
consume only 400 uA. With noise of only 40 nVrms, they enable more
accurate measurements in power-sensitive applications. The output data
rate from the devices is software programmable and can be varied from
4 Hz to 500 Hz. At 16.6 Hz they offer simultaneous rejection of 50 Hz
and 60 Hz signals.

Highly-integrated Solution Eases Instrumentation Design
In addition to these performance advantages, the devices provide all
of the functionality required for instrumentation applications,
reducing design work and eliminating many external components. The
AD779x data-converters include a high performance sigma-delta ADC,
low-noise instrumentation programmable gain amplifier (PGA),
multiplexer, current sources, clock, calibration registers, SPI
interface, and a precision low-noise, low-drift reference (except the
AD7798 and AD7799, which use an external reference for ratiometric
measurements). Designers have the flexibility to turn off the internal
reference, and use an external reference instead.

The PGA, multiplexer, excitation current sources, and input bias
voltages allow the AD779x family to connect directly to sensors in
myriad applications including PLC/DCS analog I/O measurement;
temperature measurement using thermocouples, RTDs or thermistors;
weigh scales; pressure and flow measurement; and general-purpose
measurement equipment. For pressure and weigh scale applications, a
low-side power switch is available to power down the bridge between
conversions, minimizing system power consumption; the AD7799 features
lower noise (30 nVrms) for these applications.

The AD7794 can accommodate six differential sensor channels, making it
ideal for the higher channel requirements of industrial and factory
PLC/DCS applications. The other parts in the family can accommodate
two or three differential channels.

Pricing and availability
The AD779x family of devices is sampling now and will be available in
production quantities in November 2004. The AD7792 (16-bit), AD7793
(24-bit), AD7798 (16-bit) and AD7799 (24-bit) are available in 16-lead
TSSOP (thin shrink small outline package), with prices ranging from
$3.80 to $5.10 per unit in 1,000 piece quantities. The AD7794 (24-bit)
is available in 24-lead TSSOP, and priced at $5.80 per unit in 1,000
piece quantities. For more information, please visit:
www.analog.com/AD7794.

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