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Application Notes

• Download
  Delta Sigma ADC Bridge Measurement Techniques &mdash AN96
  PDF, 232 Kb, File published: Jan 17, 2005
  AN96 features several applications that demonstrate how to take full advantage of Linear Technology's delta sigma ADCs when interfacing to sensors. In many cases, signal conditioning can be greatly simplified or eliminated completely. This note explains where it is appropriate to use amplifiers and how to optimize amplifier gain. Also included are discussions on measuring effective number of bits (ENOB) and the relationship to instrument performance, frequency response of delta sigma ADCs, and test techniques. C source code for all of the applications is included to aid firmware development.
  Extract from the document

  Application Note 96
  January 2005
  Delta Sigma ADC Bridge Measurement Techniques
  Mark Thoren
  Introduction In a typical 12-bit measurement system, the signal conditioning amplifier requires a very high gain in order to make
  use of the full ADC input range. A sensor with a 10mV fullscale output requires a gain of 500 to use the full input
  range of a typical 5V input ADC. A filter may be required to
  reduce noise at the expense of settling time. Additional
  difficulties arise when dealing with the large common
  mode voltage typical of a bridge sensor. Most instrumentation amplifiers have a large discrepancy between the
  typical CMRR and guaranteed minimum, which may require an additional trim. Sensors for pressure, load, temperature, acceleration and
  many other physical quantities often take the form of a
  Wheatstone bridge. These sensors can be extremely linear
  and stable over time and temperature. However, most
  things in nature are only linear if you don’t bend them too
  much. In the case of a load cell, Hooke’s law states that the
  strain in a material is proportional to the applied stress—
  as long as the stress is nowhere near the material’s yield
  point (the “point of no return” where the material is
  permanently deformed). The consequence is that a load
  cell based on a resistance strain gauge will have a very
  small electrical output—often only a few millivolts. In
  spite of this, instruments with 100,000 counts of resolution and more are possible. This Application Note presents …

Articles

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  No Latency Delta-Sigma ADC Techniques for Optimized Performance &mdash LT Journal
  PDF, 239 Kb, File published: May 1, 2001
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  DESIGN FEATURES Introduction Product Family Overview Linear Technology’s Delta-Sigma analog-to-digital converter product family
  simplifies a variety of applications.
  The products’ ease-of-use and high
  accuracy without the need for calibration, external clocks or complex
  interfaces enables designers to rethink
  their system architectures.
  Although 24 bits may seem excessive to some, many designers find
  significant advantages with these
  higher resolution converters. One
  such advantage is the elimination of
  front-end amplification. This enables
  direct digitization of many sensors
  while removing problems associated
  with front-end offset and gain errors
  as well as simplifying tare adjustments. One misconception commonly
  solved by designers using the
  LTC2400 family is the relationship
  between speed and resolution. Many
  designers have found that higher
  speed ADCs with averaging do not
  meet the one-shot performance of the
  LTC2400 family. The absolute accuracy of the LTC2400 family is
  demonstrated using a bridge sensor …

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Manufacturer's Classification

• Data Conversion > Analog-to-Digital Converters (ADC) > Precision ADCs (Fs < 10Msps) > Single Channel ADCs