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LT1389

Application Notes

• Download
  775 Nanovolt Noise Measurement for A Low Noise Voltage Reference &mdash AN124
  PDF, 478 Kb, File published: Jul 3, 2009
  Frequently, voltage reference stability and noise defi ne measurement limits in instrumentation systems. In particular, reference noise often sets stable resolution limits. Reference voltages have decreased with the continuing drop in system power supply voltages, making reference noise increasingly important. The compressed signal processing range mandates a commensurate reduction in reference noise to maintain resolution. Noise ultimately translates into quantization uncertainty in A to D converters, introducing jitter in applications such as scales, inertial navigation systems, infrared thermography, DVMs and medical imaging apparatus. A new low voltage reference, the LTC6655, has only 0.3ppm (775nV) noise at 2.5VOUT.
  Extract from the document

  Application Note 124
  July 2009
  775 Nanovolt Noise Measurement for A Low Noise
  Voltage Reference
  Quantifying Silence
  Jim Williams
  Introduction
  Frequently, voltage reference stability and noise define
  measurement limits in instrumentation systems. In particular, reference noise often sets stable resolution limits.
  Reference voltages have decreased with the continuing
  drop in system power supply voltages, making reference
  noise increasingly important. The compressed signal
  processing range mandates a commensurate reduction
  in reference noise to maintain resolution. Noise ultimately
  translates into quantization uncertainty in A to D converters,
  introducing jitter in applications such as scales, inertial
  navigation systems, infrared thermography, DVMs and
  medical imaging apparatus. A new low voltage reference,
  the LTC6655, has only 0.3ppm (775nV) noise at 2.5VOUT.
  Figure 1 lists salient specifications in tabular form. Accuracy and temperature coefficient are characteristic of
  high grade, low voltage references. 0.1Hz to 10Hz noise,
  particularly noteworthy, is unequalled by any low voltage
  electronic reference. …

• Download
  Buffered ADC Family Eliminates Signal Conditioning Complexity &mdash AN167
  PDF, 1.3 Mb, File published: Sep 20, 2017
  Extract from the document

  Application Note 167
  September 2017
  Buffered ADC Family Eliminates
  Signal Conditioning Complexity
  Joe Sousa, Andrew Thomas, Clement Wagner, Mark Thoren
  Engineers often assume that analog-to-digital converter
  inputs are high impedance. Direct-sampling SAR ADC
  inputs will often be high impedance when not converting, but will draw “spikes” of current at the beginning
  of sample acquisition. On average, this behavior can be
  modeled as a crude nonlinear resistance that is inversely
  proportional to the sample capacitor size and sample rate,
  but instantaneously the signal chain must be able to settle
  completely in response to this abuse before acquisition
  ends and a conversion begins. Coupling a signal chain to an ADC is an art form, often requiring a combination of theory
  and experimentation. By contrast, the LTC2358 family of
  multi-channel, buffered high voltage SAR ADCs offers
  truly high impedance inputs that simplify or eliminate the
  need for signal conditioning in many cases. When signal
  conditioning is required, it can be directly connected to
  the LTC2358 inputs without regard to its ability to drive
  a switched capacitor. The following circuits show some
  applications that take advantage of the properties of the
  LTC2358 inputs. …

Design Notes

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  Don't Be Fooled By Voltage Reference Long-Term Drift and Hysteresis &mdash DN229
  PDF, 98 Kb, File published: Apr 3, 2001
  Extract from the document

  Don’t Be Fooled by Voltage Reference Long-Term Drift
  and Hysteresis – Design Note 229
  John Wright Lies About Long-Term Drift
  Some manufacturers are now touting phenomenal
  long-term drift specifications, based on accelerated
  high temperature testing. THIS IS A DELIBERATE
  LIE! Long-term drift cannot be extrapolated from
  accelerated high temperature testing. The only way
  long-term drift can be determined is to measure it over
  the time interval of interest. The erroneous technique
  produces numbers that are wildly optimistic and uses
  the Arrhenius Equation to derive an acceleration factor
  from elevated temperature readings. The equation is:
  AF = e EA вЋ› 1 1 вЋћ
  ⎜ – ⎟
  K вЋќ T1 T2вЋ  where: E A = Activation Energy (Assume 0.7)
  K = Boltzmann’s Constant
  T2 = Test Condition in В°Kelvin
  T1 = Use Condition Temperature in В°Kelvin Equation the acceleration factor is 767 and the projected
  “bogus” long-term drift is 0.156ppm/1000hr at 30°C.
  For a 2.5V reference, this corresponds to a 0.39ОјV shift
  after 1000 hours. This is pretty hard to determine (read
  impossible) if the peak-to-peak output noise is larger …

• Download
  Driving a Low Noise, Low Distortion 18-Bit, 1.6Msps ADC &mdash DN494
  PDF, 1.1 Mb, File published: Aug 1, 2011
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  Driving a Low Noise, Low Distortion 18-Bit, 1.6Msps ADC
  Design Note 494
  Guy Hoover
  Introduction
  The LTC В®2379-18 is an 18-bit, 1.6Msps SAR ADC with
  an extremely high SNR of 101dB and THD of –120dB. It
  also features a unique digital-gain compression function,
  which eliminates the need for a negative supply in the
  ADC driver circuit. the LTВ®6203 and minimizes disturbances reflected into
  the LT6203 from sampling transients. The 32k point FFT
  in Figure 2 shows the performance of the LTC2379-18 in
  the circuit of Figure 1.
  Single Supply Driver
  The circuit of Figure 3 uses the digital gain compression
  feature of the LTC2379-18, which defines the ADC full-scale
  input swing to be 10% to 90% of the reference voltage.
  This means that for a 5V reference the full-scale swing is Designing a driver circuit to get the best possible performance from the LTC2379-18 is not difficult. The two
  circuits presented here demonstrate differential and
  single-ended solutions using dual and single supplies.
  Note that the components used here have been carefully
  chosen with the ADC’s accuracy and acquisition time
  requirements in mind, so any modifications should be
  thoroughly tested. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of …

Articles

• Download
  775 Nanovolt Noise Measurement for a Low Noise Voltage Reference &mdash LT Journal
  PDF, 1.6 Mb, File published: Dec 1, 2009
  Extract from the document

  L DESIGN FEATURES 775 Nanovolt Noise Measurement for
  a Low Noise Voltage Reference
  Quantifying Silence by Jim Williams Introduction
  Frequently, voltage reference stability and noise define measurement
  limits in instrumentation systems. In
  particular, reference noise often sets
  stable resolution limits.
  Reference voltages have decreased
  with the continuing drop in system
  power supply voltages, making reference noise increasingly important. The
  compressed signal processing range
  mandates a commensurate reduction
  in reference noise to maintain resolution. Noise ultimately translates into
  quantization uncertainty in ADCs,
  introducing jitter in applications such
  as scales, inertial navigation systems,
  infrared thermography, DVMs and
  medical imaging apparatus.
  A new low voltage reference, the
  LTC6655, has only 0.3ppm (775nV)
  noise at 2.5VOUT. Table 1 lists salient
  specifications in tabular form. Accuracy and temperature coefficient
  are characteristic of high grade, low …

• Download
  How to Choose a Voltage Reference &mdash LT Journal
  PDF, 282 Kb, File published: Mar 1, 2009
  Extract from the document

  L DESIGN FEATURES How to Choose a Voltage Reference
  by Brendan Whelan Why Voltage References? 5V It is an analog world. All electronic
  devices must in some way interact with
  the “real” world, whether they are in
  an automobile, microwave oven or cell
  phone. To do that, electronics must be
  able to map real world measurements
  (speed, pressure, length, temperature)
  to a measurable quantity in the electronics world (voltage). Of course, to
  measure voltage, you need a standard
  to measure against. That standard is
  a voltage reference. The question for
  any system designer is not whether he
  needs a voltage reference, but rather,
  which one?
  A voltage reference is simply that—a
  circuit or circuit element that provides
  a known potential for as long as the circuit requires it. This may be minutes,
  hours or years. If a product requires
  information about the world, such VIN 18k LTC1286
  1
  2 LT1634-4.096 0.1ВµF 3
  4 VREF VCC +IN CLK –IN DOUT GND CS/SHDN 8 5V 7 …

Model Line

Manufacturer's Classification

• Signal Conditioning > Voltage References > Series Voltage References<br />Space & Harsh Environment > Extended Temperature Plastic (H & MP) > Extended Temperature (H & MP) Voltage References

Other Names:

LTC6655BHMS8-1.25PBF, LTC6655BHMS8-1.25 PBF, LTC6655BHMS81.25#PBF, LTC6655BHMS8 1.25#PBF