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Minimizing Switching Noise and Its Effects in Auto-Zeroed Amplifiers

An automatic zero adjustment and amplifier technology, applied in amplifiers, differential amplifiers, DC-coupled DC amplifiers, etc., which can solve problems such as expensive filtering

Active Publication Date: 2011-12-28
MICROCHIP TECH INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Filtering can be expensive depending on how close the signal of interest is to the sampling frequency

Method used

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  • Minimizing Switching Noise and Its Effects in Auto-Zeroed Amplifiers
  • Minimizing Switching Noise and Its Effects in Auto-Zeroed Amplifiers
  • Minimizing Switching Noise and Its Effects in Auto-Zeroed Amplifiers

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Embodiment Construction

[0023] Reference is now made to the drawings, which schematically illustrate details of certain example embodiments. Like elements in the drawings will be represented by the same reference numerals, and similar elements will be represented by similar reference numerals with different lowercase letter suffixes.

[0024] see figure 1 , which depicts a schematic block diagram of a prior art auto-zeroing operational amplifier. The prior art auto-zero amplifier, generally indicated by reference numeral 100, may include at least two amplifiers 102 and 104, which are combined to produce the final signal output. A conventional wide bandwidth "main" amplifier 102 is connected directly from input to output and processes the incoming signal continuously. A second, very high gain "nulling" amplifier 104 is connected in parallel for offset correction. Amplifier 104 is nulled to offset itself to zero and to eliminate low frequency 1 / f noise below the chopping frequency. Zeroing involves...

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Abstract

Two nulling amplifiers are used with an auto-zeroed differential amplifier. While one nulling amplifier is compensating the main amplifier, the other nulling amplifier is being zeroed for both differential mode (DM) and common mode (CM) offsets. By using two nulling amplifiers, one always connected to the main amplifier, a relatively constant open-loop gain is maintained for the main amplifier. A further improvement is make-before-break timing overlap of the switch operations between the two nulling amplifiers and the main amplifier. This ensures that the main amplifier is continuously driven by one or both null amplifiers, thereby maintaining a low impedance at the main amplifier auxiliary port. Both DM and CM offset sampling and precharging of each of the two nulling amplifiers is performed so as to substantially reduce switching glitches in the output of the main amplifier.

Description

technical field [0001] The present invention relates to integrated circuit operational amplifiers, and more particularly to an integrated circuit auto-zeroing operational amplifier with minimal switching noise. Background technique [0002] An auto-zeroed operational amplifier is an analog circuit that combines analog and digital (switching) circuitry resulting in very low input referred DC offset and noise. These op amps are often used in precision applications where high gain is required to resolve very small voltages. Examples include RTDs, thermocouples, resistive current measurements, and other sensing applications. Using an auto-zero op amp relaxes the accuracy requirements on the A / D converter, saving cost. Today's auto-zeroed op amps have very little in common with the early chopping schemes used to reduce the average offset. Those circuits are very simple, using discrete amplifiers and switches to chop the input and output of the amplifier with a clock. Extensiv...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H03F3/45
CPCH03F3/45986
Inventor 詹姆斯·B·诺兰库门·布莱克
Owner MICROCHIP TECH INC