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Topic: Good choices for buffer op-amps? (Read 594 times) previous topic - next topic

Verdris

Hi all,

I have an Arduino talking to an AD7714 ADC, which is measuring voltage off two sensors. I currently have the signals buffered through a pair of CA3140E op-amps, but I'm wondering if there's a better choice. I was told that op-amps specifically designed to be buffers exist, but I can't find anything with the googlemachine or browsing around at ti.com. Any suggestions?

wanderson

A search using Digikey http://www.digikey.com/scripts/dksearch/dksus.dll


Product Index > Integrated Circuits (ICs) > Linear - Amplifiers - Instrumentation, OP Amps, Buffer Amps

with a filter for Amplifier Type = Buffer

turned up 4 pages of examples in stock
New true random number library available at: http://code.google.com/p/avr-hardware-random-number-generation/

Current version 1.0.1

CrossRoads

The AD7714 data sheet does not mention using op-amps as input buffers.
It discusses having a good voltage reference input.
http://www.analog.com/static/imported-files/data_sheets/AD7714.pdf

I would think that most buffers you could add in front of the AD7714 would add more noise that would be picked up the 24-bit conversion.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

wanderson


I would think that most buffers you could add in front of the AD7714 would add more noise that would be picked up the 24-bit conversion.


The buffer may be used in this case to increase the effective input impedance of the measurent, to reduce the effect the measuring process has upon the signal being measured.  In cases like that noise, is not the major concern,IMO.
New true random number library available at: http://code.google.com/p/avr-hardware-random-number-generation/

Current version 1.0.1

CrossRoads

"The AD7714 is a complete analog front end for low-frequency measurement applications. The device accepts low level signals
directly from a transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 24
bits of no missing codes performance. The input signal is applied to a proprietary programmable gain front end based around an
analog modulator. The modulator output is processed by an onchip digital filter. The first notch of this digital filter can be
programmed via the on-chip control register allowing adjustment of the filter cutoff and settling time."

"The programmable gain channels allow the AD7714 to accept input signals directly from a strain gage or transducer
removing a considerable amount of signal conditioning."

"AIN Input Current  1nA MAX"
"AIN Sampling Capacitance 7pF MAX"

Not much to improve on there.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

wanderson

Yep, I hadn't looked at the device's spec sheet.  You are right, it doesn't seem to be needed for that device.
New true random number library available at: http://code.google.com/p/avr-hardware-random-number-generation/

Current version 1.0.1

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