I'm really confused understanding the following device manual:https://www.endevco.com/product/prodpdf/136.pdf I don't understand most of what they write. Any one has some idea about these terminology?

1) Input impedance: 1 Meg Ohm minimum. Is that the built-in input impedance of the amplifier? If it is why doesn't it just say 1 Meg Ohm? Why does it say "minimum"?

2) What does "Common Mode" mean in this context? Isn't' it supposed to be very small for amplifiers? It says 50 Volt. Why do I have to know that?

3) Common Mode Rejection: It says 200 ohm imbalance, DC to 60 kHz. I don't understand what they mean.

4) Input imbalance adjustment: Whats that about? Do I supposed to deal with it?

5) Linear output: What is the difference between linear output and output?

6) Corner frequency? Is that a kind of limitation?

7) Cross talk between channels? 80 db RTI. What does it mean?

8 ) Resolution? Do they mean the amplification factor for the signal input?

  • 1
    \$\begingroup\$ From your questions it seems that you don't understand the basics properties and limitations of (operational and related) amplifiers. I suggest you do some reading first. \$\endgroup\$ Mar 28, 2014 at 17:27

1 Answer 1


Nothing wrong about the spec as far as I can see - it sounds like you want it couched in terms that are meaningful to your limited knowledge and application requirements.

  • 1 Mohm minimum input impedance is fine - it's 1 Mohm guaranteed or greater - most folk want high input impedances so a guarantee is a good thing.
  • Common mode input voltage range applies to differential amplifiers and it basically means, if you want to measure a small AC signal (say 100 mVp-p) it will do so even if both input wires are raised by a potentially interfering voltage of +/- 10V. Good spec I reckon.
  • Common mode rejection - this tells you how good the input amplifier is when it is connected to a source voltage with different resistance connections. 70 dB at 60 kHz is pretty good for this sort of thing - you have got to envisage that some folk may not be able to adequately control the impedances of their signals that are to be measured by this device.
  • Input imbalance adjustment - no amplifier is perfect and most will produce a small dc error at their output - this can be nulled-out by the adjuster.
  • Linear output is telling you that it won't produce significant distortion (maybe due to clipping) for output peaks up to 10V. I also read this as meaning that the nominal rated full scale output level is +/-10V.
  • Corner frequency is the point where the output starts to naturally fall when the input frequency gets above a certain value and for the default amp you are using this is 10kHz. It's adjustable.
  • Cross talk of 80 dB RTI - referred to input is what RTI means. Cross talk applies to amplifiers with multiple channels and interference between one channel's signal and another channel.
  • Gain resolution - if you want to adjust the gain there is a finite limit to how exact you may want it and this is the resolution.
  • \$\begingroup\$ thanks. but books dont show meaning of these things? how can I learn this terminology? \$\endgroup\$
    – user16307
    Mar 28, 2014 at 17:28
  • \$\begingroup\$ keep plugging away at stuff - I'm sure there are books and websites that will help. \$\endgroup\$
    – Andy aka
    Mar 28, 2014 at 17:30
  • \$\begingroup\$ btw I just googled in quote "Input imbalance adjustment". guess what there are only 36 results and none of them are descriptive. they are all words in data sheets. very weird. or i don't know where to look for the definitions. \$\endgroup\$
    – user16307
    Mar 28, 2014 at 17:50
  • \$\begingroup\$ Try "input offset voltage adjustment". \$\endgroup\$
    – Andy aka
    Mar 28, 2014 at 18:09

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