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    Re: how to boost microvolts to higher voltages?

    so the njm4558's supply voltage should be at least 8 volts. 12 volts won't violate the op amp's specifications.



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    Re: how to boost microvolts to higher voltages?

    @d109, I'm going to give you a sincere advice;

    if you are planning to go into electronics, as a profession or as a hobby, one very important skill set is to learn to draw understandable schematics.

    There are many free schematic capture tools. But even if you want to hand draw schematics (I often do it myself), make tidy, properly annotated, logical ones.

    A good start is to use cuadricule paper, such that you can draw straight lines.

    There are many examples of excellent hand-drawn schematics, but the very best were by Electronics guru Forest Mims
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    Re: how to boost microvolts to higher voltages?

    i tried using a supply voltage of 15.64 volts. the op amp still is driven to saturation. the schematic is the same as the previous schematic. why is the inverting amplifier not working? i tried an input voltage of 1.44 volts. then i tried an input voltage of 0.98 volt.



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    Re: how to boost microvolts to higher voltages?

    Hi,

    why is the inverting amplifier not working?
    Isn't that obvious?

    In post#20 I clearly showed you 3 violations.

    Then you correct 1 of them...

    --> then ... simple mathematics: 3 - 1 = 2 issues still are remaining...

    Klaus
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    Re: how to boost microvolts to higher voltages?

    The NJM4558 is a Japanese copy of a very old American one developed in 1974. It is not a modern low noise audio opamp so it cannot be used with microvolts input.
    Its inputs do not work if their voltage is within a few volts from the positive or negative supply voltage.



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    Re: how to boost microvolts to higher voltages?

    Quote Originally Posted by KlausST View Post
    Hi,


    But the Opamp in most of your cases is overdriven.

    There are many Opamp circuit tutorials, even videos in the internet.
    Use them, they are for free. You urgently need to learn basics on your own. A forum can't replace school.

    Also there are free simulator tools.
    Then you can play around, measure every voltage and current without time consuming soldering.
    *****

    Let's just calculate through one example. Let's take the 1000 ohms, 1000 ohms resistors.
    * supply voltage is 7.79V (this violates your Opamp's specifications, because it should be at least 8V. --> see "Operating Voltage" )
    * voltage at +IN node is 0V (this means that this input is connected to a supply rail. This violates your Opamp's specification, because your's is no Rail-to-rail input type.--> see "Input Common Mode Voltage Range")
    But let's assume from here on you use a suitable Opamp:
    * Rf = 1000 Ohms
    * Rin = 1000 Ohms
    * V_inp = input voltage is = (V_ Rin - V_+In) = 1.45V - 0V = 1.45V

    --> A = gain = - Rf / Rin = - 1000 Ohms / 1000 Ohms = -1

    The expectable V_out = V_+In + gain × V_inp = 0V + (-1) × 1.45V = -1.45V.
    ( This violates your Opamp's specification. --> see "Maximum Output Voltage Swing")
    -1.45V is beyound your supply rails. No opamp can output voltage beyond it's supply rails.
    --> thus it is expected to saturate close to negative rail.

    You may simplify your life with using eXcel for such calculations.

    Klaus
    i don't understand some of the things you said. is the supply rail part of the breadboard or the operational amplifier?



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    Re: how to boost microvolts to higher voltages?

    the supply rail(s) are the voltages you put on the +V power input and the -V power input
    that is, the inputs on the top side, +V and int input on the bottom side, -V

    your last diagram, in post 19, ha +7.99 V to V+ and 0V to V-
    so, in that diagram, the rails are 7.99 V and 0 V.

    If you apply 15.64 V, as in post 23, the rails are 15.64 and 0V.

    I may have missed it in a prior post:
    if the input is 5 microvolts, an inverting amplifier with a gain of 1000 should put out -5 millivolts.
    you can't do that when V- is 0V.



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    Re: how to boost microvolts to higher voltages?

    Hi,

    It's hard at first, isn't it? I mean to help with the following:

    I interpret that you are a person who is keen but making a typical beginner's mistake of rushing to make things work they don't understand, I did that when I started with circuits, it's normal. You'll waste more time with rushing and not studying what is in your hands right now than by being methodical.

    All circuits are a series of mathematical calculations that must add up or the answer will be wrong. Full stop. Circuits are not magical things we shove together and then they do the hard work for us.

    A circuit can be done in this order:
    1) I have a desire or a real need to make something.
    2) I look online for a circuit schematic that can accomplish the end goal.
    3) I read a little or a lot about the circuit and how it should work. Application notes, tutorials, etc.
    4) I read a little or a lot about the components needed that I don't understand or that I don't know how they function. Application notes, tutorials, etc.
    5) I try to do the pertinent calculations to have clear what numbers/answers my circuit and each component must provide.
    6) I suffer reading datasheets to find suitable components that have the necessary characteristics that fit the requirements and the calculations.
    7) I simulate on a free simulation tool, where possible, the circuit I will make to see if it can hypothetically work and usually learn a lot in the process.
    8) I breadboard the circuit with real components, observe functionality and/or measure voltages and/or currents and/or frequencies and/or whatever is of interest and make minor adjustments if and when seen to be needed.
    9) I prepare the PCB layout then solder the parts.
    10) I finally get to use the circuit I wanted to make, maybe having to troubleshoot bad wiring and resoldering a point or two, and at last the circuit is made.

    TI Precision Labs Op Amps tutorials, and the endless op amp pdfs of how they work, circuits with descriptions and the required calculations, how to read an op amp datasheet, and so on..., will really help. For me, circuits are 90% reading and calculations and 10% doing - I don't think I am unusual.

    You could step back from microvolts and huge gain (that's hard) and practice with e.g. inverting 100mV with a gain of 10 - notice unwanted input offset voltage is also amplified, for example. Simulate the circuit with a suitable op amp and you must use a positive and a negative supply for true -1Vout.

    Try LTSpice, I don't, I use the free version of Tina by TI. An LMC6464 (in the Tina models) has an input offset of 3mV, input voltage plus input offset voltage multiplied by the gain produces -1.030V at the output at least, and I'm ignoring additional error stuff like input bias currents and resistor noise (resistor noise is yet more unwanted voltage...). An op amp is sort of a fuzzily, imprecisely correct calculator and a wild horse you must tame in other senses, a good animal but needs proper reining in.

    Unless your circuit can be done with a positive supply only and mid-supply biasing, you need a dual supply op amp (rail-to-rail input and output would be useful) with very, very, very low input offset voltage and/or offsetting the IOV. fC is important, too - a fast op amp has a high fC, the LMC6464 is only good up to about 1kHz at best.

    I really only mean well, I empathize with you and your efforts.

    Regards,

    Daniel



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    Re: how to boost microvolts to higher voltages?

    Hi,

    I agree.

    For me, circuits are 90% reading and calculations and 10% doing - I don't think I am unusual.
    Then I'm unusual, too

    Studying the function, doing maths, deciding specifications, reading, reading again, doing (hand drawn) flow charts, finding suitable parts....
    All is time consuming ... and one sees no progress ... and somtimes boring ... and sometimes one get impatient...
    ... but then there will be a reliably working circuit. I've learned to become used to this...

    ****

    Take your time to learn things step by step.

    Klaus
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    Re: how to boost microvolts to higher voltages?

    you said "voltage at +IN node is 0V (this means that this input is connected to a supply rail. This violates your opamp's specificiations". if i connect the +IN node to ground, will that fix the second issue? +IN node is the noninverting input?



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    Re: how to boost microvolts to higher voltages?

    Hi,

    You can fix the second issue by re-reading the datasheet to see what minimum input voltage is allowed by whatever op amp you're using, clearly not 0V from the comments.
    0V rail is the same as saying ground rail to most people.
    Yes. +In node is non-inverting input.



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    Re: how to boost microvolts to higher voltages?

    i reread the datasheet. it said
    ■FEATURES
    ●Operating Voltage( ±4V~±18V )
    ●High Voltage Gain( 100dB typ. )
    ●High Input Resistance( 5MΩtyp. )
    ●Bipolar Technology●Package Outline

    does this mean the minimum input voltage is 4 volts?
    this is a link to the datasheethttps://www.njr.com/semicon/PDF/NJM4558_E.pdf

    - - - Updated - - -

    i have been studying operational amplifiers a little bit, now. the datasheet says the input common mode voltage range is
    min. +/- 12 volts, typ. +/- 14, and max is -. that means the minimum input voltage is 12 volts?



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    Re: how to boost microvolts to higher voltages?

    data sheet page 2:
    Read absolute max ratings
    read note 1

    maximum supply voltage is +/- 18V to power supply pins
    +/- 4V is the smallest supply voltage the op amp will operate according to specifications

    Maximum signal input voltage +- 15V - to inverting and noninverting inputs
    but if supply is less than +/- 15V , the signal inputs are limited to the supply voltage



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    Re: how to boost microvolts to higher voltages?

    Hi,

    Read absolute max ratings
    Just to clarify:
    When you violate absolute maximum ratings, then immediately permanent damage may occur.

    When you want to look for informations, where the Opamp will work correctly you need to look at the
    "Recommended operation conditions".

    Klaus
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    Re: how to boost microvolts to higher voltages?

    but that specifies the maximum input voltage. are you saying the minimum input voltage to the noninverting terminal is -15 volts?

    - - - Updated - - -

    Quote Originally Posted by wwfeldman View Post
    data sheet page 2:
    Read absolute max ratings
    read note 1

    maximum supply voltage is +/- 18V to power supply pins
    +/- 4V is the smallest supply voltage the op amp will operate according to specifications

    Maximum signal input voltage +- 15V - to inverting and noninverting inputs
    but if supply is less than +/- 15V , the signal inputs are limited to the supply voltage
    but that specifies the maximum input voltage. are you saying the minimum input voltage to noninverting terminal is -15 volts? i still don't know the minimum input voltage?

    - - - Updated - - -

    Quote Originally Posted by wwfeldman View Post
    data sheet page 2:
    Read absolute max ratings
    read note 1

    maximum supply voltage is +/- 18V to power supply pins
    +/- 4V is the smallest supply voltage the op amp will operate according to specifications

    Maximum signal input voltage +- 15V - to inverting and noninverting inputs
    but if supply is less than +/- 15V , the signal inputs are limited to the supply voltage
    but that specifies the maximum input voltage. are you saying the minimum input voltage to noninverting terminal is -15 volts? i still don't know the minimum input voltage?



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  16. #36
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    Re: how to boost microvolts to higher voltages?

    Datasheets say that with a +/-15V supply, the input common mode voltage range is min. +/- 12 volts, then the inputs of some of the opamps do not work if the input voltage is within 3V from the positive or negative supply voltages.

    The NJM4558 datasheet says that the opamp inputs do not work if their voltage is within a few volts from your positive supply and the inputs also do not work if their voltage is within a few volts from the negative supply. Then your circuit must use a positive and negative power supply. Then the input voltages will be far from the positive or negative supply voltages and the inputs will work perfectly. Plus and minus 4V (8V in total) is written here as +/-4V. Circuit ground is 0V.

    - - - Updated - - -

    The maximum allowed input voltage is plus or minus 15V or the positive and negative supply voltages. The minimum input voltage is 0V which is usually no input voltage.



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    Re: how to boost microvolts to higher voltages?

    KlausST said voltage at +IN node is 0V (this means that this input is connected to a supply rail. This violates your Opamp's specification, because your's is no Rail-to-rail input type.--> see "Input Common Mode Voltage Range")

    so you are saying if i use a dual supply that will fix the second issue? if i use both a postive supply voltage and negative supply voltage that will fix the second issue? sorry i am having trouble understanding how to fix the second isssue.



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    Re: how to boost microvolts to higher voltages?

    The very old NJM4558 opamp has too much input offset voltage and too much noise for your very low input signal circuit. Select a modern opamp with much less of those bad things.
    It will probably need a positive and negative power supply.



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    Re: how to boost microvolts to higher voltages?

    I feel that some points should be sorted out.

    You have been originally asking how to amplify µV signal to mV, with minimal supply voltage.
    Later you switched to 1.45 V input voltage and 8V supply. I guess you did so to have a simple problem description. But the solution will be probably different, hence we should agree if we are discussing the first or the latter question. I'm referring to high level amplifier here.

    It has been already stated, that the single supply circuit in post #19 only works with an OP that has a input common mode range including the negative supply rail. NJM4558 isn't of this kind. Even with respective OP common mode range (as exposed e.g. by LM358), the inverting single supply amplifier can't amplify a positive input voltage, as also stated.

    There are several solutions:
    - use dual supply which enables the circuit to amplify signals of positive and negative polarity
    - use an OP with input common mode range down to and including the negative supply rail

    To amplify a positive input voltage > 1V, NJM4558 can be even used in a non-inverting single supply amplifier configuration. See a simulation circuit with similar RC4558. Please notice that these OPs have no guaranteed common mode voltage range for +/-4V supply, the simulation is based on typical values. The LTspice circuit is also attached.

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    Re: how to boost microvolts to higher voltages?

    Hi,

    Hope this helps as a general overview to understand the common-mode range stuff in case you still have any doubts:

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    Further to FvM's last post, out of curiosity I simulated your circuit of 10uV * gain of 1,000 with such basic OAs as an LM324, an LMC6464 and then an OPA376 (input offset of ~5uV!) and the results were expectably grim.

    Why do you need/want that high-precision circuit?


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