# how to boost microvolts to higher voltages?

1. ## Re: how to boost microvolts to higher voltages?

Originally Posted by FvM
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.

Attachment 157799
we are discussing the latter question, because i want to make sure i can amplify the signal. so if i use njm4558 in a non-inverting single supply amplifier configuration that will amplify a positive input voltage that is greater than 1 volt?

2. ## Re: how to boost microvolts to higher voltages?

The NJM4558 inputs do not work if their voltage is within a few volts from ground in a non-inverting single supply amplifier configuration.

If the NJM4558 opamp has a positive and negative supply, then it can amplify an input from 0V to 3V less than its positive supply voltage. But some of them have inputs that work up to only 1V less than the positive supply voltage.

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3. ## Re: how to boost microvolts to higher voltages?

nobody has answered my question. 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. could somebody answer the question? will that fix the second issue?

4. ## Re: how to boost microvolts to higher voltages?

Hi,

so you are saying if i use a dual supply that will fix the second issue? i
There is no answer, because there is a lack of information.

* what do you define as 0V_node?
* where is +IN connected.

--> draw a clear and complete schematic, where we can see "0V" and the connection of "+In".

Klaus

5. ## Re: how to boost microvolts to higher voltages?

this is a schematic of the circuit

0v is the negative terminal. and +in is connected to the negative terminal. i think i am using a single supply power source. so will a dual supply power source work?

6. ## Re: how to boost microvolts to higher voltages?

Hi.

Why don't you draw the dual supply?
... when you want to discuss about...

Klaus

7. ## Re: how to boost microvolts to higher voltages?

Hi,

Originally Posted by dl09
this is a schematic of the circuit

0v is the negative terminal. and +in is connected to the negative terminal. i think i am using a single supply power source. so will a dual supply power source work?
Yes, it would. Remember, your op amp inputs need to be 'x' volts above ground. Read about mid-supply biasing to correct what's wrong with the schematic or use a dual supply to make sure the non-inverting op amp input (the 'plus' op amp input) is receiving a signal within its common-mode input range.

The circuit is still an inverting amplifier, Vout = (-R2/R1) * Vin. Single supply can't go lower than its floor of 0V to generate a negative voltage... Why is the op amp inverting input also connected to the battery negative/0V or is that just what the picture makes it look like?

8. ## Re: how to boost microvolts to higher voltages?

inverting terminal is not suppose to be connected to the negative terminal of the supply battery. sorry that is a mistake i made.

9. ## Re: how to boost microvolts to higher voltages?

nobody has answered my question.
I believe, you either don't read the answers or don't understand it. I have no other explanation for seeing the circuit in post #45 that has been already recognized as non-working. If you want to change it into a dual supply circuit, why you don't sketch it so?

so if i use njm4558 in a non-inverting single supply amplifier configuration that will amplify a positive input voltage that is greater than 1 volt?
Yes, if you refer to typical OP specs. Not necessarily, if you rely on guaranteed parameters. I presume you read the datasheet and noticed the difference between typical and minimal voltage values, also the lack of specifications for +/-4 V supply.

If you want a circuit that works by design, you should use an OP with complete low voltage specification.

10. ## Re: how to boost microvolts to higher voltages?

Originally Posted by dl09
nobody has answered my question.

Audioguru did in the previous post.

11. ## Re: how to boost microvolts to higher voltages?

Originally Posted by schmitt trigger
Audioguru did in the previous post.
i have some experience designing and building electronic circuits and i have studied electronics, but getting an inverting amplifier working is really hard.

- - - Updated - - -

i have built an inverting amplifier. it uses a dual power supply. 1 lead receives roughly +9.2 volts. the other lead receives roughly -9.2 volts. the input is 1.62 volts.
here is a schematic

i have tried changing the resistance of the feedback resistor, i think i get the same output every time i change the value of the feedback resistor. can anybody explain why the the inverting amplifier is not working? on the breadboard 1 rail serves as ground. a second rail provides +9.2 volts to 1 supply lead. a third rail provides -9.2 volts to the other supply lead. the noninveting terminal is connected the rail that serves as ground. when i use a multimeter to measure the output 1 prong is connected to the output. the other prong is connected to the rail that serves as ground. the positive terminal of the 1.62 volt battery that provides the input is connected to the inverting terminal. the negative terminal of the battery that provides the input is connected to ground.

12. ## Re: how to boost microvolts to higher voltages?

Your new schematic does not have a part number for the opamp and it has no resistor Values.
You also forgot to say what voltage is the output.

If you are using two 9V batteries then do it like this:

13. ## Re: how to boost microvolts to higher voltages?

i used the njm4558 operational amplifier. the input resistor has 1000 ohms. i tried a feedback resistor with 2000 ohms and then changed the value of the feedback resistor to 3000 ohms, the output was the same. i think the output was around -4.9 volts. so the input signal is positive 1.62 volts. and the output is negative 4.9 volts. the used 5 18650 lithium ion batteries connected in series with an output of 19.2 volts. the lithium ion batteries are connected to voltage divider to provide a dual power supply. the rail that serves as ground is connected to a point between the two resistors in the voltage divider network. so why is this inverting amplifier not working?

14. ## Re: how to boost microvolts to higher voltages?

Hi,

i have built an inverting amplifier. it uses a dual power supply.
No.
A dual power supply has three connections (at least).
+voltage, GND (or 0V), -voltage.

GND is the reference to each of the dual supply outputs as well as the referenc for your Opamp's input and output signals.

Klaus

Btw: it's not clear to me why you want an inverting amplifier at all.
It seems your input signal is positive, and you want the output signal to be positive, too.
If so, this clearly calls for a non inverting amplifier.

15. ## Re: how to boost microvolts to higher voltages?

the inverting amplifier is on 1 breadboard. the voltage divider is on a second breadboard. 1 rail on the same breadboard the op amp is on serves as ground. that rail is connected to a point between two resistors of the voltage divider network, that point serves as ground. the positive supply lead is connected to a red rail on the same breadboard the voltage divider is on. that rail provides the positive supply. the negative supply lead is connected to a blue rail on the same breadboard the voltage divider is on. that is suppose to provide the negative power supply. the 19.2 volt battery is connected to the voltage divider. the positive terminal of the 19.2 volt battery is connected to the red rail. the negative terminal of the 19.2 volt battery is connected to the blue rail. i connected the black prong of my multimeter to point between the two resistors of the voltage divider and connected the red prong to the red rail, i measured +9.2 volts. then i connected the red prong to the blue rail and the black prong to the point between the two resistors of the voltage divider and measured -9.2 volts. i thought i did provide 3 connections. how do i provide 3 connections?

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

Hi,

the rail that serves as ground
This is your mistake.
On a dual supply Opamp none of the supply rails is GND.... (with standard node naming)

Klaus

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17. ## Re: how to boost microvolts to higher voltages?

What resistances are used for your voltage divider??

18. ## Re: how to boost microvolts to higher voltages?

Originally Posted by KlausST
Hi,

This is your mistake.
On a dual supply Opamp none of the supply rails is GND.... (with standard node naming)

Klaus
so how do i create a dual power supply?

19. ## Re: how to boost microvolts to higher voltages?

Originally Posted by dl09
so how do i create a dual power supply?
I showed you in post #52. A positive supply or battery plus a negative supply or battery. They join together at circuit ground.
You never answered about the resistances you used for the voltage divider but they are probably too high. An opamp follower could be used with them at its input then its output would be a low impedance ground.

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20. ## Re: how to boost microvolts to higher voltages?

1 resistor in the voltage divider network is 9000 ohms. the other resistor is 5000 ohms.

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