Gain of two amp problem

[topeminent]

HI, I am trying to find a gain of two amplifier. I already tried the inverting op amp implementation and it worked fine but for my project i need a gain of two amp to add two signals(the first one is going through an inverter, so basically the two signals are subtracted) and multipled with 2. My problem is that my circuit enters saturation because the the gain of two circuit acts also as an inverter, so my overall outcum is negative.

Could someone recommend me another circuit or an idea for my problem? Any thoughts would be appreciated.

Sorry for my bad english.
regards,

Csaba

 

[WimRFP]

Could you describe what you want in a formula and what are the limits of the input signals?

Example formula: Y = 2*(X2 - X1) + 3

Accuracy (gain and offset) may also be important.

 

[topeminent]

Hi

My formula what i m trying to implement is y=2(z - (+vref)) or y=2(z - (-Vref)) deppending of Vrefs value which could be 500mv (-Vref) or 1v(+ref)

The input signal is a sin wave with 1V peek to peek voltage with and offset value of 1,5v

 

[WimRFP]

Hello,

I am not sure whether you are pointing to an absolute function |Vref|, as you give two options for the formula. If you need the absolute function, you can use double phase (full wave) rectifying circuit. use "op-amp full wave rectifier" in google. The output of this circuit (that is |Vref| ) goes to the summer/gain block.

You can rewrite your formula as -2*(Vref - Z). This can be done with an inverting summer based on an single OPAMP. op-amp inverting summer in google will help you.

When all your signals and outputs stay positive, you can use a single supply solution (for example + 12V and 0V as ground reference).

 

[topeminent]

First of all thank you for your answer

Yes i m trying to implement an absolute function and the desired formula what i m trying to implement is 2*(Z - Vref) which is why after using the summer amplifier my formula became -2*(Vref-Z). what is wrong. Because i want to subtract from my input signal (z, the sin wave) a constant value (Vref) and amplify by 2.

I will check the rectifying circuit.


regards,
Csaba

- - - Updated - - -

Sorry i think i misunderstood the absolute function, and i expressed myself wrong. The first signal is a sine signal and the second one is a constant value.

 

[WimRFP]

Do you mean: output = 2*(|Vref| - Z) = -2*(Z-|Vref|)?

 

[topeminent]

Do you mean: output = 2*(|Vref| - Z) = -2*(Z-|Vref|)?

what i mean is that i want to implement exactly this function 2*(|Vref| - Z) , but using summing op amp the function became -2*(Z-|Vref|), which is not good for my design

Sorry for my previous ambiguous answer, i m new in electronics domain .

 

[WimRFP]

I understand your formula and I made a mistake, I will correct it now:

output = 2*(|Vref| - Z) = -2*(Z-|Vref|) = -2*(Z+ (-|Vref|) ).

So you need to make a full wave rectifier for Vref, but with negative going output, or a positive full rectifier with an inverter behind it.

This output goes together with the Z-signal into the inverting summer. The inverting summer provides C = -2(A+B). Where A will be the Z signal and B will be -|Vref|.

Sorry for confusing you.

 

[topeminent]

thx alot, i'll get back with the results.

 

[FvM]

Normally, a reference voltage would be considered constant. Do I understand right, that it's not constant in your case, otherwise you won't need an absolute value function for it?

 

[topeminent]

Actually it s not a reference voltage, it s a rectangular wave with low=500 mv and high=1v

 

[WimRFP]

OK, but when it is always positive, you don't need the absolute function. This saves you components.

 

[topeminent]

OK, but when it is always positive, you don't need the absolute function. This saves you components.

Im working with a virtual ground wich is 1,5 V. Because my input wave is a sine with 1,5 offset voltage

 

[FvM]

At first sight, I can't imagine the purpose of adding or substraticting a square and a sine wave. I wonder if you intend something else, e.g. a digital ("sign") multiplier?

Whatsoever, the ususal steps are:
- define the intended operation unequivocally
- find a circuit that implements it

Presently, there's seems to be a problem with the first step. (Or it's just my lack of understanding...)

Add/sub of multiple signals with optional factors can performed by single OP multiple input differential amplifier, or alternatively with a combination of inverting and/or noninverting amplifiers. In so far I don't see any general problem.