need your help in designing an Operational Amplifier circuit

[brownr72]

need your help in designing an Operational Amplifier circuit
Hello
I need your help in designing an Operational Amplifier with these conditions:
The i/p signal changing from Vmax= 80 mv to Vmin=60 mv, the o/p must be Vout = + 5 V when Vmax= 80 mv and Vout = - 5 V when Vmin=60 mv
thank you very much


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Antenna Installation

 

[RCinFLA]

Delta in to Delta out = gain.

Center in to center out = offset.

 

[Roff]

Do you need a linear amplifier, or a limiting amplifier (comparator)?

 

[MrAl]

need your help in designing an Operational Amplifier circuit
Hello
I need your help in designing an Operational Amplifier with these conditions:
The i/p signal changing from Vmax= 80 mv to Vmin=60 mv, the o/p must be Vout = + 5 V when Vmax= 80 mv and Vout = - 5 V when Vmin=60 mv
thank you very much
________________________

Hello,

One way to get this which isnt too hard is to use a voltage divider on the input with the lower resistor going to a negative supply rail (like -10v for example) and setting the gain accordingly.
The -10v (and voltage divider) forces 0v out at 70mv and the gain sets the output at both 80mv and 60mv to +5 and -5v respectively.
Since the input resistor (of the voltage divider) sets the input impedance, it is convenient to have formulas that take R1 as one input parameter and since there has to be at least one negative voltage source Vs (like -10v) that can be another input parameter and from those two we can calculate everything else:

R2=R1*1000/7, and
A=(7*Vs+4955)/(80-7*Vs)
where
R1 is the upper resistor of the input voltage divider and R2 is the lower resistor of the input voltage divider and A is the gain set by two other resistors from output to inverting input and from inverting input to ground as usual.

For example, say we want at least 10k input impedance and we have a negative source voltage of -10v available and that source is stable enough for our application. If it isnt stable enough, we need to use a voltage reference diode instead. Ok, so say our -10v is stable, that makes Vs=10 and since we want at least 10k input impedance that makes R1=10k.
We then calculate R2, and that comes out to:
R2=1428571 ohms
and then the gain A:
A=502.5
which means if we make the resistor from inverting terminal to ground 1k then the feedback resistor would be 502.5k ohms.
This gives us all four resistors required for this solution:
10k, 1428571 ohms, 1k, and 502k ohms.

Note however that to get decent accuracy we would need to use a special op amp with low input offset voltage and low input offset voltage drift too.

 

[crutschow]

The OP hasn't responded in four months.

 

[MrAl]

Hello Carl,

Ha ha, yeah wow. I caught another thread where it was several YEARS since the last chat and someone responded recently and i almost joined in until i saw how old the thread was. This seems to happen now and then for some reason.

 

[Roff]

The OP hasn't responded in four months.

I didn't notice that either. I'm trying to figure out how this wound up on my "radar".

 

[MrAl]

Hi Roff,

Maybe it came in your email as a notification? That happened to me once, i got an old post saying it was rather new.

 

[Roff]

Hi Roff,

Maybe it came in your email as a notification? That happened to me once, i got an old post saying it was rather new.

I don't think that was the reason. I only get emails when I have a PM.