[SOLVED] Opamp Voltage Summer Question [Please help]

[hshah8970]

Hello everyone!

I had a question about a simple noninverting voltage summer constructed by an opamp.

My question is: at the output of the opamp, do we simply get a sum of the voltages of the input signals or do we also get a sum of the powers i.e. the sum of the currents? :?:

I need an opamp configuration of which the output signal will have power equal to the sum of powers of two input DC signals.

Humza.

 

[enjunear]

Start here: https://www.lmgtfy.com/?q=op+amp+voltage+summer

Then read the first query result: https://www.allaboutcircuits.com/vol_3/chpt_8/8.html

Follow that circuit with a unity (gain=1) inverting op-amp, and viola... you have a voltage summer.

 

[proconics]

at the output of the opamp, we simply get a sum of the voltages of the input signals.

 

[enjunear]

at the output of the opamp, we simply get a sum of the voltages of the input signals.

Not quite. An op amp is a voltage-controlled device that will drive it's output voltage in an attempt to force the positive and negative inputs to be equal to one another. Depending on the components attached to the op amp, you can develop circuits that perform particular functions. For example, a unity-gain buffer, an inverting voltage amplifier, non-inverting voltage amplifier, a signal integrator, etc. It is a voltage amplifier used to perform mathematical and functional operations... thus the moniker, "operational amplifier".

https://en.wikipedia.org/wiki/Operational_amplifier
"An operational amplifier is a DC-coupled high-gain electronic voltage amplifier..."

TI's App Note 31 is a famous collection of many circuits you can use op amps in (the inverting voltage summer is on page 1).
www.ti.com/ww/en/bobpease/assets/AN-31.pdf

 

[proconics]

For this question,

I had a question about a simple noninverting voltage summer constructed by an opamp.

My question is: at the output of the opamp, do we simply get a sum of the voltages of the input signals

The answer is,

at the output of the opamp, we simply get a sum of the voltages of the input signals.

 

[LvW]

I need an opamp configuration of which the output signal will have power equal to the sum of powers of two input DC signals.


What is the "output signal" of an opamp? Of course, a voltage.
I don't think that a voltage can be identical to the sum of two powers.
More than that - the power developed across the input resistors depends on the resistor values, whereas the output voltage (the gain) depends on resistor ratio only.

 

[crutschow]

.........................................
I need an opamp configuration of which the output signal will have power equal to the sum of powers of two input DC signals.

Since power is proportional to the square of the voltage, you need a square-law device. You could use forward a forward-biased diode, but the dynamic voltage range is quite low.

For a larger voltage range you can use analog multipliers configured to square the voltage (apply the same voltage to both inputs of the multiplier). The outputs of the two multipliers (one for each voltage you want to square) can then be summed by a summing op amp circuit to get the sum of the two powers.

 

[hshah8970]

Hello everybody and thank you for your replies. I did my own bit of thinking today while away from the computer and reached the conclusion that the voltage summer configuration simply sums the voltages of the input signals - the output power depends on what load we are driving from that particular voltage and what current throughput the opamp is capable of. As such, there is no way to simple merge the two signals and get a 'more powerful' signal.

Please point out any mistakes in my conclusion.

P.S. I will be checking out the URLs shared above shortly. Again, thanks for all who replied and who will reply.

 

[TuAtAu]

The conclusion seems valid.

But from me, I will conclude:
Op Amp only compared the voltage at the inverting and non-inverting input terminal, and using the voltage level over that input terminals to control the output voltage itself. Thus, the output voltage will 'mimic' or autoadjust to the equilibrium voltage level of your input configuration. BUT THE output voltage source and output current source is not from the INPUT terminal, its from the Voltage source terminal. Thats why every opamp will have Vs+ Vs- (V source+/-). Output power is refer to the opamp source but not sum up the input terminal of opamp. (only apply to typical configuration and yes, summer is very common configuration.)

 

[enjunear]

Hello everybody and thank you for your replies. I did my own bit of thinking today while away from the computer and reached the conclusion that the voltage summer configuration simply sums the voltages of the input signals - the output power depends on what load we are driving from that particular voltage and what current throughput the opamp is capable of. As such, there is no way to simple merge the two signals and get a 'more powerful' signal.

Please point out any mistakes in my conclusion.

P.S. I will be checking out the URLs shared above shortly. Again, thanks for all who replied and who will reply.

What kinds of signals are you trying to combine? If these are in a 50 ohm system (read: RF) you could use a simple power combiner.
**broken link removed**