Active Summing
What It Does
Summing is used to combine multiple input signals into a single output signal.
Active summing improves upon passive summing, but requires op-amps.
Non-inverting op-amp mixer
Op-amps mixing circuits are much more ideal for creating offset (bias) voltages.
- Notice the output has (less) scaling error than the passive mixer.
- Please play with the position of the potentiometer.
- Please play with the value of the potentiometer (edit component), and notice a small scaling error.
- Within the non-inverting op-amp mixer voltages still affect each other via the resistors, however a lot less than with the passive mixer.
- Please play one of the left resistor values, and notice a change in ratio.
Inverting op-amp mixer
The inverting op-amp mixer improves the last scaling error from the non-inverting op-amp mixer, however it inverts the signal.
- Notice the output has no scaling error.
- Please play with the position of the potentiometer.
- Please play with the value of the potentiometer (edit component).
- Please play one of the left resistor values (so not the feedback resistor), and notice a change in ratio.
Inverting op-amp mixer (corrected)
The inverting op-amp mixer requires two inverting op-amps in series to correct the inverted signal back again.
- This circuit can add up voltages.
- The disadvantage of this configuration is the extra opamp needed to correct the inverted signal.
- Please play with different resistor values of the first two 10K's and mind the ratio.
TIP
The inverting op-amp mixer can truly add-up voltages. But be aware if the sum is above the power rail the output will clip, or in other words: the output voltage cannot be larger than the power supply of the op-amp.
Biasing non-inverting op-amp
Sometimes you want to seperate the main signal from the offset completely. You can also use the other input pins to bias the signal.
- Notice the output has a small scaling error.
Biasing inverting op-amp
- Notice the output has no scaling error.