# Collector Amplifier (OPAMP) / The Summing Amplifier

In this article, we will discuss Collector Amplifier (OPAMP) / The Summing Amplifier in detail. Previously, in the inverting process amplifier, we have seen that the inverter riser has a single input voltage (Vin) applied to the inverting input terminal. If we add more input resistance to the input, each equal to the original input resistance (Rin), we will result in another operational amplifier circuit called a Collection Amplifier, a "collector inverter" or even a "voltage collector" circuit, as shown. you can see it in detail below.

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## Collector Amplifier Circuit

The output voltage (Vout) in this simple collection amplifier circuit is proportional to the sum of the input voltages, V1, V2, V3, etc. Next, we can change the original equation of the inverter amplifier to take into account these new ones.

But if all input impedances (RIN) are equal in value, we can simplify the above equation to give an output voltage as follows:

## Collecting the Amplifier Equation

We now have a operational amplifier circuit that will increase each input voltage and produce an output voltage signal proportional to the algebraic "SUM" of three separate input voltages V1, V2 and V3. Since each entry "sees" its own resistance, we can add more entries if necessary, as Rin single input impedance.

This is because the input signals are effectively isolated from each other by the "virtual soil" node at the inverted input of the op-amp. When all resistors are of equal value and Rε is equal to Rin, a direct voltage addition can also be obtained.

Note that when the collection point is connected to the inverted input of the op-amp, the circuit will produce a negative sum of any number of input voltages. Likewise, when the collection point is connected to the non-inverted input of the op-amp, it will produce a positive sum of the input voltages.

If individual input resistors are equal "NOT", scaling aggregation booster can be made. Then the equation should be changed as follows:

To make mathematics a little easier, we can rearrange the above formula to make feedback resistance the subject of the equation that gives the Rε output voltage:

If more input resistance is connected to the amplifiers that reverse this input terminal, the output voltage is easily calculated.

Sometimes we need a collection circuit to combine two or more voltage signals without any amplification. By bringing all the resistors of the above circuit to the same R value, the op-amp will have an output voltage equal to a unity voltage gain and the direct sum of all input voltages, as shown:

The Aggregation Amplifier is a really flexible circuit and allows us to effectively make several individual input signals together with "Add" or "Collect" (hence the name). If the input resistors, R1, R2, R3, etc. are all equal, a "unit gain reversing collector" will be made. However, if the input resistors have different values, a "scaling collection amplifier" is produced that will produce a weighted sum of the input signals.

## Collector Amplifier Circuit Example

Find the output voltage of the Aggregation Amplifier circuit below.

### Collector Amplifier

For the gain of the circuit we can use the formula previously found:

Now we can change the values of the resistors in the circuit as follows:

We know that the output voltage is the sum of two reinforced input signals and is calculated as follows:

Then the output voltage of the aggregation amplifier circuit above is given as -45 mV and is negative as an inverter amplifier.

## Inverted Collector Amplifier

However, in addition to creating reversible aggregation amplifiers, we can also use it to produce an aggregation amplifier that does not invert the inverted input of the transactional amplifier. Above we found that a reversing aggregation amplifier produces a negative sum of input voltages, then we followed that the non-inverted aggregation amplifier configuration will produce a positive sum of input voltages.

As its name suggests, the non-inverted aggregation amplifier is based on the configuration of the inverted operational amplifier circuit, with the application of the input (ac or dc) to the non-inverting (+) terminal. feedback and gain are achieved by feeding part of the output signal (VOUT) back to the inverter (-) terminal as shown.

## Inverted Collector Amplifier

So what is the advantage of non-reversible configuration compared to the reversible aggregation amplifier configuration? Besides the clearest fact that the op-amp output voltage is in the same phase as the input of VOUT, and the output voltage is the weighted sum of all inputs determined by resistance rates, the biggest advantage of the inverted total is that the input impedance is much higher than the standard inverter amplifier configuration, since there is no virtual soil condition between the input terminals.

In addition, if the closed loop voltage gain of op-amps is changed, the input collection part of the circuit is not affected. However, there is more math in selecting weighted gains for each entry at the collection junction, especially if there are more than two entries, each with a different weight factor. However, if all inputs have the same resistance values, the corresponding math will be much less.

If the closed loop gain of the inverted transactional amplifier is made equal to the total number of inputs, the output voltage of the op-amps will be exactly equal to the sum of all input voltages. This means that for a two-input non-inverter aggregation amplifier, the op-amp gain is equal to 2. For a collection amplifier with three inputs, the op-amp gain is 3, etc. This is due to the fact that the currents flowing at each input resistance have a function of the voltage in all their inputs. If all input resistors are made equal (R1 = R2), circulation currents will be canceled and output voltage inputs will be totaled because they cannot flow into the high impedance inverter input of the op-amp.

Currents flowing into the input terminals for the 2-input non-inverting collection amplifier can be defined as follows:

If we make the two input resistances equal in value, it becomes R1 = R2 = R.

Non-inverted amplifiers closed cycle voltage gain AV is given as follows: 1 + RA/RB. If we make this closed cycle voltage gain equal to 2 by making RA = RB, the output voltage is equal to the sum of all input voltages as shown in VO.

## Inverted Collector Amplifier Output Voltage

Therefore, for a 3-input non-inverting collection amplifier configuration, adjusting the closed loop voltage gain to 3 will make VOUT equal to the sum of three input voltages, V1, V2 and V3. Similarly, for a four-entry summer, the closed-cycle voltage gain is 5 for a summer with 4 and 5 inputs, and so on. Also, if the amplifier of the collection circuit is connected as a unit tracker, where ra is equal to zero and RB is forever equal, without voltage gain, the output voltage VOUT will be exactly equal to the average value of all input voltages. This is VOUT = (V1 + V2)/2.

## Collection Amplifier Applications

So, what can we use aggregation amplifiers that reverse or do not reverse. If the input resistors of a collection amplifier are connected to ponciometers, individual input signals can be mixed together in varying quantities.

For example, when measuring the temperature, you can add a negative offset voltage to allow the output voltage or screen to read "0" at the freezing point, or you can produce a sound mixer to combine or mix individual waveforms (sounds) from different source channels (vocals, instruments, etc.).

## Collector Amplifier Audio Mixer

Another useful application of the Aggregation Amplifier is predominantly in the form of a total digital-analog converter (DAC). If the input resistances of the collection amplifier double for each input, for example, 1kΩ, 2kΩ, 4kΩ, 8kΩ, 16kΩ, etc., then a digital logical voltage, a logic level "0" or a logic level "1" in these inputs will produce an output that is the weighted sum of digital inputs. Consider the circuit below.

## Digital to Analog Converter

Of course, this is a simple example. In this DAC aggregation amplifier circuit, the number of individual bits that make up the word input data and 4 bits in this example will ultimately determine the output step voltage as a percentage of the full-scale analog output voltage.

In addition, the accuracy of this full-scale analog output depends on the accuracy of the resistance values used for input bits RIN, as well as the fact that the voltage levels of the input bits are consistently 0V for "0" and 5V for "1".

Fortunately, to overcome these errors, at least from our point of view, commercially available Digital-to-Analoga and Analog to Digital devices are already available with built-in high-precision reflector ladder networks.