Eviren Yükselteç (OPAMP) / Inverting Operational Amplifier

In this article, we will examine the Inverting Operational Amplifier circuits. In our previous article, we found that the Open Loop Gain (AVO) of a transactional amplifier can be very high, 1,000,000 (120dB) or more.

However, this very high gain is not a real use for us, as it makes the amplifier both unstable and difficult to control. Because the smallest of the input signals will be enough to cause only a few micro volts (μV) to cause the output voltage to saturate and the voltage that loses full control of the output to swing towards one or the other.

Since the open loop DC gain of a transactional amplifier is extremely high, we can afford to lose some of this high gain by connecting a suitable resistor through the amplifier to the inverter input terminal throughout the amplifier to both reduce and control the overall gain. This then produces the effect, commonly known as Negative Feedback.

Negative Feedback is the process of "feedback" part of the output signal to the input. However, to make feedback negative, an external Feedback Resistance is called Rf. This feedback connection between the output and the inverted input terminal forces the differential input voltage towards zero.

This effect produces a loop circuit closed to the amplifier, which results in the amplifier's gain now being called Closed Loop Gain. Then a closed loop inverter amplifier uses negative feedback to accurately control the overall gain of the amplifier. However, the cost of this will result in a decrease in amplifier earnings.

This negative feedback results in the input voltage plus the sum of the negative feedback voltage, resulting in the input terminal having a different signal on it than the actual input voltage, giving it a Collection Point label or term. Therefore, using an Input Resistance, Rin, we must separate the actual input signal from the inverting input.

Since we do not use positive inverting input, it is connected to a common soil or zero voltage terminal, as shown below. However, the effect of this closed loop feedback circuit causes the voltage potential in the inverted input to be equal to the voltage potential in the input. Inverted input that produces a virtual world collection point, as it will have the same potential as grounded reference input. in other words, the op-amp becomes a "differential amplifier".

Reversing Operational Amplifier Configuration

inverting amplifier

In this Inverter Amplifier circuit, the transactional amplifier is connected with feedback to produce a closed loop operation. When dealing with transactional amplifiers, there are two very important rules to remember about inverter amplifiers, these: "The current does not flow into the input terminal" and "V1 is always equal to V2". But in real-world op-amp circuits, both of these rules are somewhat broken.

This is because the combination of input and feedback signal (X) has the same potential as positive ( + ) input at zero volts or in the soil. Then the merger is a Virtual World. Due to this virtual earth node, the input resistance of the amplifier is equal to the value of the input resistance, the closed loop gain of Rin and the inverter amplifier can be adjusted by the ratio of two external resistances.

  • No Current Flow to Input Terminals
  • Differential Input Voltage is Zero in V1 = V2 = 0 (Virtual Soil)

Then, using these two rules, we can deride the equation to calculate the closed-loop gain of an inverter riser.

The current ( i ) flows through the resistance network as shown.

inverting amplifier
inverting amplifier

It is then awarded as a Closed Cycle Voltage Gain of an Inverter Riser.

inverting amplifier

and this can be transferred to give Vout as follows:

inverting amplifier

The negative sign in the equation indicates that the output signal is reversed by input because 180o is out of phase. This is because the feedback is negative in value.

The output voltage Vout equation also indicates that the circuit is linear in nature for a fixed amplifier gain as Vout = Vin x Gain. This feature can be very useful to convert a smaller sensor signal to a much larger voltage.

Another useful application of a reversing amplifier is a "transducer amplifier" circuit. A Transducer Amplifier, also known as the "Transempedance amplifier", is basically a current-to-voltage converter (Current "input" and Voltage "output"). In low-power applications, they can be used to convert a very small current produced by a photo diode or photo-sensing device, etc., into an available output voltage that is proportional to the input current as shown.

Transdirenç Amplifier Circuit

inverting amplifier

Activated by the simple light above, the circuit converts the current produced by the photo diode into a voltage. Feedback resistance Rε adjusts the operating voltage point at the inverting inlet and controls the amount of output. The output voltage is given as Vout = Is x Rε. Therefore, the output voltage is proportional to the amount of input current produced by the photo diode.

Op-amp Question Example

Let's find the closed cycle gain of the inverter amplifier circuit below.

inverting amplifier

Use the previously found formula for the gain of the circuit

inverting amplifier

now we can change the values of the resistors in the circuit as follows,

Rin = 10kΩ and Rε = 100kΩ

and the gain of the circuit is calculated as follows: -Rε/Rin = 100k/10k = -10

Therefore, the closed loop gain of the above inverter amplifier circuit is given as -10 or 20dB (20log(10)).