![]() NOTE: In all the previous calculations, we took a special as R 3 = R 1 and R 4 = R 2. Using this rule, we can replace V –in the above equation with the previously calculated V + value.Īfter replacing and performing some calculations, we arrive at: Using this rule as a reference, we can apply Kirchhoff’s Current Law at the Inverting Input Terminal and we get:Īnother important rule about Operational Amplifier is that it tries to keep the Input Terminals at same voltage. So, the current entering the Inverting Terminal I 1 is same as the current leaving the terminal I 2. Now, from the basic understanding of the Operational Amplifier, we can say that no current flows in or out of the Op Amp input terminals. We already calculated this in the previous derivation using the voltage divider rule. This circuit is similar to the previous one, except this a special case of R 3 = R 1 and R 4 = R 2 of the previous circuit.įirst, we have to determine the voltage at the Non-Inverting terminal (V +). Let us assume the following circuit for a Differential Amplifier. Let us now calculate the output voltage by determining the current at the Inverting Input of the Op Amp. Alternative way to Calculate Output Voltage Now, from this equation, it is clear that the differential voltage (V 1 – V 2) is multiplied by the gain R 2 / R 1. If we apply these values in the above equation, we the output voltage as: So, to reduce the complexity and simply the equation, let us take a special case where R 3 = R 1 and R 4 = R 2. This is the output voltage of a Differential Amplifier. To get the final V OUT value, we have to add these values. ![]() V OUT+ = V 1 (R 2 / R 1 + R 2) (1 + (R 4 / R 3))Ĭoming to the Inverting Output V OUT–, we have to calculate it with respect to the inverting input V 2 and the Inverting Gain G –.įrom the above circuit, we can calculate the Inverting Gain G – as: Using the values of V + and G + in the equation of V OUT+, we get If V + is the input to the non-inverting terminal and G + is the gain of the Non-Inverting Amplifier, then non-inverting output V OUT+ is given by:įrom the above circuit, we can calculate the Non-Inverting Gain G + as: Resistors R 1 and R 2 form a Voltage Divider Network with V 1 as the Input Voltage and V + as the output voltage and this V + is applied at the non-inverting terminal. We can calculate the value of V + using the Potential Divider Rule. Let V + be the voltage at the Non-Inverting terminal and V – be the voltage at the Inverting Terminal of the above Differential Amplifier Circuit. So, to calculate the output voltage of a Differential Amplifier, we will use both the Inverting and Non-Inverting outputs and add them together. If you observe the above circuit of the difference amplifier, it is a combination of both the Inverting Amplifier and the Non-Inverting Amplifier. Here, V 1 is the Non-Inverting Input Voltage, V 2 is the Inverting Input Voltage and V OUT is the Output Voltage. The following image shows a simple Differential Amplifier using an Op Amp. So, a practical differential amplifier uses a negative feedback to control the voltage gain of the amplifier. But the open loop voltage gain of an operational amplifier is too high (ideally infinite) to be used without a feedback connection. An operational amplifier is a difference amplifier it has an inverting input and a non-inverting input. It is the input stage of every Operational Amplifier.Ī Difference Amplifier or a Differential Amplifier amplifies the difference between the two input signals. The Differential Pair or Differential Amplifier configuration is one of the most widely used building blocks in analog integrated-circuit design. For more information on Op-Amp, read Operational Amplifier Basics. Operational Amplifier is internally a Differential Amplifier (its first stage) with other important features like High Input Impedance, Low Output Impedance etc. Light Activated Switch using Differential Amplifier.Characteristics of a Differential Amplifier.Important Parameters of Differential Amplifier.Alternative way to Calculate Output Voltage.
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