Differential amplifiers simply explained
A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. Single amplifiers are usually implemented by either adding the appropriate feedback resistors to a standard op-amp , or with a dedicated integrated circuit containing internal feedback resistors. It is also a common sub-component of larger integrated circuits handling analog signals. In practice, however, the gain is not quite equal for the two inputs. A more realistic expression for the output of a differential amplifier thus includes a second term:.
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Content:
- [BEST] Applications, Advantages, Disadvantages of Differential Amplifier
- What is an Operational Amplifier?
- 1.6: The Differential Amplifier
- What is differential amplifier ? – Differential amplifier theory
- Differential Amplifier Circuit Tutorial using BJT and Opamp
- What is the purpose of using a differential amplifier? (Common-mode rejection ratio: CMRR)
[BEST] Applications, Advantages, Disadvantages of Differential Amplifier
In this tutorial, we will learn about one of the important circuits in analog circuit design: A Differential Amplifier. It is essentially an electronic amplifier, which has two inputs and amplifies the difference between those two inputs. We will see the working of a Differential Amplifier, calculate its gain and CMRR, list out some important characteristics and also see an example and an application. The Differential Pair or Differential Amplifier configuration is one of the most widely used building blocks in analog integrated-circuit design.
It is the input stage of every Operational Amplifier. A Difference Amplifier or a Differential Amplifier amplifies the difference between the two input signals.
An operational amplifier is a difference amplifier; it has an inverting input and a non-inverting input. But the open loop voltage gain of an operational amplifier is too high ideally infinite to be used without a feedback connection. So, a practical differential amplifier uses a negative feedback to control the voltage gain of the amplifier. The following image shows a simple Differential Amplifier using an Op Amp.
If you observe the above circuit of the difference amplifier, it is a combination of both the Inverting Amplifier and the Non-Inverting Amplifier. So, to calculate the output voltage of a Differential Amplifier, we will use both the Inverting and Non-Inverting outputs and add them together.
To get the final V OUT value, we have to add these values. The above equation looks complex. Hence, it is Differential Amplifier. Let us now calculate the output voltage by determining the current at the Inverting Input of the Op Amp. Let us assume the following circuit for a Differential Amplifier. We already calculated this in the previous derivation using the voltage divider rule. The value is given by:. So, the current entering the Inverting Terminal I 1 is same as the current leaving the terminal I 2.
Actually, instead of this we have to consider the ratios i. The gain of a difference amplifier is the ratio of the output signal and the difference of the input signals applied. From the previous calculations, we have the output voltage V OUT as. Due to this, the Differential Amplifier is often used at the input stage of a system to strip the DC or the Common-Mode noise from the input.
All these calculations are true if and only if the Resistances form the Balanced Bridge Condition. Since the output of a practical difference amplifier depends upon the ratio of the input resistances, if these resistor ratios are not exactly equal, the common mode voltage V CM will not be completely cancelled.
Because it is practically impossible to match resistor ratios perfectly, there is likely to be some common mode voltage. With the common mode input voltage present, the output voltage of the differential amplifier is given as,. Hence, the CMRR is infinite. A Wheatstone Bridge Differential Amplifier circuit design is as shown in the following image.
This circuit behaves like a Differential Voltage Comparator. By connecting one input to a fixed voltage and the other to a thermistor or a light-dependent resistor , the differential amplifier circuit detects high or low levels of temperature or intensity of light as the output voltage becomes a linear function of the changes in the active leg of the resistive bridge network.
A Wheatstone Bridge Differential Amplifier can also be used to find the unknown resistance in the resistive bridge network, by comparing the input voltages across the resistors. The voltage V 2 is determined by the variable resistor V R1. The resistors R 1 and R 2 act as a potential divider network. A fixed reference voltage is applied to the inverting input, through R 1 and R 2.
The same circuit can be modified to detect variations in temperature, simply by replacing the LDR with a Thermistor. By interchanging the positions of LDR and V R1 , the circuit can be made to detect dark or light or heat or cold in case of a thermistor. The differential gain of the amplifier is and the value of CMRR is. Your email address will not be published. Differential Amplifier.
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What is an Operational Amplifier?
In this post, differential amplifier using BJT and differential amplifier using op-amps are explained in detail. Please go through both of them to get a better understanding. The circuit diagrams and detailed equations are provided along with the article. Please go through them. A differential amplifier is designed to give the difference between two input signals. The circuit is shown below.
1.6: The Differential Amplifier
However, it is possible, as we will see during this article, to supply both inputs of an op-amp with signals in order to obtain an output that is directly proportional to the input difference. This new configuration is commonly known as a differential amplifier. We introduce this new configuration in the first section where we present its functioning and demonstrate its output expression. A simple example of a differential amplifier along with some basic differential-based applications is presented in the second section. Finally, the last section briefly presents the instrumentation amplifiers which are essential differential-based configurations found in acquisition chains to treat sensor outputs. The goal of this section is to introduce the reader to the differential amplifier configuration and to demonstrate its output expression. In Figure 1 , we present the circuit representation of the basic differential amplifier. The inputs are labeled V 1 and V 2 and are in connection with the op-amp inverting and non-inverting pins through the resistors R 1 and R 2. In the following, we will suppose the op-amp to be ideal, which is a very good approximation of modern real amplifiers. After rearranging this equality, we finally obtain the output expression for a differential amplifier in the general case, which is a superposition of both inputs V 1 and V 2 :.
What is differential amplifier ? – Differential amplifier theory

Most modern operational amplifiers utilize a differential amplifier front end. In other words, the first stage of the operational amplifier is a differential amplifier. This circuit is commonly referred to as a diff amp or as a long-tailed pair. A diff amp utilizes a minimum of 2 active devices, although 4 or more may be used in more complex designs.
Differential Amplifier Circuit Tutorial using BJT and Opamp
Difference amplifier is used to amplify the difference between the inputs. Along with the circuit design, we will also learn the difference amplifier equation here. After learning what is operational amplifier , we will also learn:. Difference or differential amplifiers are used in various applications where there is a need to amplify the difference between two input signals. They are first cousins of the instrumentation amplifier , the most useful and popular amplifier.
What is the purpose of using a differential amplifier? (Common-mode rejection ratio: CMRR)
Differential amplifiers are used mainly to suppress noise. Noise consists of typical differential noise and common-mode noise, of which the latter can easily be suppressed with an op-amp. There are two main causes of common-mode noise:. In either case, the ground potential, a reference for a circuit, fluctuates because of noise. It is difficult to remove common-mode noise with typical filters. Differential amplifiers are used as a means of suppressing common-mode noise. The op-amp configures this differential amplifier as the main circuit.
An operational amplifier or op-amp is simply a linear Integrated Circuit IC having multiple-terminals. The op-amp can be considered to be a voltage amplifying device that is designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. It is a high-gain electronic voltage amplifier with a differential input and usually a single-ended output.
The differential amplifier is one of the important circuits in analog systems and circuit designs. It is an electronic amplifier that has two inputs and amplifies the voltage difference between those inputs. Among these, the commonly used differential amplifier is the amplifier made using Op-Amps because they are suitably configured to result in a much practical differential amplifier. In the differential amplifier made using BJTs, input signals V1 and V2 are applied to the base terminal of the transistors and the outputs are collected from the collector terminal of the transistors. Considering the differential amplifier built using BJTs, if the input voltage V1 at transistor Q1 is sinusoidal, then as V1 goes on increasing, the transistor Q1 starts conduction which results in a large collector current in Q1 increasing the voltage drop across Rc1, causing a decrease in output voltage V
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Click Here to See how you get new Article. Amplifier , Analog Electronics , Electronics. The main application of Differential Amplifier is, it creates a difference between two input signals and then amplifies the differential signal.
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