Open loop op amp Configuration & Closed loop op amp configuration
Table of Contents
Open loop op amp Configuration
Open loop op amp Configuration
The term “Open-loop” denotes a system in which the input receives no Feedback of any kind from the output. The op-amp acts as a very high gain Amplifier when it is connected in Open-loop. There are three op-amp open loop Configurations, including
1. Differential Amplifier
2. Inverting Amplifier
3. Non-inverting Amplifier
The above Classification is made based on the number of inputs used and the Terminal to which the input is applied. The op-amp Amplifies both ac and dc input signals. Thus, the input signals can be either ac or dc voltage.
1. Open loop Differential Amplifier:
The op-amp amplifies the difference between the two input voltages when the inputs are applied to both its inverting and non-inverting input terminals in this configuration. The configuration of the open-loop differential amplifier is shown in Figure.
The input voltages are represented by Vi1 and Vi2. The source resistance Ri1 and Ri2 are negligibly small in comparison with the very high input resistance offered by the op-amp, and thus the voltage drop across these source resistances is assumed to be zero. The output voltage V0 is given by
V0 = A(Vi1 – Vi2 )
where A denotes the voltage gain for large signals. The voltage gain A times the difference between the two input voltages is therefore equal to the output voltage. This explains why this set up is referred to as a differential amplifier. The large signal voltage gain A is also known as the open-loop gain A in open-loop configurations.
2. Open loop Inverting Amplifier:
The non-inverting input terminal of the op-amp is connected to ground in this configuration, and the inverting input terminal of the op-amp receives the input signal. Figure depicts the open-loop inverting amplifier’s circuit.
The output voltage is 1800 out of phase with respect to the input and hence, the output voltage V0 is given by,
V0 = -AVi
Thus, in an inverting amplifier, the input signal is amplified by the open-loop gain A and in phase
– shifted by 1800.
3. Open loop Non-inverting Amplifier
The Open-loop Non-inverting Amplifier is depicted in Figure. The Non-inverting input terminal of the op-amp receives the input signal, and the inverting input terminal is grounded. The open-loop gain A amplifies the input signal, and the output is in phase with the input signal.
Only very small input voltage values can be used in any of the aforementioned open-loop configurations. According to the ideal transfer characteristics of the op-amp shown in figure, the output is driven into saturation even for voltage levels that are barely above zero. As a result, the output of the op-amp is either in negative or positive saturation, or alternates between positive and negative saturation levels, when it is operated in the open-loop configuration. As a result, op-amps cannot be configured with an open-loop in linear applications.
Limitations of Open loop Op amp Configuration
First, when the output voltage exceeds the Op-saturation amp’s level, clipping of the output waveform can happen in Open-loop Configurations. This is caused by the Op-extremely amp’s high Open-loop gain. With the help of this feature, it is actually possible to Accurately and Distortion-free amplify very low Frequency signals with an order of Microvolts or even lower. Though Amplification for those applications is nearly impossible to achieve in the lab, signals of this magnitude are susceptible to noise.
Second, the Op-open-loop amp’s gain is not constant and changes with changes in temperature and power supply. Additionally, the Majority of Open-loop op amps have extremely low Bandwidths. Because of this, op-amps in Open-loop Configuration are Inappropriate for use in ac applications. The widely used 741 IC’s Open-loop Bandwidth is roughly 5Hz. However, the Bandwidth Requirement is much higher in almost all ac applications.
The Open-loop op-amp is Typically not used in linear applications for the reasons mentioned. The Open-loop op amp Configurations are Utilized in a few Non-linear applications, such as stable Multivibrators, square wave Generators, and Comparators.
Closed loop op amp configuration
By sending feedback from the output to the input, either directly or via another network, the op-amp can be used effectively in linear applications. Negative feedback or degenerative feedback is the term used to describe signal feedback that is 1800 times out of phase with the input. Positive feedback, also known as regenerative feedback, is the term used when the feedback signal is in phase with the input signal.
An op – amp that uses feedback is called a closed – loop amplifier. The most commonly used closed – loop amplifier configurations are
1. Inverting amplifier (Voltage shunt amplifier)
2. Non-Inverting amplifier (Voltage – series Amplifier)