Op-amp is in closed loop configuration when there is a connection either direct or via another network exist between the input and output terminals.We can control the gain of op-amp if we introduce a modification in the basic circuit.This modification involves a feedback ie the input signal is fed back to the input either direct or via another network. Different feedback configurations An op-amp that uses feedback is called a feedback amplifier.A feedback amplifier is sometimes referred to as a closed loop amplifier because the feedback forms a closed loop between the input and the output.A close loop amplifier can be represented by using two blocks one for op-amp and the other for a feedback circuit.These connections are classified according to whether the voltage or current is fed read more

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When connected in open-loop configuration,the op-amp functions as a high gain amplifier.These are three open loop op-amp configurations. Differential Amplifier Inverting Amplifier Non-Inverting Amplifier These configurations are classed according to the number of inputs used and the terminal to which the input is applied when a single input is used. Disadvantages of open loop configurations The open loop of the op-amp is very high.Therefore only the smaller signals having low frequency may be amplified accurately without distortion. Open loop Voltage gain of the op-amp is not a constant voltage gain varies with changes in temperature and power supply as well as mass production techniques.This makes op-amp unsuitable for many linear applications Bandwidth of most open loop op-amps read more

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Vo=A(V1-V2) This is the basic op-amp equation in which the output offset voltage is assumed to be zero.The graphic representation of this equation is shown;where the output voltage ,Vo is plotted against input difference voltage Vid,keeping gain A constant.The output voltage cannot exceed the positive and negative saturation voltage.These saturation voltages are specified by an output voltage swing ratings of an op-amp for given values of supply voltages.The output voltage is directly proportional to the input difference voltage until it reaches the saturation voltages and thereafter the output voltage remains constant. This curve is called ideal voltage transfer curve read more

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An ideal op-amp would exhibit the following characteristics Infinite Voltage gain,A Infinite input resistance,Ri so that almost any signal source can drive it and there is no loading of the preceding stage Zero output resistance,Ro so that output can drive infinite number of other devices Zero output voltage when input voltage is zero Infinite bandwidth so that any frequency signal from zero to infinite Hertz can be amplified without attenuation Infinite common mode rejection ratio(CMRR)so that the output common mode noise voltage is zero Infinite slew rate so that the output voltage changes occur simultaneously with input voltage changes Equivalent Circuit of an Op-Amp Output volatge,Vo=AVid=A(V1-V2) Vid=difference input voltage V1= Voltage at the non-inverting input terminal with read more

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1)Input offset Voltage Input offset voltage is the the voltage that must be applied between the two input terminals of an op-amp to null the output.Typical value of 741 IC is 6mV dc. 2) Input offset current The algebraic difference between the current in the inverting and non inverting terminal is known as the input offset current Iio.As the matching between two terminals increases,the difference between IB1 and IB2 become smaller.Typical value for 741 IC is 200mA(max). 3)Input Bias Current IB is the average current flows in the inverting and non-inverting terminal of an op-amp. IB = (IB1 + IB2 )/2 Typical value for 741 is 500mA 4) Large Signal Voltage gain It is the ratio of the output voltage and the differential input voltage A = Output voltage/Differential input = read more

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