Branch:- Electrical (09) Analog Electronics 2130902 UNIT- OPERATIONAL AMPLIFIER Branch:- Electrical (09) PREPARED BY:- PRITESH DESAI (020) NIDHI GANATRA (026) VIVEK GARALA (029)

INTRODUCTION Electronic systems usually process information in either analog or digital form. In order to process the two different kinds of signals, analog circuits and digital circuits have been devised. Most circuits found in analog systems are linear circuits in which one voltage (or current) is meant to be linearly proportional to another. Linear active circuits are also known as amplifiers.

An amplifier can be modeled as a two-port device, that is, a box with two pairs of terminals designated as input and output, as shown in Figure Let the amplifier block be connected to a current source at the input terminals, as shown in Figure and to a load resistance RL at its output terminals. Find Vout.

PRACTICAL CHARACTERISTIC OF OPERATIONAL AMPLIFIERS The op-amp has high input impedance and low output impedance. Therfore, it will not draw much current from the connected external input voltage signal source. As a result, the loading effect is avoided. Due to low output resistance it delivers the maximum output. Based on these characteristics, due to biasing voltages applied to the IC and the current drawn by the IC from the DC-supplying (bias) voltages, various parameters are defined. INPUT RESISTANCE Ri OPEN-LOOP VOLTAGE GAIN A OUTPUT RESISTANCE Ro

COMMON-MODE REJECTION RATIO (CMRR) INPUT OFFSET VOLTAGE VOS INPUT BIAS CURRENT IB INPUT OFFSET CURRENT IOS POWER-SUPPLY REJECTION RATIO(PSRR) MAXIMUM DIFFERENTAIL INPUT VOLTAGE MAXIMUM COMMON-MODE INPUT VOLTAGE OUTPUT VOLTAGE SWING INTERNAL FREQUENCY COMPENSATION

SLEW RATE NOISE STABILITY FREQUENCY RESPONSE

INPUT RESISTANCE (Ri) :- Input resistance is the open-loop incremental resistance looking into the two input terminals, and is typically 2M. Manufacturers sometimes quote the resistance between inputs and ground. OUTPUT RESISTANCE (Ro) :- The open-loop output resistance is usually between 50 and 500 , with a typical value of 75 for the 741. Thus one can see that Figure is the representation of an op amp as a circuit element or block

OPEN-LOOP VOLTAGE GAIN A :- The op amp amplifies the difference Vd between the voltage on the non inverting (+) terminal and the inverting (−) terminal; see Figure The term “open loop” implies that there is no external feedback connection between the output and either of the inputs. A is defined as the ratio of the change in output voltage to the change in differential input voltage, usually for a load resistance of no less than 2 k. A typical value for A is 2 × 10 5

Common-Mode Rejection Ratio (CMRR):- This parameter indicates the capability of the op-amp to reject noise. The higher the value of CMRR, the better it is. CMRR is defined as the ratio of the differential voltage gain, Ad, to the common mode voltage gain, Acm. (cm = common mode)

INPUT OFFSET VOLTAGE Vos :- When both inputs are tied to ground, i.e., both differential-mode and common-mode inputs are zero, the output should be zero. In practice there will be mismatches in amplifier components, and if there is a mismatch in an input stage, the effect will be amplified, leading to a significant output voltage. The input offset voltage VOS is the differential input voltage required to make the output zero, and is typically 1 mV. With some op amps

INPUT BIAS CURRENT IB :- This is the average of the currents that flow into the inverting and non-inverting input terminals of the op-amp. For an ideal op-amp IB = 0 Amps For a practical op-amp IB = 500 nA For a precision op-amp, IB is typically 10 nA.

INPUT OFFSET CURRENT Ios:- Though for an ideal op-amp, the input impedance is ∞, it is not so practically. So the IC draws current from the source of the voltage, however small it may be. The algebraic difference between the currents into the inverting and non-inverting terminals is referred to as input offset current Iio. Iio = |IB1 − IB2|

OUTPUT VOLTAGE SWING:- Ideally this is equal to the difference between the two supply rail voltages, although in practice it is a few volts less. INTERNAL FREQUENCY COMPENSATION:- Some op amps, such as the 741, have internal RC networks which are intentionally designed to reduce gain at high frequency. The result (shown in Figure 5.2.4) is that the open-loop gain begins to fall at a few hertz and then has a characteristic falling at 20 dB/decade or 6 dB/octave (i.e.gain ∝ 1/f ) until eventually the gain becomes unity (0 dB) at about 1 MHz

OUTPUT VOLTAGE SWING :- Ideally this is equal to the difference between the two supply rail voltages, although in practice it is a few volts less. EXTERNALFREQUENCY COMENSATION:- For applications requiring a more extended high-frequency response, there are op amps with no internal compensation, and external frequency-compensation terminals are provided on these op amps (for example, the 709) so that the frequency response can be tailored to avoid instability without the heavy degrading of frequency response due to internal compensation.

. SLEW RATE: This is defined as the maximum rate of change of output voltage per unit time. The input capacitance of the op-amp circuit prevents it from responding instantaneously to high frequency signals. If a square wave input or pulse of high frequency is applied as input, at the output the slope of the leading edge and trailing edge is measured and the larger value is computed. This gives SR.

NOISE:- This refers to the small, rapidly varying, random spurious signals generated by all electronic circuits. Noise places a limit on the smallness of signals that can be used. The subject of random signals and noise belongs to a branch of electrical engineering known as communication theory.

STABILITY:- The amplifier is said to be stable when it performs its function reliably under all normal operating conditions. By definition, a system is stable if its response to an excitation that decays to zero with time also decays to zero. Instability can come about in various ways, and it is a very common difficulty, which must be prevented. In almost all cases, op-amp circuits can be classified as feedback circuits. Feedback of an improper kind can lead to instability or oscillation of an op-amp circuit.

Frequency Response :- As with all electronic circuits, op amps have limited frequency response. Because of the negative feedback of the circuit, the pass band of an op-amp circuit is usually much larger than that of the op amp by itself. Typically with a given op amp, increasing the bandwidth of an op-amp circuit will decrease the voltage gain in the same proportion..

REFRENCE :- INTRODUCTION TO ELECTRICAL ENGINEERING Mulukutla S. Sarma Northeastern University GUIDE BY :- Prof. Tushar dave

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