best op amp to fit the application, based on the required bias current, bandwidth, distortion, and so forth. CHAPTER 1. Op Amp Basics. James Bryant, Walt Jung. Op-amps are integrated circuits composed of many transistors & resistors such . LTC homeranking.info) are chopper. The operational amplifier (op-amp) is a voltage controlled voltage source with very to the open loop gain A. For a op-amp powered with VCC= +10V and .

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the internal workings of an op amp, so in this work a more macro view will be taken. There are The op amp is one of the basic building blocks of linear design. CHAPTER 1: OP AMP BASICS. James Bryant, Walt Jung, Walt Kester. Within Chapter 1, discussions are focused on the basic aspects of op amps. After a brief. Operational Amplifier Tutorial about Operational Amplifier Basics and Op-amps including Idealized Characteristics and Op-amp Open Loop Gain.

In most Op-Amps there is a small offset because of their inherent property and results from the mismatches in the input bias arrangement. It is basically the ability on how fast the output of the Op-Amp can change. This occurs because the compensating capacitor must be charged before the output voltage can change to the higher level. The use of coupling capacitors for input and output is required for this configuration. Transfer Characteristics of Op-Amp:

It had a single inverting input. John R. Ragazzini of Columbia University. In the same paper, a footnote mentioned an Op-Amp designed by a student that would turn out to be quite significant.

Goldberg designed a chopper stabilized Op-Amp. This set-up Dr. Philbrick Researches, Incorporated. With the birth of the transistor in , and the silicon transistor in , the concept of ICs becomes a reality.

The introduction of the planar process in made transistors and ICs stable enough to be commercially useful. By , solid-state, discrete Op-Amps were being produced. Varactor Bridge Op-Amp: Varactor bridge Op-Amps started to be produced in the early s. These were designed to have extremely small input current are still amongst best Op-Amps available in terms of common-mode rejection with the ability to correctly deal with hundreds of volts at their inputs.

During the s, single sided supply Op-Amps also becomes available.

The result is that it can operate in many applications with the negative supply pin on the Op-Amp being connected to the signal ground, thus Dr. The LM released in , was one the such Op-Amps that came in a Quad package four separate Op-Amps in one package and became an industry standard. Functional Blocks of Op-Amp: Figure 1. The input stage is a differential amplifier followed by more stages of gain, and a class B push-pull emitter follower. Since, a differential amplifier is the first stage; it determines the input characteristics of the Op- Amp.

In most Op-Amps the output is single ended, as shown in the symbol. With positive and negative supplies, the single ended output is designed to have a quiescent value of zero.

This way, zero input voltage ideally results in zero output voltage. Block diagram of an Op-Amp. The difference between ordinary amplifier with differential amplifier is schematically shown in Fig. Difference between ordinary and differential amplifier. For instance, some do not use a class B push-pull output, and others may have a double-ended output.

Also, op-amps are not as simple as Fig. The internal design of a monolithic Op-Amp is very complicated, using dozens of transistors as current mirrors, active loads, and other innovations that are not possible in discrete designs. For our needs, Fig 1. The equivalent circuit of the Op-Amp device is shown in Fig.

Equivalent circuit of Op-Amp. Ri and Ro are the input and output resistances of the Op-Amp. The symbol A represents the open-loop voltage gain. Transfer Characteristics of Op-Amp: The graph that relates the output voltage to the input voltage is called the voltage transfer curve and it is fundamental in designing and understanding amplifier circuits.

The voltage transfer curve of the Op- Amp is shown in Fig. The voltage transfer curve has mainly three zones, namely linear zone, positive saturation zone and negative saturation zone. The operation of these three zones of the voltage transfer curve is explained below. Case 1: Linear zone: For every Op-Amp, a linear zone is specified. As the name suggests, in this zone the output voltage is linear to the input voltages. When the error Dr. Transfer characteristics of Op-Amp.

In the linear region, the slope of the line relating to the output voltage with the error voltage v1 — v2 , is very large, indeed it is equal to the open loop gain A. Let me take an example. It is to be noted that most of the Op-Amp applications are based on the linear operating zone. Case 2: Negative saturation zone: It can be seen from the graph that the output voltage does not vary and remains constant at —VEE, even though the error voltage varies.

Case 3: Positive saturation zone: Characteristics of Ideal and Practical Op-Amps: For an ideal Op-Amp, the open loop voltage gain A is infinite. This fact resulted that the input resistance Ri is infinite, which in turn implies that the amplifier will make no power demands on the input signal source.

This means that the Op-Amp will draw minute power from input signal source to amplify it. Thus Op-Amp can be used to amplify weak signals. On the other hand, the ideal condition, i. In summary, the ideal Op- Amp conditions are: Characteristics do not drift with temperature The comparison of the various characteristics of ideal and practical Op-Amps are shown in Table I.

Table I: In the next section, I shall discuss about few important characteristics of practical Op-Amp. For practical Op-Amps, the gain decreases with the increase in the frequency. The frequency at which the gain decreases to 1 or unity, in dB it is 0 is called the unity- gain frequency.

A typical Op-Amp frequency response curve is shown in Fig. The circuit can be constructed to obtain desired gain. However, for circuit with higher gain, one has to compromise with the bandwidth.

Check the slope of the frequency response curve shown in Fig. The bandwidth decreases for circuit with higher gain. Note that the gain and bandwidth product is a constant. Here A and BW are the gain and bandwidth respectively. Hence, the gain- bandwidth product is 1 MHz.

Typical frequency response of a practical Op-Amp. Slew Rate: In most Op-Amps the output is single ended, as shown in the symbol.

With positive and negative supplies, the single ended output is designed to have a quiescent value of zero. This way, zero input voltage ideally results in zero output voltage.

Block diagram of an Op-Amp. The difference between ordinary amplifier with differential amplifier is schematically shown in Fig. Difference between ordinary and differential amplifier.

For instance, some do not use a class B push-pull output, and others may have a double-ended output. Also, op-amps are not as simple as Fig.

The internal design of a monolithic Op-Amp is very complicated, using dozens of transistors as current mirrors, active loads, and other innovations that are not possible in discrete designs. For our needs, Fig 1. The equivalent circuit of the Op-Amp device is shown in Fig.

Equivalent circuit of Op-Amp. Ri and Ro are the input and output resistances of the Op-Amp. The symbol A represents the open-loop voltage gain. Transfer Characteristics of Op-Amp: The graph that relates the output voltage to the input voltage is called the voltage transfer curve and it is fundamental in designing and understanding amplifier circuits.

The voltage transfer curve of the Op- Amp is shown in Fig. The voltage transfer curve has mainly three zones, namely linear zone, positive saturation zone and negative saturation zone.

The operation of these three zones of the voltage transfer curve is explained below. Case 1: Linear zone: For every Op-Amp, a linear zone is specified. As the name suggests, in this zone the output voltage is linear to the input voltages. When the error Dr. Transfer characteristics of Op-Amp. In the linear region, the slope of the line relating to the output voltage with the error voltage v1 — v2 , is very large, indeed it is equal to the open loop gain A. Let me take an example.

It is to be noted that most of the Op-Amp applications are based on the linear operating zone. Case 2: Negative saturation zone: It can be seen from the graph that the output voltage does not vary and remains constant at —VEE, even though the error voltage varies.

Case 3: Positive saturation zone: Characteristics of Ideal and Practical Op-Amps: For an ideal Op-Amp, the open loop voltage gain A is infinite. This fact resulted that the input resistance Ri is infinite, which in turn implies that the amplifier will make no power demands on the input signal source. This means that the Op-Amp will draw minute power from input signal source to amplify it.

Thus Op-Amp can be used to amplify weak signals. On the other hand, the ideal condition, i. In summary, the ideal Op- Amp conditions are: Characteristics do not drift with temperature The comparison of the various characteristics of ideal and practical Op-Amps are shown in Table I.

Table I: In the next section, I shall discuss about few important characteristics of practical Op-Amp. For practical Op-Amps, the gain decreases with the increase in the frequency.

The frequency at which the gain decreases to 1 or unity, in dB it is 0 is called the unity- gain frequency. A typical Op-Amp frequency response curve is shown in Fig. The circuit can be constructed to obtain desired gain. However, for circuit with higher gain, one has to compromise with the bandwidth. Check the slope of the frequency response curve shown in Fig. The bandwidth decreases for circuit with higher gain. Note that the gain and bandwidth product is a constant.

Here A and BW are the gain and bandwidth respectively. Hence, the gain- bandwidth product is 1 MHz. Typical frequency response of a practical Op-Amp. Slew Rate: It is basically the ability on how fast the output of the Op-Amp can change. This means the speed of the Op-Amp is limited while following the input to produce the output and this is known as Slew Rate. Suppose the input voltage to an Op-Amp is a positive voltage step, a sudden transition in voltage from one dc level to a higher dc.

Ideally, we would get the voltage step as output response. However, since the practical Op-Amp are not perfect, the output response is the positive exponential waveform.

This occurs because the compensating capacitor must be charged before the output voltage can change to the higher level. The initial slope of the exponential output waveform is called the slew rate. Shcmatic description of slew rate. The rate of change of the output signal, i.

This last expression shows that the product of signal amplitude and its Dr. Therefore, a bandwidth limitation maximum allowed frequency arises for large signals. Important Note: In case of practical Op-Amp, small signal bandwidth is limited by the unity gain frequency while the large signal bandwidth is limited by the slew rate.

The CMRR is thus the ratio of the differential-mode gain to common-mode gain and is usually expressed in dB: In Fig. Common mode circuits. Op-Amp is designed for small signal as well as for weak signal: In electronics, a signal having amplitude or magnitude is order of mV or less is considered as small signal.

By applying negative feedback, the voltage gain can be reduced significantly to about 10 to and which in turn allows higher input voltage amplification in the linear zone. Suppose, an Op-Amp is configured with negative feedback to provide a gain of