Home  Amplifiers

Jun 15 2019

Power Amplifier Basic and Classifications Tutorial

Making an Audio Power Amplifier

Article Core

Audio Power Amplifier

Introduction

Operational Principle

Primary Classification

Introduction

Classifications

  Class A Amplifiers

  Class B Amplifiers

  Class AB Amplifiers

  Class D Amplifiers

  Advantages

Summary

  Class T Amplifiers

Basic Structure

Three Parts:

Preamplifier

Driving Amplifier

Final Stage Power Amplifier

Active Device Components Used in the Power Amplifier

Selection Tips

Input Impedance

Distortion

Signal-to-Noise Ratio

Common Types

RF PA

RFAMP

Main Indicators

Technique Indicators

Performance Indicators

Frequency Response

Distortion

Dynamic Range

Signal-to-Noise Ratio

Output Impedance and Damping Coefficient

Related Terminology

Working Range

Operating Mode

Transmission Gain

Output Power

Receiving Gain

Note


Introduction

A power amplifier is an amplifier that produces a maximum power output to drive a load (such as a loudspeaker) at a given distortion rate. The power amplifier plays a pivotal role of “organization and coordination” in the whole sound system, which determines whether the whole system can provide sound quality output to some extent.

Operational Principle

The power of the power supply is converted to the current that varies according to the input signal by the current control action of the triode or the voltage control of the field effect tube. Because the sound is a wave of different amplitude and different frequency, that is, the AC signal current, the collector current of the triode is always β times the base current, and β is the AC amplification factor of the triode. If a small signal is injected into the base, at this time, the current flowing through the collector will be equal to β times of the base current, and then the signal is isolated by a DC blocking capacitor, getting a large current (or voltage) signal of the original β times, which is the amplification effect of the triode. After continuous current amplification, power amplification is completed.

home power amplifier

Primary Classification

Traditional digital voice playback systems consist of two main processes:

1. Transformation of digital voice data to analog voice signals (using high-precision digital-to-analog converter DAC).

2. Use analog power amplifiers for analog signal amplification, such as Class A, Class B, and Class AB amplifiers. Since the early 1980s, many researchers have worked on the development of different types of digital amplifiers that directly perform power amplification from digital speech data without the need for analog conversion. Such amplifiers are commonly referred to as digital power amplifiers or class D amplifiers.

Class A amplifiers

The main feature of the Class A amplifier is that the operating point Q of the amplifier is set near the midpoint of the load line and the transistor is turned on during the entire period of the input signal. And the amplifier can be operated in a single tube or push-pull operation. Since the amplifier operates within the linear range of the characteristic curve, transient distortion and alternating distortion are small. The circuit is simple and easy to debug, however, the efficiency is low. The power consumption of the transistor is large, and the theoretical maximum value of efficiency is only 25%, and there is a large nonlinear distortion.

Class B amplifiers

The main feature of the Class B amplifier is that the quiescent point of it is at (VCC, 0), and when there is no signal input, the output consumes almost no power. In the positive half cycle of Vi, Q1 turns on and Q2 cut off, and the output is positive half-cycle sine wave. Similarly, when Vi is a negative half-wave sine wave, it must be operated with two tubes in a push-pull mode. It is characterized by high efficiency (78%), in addition, the amplifier has a period of operation in a nonlinear region, its crossover distortion is large. That is, when the signal is between -0.6V and 0.6V, Q1 and Q2 cannot be turned on to cause this phenomenon. Therefore, such amplifiers are gradually being abandoned by designers.

Class AB amplifiers

The main feature of the class AB amplifier is that the on-time of the transistor is slightly longer than the half-cycle, and two-tube operation must be used in a push-pull mode to avoid crossover distortion. And the alternating distortion is large, which can cancel the even harmonic distortion. In short, Class AB amplifiers have the advantages of high efficiency and low power consumption of transistors.

Class D amplifiers

Class D (digital audio power) amplifier is a kind of pulse signal which converts an input analog audio signal or PCM digital information into PWM (pulse width modulation) or PDM (pulse density modulation) pulse signals to control large power switching devices turn on/off audio power amplifiers, also known as switching amplifiers. It has outstanding advantages with high efficiency. The digital audio power amplifier also looks like a one-bit power digital-to-analog converter. This kind of amplifiers consists of an input signal processing circuit, a switching signal forming circuit, a high-power switching circuit (half-bridge and full-bridge), and a low-pass filter ( LC). A Class D amplifier or a digital amplifier uses a very high frequency switching circuit to amplify the audio signal.

advantages

1) high efficiency, usually over 85%

2) small size, saving a lot of space than the analog amplifier circuit

3) crack-free noise

4) low distortion, good frequency response curve, fewer peripheral components, which is easy to design and debug

Class A, Class B, and Class AB amplifiers are analog amplifiers, and Class D amplifiers are digital amplifiers. Class B and Class AB push-pull amplifiers are more efficient and less distorted than Class A amplifiers, and their transistors consume less power and have sound heat dissipation, but poor switching characteristics during transistor turn-on and turn-off transitions or improper selection of circuit parameters of Class B amplifiers will cause alternating distortion. Class D amplifiers have the advantages of high efficiency, low distortion, and better frequency response curve, also they have few peripheral components. Class AB amplifiers and Class D amplifiers are the basic circuit forms of audio power amplifiers.

Class T amplifiers

The power output circuit of the class T power amplifier is the same as the pulse width modulation class D power amplifier, and the power transistor also operates in the switching state, in other words, the efficiency is comparable to that of the class D power amplifier. But there is also some difference compared with ordinary Class D power amplifiers:

First of all, it doesn’t use pulse width modulation, but uses an adaptive algorithm and a prediction algorithm to deal with small signals in communication technology. The input audio signal and the current entering the speaker are digitally processed by DPP to control the turn-on and turn-off of the power transistor. So that this allows the sound quality to achieve high fidelity linear amplification.

Secondly, the switching frequency of its power transistor is not fixed, and the power spectrum of the useless component is not concentrated in a narrow frequency band on both sides of the carrier frequency, but spread over a wide frequency band, which make the details of the sound clear and audible throughout the entire frequency band.

In addition, Class T power amplifiers have a wider dynamic range and flat frequency response. The emergence of DDP has pushed the power amplifier of the digital age to a new level. In terms of high fidelity, the linearity is more higher than that of the traditional class AB amplifier.


Basic Structure

A power amplifier usually consists of three parts: a preamplifier, a driving amplifier, and a final stage power amplifier.

1. The preamplifier plays a matching role, and its input impedance is high (not less than 10kΩ). Most of the previous signals can be absorbed, but the output impedance is low (less than tens of Ω), and most of the signal can be transmitted. At the same time, it is equivalent to a current amplifier as well that converts the input voltage signal into a current signal and gives appropriate amplification effect.

2. The driving amplifier acts as a bridge. It further amplifies the current signal sent by the preamplifier and amplifies it into a medium power signal to drive the final stage power amplifier to work normally. If there is no driving amplifier, the final stage power amplifier cannot deliver a high-powered sound signal.

3. The final stage power amplifier plays a key role. It will drive the current signal from the amplifier to form a high-power signal, which will drive the speaker to make sound. And its technical specifications determine the technical specifications of the entire power amplifier.

active device components used in the power amplifier

The active devices used in power amplifiers are mainly transistors (bipolar or field effect transistors), when the operating frequency is high or the output power is high, electron tubes (including high-power emission tubes) are also used, and traveling waves are used in the microwave section. Power amplifiers can be classified into Class A, Class AB, Class B, Class C, and Class D according to their working points.

Power amplifiers are often used in broadcast, communication transmitter output stages, audio system output stages, and control system drive actuators. Different applications requirements are different, also the performance requirements are different, and the circuit configuration and work type are also different. Commonly used include linear power amplifiers, resonant power amplifiers, broadband power amplifier circuits. To improve the output power, power synthesis technology can be used.

Broadband power amplifiers, use a transmission line transformer as the load for active devices. This amplifier has an upper limit frequency of hundreds of MHz and a wide band coverage. And the transmission line transformer is composed according to the working principle of the transmission line and the transformer.

Power synthesis technology, its principle is that multiple amplifiers amplify the same input signal and then combine the output power of each amplifier in a synthetic manner. In the power amplifier, due to the large heat loss, the main heating part of the active device should be added with a heat sink, and sometimes air-cooled, water-cooled or evaporative cooling is used to decrease the temperature of the device.

Linear power amplifiers are used where small nonlinear distortion is required. Common circuit forms are single-tube amplifier circuits and push-pull amplifier circuits.

Resonant power amplifiers that use a resonant loop as an active device to amplify narrow-band signals. This type of amplifier allows the current waveform to be very distorted, and then uses the resonant loop to filter out the harmonics; it allows the active device to operate in Class C for high efficiency; and more for the final stage in high-power transmitters. If the resonant loop is tuned to the harmonics of the input signal and an appropriate operating point is selected, a frequency multiplier can be constructed.


Selecting Tips

When choosing a power amplifier, some of its technical indicators should be paid attention to:

1. Input impedance: it usually indicates the anti-interference ability of the power amplifier, generally in the range of 5000-15000 Ω. The larger the value, the stronger the anti-interference ability.

2. Distortion: it refers to the degree of distortion of the output signal compared with the input signal. The smaller the value, the better the quality, generally below 0.05%.

3. Signal-to-noise ratio: it refers to the ratio between the music signal and the noise signal in the output signal. The larger the value, the cleaner the sound.

In addition, when purchasing a power amplifier, you must be clear about your real purchase intention. If you want to install a subwoofer, it is best to buy a 5-channel amplifier. Usually 2-channel and 4-channel speakers can only push the front and rear speakers, while the subwoofer only can be equipped with another amplifier, 5-channel power amplifier can solve this problem, the output power of the power amplifier should be as much as possible than the rated power of the speaker.


Common Types

RF PA

RF power amplifiers are an important part of a variety of wireless transmitters. In the pre-stage circuit of the transmitter, the RF signal generated by the modulating oscillating circuit has a small power, and needs to pass through a series of amplification-buffering stage, intermediate amplification stage, and final stage power amplification stage, and after obtaining sufficient RF power, it can feed signal out onto the antenna.

RF power amplifiers are an important part as well of the transmitting device. The main technical indicators of RF power amplifiers are output power and efficiency. In addition, the harmonic in the output should be as small as possible to avoid interference with other channels.

RFAMP

The high-frequency power amplifier is used for the final stage of the transmitting stage. The function is to amplify the high-frequency modulated signal to meet the requirements of the transmission power, and then radiate it to the space through the antenna to ensure that the receiving stage can be in a certain area. Thus a satisfactory signal level is received and does not interfere with communication of adjacent channels.

The high-frequency power amplifier is an important component of the transmitting device in the communication system, and is divided into a narrow-band high-frequency power amplifier and a broadband high-frequency power amplifier according to the width of the operating frequency band.

The main technical indicators of high-frequency power amplifiers are: output power, efficiency, power gain, bandwidth and harmonic rejection level (or signal distortion level). These indicators are contradictory, when designing an amplifier, some indicators should be highlighted according to specific requirements, taking into account other indicators. For example, some circuits in practice prevent interference as the main contradiction, require higher harmonic suppression, and it is  appropriately to reduce bandwidth requirements. The efficiency of the power amplifier is a prominent problem, and its efficiency is directly related to the operating state of the amplifier.

In addition, the high-frequency power amplifier can not be analyzed by the linear equivalent circuit because it works in the nonlinear state of large signals. So that the analytical approximation analysis method—the broken line method—is commonly used in engineering to analyze its working principle and working state. The physical concept of this analytical method is clear, and the analytical work state is convenient, but the calculation accuracy is low.


Main Indicators

A. technique indicators

1. Rate power: it refers to the continuous sine wave power. The power output is less than 1% of harmonic output at a 1kHz sine wave input and a certain load, its unit is W/CH (Watt/Channel). In general, the higher the rated power, the higher the cost.

2. Total harmonic distortion (THD): it refers to the percentage of higher harmonics in the fundamental wave. The smaller the total harmonic distortion, the better. The total harmonic distortion of a good power amplifier only has 0.02%.

3. Slew rate: it refers the voltage amplitude per unit time rise, its unit is volts/microsecond, which reflects the power amplifier's ability to track transient sound signals, thus it is a transient characteristic indicator.

4. Damping factor: it is defined as the load impedance of the power amplifier (sum of the internal resistance of the high power tube and the wiring line resistance of the speaker). The general requirement ratio is relatively large, but can not too big, it will make the speaker sound thin, and too small will make the sound turbid, resulting in poor sound level and bad sound image distribution.

5. Output impedance (or rated load impedance): its value usually has 8Ω, 4Ω, 2Ω, etc. The smaller the value, the stronger the power amplifier's load capacity. In the case of a single channel, a power amplifier with a rated load of 2 ohms can drive four speakers with an impedance of 8 ohms with small distortion.

power amplifier

B. performance Indicators

Regardless of the strict requirements of the AV amplifier and Hi-Fi power amplifier, its output power, frequency response, distortion, signal-to-noise ratio, output impedance and damping coefficient must be clearly marked.

Output power: it refers to the power delivered by the power amplifier circuit to the load. People's measurement methods and evaluation methods for output power are not uniform, so pay attention when using them.

1. Rated power (RMS): It refers to the maximum power (in other words, sine wave signal) that can be output by the power amplifier for a long period of time in a certain harmonic range. The average power when the harmonic distortion is often 1% is called the rated output power or the maximum useful power, the continuous power, the undistorted power, and the like. And it is obvious that the nominal power values will be different when the specified distortion preconditions are different.

2. Maximum output power: When the distortion is not considered, the output power of the power amplifier circuit can be much higher than the rated power, and can output a more larger value of power. The maximum power that can be output is called the maximum output power, the rated power and the maximum output mentioned before are based on different preconditions.

3. Music Power Output (MPO): it refers to the output power of the power amplifier circuit when working on music signals, that is, the output distortion does not exceed the specified value, the music signal instantaneous maximum output power of the power amplifier.

4. Peak music power output (PMPO): It is the maximum music output power and is another dynamic indicator of the power amplifier circuit. If the distortion is not taken into account, the maximum music power that can be output by the power amplifier circuit is the peak music output power.

Generally, PMPO is greater than the music output power, the music output power is greater than the maximum output power, and the maximum output power is greater than the rated output power. According to practice statistics, the PMPO is 5-8 times of the rated output power.

SIT-3 power amplifier

C. frequency response

It reflects the amplification capability of the power amplifier for each frequency component of the audio signal. The frequency response range of the power amplifier should not be lower than the hearing frequency range of the human ear, and the frequency range of the general audio power amplifier is 40-16 kHz ± 1.5 dB.

D. distortion

It is a phenomenon in which the waveform of the reproduced audio signal changes. There are many reasons and types of waveform distortion, including harmonic distortion, intermodulation distortion, and transient distortion.

E. dynamic range:

The various noises in nature form the surrounding background noise, and the surrounding background noise and the sound intensity appearing in the performance vary greatly. Under normal circumstances, this intensity difference is called the dynamic range, and the excellent sound system inputs the strong signal. There should be no overload distortion, and when a weak signal is input, it should not be overwhelmed by the noise generated by itself.

The ratio of the amplified minimum signal to the maximum signal level without distortion of the amplifier is the dynamic range of the amplifier. In practical use, the ratio uses dB to indicate the level difference between them. In addition, the dynamic range of the high-fidelity amplifier should be greater than 90 dB.

Signal-to-noise ratio: The signal-to-noise ratio refers to the ratio of the size of the sound signal to the size of the noise signal. The number of decibels of the ratio of the output signal level of the attack and discharge circuit to the various noise levels of the output is referred to as the signal-to-noise ratio.

F. output impedance and damping coefficient

The output impedance refers to the equivalent internal impedance of the amplifier output and the load (speaker); the damping coefficient refers to the ability of the power amplifier circuit to dampen the load.


Related Terminology

1) working range

The working range refers to the operating frequency bandwidth of the power amplifier under the specified distortion and rated output power, that is, the range between the lowest operating frequency of the power amplifier and the highest operating frequency, and the unit is Hz. The actual operating frequency range of the amplifier may be greater than the defined operating frequency range.

2) operating mode

The operating modes of the power amplifier mainly include the following:

TDD mode ( Time Division Duplex )

In a TDD mode mobile communication system, different time slots on the same frequency channel (i.e., carrier) are received and transmitted, and the reception and transmission channels are separated by the guaranteed time.

The TDD system has the following characteristics:

A. No need for paired frequencies, various frequency resources can be used, suitable for asymmetric uplink and downlink data transmission rate, especially IP data services

B. The uplink and downlink work at the same frequency, and the symmetrical characteristics of the wave propagation make it easy to use new technologies such as smart antennas to achieve the purpose of improving performance and reducing costs.

TDMA mode ( Time Division Multiple Access )

The carrier of the same frequency is divided into several equal small time segments within a certain time, and the users of multiple different numbers use different small time segments to implement the connected communication mode. In short, it is a digital wireless technology that divides a narrow wireless channel into frame-like time segments (especially 3 and 8) and assigns each time segment to each user.

3) transmission gain 

It refers to the ratio of the output power of the amplifier to the input power, expressed in units of dB. The output gain of the power amplifier increases or decreases as the frequency of the input signal changes. This indicator is the most important basis for assessing the quality of power amplifiers. The smaller the decibel value, the flatter the frequency response curve of the power amplifier, the smaller the distortion, and the stronger the degree of reproduction and reproducibility of the signal.

4) output power

The power amplifier's power specification is strictly divided into nominal output power and maximum instantaneous output power. The former is the rated output power, which can be interpreted as the maximum value of the output power when the harmonic distortion changes within the standard range and can work safely for a long time; the latter refers to the peak output power of the power amplifier, which is interpreted as the power amplifier accepts when the electrical signal is input, the maximum output power that can be withstand instantaneously under the premise of ensuring that the signal is not damaged.

5) receiving gain

Gain is one of the main indicators of the antenna. It is the product of the direction coefficient and the efficiency, and is the performance of the antenna radiation or the volume of the received wave. The choice of gain size depends on the requirements of the system design for the coverage area of the radio wave. In a word, under the same conditions, the higher the gain, the farther the distance the radio wave travels; the larger the receiving gain value of the power amplifier, the stronger the receiving performance.


Note

The amplifying circuit whose main function is to supply power to the load is generally called a power amplifying circuit, and its main features are as follows:

1. Output power refers to the product of alternating voltage and alternating current, that is, AC power.

2. AC power is defined when the input is sinusoidal and the output waveform is substantially undistorted.

3. The output power is large, so the energy consumed in the circuit and the energy supplied by the power supply are also large.

4. Transistors often operate in extreme applications, taking into account the necessary thermal measures, overcurrent protection, and overvoltage protection.

Impedance matching

In all electronic audio-visual equipment, there is a problem with the optimal solution of the power output, that is, obtaining the maximum power output without increasing the investment of the circuit, and this is the best combination of the power amplifier and the speaker system.

The purpose of the power amplifier combination is to achieve maximum power output for minimal equipment investment.

To achieve maximum output power, the value of the load should take the maximize product of the current output and voltage output of the power tube. The state at this time is called the power matching state. In the loudspeaker system of the audio equipment, the output impedance of the sound should be the total impedance of the combined state of the loudspeaker, so that the output power of the sound is the rated standard power, otherwise the output power of the sound will not meet the requirements.

precautions

The power tube is the most vulnerable device in the power amplifier circuit. Most of the damage is due to the fact that the actual power dissipation of the tube exceeds the rated value. In addition, if the power amplifier is mismatched with the loudspeaker or the loudspeaker is used for a long-term overload, it is also very easy to damage the loudspeaker (or audio). Therefore, in the audio equipment, the purpose of protection is to protect the expensive amplifier and loudspeaker, so the power supply, amplifier, audio overload and short circuit protection of the loudspeakers is absolutely necessary.

1. Power protection

When using a switching power supply, there is a special protection of control terminal. As long as the over current or over voltage signal is making, the protection can be done.

2. Amplifier-level transistor protection

In addition to the ambient temperature and the selection of a suitable heat sink, the power amplifier transistor is mainly concerned with overcurrent and overvoltage protection. The integrated circuit of the application has a current limiting protection and a thermal cut-off protection function, therefore, attention should be paid to overvoltage protection when making self-made amplifiers.

3. Audio system protection

The protection of the sound system has two meanings: one is the overload of the audio speaker; another is the offset of the DC potential, resulting in the OCL or BTL circuit speaker without capacitance isolation to burn.

stereo power amplifier

Related Note:

An audio power amplifier is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.

Audio power amplifier functions in circuits:

1) Voltage amplification. It means that amplify the input signal to a certain level to the signal voltage applied to the push stage. To match the machine's audio output power requirements, the number of stages of the voltage amplifier can vary, sometimes a primary voltage amplifier or a multi-stage voltage amplifier in other time period.

2) The driver. It is used to push the output stage of the power amplifier to further amplify the signal voltage and current. Sometimes there is a need to output two push signals of equal magnitude and opposite direction. The power amplifier is also a primary voltage, current amplifier that operates in a large signal amplification state.

3) Output stage. It is used to amplify the current of the signal. The voltage amplification and the driver have sufficient voltage amplification to the signal voltage, and the output stage performs current amplification to achieve the purpose of signal power amplification, in addition, the output signal power is equal to the product of the output signal current and voltage.


The understanding or evaluation of the power amplifier circuit is mainly considered from the three aspects of output power, efficiency and distortion.

1. To obtain the required output power, the circuit must select a triode with a sufficiently large collector power consumption, and the working current and collector voltage of the power amplifier tube are also high. In circuit design, the first thing to consider is how to fully exert the triode function without damaging it. Since the working state of the power amplifier tube in the circuit is often close to the limit value, the power amplifier current should be carefully adjusted and used to avoid excess limit value.

2. In terms of energy consumption, the power output of the power amplifier is ultimately provided by the power supply. For example, the power consumption of the power amplifier in the radio should account for 2/3 of the whole machine. Therefore, it is necessary to pay attention to improve the circuit efficiency, that is, the ratio of the output power to the power consumption.

3. The power amplifier circuit is required to have a large dynamic range, and if the working point of the power amplifier tube is not properly selected, the output will be seriously distorted.

application tips

For many people, the amplifier is not very well understood. It is not clear which accessories are needed in the amp speaker to play the amp effect to an optimal state.

The first one is to install a resistor under the speaker to do current sampling. In fact, the feedback is the voltage signal. It is the analog current feedback, but this circuit is defective. There are two reasons:

1. It is the output gain that varies with impedance. As a result, the non-constant voltage is applied to the end of the horn 2.

Since the sound pressure characteristic curve of the speaker is tested under constant voltage output,  the listening is not good in a simple circuit state, but there is an improved circuit, mainly based on voltage negative feedback. A proper amount of this type of current negative feedback can make a good sound, but the effect of current negative feedback is to change the damping coefficient of the power amplifier, which has little effect on the amplitude-frequency characteristics.

2. The sampling point is below the horn, and the role of the horn is an inductor. The current flows through the inductor and its phase changes. There is small effect on low-frequency state, but the high frequency can be shifted by 90 degrees, and the phase characteristics are extremely poor.

The second type: negative resistance amplifier, except for some special occasions, the first one to be used for acoustics and succeeded is Yamaha. Its main function is to improve the low-frequency extension, but the effect is bad for 200Hz or above, the frequency will degrade the sound quality, so it is generally used on ultra-low frequency active speakers.

Traditional power amplifiers operate at low efficiency due to power consumption on the output circuit. To increase the efficiency of conventional power amplifiers, an ideal Class F power amplifier uses an output filter to control the harmonic content of the transistor's output voltage or current, normalizing the voltage and current waveforms of the transistor's output. Therefore, the angle parameter of the collector current is 90°, that is, the collector waveform is half a sine wave, the collector voltage waveform is a square wave, and the phase difference between the them is λ/4, so the waveform of the collector voltage and current has no overlapping region, thus achieving an ideal efficiency of 100%.

You May Also Like

Definition of Power Amplifier and Its Classification

Operational Amplifier Principle and Circuit

Amplifier Tutorial: Amplifier Basic and Amplifier Circuit

5 comments

    • Victoria on 2019-7-27 17:35:00

    Nice information of electronic components.

    • Doctor Eric on 2019-7-27 17:39:25

    Nice notes i do really appreciate guys. But I have a question, is differetial and operational amplifiers the same thing ?

    • Herschel S on 2019-7-27 17:49:03

    Amazing ! Thank you very much for your tutorial about op amps. I’m studying for an electronic exam and these are the only notes I’m studying about op amps.. Hope they will help me.

    • Brendan on 2019-7-27 17:54:59

    Hi, When designing op-amp circuits, or calculating the transfer function of a particular op-amp configuration, we do assume ideal conditions. While an ideal op-amp has infinite input impedance, zero output impedance, infinite open-loop gain or bandwidth, some of these features are very nearly achieveable by practical op-amps, especially the FET types, and as such input bias currents or output offset voltages, etc. are generally ignored in the calculation of an op-amps feedback network or circuit configuration.

    • Henry Chey on 2019-7-30 15:54:28

    I have been looking to find information on how to start a website of how to design simple op-amp circuits to use. This just may be what I am looking for.

Leave a Reply

Your email address will not be published.

 
 
   
Rating: