An amplifier is an electronic device used to increase an electrical signal to a higher amplitude or power level so that it can drive a larger load or transmit a signal over a greater distance.

 

It is a two-port electronic circuit that uses power from a power supply to increase the amplitude (magnitude of voltage or current) of a signal applied to its input, thereby producing a proportionally larger amplitude signal at its output.

 

The amplification function of the amplifier is realized by controlling the energy source with the input signal, and the power consumption required for amplification is provided by the energy source. For a linear amplifier, the output is a reproduction and enhancement of the input signal. For nonlinear amplifiers, the output is a function of the input signal.Video Amplifiers

 

The amount of amplification provided by an amplifier is measured by its gain, which is the ratio of the output voltage, current, or power to the input. An amplifier is a circuit with a power gain greater than 1. Amplifiers usually consist of an input, an output, and a power supply.

 

Amplifiers can be used in various devices such as communication, broadcasting, radar, television, and automatic control. Amplifiers play a vital role in electronics to boost the signal and provide the required power.Transimpedance Amplifiers

 

Ⅰ. The role of the amplifier

 

  High-frequency power amplifiers are important components of transmitting devices in communication systems. According to the width of its working frequency band, it is divided into narrowband high frequency power amplifier and wideband high frequency power amplifier. Narrowband high frequency power amplifier usually uses a frequency selection circuit with frequency selection filter function as the output circuit, so it is also called tuned power amplifier or Resonant power amplifier; the output circuit of the broadband high-frequency power amplifier is a transmission line transformer or other broadband matching circuit, so it is also called a non-tunable power amplifier.

 

Ⅱ. Working principle of amplifier

 

The operating principle of an amplifier is based on the amplification characteristics and circuit design of electronic components such as transistors, vacuum tubes or integrated circuits.

 

1. Output signal: The output of the amplifier produces an amplified signal. The amplitude or power of the output signal is usually much larger than the input signal to meet specific application needs.Transconductance Amplifiers

 

2. Input signal: The input signal of the amplifier can be voltage, current or power. It usually exists in the form of an AC signal, which can be an audio signal, a radio frequency signal, or another form of signal.

 

3. Bias and amplifier circuit: The input signal first enters the bias and amplifier circuit of the amplifier. The bias circuit is used to provide the proper operating point for the amplifier to ensure that the amplifier works within the normal operating range.

 

4. Amplification stage: An amplifier usually consists of one or more amplification stages. Each amplification stage is responsible for amplifying a portion of the input signal. During each stage, as the input signal passes through an amplifying element (such as a transistor) in an amplifier circuit, the electronic element increases the signal's amplitude or power, depending on its operating characteristics.

 

Ⅲ. Basic Characteristics of Amplifiers

 

1. Ideal frequency characteristics: amplifiers have different conversion ratios for different frequencies, and an amplifier will have the best amplification band, that is, the EQ adjusted when listening to music.

 

2. Output dynamic range: The output dynamic range, usually given in units of dB, refers to the range between the maximum and minimum useful output amplitudes.

 

3. Gain: Gain is the proportional relationship between the output signal of the amplifier and the input signal. It expresses the ability of the amplifier to amplify the input signal. Gain is usually measured in dB.Special Purpose Amplifiers

 

4. Establishment time and offset: It refers to the time it takes for the output amplitude to be established within a certain ratio (such as 0.1%) of the final amplitude.

 

5. Linearity: An ideal amplifier would be a perfectly linear device, but real amplifiers are only linear up to certain practical limits and distorted otherwise. Distortion refers to any distortion or distortion of a signal introduced by an amplifier during amplification. Common types of distortion include harmonic distortion, intermodulation distortion, and phase distortion. Distortion can affect the quality and accuracy of the signal.

 

6. Stability: The stability of an amplifier refers to its ability to maintain consistency in performance under different operating conditions. Stability is critical to the reliability and predictable performance of amplifiers.

 

7. Noise: Amplifiers usually introduce some level of noise due to electronic components and environmental factors. Noise can affect the clarity and quality of a signal.

 

8. Slew rate: Slew rate refers to the rate of change of the output voltage variable, often defined as volts per second (or microseconds).

 

9. Bandwidth: Bandwidth refers to the frequency range that the amplifier can amplify. The bandwidth of an amplifier depends on its circuit design and the characteristics of its amplifying components. The wider the bandwidth, the wider the range of frequencies the amplifier can transmit.

 

Ⅳ. Classification of integrated operational amplifiers

 

An integrated operational amplifier is a high-gain, differential-input amplifier commonly used in analog and digital circuits. The following are the classifications of integrated operational amplifiers:

 

1. General-purpose integrated operational amplifier: General-purpose integrated operational amplifier refers to its relatively moderate technical parameters, which can meet the use requirements in most cases. General-purpose integrated operational amplifiers are divided into Type I, Type II, and Type III. Type I is a low-gain operational amplifier, Type II is a medium-gain operational amplifier, and Type III is a high-gain operational amplifier.

 

2. High-speed integrated operational amplifier: The output voltage conversion rate of the high-speed integrated operational amplifier is very large, and some can reach 2~3kV/μS.

 

3. High input impedance integrated operational amplifier: The input impedance of the high input impedance integrated operational amplifier is very large, and the input current is very small.

 

4. High-precision integrated operational amplifier: High-precision integrated operational amplifier refers to those operational amplifiers with small offset voltage, very small temperature drift, and very high gain and common-mode rejection ratio. These op amps are also less noisy.

 

5. Low-power integrated operational amplifier: The current of the low-power integrated operational amplifier is very small, and the power supply voltage is also very low. The power consumption of the entire operational amplifier is only tens of microwatts. This type of integrated operational amplifier is mostly used in portable electronic products.

 

6. Power type integrated operational amplifier: The output stage of the power type integrated operational amplifier can provide relatively large power output to the load.Sample & Hold Amplifiers

 

7. Optical fiber amplifier: The optical fiber amplifier can not only directly amplify the optical signal, but also has real-time, high-gain, broadband, online, low-noise, and low-loss all-optical amplification functions, which are indispensable in the new generation of optical fiber communication systems key device. Fiber amplifiers generally consist of gain media, pump light, and input-output coupling structures. At present, there are mainly three types of fiber amplifiers: erbium-doped fiber amplifier, semiconductor optical amplifier and fiber Raman amplifier. The power of the machine; the optical pre-amplifier is used before the receiver to greatly improve the sensitivity of the optical receiver; the relay amplifier is used in the optical fiber transmission line to compensate for the optical fiber transmission loss and extend the transmission distance.

 

Ⅴ. Classification of Amplifiers

 

1. Classification by frequency range:

 

Power Amplifiers: Used to drive electric motors, high-power audio systems, and industrial applications, among others.

 

Audio Amplifiers: Used in audio systems, music equipment, and amplified speakers, etc.

 

Instrumentation Amplifiers: Used in measurement and laboratory equipment such as oscilloscopes and signal generators.

 

Low Frequency Amplifier: Used to amplify signals in the lower frequency range, such as audio signals.

 

Intermediate frequency amplifier: used to amplify signals in the medium frequency range, such as intermediate frequency signals in radio frequency communications.

 

2. Classified by signal type:

 

RF Amplifier: Used to amplify radio frequency (radio frequency) signals, typically operating in the frequency range of a few hundred kilohertz to several gigahertz.

 

Audio Amplifier: Used to amplify audio signals, usually operating in the frequency range of 20 Hz to 20 kHz.

 

3. Classified by working method:

 

Class A Amplifier: Output current/voltage is constant over the entire signal cycle, with high linearity and low distortion, but relatively low power efficiency.

 

Class B amplifier: The output current/voltage only works in the positive half cycle or negative half cycle of the signal, which has high power efficiency, but may introduce crossover distortion.

 

Class D amplifier: Using switching power supply technology, the input signal is converted into a pulse width modulation (PWM) signal, and then the output signal is reconstructed through a filter, which has high power efficiency and low heat consumption.Logarithmic Amplifiers

 

Class AB amplifier: Combining the characteristics of class A and class B, it provides better power efficiency and linearity, and is often used in audio amplifiers.

 

Ⅵ.Application Fields of Amplifiers

 

1. Power amplifiers: Power amplifiers are used to drive high-power loads, such as speakers, motors, industrial equipment, and radio transmitters.

 

2. Audio amplifier: Audio amplifiers are used to amplify audio signals, including music systems, radios, TVs, audio equipment, headphone amplifiers, etc.

 

3. Control system: Amplifiers are used for feedback loops and control signal amplification in control systems, such as motor control, robot control, and automation systems.

 

4. Automotive electronics: Amplifiers are commonly used in car audio systems, car entertainment and navigation systems to amplify audio signals and drive speakers.

 

5. Communication systems: Amplifiers play an important role in various communication systems, including wireless communication systems (such as mobile communications, satellite communications), wired communication systems (such as optical fiber communications, power line communications), and radio and television transmission systems.

 

6. Sensor interface: Sensors usually output weak signals, and amplifiers are needed to enhance the signals for subsequent processing, such as temperature sensors, pressure sensors, light sensors, etc.

 

7. Medical equipment: Amplifiers play an important role in medical equipment, such as electrocardiographs, blood pressure monitors, ultrasound equipment, etc., to amplify and process biological signals.

 

8. Radar and radio frequency equipment: Radar systems, radio frequency equipment and communication base stations, etc. need amplifiers to process high-frequency signals, including radio frequency amplifiers and microwave amplifiers.

 

9. Instruments and measurement systems: In the field of instruments and measurements, amplifiers are widely used in oscilloscopes, signal generators, data acquisition systems, sensor signal amplification and other equipment to provide accurate signal amplification and measurement.

 

Ⅶ. Common faults of amplifiers and their solutions

 

1. Leakage current fault: There may be a leakage current in the amplifier, causing the current to deviate from the design value. Possible causes include damaged components, overheating, or improper use.

 

Solution: Check whether the op amp chip and other components are damaged or overheated. Replace damaged components. Ensure that amplifiers are used and operated in accordance with design requirements and specifications.

 

2. No output or output distortion failure: The amplifier may not be able to produce an output signal, or the output signal may be distorted. Possible causes include power supply problems, component failures, bias circuit errors, feedback circuit problems, etc.

 

Solution: Make sure the power supply is normal, and check whether the power supply voltage and current are within the specified range. Check feedback circuit connections and component values. Verify that the feedback circuit provides a stable feedback signal. Check that the component values and connections of the bias circuit are correct. Adjust the bias circuit to ensure the correct operating point. Check whether the operational amplifier chips, capacitors, resistors and other components are damaged or invalid. Measure the values and characteristics of components to verify that they meet specifications.

 

3. Noise failure: The amplifier may produce noise, affecting signal quality. Possible causes include power supply noise, component noise, wiring interference, etc.

 

Solution: Check the power supply noise, use the appropriate power filter and voltage regulator to reduce the power supply noise. Check wiring, pay attention to wiring and grounding to reduce interference and crosstalk. Use shielding and proper wiring techniques to reduce noise. Check component noise, choose low-noise components, and make sure they meet design requirements.

Frequently Asked Questions

 

1. How to calculate the gain of the amplifier?

 

General-purpose amplifiers (such as operational amplifiers): The gain of a general-purpose amplifier can be determined by configuring the amplifier's feedback resistors. A common approach is to use the proportional relationship of the feedback resistors to calculate the gain. The formula is: Av = 1 + (Rf / Rin)

 

Differential Amplifier: The gain of a differential amplifier can be calculated from the ratio of the input resistance to the feedback resistance. Gain depends on resistor selection and configuration.

 

Power Amplifier: The gain of a power amplifier is usually expressed in terms of power gain. Power gain can be calculated from the proportional relationship between output power and input power. The formula is: Ap= Pout / Pin

 

Inverting Amplifier: For an inverting amplifier, the formula Av = - (Rf / Rin) can be used to calculate.

 

2. How to adjust the gain of the amplifier according to the need?

 

Changing the circuit configuration of the amplifier: In some amplifier circuits, the gain can be adjusted by changing how the circuit is connected.

 

Using Variable Gain Amplifiers: Some amplifier designs use variable gain circuits. The gain in an amplifier circuit can be changed by turning a potentiometer or using other adjustable elements.

 

Changing the circuit configuration of the amplifier: In some amplifier circuits, the gain can be adjusted by changing how the circuit is connected.

 

Using a variable control signal: In some special applications, the gain of the amplifier can be adjusted by a control signal.

 

Use variable supply voltage: In some amplifier designs, gain adjustment is achieved by adjusting the supply voltage. Increasing the supply voltage increases the amplifier's saturation point, which increases gain; decreasing the supply voltage decreases the saturation point, thereby reducing gain.

 

Using Different Feedback Resistors: In a feedback amplifier, gain can be achieved by adjusting the value of the feedback resistor. Increasing the feedback resistor increases the gain of the amplifier, while decreasing the feedback resistor decreases the gain. Selecting the proper ratio of the feedback resistors can meet the desired gain requirement.