What Is an External Amplifier?
An amplifier is a device that amplifies the voltage or power of an input signal. It consists of a tube or transistor, a power transformer, and other electrical components. Used in communication, broadcasting, radar, television, automatic control and other devices.
- Chinese name
- Amplifier
- Foreign name
- Amplifier
- Subject category
- electronic circuit
- Use
- Voltage and power amplification
- An amplifier is a device that amplifies the voltage or power of an input signal. It consists of a tube or transistor, a power transformer, and other electrical components. Used in communication, broadcasting, radar, television, automatic control and other devices.
Amplifier Introduction
- A device that increases the amplitude or power of a signal. It is an important component for processing signals in automated technology tools. The amplifier's amplification effect is achieved by controlling the energy with the input signal, and the power consumption required for the amplification is provided by the energy source. For a linear amplifier, the output is the reproduction and enhancement of the input signal. For a non-linear amplifier, the output is a function of the input signal. The amplifier is divided into mechanical amplifier, electromechanical according to the physical quantity of the processed signal
- Amplifier
Amplifier effect
- Principle: The high-frequency power amplifier is used in the final stage of the transmitter. Its role is to amplify the high-frequency modulated signal to meet the transmission power requirement, and then radiate it to space through the antenna to ensure reception in a certain area. The receiver can receive a satisfactory signal level and does not interfere with the communication of adjacent channels.
- A high-frequency power amplifier is an important component of a transmitting device in a communication system. According to the width of its operating frequency band, it is divided into two types: narrow-band high-frequency power amplifier and wide-band high-frequency power amplifier. Resonant power amplifier; the output circuit of a broadband high-frequency power amplifier is a transmission line transformer or other broadband matching circuit, so it is also called a non-tuned power amplifier. A high-frequency power amplifier is an energy conversion device that converts DC energy supplied by a power source into a high-frequency AC output. It is known in the course of "low-frequency electronic circuits". The amplifier can be divided into A according to the current conduction angle , B, C working status. Class A amplifier current flow angle is 360o, suitable for small signal low power amplification. Class B amplifier current flow angle is approximately 180o; Class C amplifier current flow angle is less than 180o. Both Class B and Class C are suitable for high-power work. The output power and efficiency of Class C are the highest of the three working states. Most high-frequency power amplifiers work in Class C. However, the current waveform distortion of the Class C amplifier is too large, so it cannot be used for low-frequency power amplification, and can only be used for resonance power amplification using a tuning loop as a load. Because the tuning loop has filtering capabilities, the loop current and voltage are still very close to the sinusoidal waveform, and the distortion is very small.
Amplifier Operational Amplifier Design
- The operational amplifier is one of the most versatile and important units in the analog-to-digital conversion circuit. A fully differential op amp is an op amp with both input and output differential signals.Compared with ordinary single-ended output op amps, it has the following advantages: The output voltage swing is larger; it better suppresses common mode noise; more Low noise; even-order terms that suppress harmonic distortion are better. Therefore, high-performance op amps usually use a fully differential form. In recent years, the higher unity-gain bandwidth frequency and larger output swing of fully differential op amps have made it more widely used in high-speed and low-voltage circuits. With the increasing data conversion rate, the demand for high-speed analog-to-digital converters is becoming more and more extensive, and high-speed analog-to-digital converters require high gain and high unity-gain bandwidth op amps to meet the needs of system accuracy and rapid establishment. Speed and accuracy are the two most important performance indicators of analog circuits. However, the requirements of these two are mutually restrictive and contradictory. So it is difficult to satisfy both requirements at the same time. Folding cascode technology can successfully solve this problem. An op amp of this structure has a high open loop gain and a high unit gain bandwidth. The disadvantage of a fully differential op amp is that the common-mode loop gain of its external feedback loop is small, and the output common-mode level cannot be accurately determined. Therefore, a common-mode feedback circuit is generally required [1] .
- Choice of op amp structure
- There are three important operational amplifier structures: (a) simple two-stage op amp, (b) folded cascode, and (c) cascode, as shown in the previous stage of Figure 1. The design index of the operational amplifier for this design requires that the differential output amplitude is ± 4V, that is, the VDSAT of all NMOS tubes at the output end, the sum of N is less than 0.5V, and the sum of VDSAT, P of all PMOS tubes at the output end must also be less than 0.5V [ 1] .
- Main op amp structure
- The operational amplifier has two stages: (1) the Cascode stage increases the DC gain (M1-M8); (2), the common source amplifier (M9-M12) [1] .
- Common-mode negative feedback
- For fully differential op amps, in order to stabilize the output common-mode voltage, a common-mode negative feedback circuit should be added. When designing a fully-differential operational amplifier with balanced output, the following points must be taken into account: The open-loop DC gain of the common-mode negative feedback needs to be sufficiently large, and it is best to be comparable to the difference-loop DC gain; the unity gain of the common-mode negative feedback The bandwidth is also required to be large enough, preferably close to the differential unit gain bandwidth; in order to ensure the stability of common-mode negative feedback, common-mode loop compensation is generally required; the common-mode signal monitor must have good linear characteristics; It has nothing to do with the differential mode signal, even if the differential mode signal path is turned off [1] .
- This operational amplifier uses a continuous time method to achieve the common-mode negative feedback function.
- This structure shares the current mirror and output load in the input stage of the common-mode amplifier and the differential-mode amplifier. In this way, power consumption is reduced on the one hand; on the other hand, the AC characteristics of the common mode amplifier and the differential mode amplifier are kept consistent. Because the output stage of the common-mode amplifier and the output stage of the differential-mode amplifier can be completely shared, so is the capacitance compensation circuit. As long as the frequency characteristics of the differential-mode amplifier are stable, the common-mode negative feedback is also stable. This common-mode negative feedback circuit enables a fully differential operational amplifier to be designed like a single-ended output operational amplifier, without having to consider the effect of the common-mode negative feedback circuit on the fully differential amplifier [1] .
- Voltage Bias Circuit : Wide Swing Current
- Three voltage biases are required in the cascode input stage. In order to make the dynamic range of the input stage larger, a wide-swing current source generates the three required bias voltages [1] .
Amplifier classification
- Integrated Op Amps Main Category
- Amplifier
Amplifier General Purpose Integrated Operational Amplifier
- The general-purpose integrated operational amplifier means that its technical parameters are relatively moderate and can meet the requirements for use in most cases. General-purpose integrated operational amplifiers are divided into type I, type II, and type III, of which 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. Types I and II are basically early products. The input offset voltage is about 2mV, and the open-loop gain is generally greater than 80dB.
Amplifier High Precision Integrated Operational Amplifier
- High-precision integrated operational amplifiers are those operational amplifiers with low offset voltage, very low temperature drift, and very high gain and common-mode rejection ratios. This type of operational amplifier also has relatively low noise. The offset voltage of a single-chip high-precision integrated operational amplifier can be as small as a few microvolts, and the temperature drift can be as small as tens of microvolts per degree Celsius.
Amplifier 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 / S.
Amplifier 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. The input stage of this type of operational amplifier often uses MOS tubes.
Amplifier Low Power Integrated Operational Amplifier
- The low-power integrated operational amplifier operates with very low current and low supply voltage, and the power consumption of the entire operational amplifier is only tens of microwatts. Such integrated operational amplifiers are mostly used in portable electronic products.
Amplifier Broadband Integrated Operational Amplifier
- The bandwidth of a wideband integrated operational amplifier is very wide, and its unit gain bandwidth can reach more than gigahertz, which is often used in wideband amplifier circuits.
Amplifier High Voltage Integrated Operational Amplifier
- Generally, the supply voltage of integrated operational amplifiers is below 15V, while the supply voltage of high-voltage integrated operational amplifiers can reach tens of volts.
Amplifier Power Integrated Operational Amplifier
- The output stage of the power type integrated operational amplifier can provide a relatively large power output to the load.
Fiber amplifier
- Fiber amplifiers not only directly amplify optical signals, but also have real-time, high gain, wideband, online, low noise, and low loss all-optical amplification functions. They are an essential key device in the new generation of optical fiber communication systems. This technology not only solves the limitation of attenuation on the transmission rate and distance of the optical network, but more importantly, it has created wavelength division multiplexing in the 1550nm frequency band, which will enable ultra-high-speed, ultra-large capacity, ultra-long-range wavelength division multiplexing (WDM) ), Dense Wavelength Division Multiplexing (DWDM), all-optical transmission, optical soliton transmission, etc. have become a reality and are an epoch-making milestone in the development history of optical fiber communication. At present, practically used optical fiber amplifiers mainly include erbium-doped fiber amplifiers (EDFA), semiconductor optical amplifiers (SOA), and fiber Raman amplifiers (FRA). Among them, erbium-doped fiber amplifiers have been widely used for their superior performance. Distance, large capacity, high-speed optical fiber communication systems, access networks, optical CATV networks, military systems (radar multiplexed data multiplexing, data transmission, guidance, etc.), etc., as power amplifiers, relay amplifiers and preamps .
- Fiber amplifiers generally consist of a gain medium, pump light, and input-output coupling structures. At present, there are three main types of fiber amplifiers: erbium-doped fiber amplifiers, semiconductor optical amplifiers, and fiber Raman amplifiers. According to their application in fiber optic networks, fiber amplifiers have three different uses: they are used as power amplifiers at the transmitter side to improve transmission. Machine power; optical pre-amplifier before the receiver to greatly improve the sensitivity of the optical receiver; relay amplifier in the optical fiber transmission line to compensate the optical fiber transmission loss and extend the transmission distance.
CATV trunk amplifier
- Technical characteristics of trunk amplifier:
- *. HYF-860B, HYF-750B, HYF-550B series temperature-compensated broadband network trunk amplifiers use high-performance Philips CATV dedicated amplifier modules to ensure high output signal power, high frequency bandwidth, high gain, good linearity, and stable work.
- *. The front and back two-stage equalization adjustment circuit makes the signal level flatness, effectively solves the phenomenon of level drum, and can make the level band slope output, which is suitable for long-distance transmission of cable television.
- *. The unique integrated circuit temperature compensation can improve the influence of high and low temperature differences on cables and amplifiers, and automatically control the output level.
- *. The branch type and distribution type output selection functions are suitable for the needs of the actual circuit and save costs; the output feed display function is convenient and practical.
- *. Adopting double-sided metal holed circuit board and high-quality toroidal transformer power supply make the amplifier excellent in high frequency performance and stable and reliable operation.
- *. CATV special aluminum alloy die-casting plastic spray shell, good rainproof, heat dissipation and shielding characteristics.
- *. 220V AC power supply or 60V centralized feed type is optional.
- Technical Parameters:
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- CATV trunk amplifier
Amplifier History
- The invention of the first Lock-in Amplifier (LIA) of EG & G PARC (predecessor of SIGNAL RECOVERY) in the United States in 1962 made a breakthrough in weak signal detection technology and greatly promoted basic science and engineering. Development of technology. At present, the continuous improvement of weak signal detection technology and instruments has been widely used in many scientific and technical fields. Future scientific research not only puts higher requirements on weak signal detection technology, but also the development of new science and technology has in turn promoted The birth of a new principle and new method for weak signal detection.
- The early LIA was realized by analog circuits. With the development of digital technology, there has been a mix of analog and digital LIA. This LIA only uses digital filters in the signal input channel, reference signal channel and output channel to suppress noise. Or add analog-to-digital conversion (ADC), digital-to-analog conversion (DAC) and various general digital interface functions on the basis of analog phase-locked amplifier (referred to as ALIA), which can realize auxiliary functions such as computer control, monitoring and display. However, its core phase-sensitive detector (PSD) or demodulator is still implemented using analog electronic technology, which is essentially ALIA. Until the phase-sensitive detector or demodulator was implemented with digital signal processing, a digital lock-in amplifier (DLIA) appeared. DLIA has many outstanding advantages over ALIA and has been favored. It has become a hotspot in weak signal detection research. However, in some special occasions, ALIA still plays an irreplaceable role in DLIA.
Amplifier basic structure
- The signal to be measured is input, and the result obtained by inputting the multiplier together with the reference signal after amplification and band-pass filtering is filtered by a low-pass filter and output.
Amplifier principle
- The phase-locked amplifier is actually an analog Fourier converter. The output of the phase-locked amplifier is a DC voltage, which is proportional to the signal amplitude of a specific frequency (parameter input frequency) in the input signal. The other frequency components in the input signal will not make any contribution to the output voltage.
- The two sinusoidal signals have a frequency of 1 Hz and a phase difference of 90 degrees. The result obtained by multiplying them by a multiplier is a sinusoidal signal with a DC offset.
- If it is a 1Hz and 1.1Hz signal multiplied, the result obtained by multiplying with a multiplier is a modulation signal with a sinusoidal profile and a DC offset of 0.
- Only signals that are completely consistent with the frequency of the reference signal can get a DC offset at the output of the multiplier. Other signals are AC signals at the output. If a low-pass filter is added to the output of the multiplier, all the AC signal components are filtered out, and the remaining DC components are simply proportional to the amplitude of the signal components of a specific frequency in the input signal.
Amplifier use
- It is mainly used to detect weak signals with very low signal-to-noise ratio. Even if the useful signal is drowned in the noise signal, even if the noise signal is much larger than the useful signal, as long as the frequency value of the useful signal is known, the amplitude of this signal can be accurately measured.