Radio frequency amplifiers are fundamentally a positive feedback system in our radio system, typically located on the transmitted link. Since the link attenuation of wireless transmission is considered, the transmitting end needs to radiate enough power to obtain a relatively far communication distance. Therefore, the radio frequency amplifier is primarily enlarged to a larger-enough feed to the antenna radiation, which is the core device in the communication system.
So what are the main types of RF amplifiers for such important devices?
1) Classification from the working frequency band
Classified by operating frequency band can be divided into narrowband RF power amplifiers and broadband RF power amplifiers. The narrowband RF power amplifier generally uses the SEF network as a load loop, such as an LC resonant circuit. The broadband RF power amplifier does not use the SVT network as the load loop, but the transmission line with a wide frequency response as a load.
2) Classification from matching network
Depending on the nature of the matching network, the power amplifier can be divided into non-resonant power amplifiers and resonant power amplifiers. The matching network of the non-resonant power amplifier is a non-resonant system, such as a non-resonant system such as a high-frequency transformer, a transmission line transformer, and its load properties present a pure resistance property. The matching network of the resonant power amplifier is a resonant system, and its load properties present reactance properties.
3) Press current guiding corner classification
According to the current conductor, the RF power amplifier can be divided into Class A, Class C, Class C, C, D, C class, etc. These categories can be found in the table below.
In the classification of the amplifier, what we often say is still on the A-to-E-class amplifier. The output power and efficiency of the apex working state is the highest working state, and most of the amplifiers used in the working state work in the C (C) class.
The classification of the amplifier is so complicated, and the main performance indicators will certainly not be simple. It is actually the case.
The main indicators of the amplifier are as follows:
Working frequency range
Generally speaking, it means the linear operating frequency range of the array. If the frequency starts from DC, it is considered that the amplifier is a DC amplifier.
2. Gain
Work gain is the main indicator of measuring the amplifier amplifier. The definition of the gain is the ratio of the power of the amplifier output port to the load and the source actually transmitted to the amplifier input port.
The gain flatness refers to the range of the amplifier gain in the entire operating band, which is also a major indicator of the amplifier at a certain temperature.
3. Output power and 1DB compression points (P1DB)
Referring to the above figure, after the input power exceeds a certain amount, the gain of the transistor begins to fall, and the final result is that the output power is saturated. This point is a famous 1DB compression point (P1DB) when the gain deviation of the amplifier is 1 dB is lower than the other small signal gain. Generally speaking the power capacity of the amplifier is to take 1dB compression points.
4. Efficiency
Since the power amplifier is a power component, it is necessary to consume the supply current. Therefore, the efficiency of amplifiers is extremely important for efficiency of the entire system. Power efficiency is the ratio of the RF output power of the amplifier to the DC power of the supply transistor. ηP = RF output power / DC input power
5. Interchange Distortion (IMD)
Attractive distortion refers to a mixed component generated by two or more input signals having different frequencies. This is due to the nonlinear traits of the amplifier. Among them, since the third-order coordination product is particularly close to the fundamental wave signal, the most important consideration is three-order interchange. The lower the third-order coordination product, the better.
6. Third-order interpretation cutout (IP3)
Figure 2 The intersection of the base wave signal output power extension line and the third-order interpolation extension line is referred to as a three-order interval cutout, indicated by symbol IP3. IP3 is also an important indicator of nonlinearity amplifier. When the output power is constant, the larger the output power of the third-order cross-strip cutout point, the better the linearity of the amplifier.
7. Dynamic range
The dynamic range of the amplifier is generally the difference between the minimum detectable signal to the maximum input power of the linear workspace. Natural, this value is definitely, the better.
8. Harmonic distortion
When the input signal is increased to a certain extent, the amplifier will generate a series of harmonics due to the work of the nonlinear zone. For large power amplifier systems, it is generally necessary to reduce harmonics to 60 dBC with a filter.
9. Input / output standing wave ratio
This is also very important indicator, indicating the degree of matching of the amplifier and the entire system. Input, output ratio deterioration can cause the system's gain undulation and group time to delay. However, the amplifier of the high-in-wave ratio is more difficult, and in the general system, the input stand wave ratio of the amplifier is less than 2: 1.
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