What Is a Radio Frequency Amplifier?

RF amplifiers can be divided into high gain amplifiers, low noise amplifiers, and medium-high power amplifiers. The core of the amplifier circuit is a microwave transistor.

RF amplifiers can be divided into high gain amplifiers, low noise amplifiers, and medium-high power amplifiers. The core of the amplifier circuit is a microwave transistor.

Chinese name

RF amplifier

Foreign name

radio frequency amplifier

Use

Signal amplification emission

RF amplifier introduction

Radio frequency power amplifier (RF PA) is an important part of various wireless transmitters. In the pre-stage circuit of the transmitter, the RF signal power generated by the modulation and oscillation circuit is very small, and it needs to pass a series of amplification-buffer stage, intermediate stage, and final stage power stage. Radiate to the antenna. In order to obtain sufficient RF output power, RF power amplifiers must be used.

Classification and application of RF amplifier

The RF power amplifier has a high operating frequency but a relatively narrow frequency band. Generally, the RF power amplifier uses a frequency selection network as a load loop. The RF power amplifier can be divided into three working states: A (A), B (B), and C (C) according to the current conduction angle. The conduction angle of Class A amplifier current is 360 °, which is suitable for small signal low power amplification. The conduction angle of Class B amplifier current is equal to 180 °, and the conduction angle of Class C amplifier current is less than 180 °. Both Class B and Class C are suitable for high power working conditions. The output power and efficiency of Class C working conditions are the highest of the three working conditions. Most RF power amplifiers work in Class C, but the current waveform distortion of Class C amplifiers is too large, and can only be used to use the tuning loop as the load resonance power amplifier. Due to the filtering capability of the tuning loop, the loop current and voltage are still close to a sinusoidal waveform with little distortion.

RF amplifier technical parameters

The main technical indicators of the amplifier:

(1) Frequency range: The operating frequency range of the amplifier is the selection of components and power

The premise of road topology design. ^[1]

(2) Gain: It is the basic index of the amplifier. According to the gain can be determined

The number of stages and device types of the amplifier. G (db) = 10log (Pout / Pin) = S21 (dB) ^[1]

(3) Gain flatness and return loss

VSWR <2.0orS11, S22 <-10dB ^[1]

(4) Noise figure: The noise figure of the amplifier is the ratio of the signal-to-noise ratio of the input signal to the signal-to-noise ratio of the output signal, and it indicates the deterioration of the signal quality after the signal passes through the amplifier. NF (dB) = 10log [(Si / Ni) / (So / No)] ^[1]

Power parameters of RF amplifier

In modern wireless communication, the use of radio frequency equipment is quite popular, and radio frequency amplifiers play a vital role in the equipment. The measurement of power parameters in the amplifier has also caused considerable attention, and power is There is a certain misunderstanding in the understanding and application of the parameters. The following explains the meaning and application of related power parameters based on the characteristics of an amplifier ^[2] .

When describing an amplifier, the basic parameters are gain and maximum output level (power). In order to have a more accurate description of the gain, a parameter that attracts linear characteristics is used to balance t. It is usually expressed by the ldB compression point corresponding to the input power and the linear input level. The difference between the two is the input dynamic range of the amplifier. . The ldB compression point is described in the GSM repeater standard YD Ting 952-1998 as follows: The output power of the ldB compression point refers to the input power of the amplifier when the gain drops ldB. It means that the actual output power at that time was smaller than the corresponding output power of the ideal linear amplifier by ldB ^[2] .

In order to further describe linearity. There is also an index of gain step error, which indicates whether the output changes by the same magnitude when the input unit changes the unit signal strength ^[2] .

An actual amplifier, due to the physical characteristics and noise, cannot maintain a linear state when the input level is too small. Therefore, the concept of the minimum output level is introduced. Generally, the corresponding input power level when the output is 3dB higher than the noise level. Level is the minimum input level. The output noise power of the amplifier is: P = kTBGF ^[2] .