Introduction of low noise amplifier
Low noise amplifier (low-noise amplifier) is a special type of electronic amplifier, mainly used in communication systems to amplify the signal received from the antenna for processing by subsequent electronic equipment. Since the signal from the antenna is generally very weak, the low-noise amplifier is generally located very close to the antenna to reduce the signal loss through the transmission line, so its characteristics directly affect the quality of the signal received by the entire receiver. This "active antenna" configuration is widely used in microwave systems such as the Global Positioning System (GPS). This is because the coaxial cable has a large loss in the microwave frequency range.
1. Noise figure NF
The noise figure is the ratio of the signal-to-noise ratio of the input signal to the signal-to-noise ratio of the output signal, which indicates the deterioration of the signal quality after the signal passes through the amplifier. In a cascaded network, the more front-end components have a greater impact on the overall noise figure. At the receiving front end, low noise design must be done. The design of the amplifier should be far away from the unstable zone. The quality of noise mainly depends on the device and circuit design.
2, gain G
It is the basic indicator of an amplifier. According to the gain, the number of amplifier stages and device types can be determined.
3, dynamic range
Dynamic range refers to the range of the minimum power and maximum power allowed by the input signal of the low noise amplifier. The lower limit of the dynamic range depends on the noise performance.
4, frequency range
The operating frequency range is the prerequisite for selecting the device and circuit topology design.
5. Standing wave ratio and reflection coefficient of input and output
The low noise amplifier has a very low noise figure and a wide frequency range. When the signal is weak, the output of the probe is first amplified by the low noise amplifier and then sent to the receiver.
The main function of the low noise amplifier is to amplify the weak signal received by the antenna from the air, reduce noise interference, so that the system can demodulate the required information data, and increase the gain of the low noise amplifier is very beneficial to reduce the noise figure of the whole machine, but The gain of the low noise amplifier is too high, which will affect the linearity of the entire receiver and put forward high requirements.