In the wireless communication terminal, the low noise amplifier is the first stage active circuit in the radio frequency receiving system, and the main function is to amplify the weak signal received by the antenna from the air to reduce the noise interference, so that the system can demodulate the required information data. The design of the low noise amplifier is critical to the overall receiver. Low-noise amplifiers should provide as much noise as possible while providing maximum gain without distortion and good linearity. Based on the in-depth analysis of the noise problem, a common-basic differential input structure is proposed to design the circuit structure of the low-noise amplifier. The circuit includes a controllable gain amplifier and a gain control circuit. The output voltage of the low noise amplifier is directly reflected to the input of the automatic gain control circuit. According to the magnitude of the output voltage, the output voltage of the automatic gain control circuit is fed back to the input of the comparator of the gain control circuit of the low noise amplifier, thereby affecting the amplifier. The overall gain. Based on JAZZ O. The 35 μm BICMOS process design amplifier circuit, which has low noise and high gain. The most common source of noise is flatband noise, also known as white noise. Flat-band noise sources produce shot noise and thermal noise. Shot noise is generated by the discrete quantum properties of electrons through a barrier, usually associated with diodes and bipolar transistors. The generation of shot noise must have two conditions: the presence of DC current and the charge carriers must cross the barrier to generate current. Shot noise calculation formula: Where q is the electronic charge, ID is the forward junction current, and Δf is the noise bandwidth per unit frequency. It can be seen that the shot noise is proportional to the square root of the junction current, independent of frequency magnitude and temperature. Multiplying the shot noise current by the dynamic junction impedance expresses the shot noise as a noise voltage. Thermal noise is generated by random movement of carriers within the device. Any component, as long as there is a DC resistance, there is thermal noise (AC resistance is an equivalent concept, no thermal noise is generated separately). Since the noise process is random and its amplitude is Gaussian, the usual way to characterize thermal noise is to measure the average noise power of the device that produces the noise. The noise power formula is as follows: Where K is a Boltzmann constant, K = 1.38x10-23J/K, T is the absolute temperature, and Δf is the noise bandwidth per unit frequency. Therefore, thermal noise is independent of the frequency. The thermal voltage of the resistor is a function of resistance, temperature, and measurement bandwidth: Where, En is the RMS (root mean square) noise voltage produced by the resistor R at the given temperature at the bandwidth Δf. The Norton equivalent noise source is obtained by dividing the two sides of equation (3) by the resistance value: The RMS noise voltage and noise current are normalized by a 1 Hz bandwidth to obtain the spectral density: As in the case of shot noise currents, if the signal amplitude increases faster than noise, the performance of the circuit can be improved by increasing the absolute amplitude of the noise. 2.1 Structural design of low noise amplifier circuit Two common low noise amplifiers are: bipolar input and CMOS input. Traditionally, CMOS amplifiers are known for their low input bias currents, but are always subject to high voltage noise. A typical CMOS amplifier has a flat-band noise of tens of nV/Hz, and a peak-to-peak range of 1/f noise is a few microvolts. The bipolar amplifier itself has low noise and is the most common choice for low noise applications. In the RF range, the main noise sources of MOS transistors are channel thermal noise, gate induced noise and gate distributed resistance thermal noise. Since the channel resistance of the MOS transistor produces relatively large thermal noise, selecting a bipolar input results in a relatively good noise figure. Low noise bipolar amplifiers provide extremely low input voltage noise density and relatively high input current noise density. The single-ended LNA structure is very sensitive to the parasitic inductance of the ground. The differential structure is grounded by the incremental (AC) ground at the symmetry point and is not affected by parasitic parameters in the current source ground loop. Another important advantage of the differential structure is its ability to reject common mode interference. This consideration is especially important in mixed-signal applications because both the supply voltage and the substrate voltage can contain noise. In order to maximize the common mode rejection ratio at high frequencies, the key is to make the layout as symmetrical as possible. A differentially structured amplifier also has a significant effect on noise suppression. The bipolar LNA common base structure has three significant advantages over the common emitter circuit: simpler input matching, higher linearity, and greater reverse isolation, so the circuit uses a common base input. 2.2 Circuit design of low noise amplifier The overall structure of the low noise amplifier is shown in Figure 1. The circuit is divided into three parts, in which the module VGLNA is a controllable gain amplifier, and the gain of this part can be changed. Modules CON1 and CON2 are gain control circuits that adjust the gain of VGLNA by the control voltage of the AGC. The design goal for the module VGLNA is to achieve a gain of more than 25 dB. The design goals of modules CON1 and CON2 are such that the gain of the VGLNA does not vary beyond the dynamic range of the AGC by changing the voltage values ​​of the nodes IN1, IN2. 2D Fixed Mount Barcode Scanner 2D Fixed Mount Barcode Scanner,Datalogic Fixed Mount Scanner,Fixed Mount 2D Barcode Scanner,Fixed Mount Barcode Scanner Guangzhou Winson Information Technology Co., Ltd. , https://www.barcodescanner-2d.com