The Design And Analysis For Broad-band Differential CMOS LNA With Variable Gain

A broad-band variable-gain differential LNA for Satellite-broadcast TV operating in the frequency bands of 900MHz~2250MHz is presented.By analyzing the traditional LNA design flaw: the conflict between the communication band and gain, the noise performance and power consumption, and the deterioration of noise performance and large power fluctuations in the adjustment process of gain, this paper adopts a relatively new LNA circuit, namely the use of filter technology and shunt-peaking structure to expand the bandwidth. Then by finding the best match value, an algorithm is introduced to solve the passive filter component values. This algorithm roundly takes into account the realization of passive components, the degree of tolerance for process variation, and the value of components must also meet certain conditions for the return loss. Through the introduction of Miller resistance and negative feedback based on the transistor drain to achieve LNA's gain control, and it will not introduce additional noise and cause greater fluctuations in power consumption in the gain adjustment process of LNA, and will improve the noise performance and power stability of LNA.Aiming at the inherent contradiction between the bandwidth and gain of shunt-peaking structure, in order to acquire a higher gain while ensure the wide communication band of LNA, the paper uses the two-stage amplifier circuit after the filter to overcome this contradiction, and the two-stage amplifier are to achieve the main performance of the division of labor based on theoretical analysis and qualitative description, greatly reducing the mutual constraints among the change of parameters, and also bringing the circuit design convenience.In order to obtain high gain and good gain flatness, this paper roundly takes into account the realization of passive components, the degree of tolerance for process variation, high and low frequency amplification requirements for each level amplifier, as well as the gain constraints for each amplifier, and adopts a novel algorithm to search the passive components value of shunt-peaking structure.For LNA circuit design, a detailed analysis of this LNA designed in principle for determining the size of each transistor, the realization of gain control, and the implementation of high linearity is proposed.Finally, based on this LNA circuit design analysis, a general LNA design process in order to benefit other LNA circuits design is introduced. In the TSMC 0.18μm CMOS technology, 1.8V operating voltage and 1.3V~1.6V control voltage of gain, this LNA achieves input and output matching and broad variable-gain ranges, moreover, acquires excellent noise performance, linearity and low power consumption.