CMOS Analog Bandpass Filter Based On Active Inductor And Capacitor

In the structure of analog receiver,the Armstrong’s structure has been using for almost 70 years.The main components consist of bandpass filter(BPF),low noise amplifier(LNA),mixer,phase-locked loop(PLL),oscillator,analog to digital converter.Bandpass filter is the first component that signals pass through after received by antenna,selecting the necessary signals while filtering out the noise and harmonics,which plays an important role in the receiver’s system.Currently,along with the Moore theory’s application on CMOS(Complementary Metal of Semiconductor)technology,the channel length of the digital circuits of integrated circuits is decreasing by 0.7 times of the last generation.The CPU in the market this year can achieve a channel length of 10 nm,improving the speed of the calculation and logic functions with smaller chip size.For example,the A10 of CPU of iphone has accomplished a fast speed of 2.4GHz.However,due to the fabrication of spiral coiled inductors in analog circuits,it is hard to maintain good performance and keep small size of receiver fabricated with digital circuits at the same chip.There are two main design methods by several research groups of different countries:(1)replacing the planar spiral inductor with a new passive inductor is a way that improved self-Q factor can limit the resistive loss,which improves the bandpass filter’s performance;(2)several CMOS transistors constitute this active inductor,leading to a smaller size compared with the passive spiral inductor.However,the first method can’t reduce the chip size and the second method can’t have a better performance because of the self-resistance.This work builds a Chebyshev bandpass filter based on the resonator by implementing the active inductor and capacitor.The negative resistance of the active capacitor neutralizes the resistive loss of the active inductor,improving the quality factor of the resonator,which also improves the center frequency,rejection ratio,bandwidth of the analog bandpass filter.The proposed active capacitor achieves an almost constant capacitance value and negative resistance within a large frequency range.This characteristic is the key point in eliminating resistive loss of active inductor and improving the stability of the analog bandpass filter.The proposed active inductor consists of two gyrator-C structures,making itself a single-ended active inductor.The simple structure provides the chip with smaller size while its resistive loss can be eliminated by negative resistance of the active capacitor.Based on such structure,the analog bandpass filter not only has a good performance but also achieves the goal of reducing the chip size and cost,opening a new direction for fully integrated circuit of digital circuits and analog circuits.The simulation of CMOS analog bandpass filter of Cadence proves the validity of such structure meanwhile captures the corresponding parameters of highest frequency,providing a future guidance for both theory and application.