LIST OF TABLES
1.2 Thesis Organization
In this dissertation, we first focus on the design of a low noise amplifier using planar spiral inductor. And then, the principles and the characteristics of the active inductor are described. We proceed with the RF amplifier circuit designs with the original active inductors to verify that die area using an active inductor is smaller than that of the die area using a planar spiral inductor. To improve the performance and reduce the complexity of the active inductor, we concentrate on the circuit design of the active inductors. By means of mathematical analysis, the simulated verification, and the measured results show that the active inductors based on several compensated methods can significantly improve quality factor (Q), inductance (L), and operating frequency of the RF CMOS active inductors. And for the CMOS RF circuit applications, the wideband amplifier and the LC oscillator applying with the improved active inductors are proposed. As a result, the proposed RF front-end circuits obtain competitive performances compared with the circuit based on planar spiral inductors and used active inductor published previous literatures. Consequently, die area of the circuits using the active inductor is much smaller than that of the conventional circuits using planar spiral inductors.
In chapter 2, we present a low noise amplifier with planar spiral inductors for discussing the related problems caused by using passive inductors within RF circuits.
Although, the amplifier based on the planar spiral inductors obtains good performances, the amplifier results in many drawbacks. Especially, the passive spiral inductors are main components that occupy larger die area than other components such as resistors, capacitors, and transistors. Furthermore, due to process variation, to obtain an accurate passive spiral inductor is very difficult. Therefore, we propose a solution of applying active inductors for overcoming the disadvantages caused by using planar spiral inductors. We present an overview of a CMOS active inductor. The principle of the active inductor for the inductance
impedance is caused by the feedback configuration of back-to-back connection of transistors.
The inductance impedance includes both of the inductance and the internal loss. The internal loss is a main factor, which affects the performance of the active inductor. The performances of the active inductor will depend on the various circuit topologies. In recent years, various CMOS active inductors have been explored in some literatures. We survey some CMOS active inductor circuits and applications in this chapter.
In chapter 3, using the active inductors of the previously published literatures to design the availability for the inductor-less RF amplifier is proposed. According to the simulation results, the performances of the RF amplifiers based on an active inductor are similar with that using planar spiral inductor. But the die area of the RF amplifiers with active inductor is much smaller than that with planar spiral inductor. Moreover, the performance of these ordinary active inductors can be improved by compensation techniques to obtain a higher performance. Although compensation such as negative impedance converter has been presented, the active inductor circuits are very complicated. Therefore, in this work, we present simple compensated techniques to achieve a simpler active inductor circuit than those designs published in the literatures. Besides, the proposed active inductor circuits are very simple and the active inductors achieve higher Q, higher operating frequency, and higher inductance.
In chapter 4, the improved active inductor circuit designs using four simple distinct loss compensated techniques to obtain higher performance and reduce circuit complexity are presented. To improve Q-value, operating frequency, and inductance of the active inductor, four different loss-compensated techniques such as cascode RC feedback, gain-boosting and current-reused, using a capacitor, and only using a resistor to aim at different circuits of the active inductor are described. According to the measured results, the proposed active inductors can achieve higher Q-value, higher inductance, higher operating frequency, and less
circuit complexity. As a result, the performance of the proposed active inductors is better than those from previous designs [34, 36, 37, 38, 41].
In chapter 5, the designs for wideband amplifier and LC oscillator using the proposed active inductor with distinct loss compensated techniques are presented. In these applications, the wideband amplifier is designed with the proposed active inductor based on cascode RC feedback loss compensated circuit to obtain wide frequency response, high enough power gain, and reasonable noise figure. The LC oscillator circuit is implemented by using the improved active inductor based on a resistor loss compensated technique to achieve wide tuning range, low phase noise, constant power consumption, and frequency-independent phase noise. According to the simulated and measured results, we’ve got an 18dB wideband amplifier gain and 1GHz bandwidth with the requirements of 8dB noise figure and a reasonable linearity (-16dBm of IIP3). Moreover, the VCO circuits presented a reasonable output voltage, wide tuning range (1GHz to 3GHz), and without changing the phase noise (-98dBc/Hz) and the power consumption (10mW) due to the change of output frequency. So, the sub-circuit of the RF front-end based on the active inductor can be realized.
In chapter 6, we make some conclusions and outline future research directions. In the active inductor designs, the characteristics are better than the planar spiral inductor such as Q-value, inductance, operating frequency, and die area. In RF front-end applications, the main keys to complete high performance CMOS active inductor and wideband amplifier and LC oscillator, are briefly summarized. And performances of the RF front-end circuit can compete with the circuits using the planar spiral inductor. Although higher Q-value, higher inductance, and higher operating frequency CMOS active inductor can be obtained, other design issues such as noise, power consumption, and dynamic range of the active inductor need to be further improved. Furthermore, sub-circuits of the RF front-end in this research can be integrated together to reach a single chip solution.