Digital Tcxo Voltage-controlled Oscillator Circuit Design

X-tal oscillators play an important role in the field of modern communication and precision measuring instruments, etc. The access coefficient of an X-tal is very small and its quality factor is very high. Whenever an application requires precise definition of oscillation frequency and low phase noise, an X-tal oscillator is the best candidate. However, in the field of Mobile communication, precision measuring, etc. stability of oscillator is so critical that deviation of frequency due to temperature variation causes a serious problem. To improve accuracy of frequency, compensation circuits should be added to X-tal oscillator. Recently, Digital Temperature Compensation X-tal Oscillator (DTCXO) is popular because of its accurate compensation ability, small size, low power dissipition, and high reliability, which make it widely used in VLSI possible and possibility of implementation in VLSI.The design of DTCXO is divided into Digital Temperature Compensation Voltage Generation circuit design and Voltage-Controlled X-tal Oscillator (VCXO) circuit design. We have studied and designed the latter one. After analyzing and summarizing a variety of VCXO circuits, an optimal program has been deserved. This design is divided into three parts: X-tal Oscillator circuit design, Voltage Controlled circuit design, and Bias circuit design. The X-tal circuit is Santos oscillator, uses the automatic gain control method to stabilize its oscillation amplitude, reduces the distortion effectively, improves the frequency stability, otherwise, Santos oscillator has only one package pin, which saves the production cost. In addition, we also analyze the frequency stability and phase noise. The X-tal circuit uses AT-cut crystal resonator, and we analyse the frequency-temperature characteristics of crystal oscillator. Based on this theory, we use a varactor to design a micro frequency modulation VCXO, and give a theoretical voltage compensation algorithm. This VCXO has a large tuning range which can cover X-tal oscillator deviation of frequency due to temperature variation, Frequency Stability vs. Temperature of this circuit is 5.25×10 ?7/ ? 40 ~ 80 C. In order to improve the stability of the VCXO, we designed a Curvature Compensated CMOS Bandgap Voltage Reference, which uses a first-order and nonlinear exponential order curvature compensation method. This bandgap has a high power supply rejection ratio (PSRR) and low temperature coefficient (TC). The reference voltage is converted into a current by using of an Operational Amplifier (OPA) and a resistor, which constitutes a current reference.After finishing the blocks and system simulation, we have given the layout design. In the last chapter, we point out the deficiency of this design and analyse the main result. Also some improvement method has been given.