Design Of VCO In Digital TV Tuner

VCO(Voltage Controlled Oscillator) is the core block of PLL based frequency synthesizer. Its performance determines the whole synthesizer to a large extent. Integrated voltage controlled oscillators are one of the most challenging parts of radio transceivers to integrate in standard CMOS technologies. In many RF processes (GaAs, SiGe, Bipolar, CMOS), CMOS RF process is widely applied gradually for its high integrated density, low cost. Therefore, CMOS VCOs On chip become the hotspot of many RF applications.The CMOS wideband VCO designed in this thesis is used in an ASIC for single-conversion digital TV tuner. Because down-converter of the chip converts the wide spectrum of TV signals (48MHz～860MHz) to a fixed middle frequency (36MHz), on-chip VCO must have quite wide tuning range and high performance. This design adopts a digital signal controlled automatic amplitude control (AAC) loop, so it is a typical Mix-signal circuit.At first, this thesis introduced the status of the design of on-chip VCO and the design request was proposed: a VCO of tuning range from 435.25 MHz-899.25MHz, phase noise is-85dBc/HZ offset 10KHz. Then, the thesis elaborated on the basic theory of the VCO (especially on LC-VCO), i.e. the oscillating theory, the amplitude calculating, the typical structure, the varactor theory, etc. This thesis highlights and analysis of the VCO phase noise theory, and make a summary analysis of the pop optimization way of phase noise.Then the thesis focused on the scheme of the wide-tuning-range VCO, and achieved the design parameters, which is typical digital and analog mixed circuits (AMS). The scheme adopted off-chip LC oscillating tank, which provide wide tuning range and high Q value. The thesis made a precise model of the off-chip LC-tank. Using complementary cross-coupling VCO with tail-current control scheme achieve the VCO core. The automatic amplitude control loop is implemented in a mix-signal way, and then the VCO buffer is designed. EldoRF is used to simulate the performance of the circuit. Layout of the whole circuit is drawn with the help of IC-Station. The simulation results show that the amplitude of the VCO tuning range, phase noise performance met the design requirements. Besides, it has low power consumption, amplitude stability characteristics of the entire frequency range.