A CMOS VCO with 2GHz tuning range for wideband applications Speaker ： Shih-Yi Huang

Outline Introduction Band-Switching LC Tank The Designed LC VCO Simulation Result Conclusion References

Introduction Ultra-wideband (UWB) system, WPAN UWB system ： 3.1~5 GHz, 6~10.6 GHz The low-frequency band, the first-generation UWB system.

Introduction (cont.) Voltage-controlled oscillators, modern communication systems, LO (local oscillator) Wide frequency range, low phase noise, low harmonic distortions, stable output amplitude and low power consumption. LC VCO design, narrow tuning-range, limited range of the variable capacitance of the varactors

Introduction (cont.) Band-switching wide-band CMOS VCO LC tank ： switched capacitors and PMOS varactors Accumulation and inversion region of operation the MOS capacitor exhibit a maximum of oxide capacitance, C ox

Band-Switching LC Tank RF VCO with a large enough tuning range to compensate the process-variation and temperature offset, we adopt the switched capacitor topology Figure 1. (a) The schematic of LC tank for the band-switch of VCO, (b) using a switched capacitor topology to achieve wide tuning range

The Designed LC VCO Figure 2. Wide-band LC VCO M1~M4 ： equivalent to negative resistors to compensate for the energy loss in the LC tank. M5~M10 ： are used for band switch. M11~M14 ： use to accomplish 50 output impedance.

PMOS varactor Figure 3. PMOS varactor (a) cross section, (b) characteristic of the device

AMOS varactor & PMOS varactor Figure 4. The capacitance of 3 series AMOS varactors Figure 5. The capacitance of 3 series PMOS varactors

Simulation tuning range Figure 6. Simulated tuning range GHZ 5.03GHz

Simulation output power Figure 7. Output power versus the control voltage dBm -2.2 dBm

Simulation phase noise Figure 8. Phase noise from 2.95GHz to 5.03GHz. -92 dBc/Hz at 1-MHz offset -124 dBc/Hz at 1-MHz offset

Chip photo Figure 9. Layout photograph of the VCO.

Table 1 Comparison of published CMOS VCOs

Conclusions A CMOS VCO with 2GHz tuning range is designed. With 8.5mA current from 1.8V power supply, the VCO achieves 2.95~5.03GHz tuning range. The phase noise -124 dBc/Hz ： 2.95GHz -92 dBc/Hz ： 5.03GHz. Better performance with very wide tuning range. VCO is suitable for the UWB low-frequency band applications.

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