Linear frequency modulation of voltage-controlled oscillator using delay-line feedback

This letter proposes a structure for a voltage-controlled oscillator (VCO) circuit which operates in a frequency range of 4.0-4.3 GHz and can achieve a highly linear frequency sweep without any additional compensation circuit. The VCO consists of an amplifier and a feedback circuit only. The feedback circuit compensates for the phase delay of a transmission line with a varactor and sets the closed-loop phase change close to 360/spl deg/. The measured maximum deviation from a linear frequency sweep is /spl sim/1.2 MHz when the varactor capacitance C/sub V/ of the VCO is related to the control voltage V/sub C/ by C/sub V//spl prop/V/sub C//sup -1.06/. The spectral distribution of the beat frequency between the VCO output and delayed VCO output shows that the proposed VCO has excellent linearity in frequency modulation.

[1]  Krzysztof Kulpa,et al.  Focusing range image in VCO based FMCW radar , 2003, 2003 Proceedings of the International Conference on Radar (IEEE Cat. No.03EX695).

[2]  Young Hwan Kim,et al.  Nonlinearity compensation circuit for voltage-controlled oscillator operating in linear frequency sweep mode , 2000 .

[3]  P. J. Burke,et al.  Ultra-linear chirp generation via VCO tuning predistortion , 1994, 1994 IEEE MTT-S International Microwave Symposium Digest (Cat. No.94CH3389-4).

[4]  Douglas L. Maskell,et al.  A microprocessor controlled microwave ranging system for high accuracy industrial applications , 1994, Conference Proceedings. 10th Anniversary. IMTC/94. Advanced Technologies in I & M. 1994 IEEE Instrumentation and Measurement Technolgy Conference (Cat. No.94CH3424-9).