Ivan Uzunov

Dual-Band LC VCO Architecture With a Fourth-Order Resonator

A dual-band LC voltage-controlled oscillator (VCO) architecture suitable for GSM/PCS/DCS applications is presented. The VCO utilizes a fourth-order resonance tank and avoids quality-factor-deteriorating switches. The paper outlines the design tradeoffs and the VCO when using a fourth-order resonator. The 0.8-GHz/1.8-GHz test chip was fabricated in the 0.5-mum IBM-5AM SiGe process and has achieved phase noise of -134 dBc/Hz at a 1-MHz frequency offset from the carrier, with 56-MHz and 121-MHz tuning ranges in the corresponding bands. The VCO core consumes 15 mW from a 2.5-V power supply

Novel VCO Architecture Using Series Above-IC FBAR and Parallel LC Resonance

A quasi-monolithic voltage-tunable film bulk acoustic resonator (FBAR) enhanced oscillator for 2.1 GHz in 0.25-mum SiGe BiCMOS technology is designed, fabricated, and evaluated. The narrow-band FBAR was built above the SiGe circuit through later Si post-processing steps. The oscillator is based on a two-transistor loop structure and uses two resonators, namely a parallel LC tank and an above-IC FBAR in its series-resonant mode. The improvement in phase noise performance is significant compared to a similar reference LC voltage-controlled oscillator (VCO), with the best phase noise being -144.1 dBc/Hz at an offset of 1 MHz and -149.6 dBc/Hz at 3 MHz. The architecture offers advantages in overcoming frequency tuning difficulties usually present when using high-Q resonators. Although the width of the tuning range comes at some cost on phase noise, the measured performance satisfies contemporary wireless standards such as GPS

High tuning accuracy design of variable IIR digital filters

Our recent results in the design of high tuning accuracy variable IIR filters are given in this work. The accuracy and the range of tuning are increased by minimization of the sensitivity of the structures (real and complex) used and by developing of new method of design based on cascaded identical sub-filters. Several new variable multioutput second-order IIR digital filter sections also are proposed. All theoretical results derived are verified experimentally.

Theoretical Model of Ungrounded Inductance Realized With Two Gyrators

The traditional approach to simulate ungrounded inductors in active gyrator filters uses two gyrators with all equal transconductances. However, this paper shows that the differences between gyrator transconductances can be employed to obtain certain advantages. The filter can be designed with extra gain and with different terminating resistors, but without need of any additional buffer amplifiers. These advantages are achieved by using an appropriate theoretical model of the gyrator simulated floating inductance in the filter design process. The model separates the simulated inductance from the amplification, thus suggesting more flexible filter design. Further the model is extended to reflect also some OTA imperfections-their input and output impedances and their noise generation. In addition, the discussed model gives a unified approach for theoretical analysis of gyrator LC filters with floating inductors.

High tuning accuracy design of variable IIR filters as a cascade of identical sub-filters

The limits of application, tuning accuracy and sensitivity of variable IIR digital filters realized as a cascade of several identical sub-filters are investigated in this paper. Sub-filters of first and second-order are realized with bilinear and biquadratic sections with independent tuning, developed by the authors, while sub-filters of higher order are realized as parallel allpass structures using first and second-order allpass sections with minimized sensitivities. It is shown that filters so designed have higher accuracy and wider ranges of tuning compared to other known variable filters and behave much better in a limited word-length environment.

Design Considerations in Tapped-Inductor Fourth-Order Dual-Band VCO

A theoretical analysis of the constraints posed by a tapped inductor on a dual-band fourth-order voltage-controlled oscillator (VCO) is presented. The analysis provides guidelines for frequency band selection, tapped-inductor design, and VCO optimization. The guidelines are utilized in a VCO design example simulated on a 45-nm CMOS process. An adaptive frequency-tuning scheme exploits unique features of the fourth-order tank to optimize VCO performance.