A Flash Frequency Tuning Technique for SC-Based mm Wave VCOs

Alessandro Parisi,Alessandro Finocchiaro,Giuseppe Palmisano,Andrea Cavarra,Giuseppe Papotto

doi:10.3390/electronics11030433

Alessandro Parisi, Alessandro Finocchiaro + Show 3 more

Open Access

https://doi.org/10.3390/electronics11030433

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Abstract

This paper presents a flash frequency tuning technique for switched-capacitor-based, voltage-controlled oscillators operating at mm wave frequencies. The proposed strategy exploits a capacitor array and a small varactor for coarse and fine tuning, respectively, which are simultaneously operated thanks to a flash A/D-based control circuit. This avoids additional delay in the frequency calibration, thus enabling very fast-frequency locking operation. The VCO was fabricated in a 28 nm FD-SOI CMOS technology and provides an oscillation frequency around 39 GHz with an overall tuning range of 3.3 GHz. The circuit dissipates 8.4 mW from a power supply as low as 0.7 V, while occupying a silicon area of 210 µm × 150 µm.

Highlights

Mm wave phase-locked loops (PLL) are highly demanded in a wide range of applications, such as medical imaging [1,2,3], wireless communications (e.g., WLAN [4,5,6], 5G generation cellular networks [7,8], etc.) and automotive radar sensors [9,10,11,12,13]
The voltage-controlled oscillator (VCO) was fabricated in a 28 nm FD-SOI CMOS technology by STMicroelectronics, which provides a very fast active device with fT and fMAX up to 300 GHz [23] and a standard back end of line (BEOL)
The VCO was embedded within an on-chip PLL designed for testing purposes, which uses an off-chip second-order low-pass filter (LPF)

Summary

Introduction

Mm wave phase-locked loops (PLL) are highly demanded in a wide range of applications, such as medical imaging [1,2,3], wireless communications (e.g., WLAN [4,5,6], 5G generation cellular networks [7,8], etc.) and automotive radar sensors [9,10,11,12,13]. Varactor parasitic capacitances greatly increase their contribution to the overall tank capacitor, still reducing tuning range To overcome such limitations, arrays of switched capacitors (SCs) along with fully digital or analog/digital control circuits are employed for a coarse frequency calibration [16,17,18,19,20,21], leaving the fine tuning to a small varactor. Arrays of switched capacitors (SCs) along with fully digital or analog/digital control circuits are employed for a coarse frequency calibration [16,17,18,19,20,21], leaving the fine tuning to a small varactor This approach has the advantage of avoiding large area varactors to cover the overall tuning range with the double benefit of increasing the tank Q-factor and reducing parasitic capacitances.

Circuit Description

Experimental Results

Conclusions