Title :
A digitally controlled oscillator system for SAW-less transmitters in cellular handsets
Author :
Hung, Chih-Ming ; Staszewski, Robert Bogdan ; Barton, Nathen ; Lee, Meng-Chang ; Leipold, Dirk
Author_Institution :
Wireless Analog Technol. Center, Texas Instruments, Dallas, TX, USA
fDate :
5/1/2006 12:00:00 AM
Abstract :
A complete digitally controlled oscillator (DCO) system for mobile phones is presented with a comprehensive study. The DCO is part of a single-chip fully compliant quad-band GSM transceiver realized in a 90-nm digital CMOS process. By operating the DCO at a 4 × GSM low-band frequency followed by frequency dividers, the requirement of on-chip inductor Q and the amount of gate oxide stress are relaxed. It was found that a dynamic divider is needed for stringent TX output phase noise while a source-coupled-logic divider can be used for RX to save power. Both dividers are capable of producing a tight relation between four quadrature output phases at low voltage and low power. Frequency tuning is achieved through digital control of the varactors which serve as an RF DAC. Combining a MIM capacitor array and two nMOS transistor arrays of the varactors for the RF DAC, a highly linear oscillator gain which is also insensitive to process shift is achieved. The finest varactor step size is 12 kHz at the 1.6-2.0 GHz output. With a sigma-delta dithering, high frequency resolution is obtained while having negligible phase noise degradation. The measured phase noise of -167 dBc/Hz at 20 MHz offset from 915 MHz carrier and frequency tuning range of 24.5% proves that this DCO system can be used in SAW-less quad-band transmitters for mobile phones.
Keywords :
CMOS integrated circuits; MIM devices; UHF oscillators; cellular radio; digital-analogue conversion; frequency dividers; mobile handsets; phase noise; radio transmitters; varactors; 1.6 to 2.0 GHz; 12 kHz; 20 MHz; 90 nm; 915 MHz; MIM capacitor array; SAW-less quad-band transmitters; cellular handsets; digital CMOS process; digital controlled oscillator system; digital varactor control; frequency dividers; gate oxide stress; high frequency resolution; mobile phones; nMOS transistor arrays; on-chip inductor; quad-band GSM transceiver; quadrature output phase; sigma-delta dithering; Control systems; Digital control; Frequency; GSM; Mobile handsets; Oscillators; Phase noise; Telephone sets; Transmitters; Varactors; Cellular phone; GSM; channel hot carrier (CHC); deep-submicron CMOS; digitally controlled oscillator (DCO); electromigration (EM); gate-oxide reliability; mobile phone; quantization noise; sigma-delta modulator; varactor; voltage-controlled oscillator (VCO);
Journal_Title :
Solid-State Circuits, IEEE Journal of
DOI :
10.1109/JSSC.2006.872739