A digitally controlled 2.4-GHz oscillator in 65-nm CMOS

This paper presents a 2.4-GHz digitally controlled oscillator (DCO). The circuit is designed using a 65-nm six-metal CMOS technology with an operating voltage of 1.2 V. The DCO comprises an LC oscillator core and the digital interface logic. It has a frequency range of about 200 MHz covering the 2.4-GHz ISM band, with around 5 MHz available for frequency modulation. Its frequency quantization step is approximately 20 kHz, with a digital ∑Δ-modulator used to allow a 5-bit fractional digital control and provide an effective frequency resolution better than 1 kHz. Its free running oscillation phase noise is −125 dBc/Hz at 1 MHz frequency offset with 4.8 mA biasing current. The power consumption is adjustable from 1.8 mW to 12 mW.