Frequency modulation and control in quadrature ring oscillator for multiband FM/FSK transmitters

Abstract

A circuit for wide range frequency modulation and control in a quadrature ring oscillator for multiband FM/FSK transmitter is presented. The modulation and control signal are applied to the oscillator transmission gates via the floating current source circuit. The current of this source repeats the input control current that includes two components, one of which tunes the mid-frequency and the other tunes the modulation depth. Each of the control components is set independently. This precise and wide-range frequency control allows one to use it in multiband applications. The proposed circuit is designed in 0.18 mum standard digital CMOS process for intended carrier frequencies of two ISM bands (900 MHz, and 2.4 GHz).