A Sigma-Delta Fractional-N Closed-Loop Modulator for DECT
- D.D.S. Hermansen, E. F. Buskgaard, P. Olesen, F. H. Andreasen, T. Larsen
This paper addresses the design and implementation of a digitally controlled oscillator (DCO) as a possible step towards an all-digital closed-loop modulation implementation for DECT applications. Based on a complete transmitter system model a simplified model describing only the modulation is developed. Simulations based on this system shows that a simple 5 bit modulator is sufficient for acheiving the required modulation accuracy. The complete system is tested and measured using a prototype chip. The DCO design uses a standard 6 metal layer 0.18 μm CMOS technology. The experimental results show that the acheived modulation performance complyes with the DECT specifications. The design can be extended for compliance with other frequency modulation systems such as GSM, Bluetooth, DCT, WLAN etc.