An LC CMOS injection-locked frequency divider for divide-by-two and divide-by-three operation

Numerous circuit topologies have been proposed for divide-by-m injection-locked frequency dividers (ILFDs), most of which have been optimized for division by even numbers, especially divide-by-2. It has been more difficult to realize division by odd numbers, such as divide-by-3. This paper describes a CMOS injection locked frequency divider (ILFD) that can operate equally well in both divide-by-two and divide-by-three modes. The ILFD is based on a cross-coupled CMOS LC-tank oscillator having capacitive and direct injection via both NMOS and PMOS transistors connected across the LC tank. The circuit is similar to a conventional CMOS ILFD for divide-by-two operation with direct injection, but it combines the effects of two independent injection techniques to maximize the width of its divide-by-three locking range. The paper presents the circuit architecture, SPICE simulations, and experimental measurements.