A “divide-by-odd number” direct injection CMOS LC injection-locked frequency divider

The use of resonant CMOS frequency dividers with direct injection in frequency synthesizers has increased in recent years due to their lower power consumption compared to conventional digital prescalers. Numerous circuit topologies have been proposed, 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 proposes a simple modification to a CMOS injection locked frequency divider (ILFD) with direct injection, which gives it a wide locking range both in the “divide-by-odd number” mode and in the conventional “divide-by-even number” regime, thereby opening up applications which require frequency division by an odd number. The paper presents the circuit architecture, SPICE simulations and experimental validation.