True 50% duty-cycle high-speed divider with the modulus of odd numbers

Abstract

This paper proposes a true 50% duty-cycle highspeed prescaler with an odd modulus, based on current switchable D flip-flops. Each D flip-flop can sample data at the positive and negative clock edges, because of the changeable trigger mode. The proposed divide-by-N prescaler, with a 50% duty cycle, is formed as a ring with an N number of D flip-flops. Two types of 50% duty-cycle divide-by-five prescalers, the sample-hold-sample-hold-hold (SHSHH) prescaler and the sample-sample-hold-sample-hold (SSHSH) prescaler, are implemented using the 0.35 µm SiGe HBT technology. The SHSHH divider has a better performance, up to 7 GHz, thanks to the synchronization of data and control signals.Index Terms -50% duty cycle, divide-by-N, prescaler, SiGe HBT.

Simple odd number frequency divider with 50% duty cycle

“…It is because both of rising and falling edges of the divided clock signal can be used for efficient high speed operation. To obtain 50% duty cycle, special types of latches or flipflops have been generally used for odd number frequency dividers [2,3,4,5]. A negative level sensitive latch was used in [2] and a current switchable D flipflop (DFF) was used in [3,4,5] for dual edge triggering operation in odd number frequency dividers.…”

“…To obtain 50% duty cycle, special types of latches or flipflops have been generally used for odd number frequency dividers [2,3,4,5]. A negative level sensitive latch was used in [2] and a current switchable D flipflop (DFF) was used in [3,4,5] for dual edge triggering operation in odd number frequency dividers. However, those special latches and flipflops require more circuit complexity and are not appropriate when a rail-to-rail signal swing is needed.…”