Dual-Modulus Prescaler based on transmission gates and pseudo-PMOS logic

The Dual Modulus Prescaler is a critical block in CMOS systems like high speed frequency synthesizers. The design of high divide-by-value, high speed and low power dual modulus prescaler, however, remains a design challenge. In order to face the challenge, this paper introduces an idea of using transmission gates and pseudo-PMOS logic in realization of the dual modulus prescaler. The topology of the prescaler proposed in this paper is different from the prior designs primarily in two ways: (i) it uses transmission gates in the critical path and (ii) the D-flip flops used in the synchronous counter are comprised of pseudo-PMOS invertors and ratioed latches. A design of the pseudo-PMOS logic based DFF is introduced and used in the proposed prescaler design. Based on the proposed topology, a dual-modulus divide-by-127/128 prescaler is implemented in 0.35 mu m CMOS technology. Its maximum operating frequency is observed as 2.4 GHz. It consumes 4.8 mW power from a 3 V supply. Circuit operations and measurement results are provided. The silicon estate required is only 0.06 mm(2). There is no flip flop and logic gate in the critical path. The proposed topology is suitable firstly for the high speed and high divide-by-value prescaler designs. Secondly, it reduces: (i) design complexity, (ii) power consumption and (iii) load to preceding circuit.