circuit share
- 1. DESIGN AND IMPLEMENTATION OF CS2FF FOR LOW POWER DIGITALVLSI’S M.V.MOUNIKA , 14204116.
- 2. INTRODUCTION Ultra-low power CMOS VLSIs have attracted much attention for use in power- aware applications such as wireless smart sensor networks and implantable bio- medical systems. Several low-power techniques have been investigated . Among them, reducing the supply voltage for digital circuits is the most direct and effective way to achieve low power dissipation because of the quadratic dependence of the power dissipation on the supply voltage.
- 3. One big issue for ultra-low voltage digital circuits is in the design of a flip- flop (FF) circuit because FFs are widely used in modern digital VLSI systems such as a general purpose register, a pipeline register, and a finite state machine. However, their performance tends to degrade at lower supply voltage and, moreover, they require a number of transistors to achieve stable and low voltage operation.
- 5. CONVENTIONAL FFS The TBFF consists of only 24 transistors and is used in most standard cell libraries. However, the function becomes difficult to operate at extremely low supply voltage, such as below the threshold voltage, because the outputs of the tri-state buffers are connected in wired-OR
- 6. And the contention increases power dissipation and results in functional error . Moreover, both the operation of tristate buffers and that of transmission gates used in the TBFF tend to fail at lower supply voltage. The NLFF and CLFF consist of only static CMOS gates. The NLFF are suitable for low voltage operation because they are composed of only general-purpose CMOS gates without using additional stacking transistors.
- 7. TSFF
- 8. CLFF
- 9. NLFF
- 10. The stacking transistors need higher supply voltage as the number of stacking transistors increases . However, the NLFF requires 40 transistors and occupies a large area, resulting in high power dissipation. The CLFF can slightly reduce the number of transistors, but it uses modified NAND and NOR gates marked with asterisks to introduce delay time for proper operation and still requires 34 transistors.
- 11. Proposed cs2 ff In light of this background, we herein propose a circuits shared static FF (CS2 FF) suitable for extremely low-power digital circuits with a small number of transistors. The CS2 FF consists of five static NORs and two inverters (INVs). Thus, the CS2 FF uses only 24 transistors
- 12. CS2 FF
- 13. The INVs are used to generate control signals of CKB and CK2 from root clock of CK. NOR1, NOR2, and NOR3 form a master latch,while NOR3, NOR4, and NOR5 form a slave latch. Note that NOR3 is shared both in the master and slave latches, and is used to acquire data in the master latch and transfer it to the slave latch.
- 14. The master latch operates using a positive edge of control signal of CK2. When input data, CK2, and CKB are “D0”, low, and high, respectively, NOR1 works as an inverter and the output of NOR3 is reset to low. Thus, NOR2 also works as an inverter, and the data is transferred to QM as“D0”. Then, when CK2 and CKB become high and low, respectively, the output of NOR1 is reset to low. Therefore, NOR2 and NOR3 form the master latch, and the data is held at MFB as “D0B”. Meanwhile, the slave latch operates using a negative edge of clock signal of CK.
- 15. When CK and CKB are high and low, respectively, the output of NOR4 is reset to low and NOR5 works as an inverter. Therefore, the data is transferred from MFB to the output of Q as “D0”. Then, when CK and CKB become low and high, respectively, the output NOR3 is reset to low. Therefore, NOR4 and NOR5 form the slave latch, and the data is held at Q as “D0”. This way our proposed CS2FF operates as a master-slave flip-flop with a small number of transistors.
- 17. CONCLUSION • In this paper, we proposed a compact and low-power circuit shared static flip-flop (CS2FF) for extremely low-power digital VLSIs. The circuit consists of five static NORs and two inverters (INVs). The total number of transistors was only 24, which is the same as the conventional tri-state buffer based flip flop (TBFF) used in most standard cell libraries. SPICE simulations demonstrated that our CS2FF achieved.