CML Current Mode Full Adders for 2.5-V Power Supply
نویسندگان
چکیده
We present the basic structure and performance of CML current mode full adders, that are used as Carry Save Adders (CSA) in combinatorial multipliers. A 1.2 μm BiCMOS technology is used for simulations but the schematic assumes a 2.5-V power supply. Compared with binary voltage mode CSAs, the multivalued current mode CSAs have chip area and power dissipation advantage, but speed disadvantage. The current mode version is far more sensitive to power supply and temperature shifts. It is widely acknowledged that the binary circuits have better performance than the multivalued ones [1]. However, there exist some cases where multivalued circuits could be interesting. For many years, multivalued current-mode circuits have been considered as potential candidates to implement efficiently arithmetic functions. As an example, a 2 μm current-mode CMOS 32 x 32 bit multiplier [2] has been demonstrated, with the same speed and half chip area and power dissipation compared with the best corresponding binary one at the same period. A potential drawback of current mode circuit is that fanout is one. This is not a problem in the multioperand addition which is the critical path to implement combinatorial multipliers. In this paper, we present a current mode CML 1 bit full adder which can be used as a Carry Save Adder in the reduction tree of a multiplier. It only uses bipolar transistors and resistors, but it is suitable to be used with a BiCMOS technology, where CML circuits are mixed with CMOS circuits. Although we use the simulation parameters and the layout design rules of a 1.2 μm BiCMOS technology of SGS-Thomson, we only consider circuitry that will be usable with advanced BiCMOS technologies, using reduced power supply voltages. Our CML current mode adder is designed with a 2.5-V power supply. The main features of the technology are given in table 1. Speed, power dissipation and device complexity are compared for the current mode multivalued full adder and the binary voltage mode full adder that can be designed with the same power supply. 2. Four-valued CML circuitry for 1-bit adder 2.1. Basic building blocks
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