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Design of the hybrid CAM register
Authors
	Solovyeva L.A.
Date of publication
	2016
Abstract
	Article describes the development method of a CAM (content addresable memory) register as a part of which there are both static and dynamic memory cells. The first part of the article concerns static and dynamic implementation of the CAM register. For each type of implementation the average power consumption and delay time of match line was counted. Each implementation has advantages and shortcomings. The main advantage of a static CAM register is the high noise stability which is important for technologies with a low power supply voltage. However, for 28-nm process CAM register power consumption is relatively high. It is caused by the circuit of common match line signal generation, which consists of a large number of logical elements. Power consumption of a dynamic CAM register, for 28-nm process, is rather low. However, the dynamic register has very low noise stability and that is critical for technologies with a low power voltage. Also, the dynamic CAM register delay of output match signal has the strong dependence on the register capacity. In the second part of article the static and dynamic memory cell join method was considered. In particular, a static CAM register common match line signal generation approach was used for a dynamic CAM register. To adopt the circuit fragmentation of the dynamic register was made. After that we joined each fragment match line by the common match signal generation circuit similar to the same of the static register. It allowed to increase reliability of the dynamic register significantly and to decrease match line delay. At the following stage the additional logical element of XOR was entered to the match line generation circuit. It allowed to simplify the synchronization of whole CAM and also to reduce power consumption. Lowering of power consumption, at this stage, became achievable due to reduction of logical steps of the common match line generation tree. However, despite the reached improvement, this option is not the best from power consumption point of view. Therefore in the modified register the part of dynamic cells was replaced with static ones. Introduction of static cells allowed to reduce the power required for precharge of the match line. In final part several versions of registers in which was a different static/dynamic cells ratio are provided. The analysis af all available options let us to find an optimal one from power consumption and speed point of view. Characteristics of the final hybrid register are the best, for chosen process in comparison with characteristics of the registers considered earlier. The method described in article allows to pick up a ratio of dynamic and static memory cells for the register of any digit capacity. At the same time characteristics, such as the power consumption, delay of the match line signal and reliability will be better than in registers made of the memory cells of one type only.
Keywords
	CAM memory cell, power consumption, leakage current.
Library reference
	Solovyeva L.A. Design of the hybrid CAM register // Problems of Perspective Micro- and Nanoelectronic Systems Development - 2016. Proceedings / edited by A. Stempkovsky, Moscow, IPPM RAS, 2016. Part 3. P. 171-177.
URL of paper
	http://www.mes-conference.ru/data/year2016/pdf/D065.pdf