Browse Prior Art Database

Bit Select Sense Amplifier

IP.com Disclosure Number: IPCOM000049004D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Chan, YH: AUTHOR

Abstract

In bipolar RAM (random-access memory) using CTS (Complementary Transistor Switch) (*) cells, selection of a cell from a word group of n bits is done by selecting both its word address and bit address. For a read operation, the selected cells are read by bit line sense amplifiers to output the requested data. Fig. 1 discloses a high speed sense amplifier circuit designed for this application. The circuit uses current-mode operation to enable very fast switching at low power level. Switching delay is also independent of input capacitive loadings as well as the number of bits in the word group. Sensing Scheme

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Bit Select Sense Amplifier

In bipolar RAM (random-access memory) using CTS (Complementary Transistor Switch) (*) cells, selection of a cell from a word group of n bits is done by selecting both its word address and bit address. For a read operation, the selected cells are read by bit line sense amplifiers to output the requested data. Fig. 1 discloses a high speed sense amplifier circuit designed for this application. The circuit uses current-mode operation to enable very fast switching at low power level. Switching delay is also independent of input capacitive loadings as well as the number of bits in the word group. Sensing Scheme

Fig. 2 is a schematic of the sensing operation for word groups consisting of 16 cells. Each word group contains a sense amplifier whose state is determined by the selected cell. During the selection of a cell, the word lines are pulled down by its corresponding word decoder (not shown), and the selected bit rail is raised up by its bit decoder (not shown). Bit selection in the group is hence always 1 out of 16, only two of the 32 bit lines are up at any one time. The higher of these two selected bit lines will then turn on the corresponding sense transistor from the sense amplifier.

Since there are n cells per word group (16 for the application discussed here), a total of n pairs of sensing transistors are attached to the bit rails. Due to the numerous devices, the sense amplifier input nodes A, B and C are very capacitive. Switching of these nodes voltage-wise is, therefore, slow and requires high current. The problem can be overcome by employing current mode switching as disclosed here. Sense Amplifier Circuit Operation

Referring to Fig. 1, the 32 sensing transistors TL1 to TL16 and TR1 to TR16 form a big current switch input for the sense amplifier. The bases of these transistors are connected to the 16 bit rails in the word group. Transistors T1 and T2 are emitter fol...