Double-level bipolar scan amplifier for BICMOS SRAMS with a common base amplifier in the final stage.

摘要

There is described a double stage sense amplifier (4) in bipolar technology achieving very high speed operation without saturation or dotting problems. For each memory cell column of the computer memory system (1), a first stage or column sense stage (4.1) amplifies the differential input signal (V) produced on the pair of bit lines (BLL, BLR) according to the information read from one CMOS memory cell of the memory cell array (3.1) to provide a first differential output signal (V1) available at output terminals (10.1, 10.2). The output terminals of all the first stages (4.1 to 4.n) are dotted to a first data out bus comprised of the data lines (DCL1, DLT1). A second stage or final stage (4 min ) amplifies said first differential output signal developed on the data lines to provide a second differential output signal (V2) at output terminals (17.1, 17.2). The second stage of the common base amplifier type is comprised of two transistors (T9, T10). The base electrodes of these transistors are connected to a reference voltage generator (13) which supplies a reference voltage VREF such as VREF = VH - 1.5 VBE. This special value greatly helps both first and second stages not to saturate and in addition, minimizes the sensibility of the sense amplifier to the dotting of additional memory cell columns on the data lines (DCL1, DLT1). Both stages are provided with various antisaturation circuits (9, 11.1., 11.2, 16.1, 16.2) which cooperate with said reference voltage generator to keep any transistor far from saturation.