Amplifier and Driver Circuits for Thin Film Memories with 15 Nanoseconds Read Cycle Time
Amplifier and driver circuit design principles for an experimental 4608-bit nondestructive thin film memory with 13.5-nsec read and 60-nsec write cycle times are given. The bit noise problems inherent in the common bit sense line concept are solved by using tunnel diodes in a nonlinear balancing circuit. A further improvement of the signal-to-noise ratio is achieved by employing a noise resistant sense amplifier with nonlinear negative feedback. The word driver described is capable of delivering 700 ma pulse amplitude at 50 mc repetition rate at a pulse width of 7 nsec.
A High-Speed Direct-Coupled Magnetic Memory Sense Amplifier Employing Tunnel-Diode Discriminators
Because of a multiplicity of conflicting requirements, sense amplifier design is probably the most difficult circuit problem in a large, high-speed digital computer memory. The requirements include absence of pattern sensitivity, controllable input impedance, a wide band pass, stable gain, high common mode rejection, the ability to handle bipolar signals, stable reference levels, a fast comparator, low threshold level, and, one hopes, low cost. This paper discusses a new circuit which fulfills these requirements with simplicity. Intended for large size (> 1000 words) random access core and thin-film memories, it is capable of handling, for example, a 50-mv ``1'' with approximately 50-nsec delay for transmission and comparison. Common mode signals of as high as 10 volts do not affect discriminator performance. Two key features of the circuit are the use of a dc-coupled, ``long-tail pair'' preamplifier and a pair of tunnel diodes as the discrimination elements. The dc-coupled differential preamplifier provides high common mode rejection, stable gain, is pattern insensitive, and has the ability to handle bipolar signals. The tunnel diode provides a superior discriminator, since it is fast, and has a low-level threshold which is controllable and stable with temperature variations. Thus, requirements on the magnitude and stability of the preamplifier gain are less severe. Design equations are derived and a complete dc worst-case analysis is performed. Variations in the circuit for several specific applications and experimentally determined performance data are described. The generalized problem of a tunnel-diode discriminator used with a preamplifier is treated in Appendix II.
Some design considerations for high-frequency transistor amplifiers
The major problem in the design of high-frequency transistor amplifiers is the interaction between the output and the input of the amplifier caused by the internal feedback of the transistor. This problem is illustrated and the two common design approaches to a solution of the problem are discussed. Nyquist's criterion of stability and Bode's feedback theory are then used to obtain an engineering evaluation of the relative merits of these two design approaches from a stability standpoint. The positive nature of the internal transistor feedback is established in this stability evaluation. Finally, Bode's feedback theory is used to consider the relative merits of some of the broad banding techniques used in transistor video amplifier design. The over-all analysis shows that many of the most practical and stable linear transistor amplifiers are very simple and can be built with a minimum of design effort.