DRTE Computer - Transistor Research

Transistor Research

In the early 1950s transistors had not yet replaced vacuum tubes in most electronics. Tubes varied widely in their actual characteristics, and engineers had developed techniques to ensure that the overall circuit was not overly sensitive to these changes. The same techniques had not yet been developed for transistor-based systems, they were simply too new. While smaller circuits could be "hand tuned" to work, larger systems using many transistors were not well understood. At the same time transistors were still expensive; a tube cost about $0.75 while a similar transistor cost about $8. This limited the amount of experimentation most companies were able to perform.

The DRTE was originally set up to improve communications systems, and to this end they started a research program into using transistors in complex circuits in a new Electronics Lab under the direction of Norman Moody. Between 1950 and 1960, the Electronics Lab became a major center of excellence in the field of transistors, and through an outreach program, the Electronic Component Research and Development Committee, were able to pass on their knowledge to visiting engineers from major Canadian electronics firms who were entering the transistor field.

The key development that led to the eventual construction of the computer was Moody's invention of a new type of flip-flop circuit, a key component of all computer systems. Moody's design used a P-N-P-N junction, consisting of a PNP and NPN transistor connected back-to-back. His design offered much more output power than the common Eccles-Jordan system used up to that time, which was simply a re-implementation of an existing tube-based circuit, replacing the tubes with transistors. The P-N-P-N circuit offered much higher power output, allowing it to drive a number of "downstream" circuits without additional amplifiers. The overall effect was to reduce, sometimes greatly, the total number of transistors needed to implement a digital circuit. One downside, only realized later, is that the current draw of the flip-flop was not balanced, so storing different numbers in them could lead to dramatically different current needs on the power supply—something that should be avoided wherever possible to reduce noise generated when the power draw increases or decreases. At very low power levels, as in a computer, these pulses of noise can be as powerful as the signals themselves. Moody published his circuit in 1956.