On the path to exploring complex logic, let’s discuss the electrical properties that digital logic signals are comprised of. While there are many types of digital signals, here we are talking about the more common voltage based single-ended signals and not the dual-conductor based differential signals.
I think of most logic as being in one of two major divisions as far as the technology used for today’s logic: Bipolar and CMOS. Bipolar is characterized by use of (non-insulated gate) transistors and most often associated with Transistor Transistor Logic (TTL) based logic levels. As CMOS technology came of age and got faster and became able to drive higher currents it began to augment or offer an alternative to bipolar logic families. This is especially true as power supply voltages dropped and the need for low power increased. We will talk more about CMOS in the next installment.
TTL was a result of a natural progression from the earlier Resistor Transistor Logic (RTL) and Diode Transistor Logic (DTL) technologies and the standards used by early TTL became the standard for a multitude of logic families to follow.
Continue reading “Gates To FPGAs: TTL Electrical Properties”
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