Interfacing TTL and CMOS Logic Levels in the Laboratory

ABSTRACT Interconnectivity of electrical components, such as triggers and detectors, is intrinsic to operating time-sensitive experiments. As labs become more digitized, equipment integration and compatibility become larger factors in experimental setups. Complications can arise when instruments with different signal levels, or logic levels, are integrated because each instrument requires its own particular input signal, with a specific threshold voltage, to function. When incorrect logic levels are used or the delays in conversion are too long, these instruments are not properly triggered and the experiment becomes inoperable. To perform multi-component, time-sensitive experiments, a logic-level converter with minimal time delays is necessary. Commercial solutions, however, are not viable when the nature of the experiment is highly time-sensitive, such as in laser spectroscopy, because the delay on the signal conversion is several hundred nanoseconds and would result in missed events. In this paper, three different logic-level converter circuits are presented for conversion between the TTL and CMOS logic levels, the most commonly used logic levels in experimental applications, based on the concept of an emitter follower design that only produces a delay in the tens of nanoseconds. Circuits were developed for conversion from CMOS to TTL, from TTL to CMOS, and a TTL buffer circuit. These circuits allow for inter-conversion between the two most common logic families, TTL and CMOS, as well as buffering weak signals, to offer a simple, low-cost solution to synchronization in time-sensitive experimental setups.