3 Categories of Digital Logic Families

Jan 14, 2024

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Digital ICs are usually fabricated using either bipolar devices or MOS devices or a combination of the two. We can classify the logic families into the following categories based on whether they are manufactured using bipolar, MOS or a combination of the two:

Contents

1 Bipolar Families
2 MOS Families
3 Bi-MOS Families

Bipolar Families

The families in this category include: diode logic (DL), resistor transistor logic (RTL), diode transistor logic (DTL), transistor transistor logic (TTL), emitter coupled logic (ECL), also referred as current mode logic (CML) and integrated injection logic (I²L).

Figure 1.0 Diode transistor logic (DTL)

The logic families: diode logic (DL), resistor transistor logic (RTL) and diode transistor logic (DTL) are not currently used in any digital circuit development. Diode logic used diodes and resistors. This family was however never put into use in any integrated circuits. The RTL family used resistors and bipolar transistors. The DTL family used resistors, diodes and bipolar transistors. Both RTL and DTL were affected by large propagation delay due to the need for the transistor base charge to leak out if the transistor were to switch from conducting to non-conducting state. The introduction of TTL rendered DL, RTL, and DTL obsolete.

The integrated injection logic (I²L) which was meant for custom large-scale integrated (LSI) circuit devices has also been rendered obsolete by NMOS logic family which has replaced them for LSI applications.

From this category, transistor transistor logic (TTL) and emitter coupled logic (ECL) are the logic families that you will find in use today.

MOS Families

The logic families that are fabricated using MOS devices are known MOS families. The families that belong here include: PMOS family (using P-channel MOSFETs), the NMOS family (using N-channel MOSFETs) and the CMOS family (using both N and P-channel devices).

CMOS, NMOS and Bi-CMOS are used in many digital circuit applications. The PMOS which was also intended for use in custom large-scale integrated (LSI) circuit devices has been rendered more or less obsolete with the NMOS logic family replacing them for LSI and VLSI applications.