connecting two totem pole outputs together

One way to improve the rise time is to reduce the resistance value as is often done, but this also increases the power dissipation when the output is low. If we look at the circuit, we observe that when the transistor is saturated, it presents a very low effective resistance to ground. The problem arises when the output is high and the pull-up resistor is too large. Ideally we would like to have a very low resistance pull-up when the output is high, but a very high pull-up resistance when the output is low. In this way, we could get quick charging and very low power dissipation. The totem-pole output stage for TTL, shown in Figure. Low-power Schottky TTL designed as 74LS or 54LSĪdvanced low-power Schottky TTL designed as 74ALS or 54ALSĪdvanced Schottky TTL designed as 74AS or 54ASĪn alphabetic code preceding this indicates the name of the manufacturer. TOTEM POLE OUTPUT FOR TTL LOGIC FAMILIES CODE

TOTEM POLE OUTPUT FOR TTL LOGIC FAMILIES CODE.

For example, NXP has a 74LVC1G00 (single 2-input NAND) and a 74LVC2G00 (dual 2-input NAND) version of the classical 74HC00. Several manufacturers offer single-gate and dual-gate versions of logic gates. With miniaturization (SMT) came the demand for smaller packages, even if they contained less gates. Many ICs in the 74HCxx series were originally released in 14 or 16 pin DIL packages, which meant that they would fit four 2-input gates. The transistor you show in the picture is a BJT, which you can tell from the pin designation: Microcontrollers are built in HCMOS technology, so they use MOSFETs. Later more variants were developed, like Advanced CMOS (74ACxx).

Most 74LSxx types have been released as HCMOS in the 74HCxx series, or the 74HCTxx series, which is TTL compatible. Later standard CMOS developed into HCMOS, 'H' for High-speed. Their construction is simpler than TTL and they use far less power. The 'C' in CMOS stands for Complementary, meaning it's a combination of N-channel and P-channel MOSFETs. At the same time the CMOS 4000 series was developed. As the name implies these used less power than the rather power-hungry TTL, and were faster too.

Later there came variants like the often used 74LSxx, where the 'LS' stands for Low-power Schottky TTL. This used BJTs (Bipolar Junction Transistors).

The first comprehensive logic series was the TTL series 74xx.

Connecting two totem pole outputs together