![]() A phase splitter transistor controls which transistor is active.One of the problems with the TTL gate circuit is that the pull-up resistor on the output transistor will prevent rapid charging of any wiring capacitance on the output. 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
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