There is an IR transmitting LED (SFH415) with an NPN driver transistor (BC547) driver transistor.

The base (47) of a p-n-p transistor (46) is held at the voltage (A).

NPN transistor) can be replaced by almost any cheap NPN transistor.

The NPN transistor alone will conduct the positive half cycle and PNP transistor alone will conduct the negative half cycle.

The transistor is NPN handles amplify the positive half cycles and PNP handles half cycles negative.

A first PNP transistor (24) has an emitter connected to a first resistor (25) and conducts a first current.

A second PNP transistor (21) has an emitter connected to a second resistor (23) and conducts a second current.

The integrated circuit beneficially includes silicon-based elements such as a lateral pnp transistor, a varactor, and a polysilicon transistor, which are formed on a common substrate with an npn SiGe bipolar transistor.

A driver circuit with pull down npn transistor drives an output voltage signal in response to an input voltage signal, without high-speed pnp transistors.

The function of the PNP type transistor is similar to that of the NPN type.

The pnp transistor works essentially the same as the npn transistor.

The NPN transistor has three terminals: emitter, base and collector.

The pnp transistor works essentially the same as the npn transistor.

The function of the PNP type transistor is similar to that of the NPN type.

N-type material is implanted in the epi layer (20) to complete the isolation wall (22) for the pnp transistor, and to complete the collector (24) for the npn transistor.