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For an NPN open emitter output, the collector is connected to the positive voltage rail, so the emitter outputs a high voltage when the transistor is on and is hi-Z when off. For a PNP open emitter output, the collector is connected to the low voltage supply, so the emitter outputs a low voltage when the transistor is on and is hi-Z when off.
A common variation omits the collector resistor of the output transistor, making an open-collector output. This allows the designer to fabricate wired logic by connecting the open-collector outputs of several logic gates together and providing a single external pull-up resistor. If any of the logic gates becomes logic low (transistor conducting ...
When using open collector or similar outputs (which can be identified by the ⎐ symbol in schematics), wired AND only requires a pull up resistor on the shared output wire. In this example, 5V is considered HIGH (true), and 0V is LOW (false). This gate can be easily extended with more inputs. When all inputs are HIGH, they all present high ...
three-state and open-collector (48) SN74GTLP2034: 74x2040 1 8-bit Futurebus transceiver with split TTL I/O three-state and open-collector (48) SN74FB2040: 74x2041 1 7-bit Futurebus transceiver with split TTL I/O three-state and open-collector (52) SN74FB2041: 74x2107 1 12-bit GTL to 3.3V TTL level translator open-collector (28) SN74GTL2107 ...
The disadvantage of RTL is its high power dissipation when the transistor is switched on, by current flowing in the collector and base resistors. This requires that more current be supplied to and heat be removed from RTL circuits. In contrast, TTL circuits with "totem-pole" output stage minimize both of these requirements.
The open collector input/output is a popular alternative to three-state logic. For example, the I²C bus protocol (a bi-directional communication bus protocol often used between devices) specifies the use of pull-up resistors on the two communication lines. When devices are inactive, they "release" the communication lines and tri-state their ...
This time each year, families gather by fireside and candlelight, by holiday lights and the warm glow of the television, to ponder a timeless question: What would your familiar, beloved world be ...
The output voltages at the collector load resistors R C1 and R C3 are shifted and buffered to the inverting and non-inverting outputs by the emitter followers T4 and T5 (shaded blue). The output emitter resistors R E4 and R E5 do not exist in all versions of ECL. In some cases 50 Ω line termination resistors connected between the bases of the ...