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The output is usually connected to an external pull-up resistor, which pulls the output voltage to the resistor's supply voltage when the transistor is off. For PNP open collector outputs, the emitter of the PNP transistor is internally connected to the positive voltage rail, so the collector outputs a high voltage when the transistor is on or ...
Open-collector buffers connected as wired AND. The wired AND connection is a form of AND gate. 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).
The circuit can be explained by viewing the transistor as being under the control of negative feedback. From this viewpoint, a common-collector stage (Fig. 1) is an amplifier with full series negative feedback. In this configuration (Fig. 2 with β = 1), the entire output voltage V out is placed contrary and in series with the input voltage V in.
Transistors are used for current sources on integrated circuits because they are much smaller than resistors. Because the inverter is open collector, a wired AND operation may be performed by connecting an output from each of two or more gates together. Thus the fan-out of an output used in such a way is one. However, additional outputs may be ...
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 ...
The fast operation of CML circuits is mainly due to their lower output voltage swing compared to the static CMOS circuits, as well as the very fast current switching taking place at the input differential pair transistors. One of the primary requirements of a current-mode logic circuit is that the current bias transistor must remain in the ...
The input signal is applied across the ground and the base circuit of the transistor. The output signal appears across ground and the collector of the transistor. Since the emitter is connected to the ground, it is common to signals, input and output. The common-emitter circuit is the most widely used of junction transistor amplifiers.
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 ...