![]() When such a resistor is used to provide a “low” (0) logic level in the event of a floating signal source, it is known as a pulldown resistor. When used to provide a “high” (1) logic level in the event of a floating signal source, this resistor is known as a pullup resistor: This resistor’s value is not critical: 10 kΩ is usually sufficient. Whenever a single-throw switch (or any other sort of gate output incapable of both sourcing and sinking current) is being used to drive a CMOS input, a resistor connected to either V dd or ground may be used to provide a stable logic level for the state in which the driving device’s output is floating. Because such a TTL gate’s output floats when it goes “high” (1), the CMOS gate input will be left in an uncertain state:įortunately, there is an easy solution to this dilemma, one that is used frequently in CMOS logic circuitry. This may cause a problem if the input to a CMOS logic gate is driven by a single-throw switch, where one state has the input solidly connected to either V dd or ground and the other state has the input floating (not connected to anything):Īlso, this problem arises if a CMOS gate input is being driven by an open-collector TTL gate. Please note that this is very different from the behavior of a TTL gate where a floating input was safely interpreted as a “high” (1) logic level. For this reason, it is inadvisable to allow a CMOS logic gate input to float under any circumstances. ![]() Their inputs are, however, sensitive to high voltages generated by electrostatic (static electricity) sources, and may even be activated into “high” (1) or “low” (0) states by spurious voltage sources if left floating. Clearly, this circuit exhibits the behavior of an inverter, or NOT gate.ĬMOS circuits aren’t plagued by the inherent nonlinearities of the field-effect transistors, because as digital circuits their transistors always operate in either the saturated or cutoff modes and never in the active mode. Thus, the output of this gate circuit is now “low” (0). ![]() The upper transistor, having zero voltage applied between its gate and substrate, is in its normal mode: off. Now the lower transistor (N-channel) is saturated because it has sufficient voltage of the correct polarity applied between gate and substrate (channel) to turn it on (positive on gate, negative on the channel). Next, we’ll move the input switch to its other position and see what happens: This makes the output “high” (1) for the “low” (0) state of the input. Thus, the action of these two transistors are such that the output terminal of the gate circuit has a solid connection to V dd and a very high resistance connection to ground. The lower transistor, having zero voltage between gate and substrate (source), is in its normal mode: off. So, in the above illustration, the top transistor is turned on. When the channel (substrate) is made more positive than the gate (gate negative in reference to the substrate), the channel is enhanced and current is allowed between source and drain. The upper transistor is a P-channel IGFET. It takes an applied voltage between gate and drain (actually, between gate and substrate) of the correct polarity to bias them on. Please note that these IGFET transistors are E-type (Enhancement-mode), and so are normally-off devices. Let’s connect this gate circuit to a power source and input switch, and examine its operation. Manufacturers, Thyristor manufacturers, TRIAC manufacturers, and Others.\)įield Effect Transistors in Gate Circuits Indexed by Transistors manufacturers,ĭiode manufacturers, FET manufacturers, IGBT manufacturers, SCR Diac: a bidirectional trigger diode which is designed specifically to trigger a triac or SCR.Ī General listing of Discrete Semiconductor Manufactures and vendors, This quick shut-off response protects valuable semiconductor devices and circuits from common load short-circuit failures. ![]() HEMT: High Electron Mobility Transistor UJT: Uni Junction Transistor PUT: Programmable Unijunction Transistor ICP: The IC (Integrated Circuit) Protector (ICP) is an over-current protection device having stable and high-speed circuit tripping characteristics which enable these devices to shut off the circuit quickly and safely. TVS ĭevices are listed on the Diode manufacturers page. Manufacturers, SCR Manufacturers, Thyristor Manufacturers, & TRIAC Manufacturers, Diode Manufacturers, FET Manufacturers, IGBT A General listing of Discrete Logic Manufacturers and ![]()
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