Why do logic gates need resistors?
The resistor is there to limit the base current to a value that is safe for both the transistor and the logic gate output stage.
What is RTL DTL TTL?
Transistor-transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. *TTL contrasts with the preceding resistor-transistor logic (RTL) and diode-transistor logic (DTL) generations by using transistors not only to amplify the output but also to isolate the inputs.
Why do you need a gate resistor in a transistor?
It is generally a good idea to include a gate resistor to avoid ringing. Ringing (parasitic oscillation) is caused by the gate capacitance in series with the connecting wire’s inductance and can cause the transistor to dissipate excessive power because it doesn’t turn on quickly enough and hence the current through drain/source in…
When to use a resistor on a MOSFET?
Not only do MOSFETs not have bases (they have gates), but the gate is (very) high impedance. Except when the MOSFET is changing states, the gate current is essentially zero. Sometimes, a gate resistor is prudent to reduce ringing, especially if the trace driving the gate is long, or if you are concerned with generating electromagnetic interference.
When to use a high value resistor to ground?
As @PhilFrost mentiones, a high value resistor to ground is a good idea to avoid capacitive coupling driving the transistor when it is otherwise not connected. At all times keep the wiring between logic output, transistor gate, transistor source and ground as short as possible.
How does a pull up resistor work in a logic gate?
With a pull-up resistor connected, the output still works in the same way as a normal logic gate in that when the output transistor is OFF (open), the output is HIGH, and when the transistor is ON (closed), the output is LOW. Thus the transistor turns ON to pull the output to a LOW level.