# Diode OR Gate - the role of resistor

• dobry_den
In summary, the removal of the resistor in the attached diode OR gate would result in an undefined output voltage when both inputs are low. This is because, in digital logic, a logic zero or low occurs when the input is in the range of 0-2V, and without the resistor, the output would be grounded. However, the output is always grounded via the resistor, and the current through the resistor is not the same as the current going to the output.
dobry_den
Hi! What would happen if the resistor in the attached diode OR gate removed (connection with the ground would be preserved)?

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• or_gate.GIF
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It ensures that the output is low when both of the inputs are low. Without the resistor, the output voltage would be undefined in that case.

What do you mean by the word "low".. like when the inputs are of zero potential, when they're grounded? In that case the output would be also grounded and therefore defined... Or am I mistaken?

In digital logic, a logic zero or low would occur when the input is somewhere in the range of 0 - 2V. Its probably less than 2V, that varies depending on technology being used. For TTL devices, I believe it 0V-0.8V for a logic zero.

The output is always grounded via the resistor i.e. the output is voltage drop across the resistor and not taken directly from ground.

ok, thanks a lot. Another problem occurs when I am about to calculate the current in the output - should I take the output branch and the resistor-ground branch as connected in parallel?

Yup. The current through the resistor is not the same current going to the load connected to the output. The voltage however is the same.

Ok, that makes it clear. Thanks

## 1. What is a Diode OR Gate?

A Diode OR Gate is an electronic circuit that allows current to flow through it if at least one of its inputs is receiving a signal. It is called an OR gate because it performs the logical operation of "OR" on its inputs.

## 2. How does a Diode OR Gate work?

A Diode OR Gate works by using diodes to control the flow of electricity. When one of the inputs receives a signal, the diode connected to that input allows current to flow through it, completing the circuit and producing an output. If both inputs receive a signal, then both diodes will allow current to flow, resulting in a stronger output signal.

## 3. What is the purpose of a resistor in a Diode OR Gate?

The role of a resistor in a Diode OR Gate is to limit the amount of current that can flow through the circuit. This prevents the diodes from being damaged and ensures that the output signal is not too strong. Resistors also help to stabilize the circuit and prevent unwanted fluctuations in the output signal.

## 4. What happens if both inputs receive a signal in a Diode OR Gate?

If both inputs receive a signal in a Diode OR Gate, then both diodes will allow current to flow, resulting in a stronger output signal. This is because the resistor will limit the amount of current that can flow through the circuit, causing the output to be a combination of both input signals.

## 5. What are the advantages of using a Diode OR Gate with a resistor?

The main advantage of using a Diode OR Gate with a resistor is that it allows for a stronger output signal when both inputs receive a signal. This can be useful in applications where a stronger signal is needed, such as in logic circuits. Additionally, resistors help to stabilize the circuit and prevent damage to the diodes, making the circuit more reliable.

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