Boolean and truth table for circuit

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Discussion Overview

The discussion revolves around converting a circuit involving transistors into a boolean expression and understanding the behavior of the circuit under different input conditions. Participants express confusion regarding the application of transistors in logic circuits, specifically in relation to traditional logic gates.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • Some participants express uncertainty about how to approach the problem involving transistors as opposed to traditional gates like AND and OR.
  • There are questions about the output of the circuit under specific conditions, such as when inputs A and B are low or high.
  • One participant suggests that if A and B are low, the output is 0, and if either A or B is high, the output is 1, but this claim is challenged.
  • Another participant emphasizes the role of transistors as voltage-controlled switches that perform the gating operation, indicating their importance in the circuit.
  • A suggestion is made to consider the current path when transistors are enabled to better understand the logic of the circuit.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the outputs of the circuit under different input conditions, and there is disagreement regarding the understanding of how transistors function in this context.

Contextual Notes

Participants have not fully resolved the assumptions regarding the operation of transistors in cutoff or saturation, nor have they clarified the mathematical steps needed to derive the boolean expression from the circuit.

pyroknife
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I attached the problem statement.

The problems I have done in the past always involved gates (AND, OR, etc...)
Now this involves transistors, I honestly don't know how to go about doing this.

One of the hints for the problem is to assume the ideal transistors are operating in cutoff or saturation.

I don't understand how this circuit can be turned into a boolean expression.
 

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pyroknife said:
I attached the problem statement.

The problems I have done in the past always involved gates (AND, OR, etc...)
Now this involves transistors, I honestly don't know how to go about doing this.

One of the hints for the problem is to assume the ideal transistors are operating in cutoff or saturation.

I don't understand how this circuit can be turned into a boolean expression.

If A and B are low, what is the output?

If either A or B are high, what is the output?

Makes sense?
 
berkeman said:
If A and B are low, what is the output?

If either A or B are high, what is the output?

Makes sense?

If A and B are low then the output is 0.
If A and B are high then the output is 1.

If A or B are high, the output is 1.

But what do the transistors do for this case?
 
pyroknife said:
If A and B are low then the output is 0. ✗[/size][/color]
If A and B are high then the output is 1. ✗[/size][/color]
If A or B are high, the output is 1. ✗[/size][/color]
How did you work out these answers? Do you understand how transistor switches operate? (Not exactly a rhetorical question, though it may appear so.)

But what do the transistors do for this case?
The transistors are the voltage-controlled switches that perform the gating operation. Without them, you don't have logic gates.
 
Perhaps the best way to look at the logic is 'what path will the current take when either transistor is enabled. Remember when no current is flowing, the potentials across either side are the resistor are the same. Hope that provide a clue.
 

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