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Questions tagged [logic-gates]

Symbolic representation of ideal devices implementing boolean functions

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12 transistor XOR CMOS gate

I have come across this circuit for an XOR gate (see below) using 12 transistors in CMOS technology. I am having trouble understanding the circuit, mainly in identifying the logic gates. I know that ...
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4 answers
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Tri-state buffer, why is it called high-impedance?

I found this picture of a tri-state buffer: When the enable signal is 0, the output is disconnected from the voltage sources. But why is this called high-impedance? From what I understand impedance ...
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How do I make a gate diagram for \$a'c'+abc+ac'\$? [closed]

I have checked with the program Logic Friday and it checked the shown gate diagram, which showed me another result and came with this gate diagram: Is this the correct answer?
Invulnerable Immortal's user avatar
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555 timer and JK flip-flop activation problem

I need to toggle a MOSFET after I hold a button for 3 seconds. Here is my circuit: I have a JK flip-flop for the toggle function. When the clock pin of the JK flip-flop goes high to low, output of ...
Alican Uçar's user avatar
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Why would I use HNM (high noise margin) gate drive over a TTL gate drive for DC motor driving application?

I am making a very simple half bridge DC motor drive using the MAX1760 gate driver. Looking through the datasheet I saw that it offers two types of logic level technologies (if that's the right word?);...
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Is it possible to create a logic gate design for a clocked D flip-flop register where there is a synchronous reset and an enable pin?

I'm currently designing a register where there needs to exist a data input pin (DIN), Clock (CLK), Reset (RST), and a RUN pin. The register is designed such that, only at positive edges of the clock ...
RizqiBusiness 's user avatar
7 votes
1 answer
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Unknown logic gate on circuit

I'm studying the CMI decoder circuit from Maniatopoulos, Antonakopoulos and Makios, 1995, but I can't understand some symbols in the diagram. They look like a small logical OR. Can anyone tell me what ...
P0nyL0v3r's user avatar
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1 answer
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Which is the preferred circuit layout? Horizontal vs. Vertical (Combinational logic)

I have 2 equivalent circuits Picture 1 (Compact, a bit messier) Picture 2 (Easier to read, less compact)
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Output of a logic gate when its inputs are floating

As per this answer, the output of an OR gate when one of its inputs is 1 is 1 regardless of the other inputs, even if they are floating/disconnected. However, what is the output of an OR gate when ...
Kushagr Jaiswal's user avatar
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How do I integrate this MOSFET NOR logic gate with my circuit?

I have got an H bridge circuit controlled by a bridge driver (not in the schematic here). I want to control the disabling of it cutting of the conection to ground. I need the logic of a NOR gate but I ...
Developing Electronics's user avatar
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Clock logic for 8-bit computer

I have been in the process of remaking Ben Eater's 8-bit-computer, and have a few questions. I got to the part where the clock, which consists of 3x 555 timer, is connected with logic gates. However, ...
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7404 IC Always outputting high

I'm new to electronics, and it's my first time using a hex inverter. The following pins are connected: 1(Input A)-GND or VCC 2(Output A)-LED 7-GND 14-VCC VCC is 5V, but whatever I do the output is ...
lukasm06's user avatar
2 votes
1 answer
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Diodes for implementing digital logic

This diagram in this post is from Microelectronic Circuits by Sedra and Smith. The question corresponding to this picture asks to write a truth table with A and B as inputs and X and Y as outputs and ...
Hamza Beder's user avatar
-1 votes
2 answers
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Wired AND and OR question, logic levels?

In the "wired AND and OR" gates pictured can anyone explain what the voltage levels will be for each function? For AND, I see the output is A*B and for OR, A+B. Is this correct? Also, is ...
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NAND and NOR gate, question on choice and function

I see both described in following images 1, 2 and 3. Does anyone know why image 3 has more transistors? Also, the basic advantage to using NAND or NOR gates in digital electronics? 1. 2. In the ...
notaorb's user avatar
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How to turn an LED on in an inverter circuit

I am currently trying to build an inverter circuit which turns on an LED (on a simulation before building it physically). I am using an 2N3904 NPN transistor, 5V voltage sources, a 220k and a 47k ...
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Using a logic driver with a 50 ohm load

I have a load which is an external trigger input of the Highland Technology T130 single-channel picosecond EOM driver (technical manual - Google Drive link) which is 50 ohm and it requires a pulse ...
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How does this inverter make the AND-gate better?

I am very new to electronics and just started learning about logic gates. I read about the AND gate and learned about its boolean algebra, but I also wanted to make one myself using MOSFETs which I ...
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Exercise asking what a gate-level circuit output signify

This exercise from Introduction to Computing Systems from Bits and Gates to C/C++ & Beyond by Yale N. Patt and Sanjay J. Pattel asks what the value of OUT signifies in this circuit. If it's 0, ...
oabdullae's user avatar
2 votes
3 answers
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What prevents this transistor based discrete logic gate design from having been used?

I am interested in building discrete logic gates as a teaching / learning tool to explore computer fundamentals. The easiest logic gate design I can come up with consists of the following: It is ...
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AND gate with MOSFETs to close a MOSFETs circuit

I want to add a circuit to my design in order to build a AND logic gate (preferably with MOSFETs) where in the next schematic you can find a rectangule. A and B would be the inputs, and the output ...
Developing Electronics's user avatar
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2 answers
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Why does the LED turn off when I touch the insulating part of the wire?

This is a NAND gate IC. I have one input connected to the positive terminal of the battery while the other input is not connected to the battery as you can see in the image. Why does the LED turn off ...
Rx6rx's user avatar
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Level shifting to lower voltage: logic-gate vs voltage divider

In my design I need to level shift 5V signals to 1.8V, for now I'm planning to use AND gates with the same 5V signal on both inputs and 1.8V as the power source. I got the idea from this document. ...
StefanoN's user avatar
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What is wrong with my Dmux8way? How can I fix it?

The problem is something with the sel spliter and the leftmost DMUX4WAY, the automatic check returned - "have different bit width and cannot be connected". But I don’t know how can I fix it. ...
Sonya Lyu's user avatar
1 vote
1 answer
198 views

AND logic gate with diodes not working

I am currently working on an AND logic gate using 2 diodes. My first logic input is 3.3V/5mA from a Raspberry Pi Zero W GPIO pin. The second is 3.3V/500mA from a door access system. This input is ...
Omayma Raji's user avatar
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1 answer
177 views

LED stays lit when using IC

I made a simple circuit with a CD4081 IC (2-input AND gates), a DIP switch, and an LED. The dip switch is set to 00 but the LED will light up regardless. The output from pin 3 on the IC appears to ...
TheTruth's user avatar
-1 votes
1 answer
124 views

What are the components inside ADC and DAC? [closed]

My question is this: What are the components inside ADC and DAC? Is there only transistors/logical gates and is there difference between like analog audio to digital audio ADC or other types of ADC ...
NearEternal's user avatar
11 votes
3 answers
3k views

With this AND gate made of transistors, why does the LED need a resistor in parallel instead of in series?

I'm building an AND gate out of transistors. Knowing how the basics work, I built my own (naive) circuit using the following design. In testing, it didn't work like an AND gate. A B LED 0 0 Off 1 ...
Morgan Kenyon's user avatar
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1 answer
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Type of output of this AND Gate

I am unable to find whether the output of this IC is a push-pull output or an open drain output. I didn't notice either words in the datasheet. Hence, can someone help me to tell which output type is ...
Freshman's user avatar
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Why does NOR need one more output to the multiplexor but NAND not in ALU?

Recently, I was learning "Computer Organization and Design: The Hardware/ Software Interface" riscv 2nd Edition by "David A. Patterson" In appendix A, A-37 shows the question in &...
An5Drama's user avatar
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How do I limit a down counter so that it counts from 3 to 0?

I've been studying binary counters and learned how to build an up counter that starts at 0 and counts to a set value before resetting. Now, I need to learn how to build a down counter that starts at a ...
elvishpotato's user avatar
2 votes
6 answers
1k views

Do all logic circuits have to have negligible input current?

There are common configurations where, for example, a logical HIGH input (a voltage source) is connected to the input of some logic circuit through a resistor as shown there. Typically this logic ...
Sgg8's user avatar
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How do I implement a synchronous reset switch to my D-Flip Flop

This is my master slave D Flip Flop and I was wondering where do I put the reset switch to make it into a D Flip Flop positive edge with a synchronous switch. I know that for synchronous, you can ...
Red Pen's user avatar
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3 answers
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Electrical counterpart: Logical not

I'm building a circuit where I must receive a signal from a logical not. More specifically, I'm looking for a real-life electrical circuit element/component that provides power/signal on the output ...
nikola's user avatar
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1 answer
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Logic gate without transistor

I wonder how to make logic gates without transistors, logic-integrated circuits, or diodes. The components that I need are: two terminal push switches, a resistor, a 3v battery, led.
Jadon Jung's user avatar
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1 answer
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How can I convert boolean algebra to logic gates?

I have a very large boolean algebra equation that I designed in Logic Friday, but it got too complicated for it to turn into gates. Note that I am a programmer, not an electrical engineer, so please ...
ShadowProgrammer's user avatar
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2 answers
96 views

Clock Signal in Finite State Machines

I got this circuit from the book Introduction to Logic Circuits & Logic Design with Verilog, Second Edition. It's on page 248 for reference. It is supposed to be a circuit that opens or closes a ...
vigilante_fresh's user avatar
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1 answer
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Converting a 4 input NOR into a 2 input NOR

I am working on homework but I am racking my brain on this one: F(A,B,C,D,E)=(A+B+C+!D)!E I am trying to convert this into one that only uses two-input NOR gates. This is what I have so far: !(A+B+C+!...
Cody Bijeaux's user avatar
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1 answer
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Retrieval of information from a sequential circuit

SR-NOR Latch circuit is a sequential circuit in which there exist two, different modes Reset and Set. Electricity flows along ...
Cake's user avatar
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1 answer
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What is a voltage-controlled differential current source & how do you simulate it in simulink?

I am trying to achieve the same circuits designed in this paper: https://arxiv.org/abs/1512.05064 by simulating it in simulink, yet I can't seem to understand what it is referring to by saying voltage-...
Salah Elabyad's user avatar
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1 answer
95 views

How to express this logic circuit with output feedback as boolean expression?

Q1. How to express this circuit as boolean expression? It uses the output as input (feedback??) to part of the circuit. Is it a special type of circuit? Q2. How do I simplify it as Nand-only ...
bendtherules's user avatar
5 votes
1 answer
908 views

Why are my 74F chips incompatible with 74LS?

I have a functioning electronic project I made as a hobby using SN74LS161 4 bit counters and SN74LS08 quad AND gates. I replaced the counters with SN74F161 which are supposed to be faster but have the ...
Andrea Bianchi's user avatar
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0 answers
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Theoretical calculation of gate delay

I am currently working on not-gate based ring oscillators and I was wondering if there was a way to theoretically calculate without having to look at the simulation graphs the rise time and fall time ...
KaBe2003's user avatar
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0 answers
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Logism: Further reducing number of logic gates in a circuit

I have this circuit attached below that has an arbitrary behavior. I want to reduce the number of gates more if possible. I've taken its expression and passed it through multiple boolean expression ...
123Questions's user avatar
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2 answers
269 views

Boolean circuit - 4 inputs (A, B, C, D), and output Z performs the function: Z =1 for all numbers divisible by 3 [closed]

I need to draw a circuit using the minterm, with 4 inputs (A, B, C, D) and an output (Z) that performs the function: Z =1 for all numbers divisible by 3, in Xilinx ISE with only using Schematic ...
TheDegman's user avatar
-1 votes
1 answer
113 views

How do I implement a bit adder?

I want to design a circuit in logism that takes as input a 16-bit signal, and then counts the number of set bits and outputs a 4-bit signal that is the sum of those set bits. Example: input ----> ...
123Questions's user avatar
1 vote
1 answer
181 views

How do I create a 8-bit binary digit out of the combination two 7-bit ASCII values?

I am implementing a circuit that takes two ASCII values that are in the range 0x30 - 0x39[0 - 9] for the tens digit and ones digit, and then combine them, and output a proper 8-bit binary value ...
123Questions's user avatar
1 vote
1 answer
254 views

How to split an n-bit pin into n 1-bit wires [in Logisim]

For example, I want to take a 4-bit pin A and find a way to split it into 4 1-bit wires to it is functionally the same as the B pins. Also, how would I scale this up to a 16-bit pin for 16 1-bit wires....
123Questions's user avatar
0 votes
1 answer
412 views

Hidden pins in Proteus

I'm implementing the following scheme and I have trouble with IC4 element (7430: 8-pin NAND) that have 7 and 14 pins, as I understand, VCC and GROUND respectively. But in Proteus 8 NAND don't have ...
EpicMandM's user avatar
1 vote
2 answers
258 views

How do I implement a combinational circuit that finds which input has more ones? [closed]

I have 2 16-bit inputs: A[15, 0] and B[15: 0]. There are also two outputs: OUT[15: 0] and Z[1: 0]. The way it works is if # of bits that are 1 in A is greater than or equal to the # of bits that are 1 ...
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