Questions tagged [rise-time]

Anything related to the rise time of a signal. The rise time is a parameter used to characterize abrupt transitions in a signal waveform. It is usually defined as the time needed by the signal to go from the 10% to the 90% of the level it attains at the end of the transition.

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9
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4answers
8k views

How is rise time related to bandwidth of the signal?

Say, I want to limit the rise time of my digital signal edges to avoid dealing with transmission line effects. How do I determine the maximum frequency of harmonics in my signal knowing that my rise ...
8
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1answer
855 views

Do long transmission lines degrade rise/fall times, and if so, by what mechanism?

I remember someone telling me long ago that if a voltage step is sent down a transmission line, the step will become smeared as it travels down the line, and the rise time will become degraded. I'm ...
8
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1answer
141 views

How do I calculate rise times for a push pull GPIO with load with hand calculations?

simulate this circuit – Schematic created using CircuitLab This is a simplified example of a push pull GPIO found in most microprocessors, with a load attached. Using the capacitance and ...
7
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2answers
3k views

How to control rise time of output of LTSpice's Voltage Controlled Switch?

I have a RC delay circuit as input into a Voltage Controlled Switch in LTSpice. It's working the way I want, except I can't figure out how to shorten the rise time of the signal that emerges from the ...
7
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1answer
3k views

How to determine BJT switching time

Is there some standard way to get information about BJT (Bipolar Junction Transistor) rise and fall times (the high power ones) ? In essence a IGBT is a BJT being driven by a FET, so there should be ...
6
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4answers
5k views

Driving a MOSFET with fastest rise time possible

I'm working a circuit to send very short pulses to a load, with the requirement that the pulses have the fastest rise time possible (~10ns or less). I've picked out a driver that has a fast rise time,...
6
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2answers
1k views

Real rise time with oscilloscope and probe

I'm still a bit new to this domain, just wondering if the rise time of a probe and the oscilloscope itself have to be substracted to the measure in order to recover the real measured rise time? Let's ...
6
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1answer
3k views

Is this measured rise time inaccurate because of limited oscilloscope bandwidth?

I don't have an LCR meter and wanted to learn how to use a fast edge pulse generator and an oscilloscope to do capacitance measurements as an academic exercise. In W2AEW's videos, he builds a simple ...
6
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1answer
265 views

Why is BJT NAND rise time so high?

I'm testing a few different circuits for basic gates, made in DTL (Diode-Transistor Logic). One of the more popular layouts for NAND seems to be: simulate this circuit – Schematic created using ...
5
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2answers
462 views

How come you cannot determine the capacitance of a MOSFET gate based on the other supplied values on the datasheet?

Conjecture If it's the case that $$ Cg = {Qg \over Vg} $$ It must be the case that $$ (Ciss + Coss + Crss)Vg = Qgon $$ But it turns out that it is not. I don't understand what I'm missing. I ...
4
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2answers
2k views

How to determine if a signal path needs to be treated as a transmission line?

I remember reading this somewhere but cannot find the ratio of the rise time vs. the propagation time (i.e. the trace length?) of a signal when transmission line effects come into effect? For example ...
4
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3answers
865 views

Improve rise-time of NPN current mirror

I'm looking for a way to improve the rise-time of a current mirror. My problem is as follows: I want to interface with an obscure single wire protocol. I'm starting with a digital signal that has a ...
4
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2answers
694 views

Square wave generator has nigh-useless output

I have a system that was designed for testing digital components. I have a device in the system which is used for generation and acquisition of digital signals. Now, I will happily admit to not ...
4
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2answers
1k views

Building an oscillator out of discrete gates

I want to buid an ocsillator out of discrete XOR gates, I want to acheive 80MHz. I've tried building one from SN74LVC2G86, but rise/fall times I get is about 25ns. Datasheet does not specify the ...
3
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1answer
219 views

How to correctly set logical high level on a PS/2 port?

I'm trying to make a keyboard emulator on ATmega16A. I'm currently implementing logical low as output-zero, and, since the host(?) is supposed to pull up the line, I send logical high state as input ...
3
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2answers
721 views

Do LED and photodiode rise times matter for time-of-flight (TOF) measurement?

Do I need small rise times of an LED and a photodiode/APD when considering time-of-flight measurement? Given I know rise time of both diodes I am always able to count time of flight by subtracting ...
3
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2answers
519 views

Square signal's rise time and frequency

simulate this circuit – Schematic created using CircuitLab I am analyzing work of amplitude limiter built on transistor, and I can see an incoherence as far as rising times for different ...
3
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0answers
28 views

Can I calculate minimum rise time of a transmission line if I know the length and the loss tangent?

Overview: I am trying to work out if it's possible to transmit my 1.2Gbps MIPI data down a 600mm long flexible PCB strip. Assuming I have the impedance correct, will the signal still be degraded by ...
2
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1answer
794 views

How to determine rise time from a datasheet?

I am trying to determine the rise time for a component in my circuit. I am unsure if my current method is correct and could use some verification. I would love help in the general case as well. Case ...
2
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2answers
5k views

Why is CMOS fall time faster than rise time?

I've just started a computer architecture class, and the slides from a lecture says that the reason why fall time is faster than rise time is that the NMOS electrons have more mobility than PMOS which ...
2
votes
1answer
393 views

Rise/fall time constrains for ADC?

Does the sampling clock rise/fall times for ADCs matter, or they can be virtually 0 seconds? Can they be slow? In particular, I could not find anything about rise/fall time constrains for AD9235. ...
2
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2answers
134 views

How to increase voltage rise time for micro controller?

I am working with a micro controller which has this written in its data sheet: "A step increase in supply voltage of 300 mV or more, with rise time of 300 ms or less, within the valid supply range, ...
2
votes
1answer
803 views

High voltage nanosecond pulse generator

I am trying to build a PCB based pulse generator that can produce a pulse with a width of about 100 ns and 500V-1000V peak amplitude to a 50 ohm resistive load. I will use the circuit for burst pulse ...
2
votes
1answer
487 views

No Feasible Entries for Subprogram “rising_edge”

It's my first time coding in VHDL and I ran to some problem I have absolutely no idea how to solve. When I try to compile my code in modelsim it gives me "No Feasible Entries for Subprogram ...
2
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1answer
3k views

LTspice MOSFET width sweep

I am trying to simulate the transfer characteristics of a CMOS inverter using LTspice. I want to sweep the MOSFET width and length and observe the effects on rise and fall times of the CMOS inverter. ...
2
votes
1answer
2k views

How does the improved transistor astable multivibrator work?

This is an astable multivibrator circuit. Assuming that TR2 is initially on, the right pin of C2 is grounded and since C2 isn't charged, the left pin of it is also at 0V. Now, Out 2 is low. C2 is ...
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5answers
513 views

How to equalise highly asymmetrical rise and fall times?

This question is kinda similar to highly-asymmetrical-rise-and-fall-times, but I think that the data sheet is already suggesting that I'm at the optimum design. Resistor changes were the answer to ...
1
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3answers
1k views

RF FETs - how exactly are they different from regular FETs?

I've browsed through DigiKey and there are these RF FETs. Are they for final stage amplification? Say you have an opamp that doesn't go for the final desired voltage, so one uses these FETs as Common ...
1
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1answer
160 views

Pen-type barcode scanner

I am designing a pen-type barcode scanner (1D) which is operated by user, which means that the speed at which the scanner moves is random. Even worse is that it gets stuck sometimes, so the signal ...
1
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1answer
54 views

RC Time Constant simulator

I am trying to write a simple simulation of a Resistor / Capacitor network. I need to calculate the voltage across the capacitor as the input moves up and down. The problem is that there is two ...
1
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1answer
579 views

Reverse biased photodiode gain resistor selection

I have a reverse biased photodiode as shown below. where R1 = 100kΩ. The output is quite low around 50mV. I would like to replace R1 with 1MΩ to get 10x the output. My concern is, if it will have ...
1
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1answer
228 views

Attiny84 has a slow rising and falling edges

I'm using an Attiny84 to generate 100us pulses for a totem pole gate driver. I was expecting rise and fall times in the order of 10's of nanoseconds, what I got was rise times of 7.8us (10% to 90%) ...
1
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1answer
186 views

Delayed VCC rise time with Parallax Smart Card Adapter

While implementing a T=0/1 protocol using a smart card reader I had obtained from Parallax, I noticed a behavior when applying power to the card. It seems that once the 3.3v VCC pin is brought high, ...
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2answers
998 views

74HCT14 schmitt trigger doesn't improve rise/fall times

I have a square wave signal whose rise and fall times are too big to feed into another 74xx-series logic chip, such as the 74HC175 flip-flop, which requires rise and fall times in the nanosecond range....
1
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2answers
236 views

Op-Amp Unity Gain Frequency

I'm tasked with finding the unity gain frequency of an op-amp using the datasheet specs provided to me (just a homework exercise, not a real op-amp). There is no direct spec given for "Unity Gain ...
1
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1answer
125 views

CMOS Gate and Coupling Noise from Loose Wires

I am currently working on this small circuit which as you can see, has to level shift a 3.3v 1Hz PPS signal into a 5v pulse. Everything is marvelous when I measure the level shifted pulse with the ...
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3answers
44 views

CMOS inverter in series

I have the circuit below. Now my question is: why the rise time and fall time measured on Vout are the same as in a circuit using only one inverter gate? I know the propagation delay is the sum of ...
1
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1answer
54 views

Relationship between harmonic's amplitude and square wave's Tr and Pw

I started reading this TI guide on high speed layout guidelines and had some question on the theory of clock signals (pages 2 and 3). From the image below it's clear that the amplitude of the first ...
1
vote
1answer
964 views

Transistor - rise time for switching applications

I've been looking at basic theory of Bipolar Junction Transistor. In switching application design, in order to have a saturated transistor it is often required to find an appropriate value of the ...
1
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1answer
316 views

Measuring the rise time of remote device

Given a radio transmitter (like a cell-phone or wireless computer), how can you measure the rise time remotely? I understand that you can use an oscilloscopes to measure it on components at hand, ...
1
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2answers
116 views

How does risetime affect transmissionline effects?

How do rise and fall times affect reflection in a transmission line? Reflection will occur with shorter lengths as rise times becomes shorter, does this mean risetime effects the wavelength of a ...
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0answers
51 views

Generate ultrashort rise times with photoconductive switch or photodiode

I am trying to produce voltage pulses with very short rise time (<15 ps), medium width (20 ns) and amplitudes up to 15 V. As a promising candidate I selected photoconductive switches and ultrafast ...
1
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1answer
64 views

Need help understanding rise time parameter in nc7wz04p6x datasheet

I am looking at the datasheet of nc7wz04 UHS dual inverter. The propagation delay specified is 2.3ns. The rise time/ fall time of input pulse in the fig 6 is 3ns. But in recommended operating ...
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0answers
168 views

Impedance discontinuity problem at transmission line?

I am confused about how the waveform will be to the left of discontinuity. Please help me understand it better. Here is my understanding: When the unit step hits the inductive discontinuity, at the ...
0
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3answers
137 views

Is the rise time of the output of a logic IC or optocoupler independent of the rise time of the input?

Is the rise time of the output of a logic IC (e.g. flip-flop or inverter) or optocoupler independent or dependent on the rise time of the input? If the answer is dependent, are there any other ...
0
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2answers
63 views

What does fall and rise of clock mean?

Im new to electronics. In fact, I'm a computer scientist looking into embedded systems. I am going through Vol. 1 of Jonathan Valvano's book on embedded systems and got stuck when i read on Gated D ...
0
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2answers
304 views

Are overdamped rise waveforms really “curvier”? Or is that just time scale?

Do the rising waveforms for overdamped circuits of different \$\zeta >= 1\$ actually have a different "curviness"? Or does it just look that way because they're all shown on the same time scale? ...
0
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2answers
2k views

LTspice default rising/falling times of pulse edges

Above is how I set up a pulse in LTspice. When I set the rising and falling edges as zero or if I do not register any value, in that case LTspice automatically sets the rising and falling edge ...
0
votes
1answer
435 views

Slow rise time on MOSFET

I'm doing this project, where i control the speed of a motor with a 0-3.3 V PWM signal from a microcontroller. In the test setup i use a function generator (Digilent Analog Discovery). I would like ...
0
votes
3answers
176 views

When does an RC Transient period end?

I have struggled with this question and read many articles and watched youtube videos but to no avail. For this circuit the time constant or "Tau" is 80 micro Farads (or$$80*10^-6$$) My issue lies ...