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Questions tagged [parasitic-capacitance]

Capacitance that arises from the physical layout of the circuit and the placement of components. Particularly notable when the addition of capacitance is undesirable.

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how to isolate coupled noise source in parasitic capacitance in high voltage pcb design?

I'm new designing a high/medium voltage (V <=10kV) with low voltage and low current (10mA). There will be only a few HV relays. Their coils will be triggered by LV. I have read some literature ...
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60 views

Relaxation Oscillator Issue, comparator self-oscillating at 25 MHz (40ns propagation delay)

I have a relaxation oscillator circuit, which is supposed to oscillate around 6 MHz, and mostly it oscillates in a very stable manner around it. However sometimes it starts to oscillate at 25 MHz, ...
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MOSFET Controled Relay Problem

As a way to power-on/-off a circuit load, a MCU is used to drive a relay through two MOSFETs. The problem is, when the MCU GPIO output is measured 0-volt, the relay could stay connected. Can anybody ...
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How to perform parasitic extraction in CST Studio?

I'd like as the title suggests to perform a parasitic extraction of an inverter PCB design using PEEC Method in CST Studio Suite but, unfortunately I can't seem to find documentation or resources ...
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110 views

Using only stray capacitance for MCU oscillator circuits

I've included a diagram of typical Pierce oscillator circuit taken from ST Application Note AN2867: The note suggests that C_L1 and C_L2 should be chosen such that the following equation holds: ...
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Does (stray) capacitance depend on voltage?

While thinking about how to reduce stray capacitance on my pcb, I got triggered by the question: Should the stray capacitance depend on the voltage difference? Acccording to the equation of ...
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Spike in RTL Inverter

I do not understand the cause of this spike which can be observed in an RTL inverter (but also in a CMOS inverter). In the following image it is the peak at 10 mS (I have considered as input a signal ...
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Measurement of Cmos Parasitic capacitors

i've had a question which asks if we assume that capacitance of capacitors with w/l of 1u/0.5 are then what are capacitance of capacitors (with the actual w/l) now i know cgs in saturation for ...
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Tower Sawyer Circuit - High impendance DUT

I am trying to assemble a Tower-Sawyer circuit for measuring Ferroelectric loops. On a picture below you can see the most simple design of Tower-Sawyer circuit, with a parasitic capacitance in ...
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Measuring current vs voltage

Let's say that I have a periodic charge build-up across the capacitor C1. I could either choose to measure the current using a transimpedance amplifier as shown below or could measure the voltage ...
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60 views

Electrical properties of a stack of strip board connected by through-hole pins/sockets

I'm aware that breadboards have a limit of 1-2MHz. I think this is because of capacitance. Are there similar limits for a stack of stripboard connected by through-board sockets/pins? Would breaking ...
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Do MRI magnets oscillate due to parasitic capacitance?

Moved here from SE Physics. Do MRI magnets oscillate during charging or even during persistant mode due to parasitic capacitance? What problems can this cause? I am planning a low temp ...
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Captab results in Cadence virutuso

I Wanted to get the transistor parasitic capacitance in a circuit so I printed DC operating Point. The values were negative so I gave up and started to find other ways. I found that there is a captab ...
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65 views

Tesla coil, where do the sparks from the secondary coil ground to?

This might be an obvious question, but I was wondering how a Tesla coil emits sparks that's seem to complete a circuit in thin air, and how one end of the secondary completes a circuit with the other ...
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determine the cutoff frequency of a nMOS in common gate with gate resistance

I have to determine the upper cutoff frequency of this circuit. I absolutely mustn't use the laplace domain because it's too time consuming so not compatible with the time I have at the exam. A rapid ...
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35 views

What is the use of CC_to_GND option in starrc extract?

While doing parasitic extraction using starrc tool, I see there is a switch CC_ti_GND. It combines all the coupling caps and gives the cap with GND. So my doubt is, in which case would it be useful ...
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Approximate Capacitance of a Toroidal Coil

I'm interested in an expression for the capacitance or resonant frequency of a Helmholtz like (the windings are parallel to the plane of the coil) of circular cross section and of the order 1 meter in ...
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203 views

Measuring Vackar Oscillator Output Amplitude and High Frequency Effects

This is somewhat related to my previous question regarding why I wasn't seeing a clamp biasing effect with my JFET Vackar oscillator. I think I figured it out and I'm wondering if you guys agree. ...
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How do the parasitic elements behave in a bidirectional power switch made from back-to-back MOSFETs?

I would like to know how to determine the value of the total internal gate mesh resistor (Rg) and different parasitic capacitors especially Cgs and feedback capacitor Cds of a bidirectional power ...
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248 views

Need help modelling the circuit with parasitic capacitance of a power supply in this scenario in SPICE

A single-ended source is connected to an inAmp of a data-acquisition board as follows: As you see above, the shield is shielding the twisted shielded pair cable. The shield is tied only to the earth ...
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504 views

Calculating parasitic capacitance of serial zener diodes

simulate this circuit – Schematic created using CircuitLab I have 2 series zener diodes like these in the schematic. Their capacitance is C=225pF How do I calculate their equivalent ...
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285 views

Parasitic Capacitor current of an inductor

I am doing a double pulse test on SiC MOSFETs from 100-800 V and current from 20-80 A. The schematic is shown in figure (the values are not correct though). In my first round of tests (Figure 2), I ...
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What will it happened when capacitance is almost the same as parasitic capacitance

I make a sample and hold (IC design),and it is combined with transmission gate and a 550fF capacitor,and my classmate told me that my capacitor is too small,almost the same as the parasitic ...
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Capacitive Voltage Divider and Discrepency in Output Signal

Question: Why is my measurement of the output voltage of my capacitor voltage divider not matching the theory? Background: I designed a capacitor voltage divider for the purpose of measuring the ...
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695 views

PCB trace length

I have some doubts. At the output of my phono preamp there are very big coupling capacitors and i didn't have choice (i think so) - i had to make long traces with output signal. The trace width is 1....
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What order of magnitude should I expect the parasitic capacitance to be for a solderless breadboard?

I'm trying to account for some error in measurements for a circuit I have produced physically and simulated in spice. The only suspect seems to be the solderless breadboard as the error seems to ...
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Why do parasitic elements (e.g capacitance) appear on only high frequencies?

We know that the impedance of a capacitor is inversely proportional to the frequency then why is it not negligible when at higher frequencies ?
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339 views

PCB design Gnd copper pour near signal

im new to pcb design,im trying to add copper pour in my design ,I always seen PCBs with signal line between copper pour, but in my case copper pour is on one side since board width is 5mm only just ...
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How is it possible that the reverse transfer capacitance of this FET is so low?

A FET has parasitic capacitance, which can be modeled as a capacitor between each of its terminals (gate, drain and source), which I refer to as Cgd, Cgs and Cds, as shown in the image below. FET ...
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3k views

adjacent trace capacitance (horizontal)

I find a lot of online tools to calculate the capacitance between two traces (or a trace and a plane) on opposite pcb layers. One such tool can be found here: http://chemandy.com/calculators/...
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556 views

CML/LVDS driver for several GHz, parasitic RC filter formed by terminating resistance and load capacitance

Update: Based on useful comments of The Photon, Andy aka and PlasmaHH. As I got, there is indeed the parasitic low-pass. There is no magic bullet that will mitigate it. Large receiver capacitance is ...
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683 views

Header frequency limit

At what point will I start having trouble with noise and parasitic capacitance/inductance when using standard 0.1in header pins? If I'm using an MCU capable of driving a 20MHz SPI bus, would it be ...
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Crystal oscillator load capacitance, again

There's a lot of seemingly conflicting information regarding how the load capacitance for a parallel resonant crystal is calculated. Faced with a lot of problems in recent years with non-oscillation ...
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How MOSFET gate capacitances (Cgs, Cgd) are calculated?

I have read somewhere that the gate capacitance (Cgs, Cgd) of a MOS is calculated as below: Strong inversion: Cgs=(2/3)Cox.W.L + Cov Non-saturated: Cgs=Cgd=(1/2)Cox.W.L + Cov where Cov is ...
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353 views

BJT Capacitance at RF limmitations

I am trying to design a simple RF signal buffer using a MPSH10 BJT transistor. This is to operate at ~90MHZ and simply buffer an input RF signal to lower the out impedance of my oscillator which feeds ...
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250 views

SPI to Numerous Chips on Different PCBs with FFC Cables?

I want to drive numerous chips on several different PCBs with SPI from a microcontroller over FFC cables. Here is a crude diagram: UPDATE: Green wires are ground scheme I have never attempted such ...
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Audio transformer: What to do with an unused winding?

For the purpose of impedance matching and floating a single-ended, ground-referenced signal, I am planning to use an audio transformer like this one. Here's the schematic from the data sheet: My ...
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332 views

Does mutual capacitance increase for two positively charged plates when brought close?

My understanding is that any two charge carriers will exhibit what is known as mutual capacitance. That is, there is an amount of charge that can be stored between any two objects, which is called ...
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Frequency of Natural Resonance with Parasitic Component due to Oscilloscope

So, I've just performed a lab on measuring the resonance of an LCR circuit. I rearranged the circuit so each time the component in question had one lead on the ground plane, and then measured it's ...
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365 views

Are low ESR SMD capacitors with jumper wires between their legs and the circuit OK?

I have a board with two super low ESR SMD electrolytic capacitors which came off the switching power supply of a notebook motherboard. The legs of the capacitor are still soldered on the board. One of ...
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108 views

Understanding the Difference Between Two Capacitance Sensors

I'm slowly beginning to understand more about how these work thanks to answers I have received on this site. I believe one area of confusion for me has been I've looked at two differently designed ...
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1answer
2k views

Tesla coil miniature model (slayer exciter) parasitic capacitor

I have been trying this miniature Tesla coil based on Slayer's exciter circuit (shown below). The part that I don't understand is how this parasitic capacitor exists? I know that for a capacitor there ...
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1answer
507 views

MOSFET fast turn-off not enough

I have a PWM bridge driving a higher than 1k load from 200V supply. The simplified, equivalent schematic is this: The drivers I'm using are slow turn-on/fast turn-off and, in the schematic, it's a 50%...
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1answer
660 views

How to measure parastic capacitance of a trace

I have a 24 MHz, crystal on my board and datasheet of IC defines the load capacitance between 5-9pF. The reference design I follow don't use any load capacitor. My traces look like this: shorter ...
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1k views

Why is parasitic capacitance much more mentioned than parasitic inductance in MOSFET?

It seems to me that in MOSFETs, parasitic inductance would be equally as important as parasitic capacitance. However, I have never seen anyone discussing parasitic inductance seriously. Is parasitic ...
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99 views

How does a device's physical size affect its parasitic capacitance?

I'm looking at a very small bi-directional diode and for this RF circuit, an ESD with parasitic capacitance << 1pF is recommended. The diodes I've seen for this application are VERY small. ...
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2answers
844 views

Capacitance in serial communication

When we say capacitance is important in serial communication, whether we think of parasitic capacitance? So the lower parasitic capacitance in cable, less is voltage drop and the longer distance we ...
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347 views

Reducing parasitic capacitance in momentary latching circuit

I'm using this circuit (http://www.edn.com/design/power-management/4427218/Latching-power-switch-uses-momentary-pushbutton) to get latching on/off behavior from a standard momentary switch (an Omron ...
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2k views

How to calculte mosfet capacitors (Cgs Cds Cdg) knowing the charges Q

I need to use the best model for the MOSFET in my circuit I'm simulation on PSIM, the MOSFET is Si4108-TI-GE3. But I am not given the parasitic capacitance values (Cgs Cds Cdg), I am only given this: ...
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710 views

Capacitance of a single charged plate?

Lets say we have a single plate that has a charge of +Q on it. A plate with charge -Q is infinite distance away. Will the plate with +Q have a capacitance associated with it? Why or why not? I was ...