A capacitor, usually ceramic, used to provide instantaneous energy to a local circuit.

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8
votes
2answers
645 views

Why is it usually the case that the negative rail for ICs needs more decoupling capacitance (has worse PSRR) than the positive rail?

That the premise in the question seems to hold can be seen from various sources, including: comparing the datasheets of various clones of LM317 and LM337 (too many to list, but generally the ...
0
votes
1answer
42 views

Do I need a decoupling cap for a line buffer gate?

The data sheet does not say anything about the decoupling capacitors for this buffer gate. Would it be correct to assume that no caps needed? Please, explain.
11
votes
4answers
835 views

Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters?

Why don't decoupling/bypass capacitors need resistors to perform their function, like regular filters? Is it because the stray resistance of copper traces is enough to filter, along with the ...
0
votes
1answer
55 views

Capacitor grounded between 2 resistors

This is part of a segment of a design I came up with using schmitt triggers as relaxation oscillators. The picture below shows the 4 possible states of the circuit at any given time. Basically, the ...
0
votes
1answer
47 views

Can decoupling capacitors be doubled up? Xbee + VR both have them

I'm using an MCP1700 low-dropout voltage regulator to power an XBee separately from my other Arduino circuit, because it can use up to 215mA all on its own. There are 1uF decoupling caps on both the ...
0
votes
0answers
72 views

Trouble with decoupling capacitor on simple low-pass circuit

I'm trying to filter all signals above ~350Hz from an electret condenser microphone's output and amplify what's left for analog input / DSP. I'm a beginner, so I cobbled together the design from a few ...
1
vote
2answers
79 views

Which capacitor for DC blocking in audio applications?

Which capacitor (electrolytic, film, ceramic) do you use for DC blocking in audio applications? From what I have seen most people use electrolytic capacitors. But, also from power decoupling theory ...
0
votes
0answers
54 views

Can the decoupling capacitor for WS2812 be further away?

I have (many) sticks of 8x WS2812b already soldered and completed. Now I've read that it would have been a very good idea to include a 100nF capacitor for each chip on Vcc. I haven't designed the ...
0
votes
1answer
58 views

which of these is more efficient for AC coupling

In the beginning I was using the circuit (at the bottom) to separate the AC from the DC ( the second order filter ) which in fact is just a second order high pass filter and the DC is a zero Hz ...
1
vote
3answers
82 views

Help with understanding strange capacitor configuration arrangement

I am on a chapter of my electronics beginner’s book where the author talks about the PICAXE microcontroller. One of the first things the author mentions in this chapter is to make sure that the PICAXE ...
0
votes
0answers
38 views

AVR decoupling capacitors in 64kHz switching power supply

I am working on a compact variable switching power supply (sepic topology) that is controlled by an Atmega328p microcontroller. The unit is powered by li batteries at 3.7 volts. Everything works ...
0
votes
1answer
58 views

Power rail decoupling caps for analog circuitry

First off, the terminology I'm using could be complete rubbish - I'm still learning I have a mixed signal board for measuring bio-signals. The 4 layer board will have a split ground plane, analog ...
3
votes
1answer
93 views

Thermal pads under IC, how to place vias without soldermask / Decoupling question

I'm looking for a good solution on how to design a thermal pad that is good for solderpaste assembly. PCB fab that I'm using can't place any soldermask on vias like in this example: And I'm not ...
-1
votes
1answer
88 views

This is a good connection for a decoupling cap on an IC?

Since I have no space on the BOT layer to place a cap near IC. I need to place a decoupling cap on the other side of the board, this is a good connection?
0
votes
2answers
75 views

Choice of bypass capacitors for PIC18F4455

Does anyone know how many and what values of bypass capacitors I need for a PIC18F4455? The datasheet does not provide any information on this and I don't want to use more than what I strictly need, ...
-1
votes
2answers
80 views

Books on Bypassing, decoupling and Grounding [closed]

I am really sorry to ask this question but I am new to PCB designing and Its pretty challenging for me. The layout works in LAB but does not work well outside. I observe glitches in system. I am a ...
2
votes
2answers
74 views

Should every logic IC be power decoupled?

I've read before that "every IC" should be decoupled. I've never before bothered on gates, buffers, etc. No datasheet that I've read for those chips has ever suggested to do so, until I came across ...
1
vote
1answer
133 views

Problem understanding the operations of capacitor

So far I've learnt about some different types of capacitor arrangements , such as coupling , decoupling , bypass , filtering , and smoothing capacitor. Decoupling and bypass capacitors are the same ...
2
votes
2answers
229 views

AC-coupling capacitors for high-speed differential interfaces

Can you explain me why and where I should put AC-coupling capacitors (usually around 0.1uF) on high-speed (1...5 GHz) differential serial interfaces (like SerDes for Gigabit Ethernet SFP modules)? ...
10
votes
5answers
2k views

Forgot to put a via near bypass capacitor, and now the boards have been fab'd - what can I do?

I goofed and didn't notice this until the board was already fab'd and assembled. The board is an RF amplifier; the portion I have pictured is a part of the DC control pat (so no RF is nearby but we're ...
0
votes
1answer
85 views

DDR2 decoupling/bypassing - 100nF or 10nF?

I am slightly confused in deciding decoupling/bypass capacitor for DDR2 power supply pins. Some recommendations mention using 100nF and some mention using 10nF. I know that lower capacitance is more ...
1
vote
1answer
78 views

Use of RC circuit in amplifier output stage

I have to use a LM384 amp circuit (shown below) for a school project and need to explain how it works. I've read the datasheet (http://www.ti.com/lit/ds/symlink/lm384.pdf) and thus have a guess about ...
0
votes
1answer
61 views

1/4" TRS cross-coupled output with bypass capacitor. Is TRS jack wired for cross-coupled or not?

I'm a newbie. I wrote Alesis to get the specs on my mix board main out. Here is what their engineers said: The main outs are cross-couple, capacitor bypassed, single-ended output, for a TRS jacks. ...
1
vote
0answers
90 views

EMI filtering at end of a long copper wire transmitting high DC power

I have a long (20 - 50 m) copper wire for supplying DC power. One one end there is a AC-DC converter supplying 600W-1000W of power at 60V output. At the other end I have a switching type (100-140 kHz) ...
0
votes
1answer
61 views

LDO layout: position of output cap relative to load

simulate this circuit – Schematic created using CircuitLab In above figure, "LDO layout A" and "LDO layout B" are indicative PCB layouts of an LDO - focusing on its output capacitor. ...
0
votes
1answer
38 views

Small UPS for bluetooth audio device

I've got a bluetooth audio receiver in my car and am finding it annoying that it turns off immediately after the ignition is turned off. For example if we're stopped for a while I prefer to turn the ...
2
votes
2answers
216 views

How does Stitching capacitor provide shortest return current path between plane splits, as we know that it blocks DC current?

I heard that Stitching capacitors are used to provide shortest return path whenever a signal is routed along the 2 power plane splits. As we know the return current path will be right under the trace. ...
1
vote
2answers
241 views

LM7805 followed by LD1117-3.3

The LM7805 datasheet recommends a 0.33uF cap on the input and a 0.1uF cap on the output. The LD1117-3.3 datasheet recommends a 0.1uF cap on the input and a 10uF cap on the output. I am building a ...
-1
votes
1answer
133 views

Floating vs Grounded Source, and Decoupling Capacitors

I am confused about the following: in my lab, we all run electromagnets off of pretty beefy power supplies. Everyone else grounds their supply. Mine is floating. I do not have even a remotely good ...
0
votes
0answers
42 views

Shift register HC164 sensitivity issue

I am controlling 5 shift registers (74HC164) from TI's cc3200 launchpad. I am clocking the data using GPIO pin and controlling LEDs though it. But my shift register is giving weird results. It gives ...
0
votes
1answer
70 views

What is a tank capacitor?

This is from a microchip datasheet What is a tank capacitor ? It doesn't sound like a tank circuit because why would they use "capacitor" and not the other element in the tank.
1
vote
1answer
65 views

Understanding the capacitors in an op amp circuit

I am a computer programmer forced to make some circuits for a Langmuir probe our lab is making (the main task is programming the analytic software on the computer, but I have to make a basic amplifier ...
0
votes
2answers
72 views

Is there a way to fix a unsoldered SMD decoupling capacitor?

I'm rather a newbie regarding electronics but I came here to seek for a simple response. I realized that a electronic appliance I have doesn't work anymore. I tried to investigate the issue and found ...
3
votes
1answer
97 views

PCB Short Issue

I recently designed two boards and had them manufactured for a project I am working on. Before I soldered any components, I checked the continuity of some of my connections and discovered that there ...
10
votes
1answer
835 views

Decoupling capacitor with resistor in series

I am looking over a datasheet, and I saw something that puzzled me. Why is there a 1 ohm resistor (R2) in series with the capacitor? This is a power rail, so I'll assume it is a decoupling ...
1
vote
3answers
355 views

Why does my circuit work with ceramic capacitors but not electrolytic?

I had used some capacitors as decoupling capacitors for my USB powered device. Due to some chip issues, this resulted in using three 47 uF capacitors. I used electrolytic capacitors. Three in ...
3
votes
3answers
641 views

Layout of decoupling capacitors

So I've been attempting to create my first development board and layout. I'm first working on the decoupling capacitors, power and ground portions of the layout. The MCU I'm trying to properly ...
0
votes
2answers
126 views

Use expensive or inexpensive capacitor for decoupling

I'm in the middle of a project to create a small development board using a 100Mhz Cortex M4 MCU and have to buy some decoupling SMT capacitors. I've found the following options: Cheap 10 cent from ...
1
vote
1answer
440 views

Minimal circuit for ARM STM32F411

I'm trying to determine what a "minimal" circuit is to get an STM32F411 processor running and able to blink an LED. I wish to use the internal PLL and no external crystal at this point. I've looked ...
1
vote
1answer
291 views

LC filter and ferrite bead

Suppose I've a circuit that is affected by EMI noises that have a freq. less than 80khz and noises above 2ghz. I want to cut off this noise freq. before they reach my ICs. The circuit is powered by 5 ...
7
votes
3answers
523 views

Protecting microcontroller from inductive loads

I'm working on a project where I will be controlling a variety of loads (relay, solenoid, motor) from an Arduino and I'd like to make sure I build in enough protection for the microcontroller and ...
0
votes
0answers
143 views

Use X5R 4.7uF ceramic for bulk capacitor?

The Freescale FXOS8700CQ specifies a 100nF ceramic and a 4.7uF bulk capacitor close to pin 14 (VDD). Most designs I see use a tantalum for the bulk capacitor, but I have quite a few unused 4.7uF 6.3V ...
0
votes
1answer
174 views

Decoupling Capacitor Value [duplicate]

I am taking 12V from Power card to my backplane card to use for Hard disks. I have been advised to put decaps of 330 uF on 12V supply. Can I use 220 uF or even lesser value. What is the criteria for ...
11
votes
2answers
577 views

Why does ST recommend 100nF decoupling caps for a 72MHz MCU? (And not 10nF)

I've been reading about decoupling caps, and I can't seem to understand why ST recommends 100nF decoupling caps on a 72MHz arm mcu. Usually 100nF decoupling caps are only effective up to about ...
2
votes
1answer
190 views

Optimal Capacitor Placement on DC/DC Convertor

I'm trying to decide on the best layout for caps on a DC/DC converter. Which of the following options (or another, unlisted option) is the best choice? GND Out plane with 5V Out going the opposite ...
11
votes
3answers
996 views

Parallel Capacitor Conundrum [duplicate]

I have recently taken on a project that involves improving a circuit and there is a couple of instances where there are two capacitors in parallel with each other. The values of these capacitors ...
1
vote
1answer
311 views

Decoupling Capacitor

For power pins of IC we add a decoupling capacitor, suppose a design misses the decoupling cap. Is there anything that can be done on layout to counter the missing decoupling capacitor? My first guess ...
0
votes
2answers
179 views

Using a shunt cap to create a delay - good idea? [closed]

simulate this circuit – Schematic created using CircuitLab C1 is a decoupling capacitor. If the input of U1 is experiencing undesired phase shift, can a decoupling capacitor correct the ...
1
vote
1answer
25 views

PCM4202 AGNDL/AGNDR connection

First, sorry if my english is not perfect. I have a question regarding AGNDL and AGNDR connectiof for PCM4202 . In the data sheet document ( figure 12, page 21) the decoupling caps are not connected ...
0
votes
2answers
107 views

Decoupling Capacitor - Multiple Vss pins

I'm about to start using a chip that has one positive and two ground connections - I've only used chips with one positive and one ground before. How should I attach the decoupling capacitor(s?) to ...