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Analog Angle

Extreme Analog Design: Don't Forget Those Passives

Bill Schweber
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yalanand
yalanand
11/30/2013 8:41:00 AM
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Re : Extreme Analog Design: Don't Forget Those Passives
If we compare circuit with passive elements like capacitors , resistors, inductor etc then there are many many parameters to consider which may go wrong with different conditions. That is the reason analog circuit design with these elements is complex than digital design.

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JAYARAMAN KIRUTHI VASAN
JAYARAMAN KIRUTHI VASAN
11/28/2013 1:54:20 AM
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Re: Ferrite beads
@Samicksha,

Selecting the right ferrite bead for the application does matter as there are plenty of ferrite bead variants.

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samicksha
samicksha
11/27/2013 3:47:52 AM
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Re: Ferrite beads
You are right Victor, and to add at high frequencies, ferrite bead inductors work like resistors instead of inductors.

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Victor Lorenzo
Victor Lorenzo
11/27/2013 3:35:25 AM
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Re: Ferrite beads
Good point, and ferrite beads not only contribute to reducing HF noise which affect other parts of the circuit, they also contribute to reduce or minimize the conducted high frequency signals (conducted emissions) that could lead to serious EMI compatibility problems.

--Victor

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Victor Lorenzo
Victor Lorenzo
11/27/2013 3:29:32 AM
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Sometimes the 'extreme' is not so far from the 'normal'
Hello All,

Thanks Bill for the article.

Yes, some times we overlook the real importance of some parameters from those 'tiny' passive components and just concentrate on the 'big' diigital components.

A couple of years ago we designed one portable device that included one ISO15693/ISO14443A RFID reader for securing accesses. As of course housing size was a constrain, we had some difficulties in the design for achieving the intended reading distance (>7cm), mostly due to antenna size. The device was designed so it could stand for more than 12 hours inside a freezer at 4ºC and included conformal coating so it could also withstand over 80% condensing RH when taken out to ambient temperature.

Everything was fine with the first production batch (at that time the designers were in charge of component stockage before phase-0 production)... but the devices from the second production batch (real production) had a 'small' problem, they were not able to read the RFID tags just after being taken out from the freezer.

The root cause for it was, as lead time for some capacitors was too long, in the production department they decided to replace them with some others of same package, tolerance and value (and of course with a very lower price), but they did not pay attention to that small parameter called 'temperature coeficient'. At the end we needed to replace the affected capacitors in all devices from the second batch (fortunately not too many, around 150 devices in total).

--Victor

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Ranasinghe
Ranasinghe
11/26/2013 12:01:47 PM
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Re: Ferrite beads
Thanks Bill for the paradigm shifting article. 

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samicksha
samicksha
11/26/2013 1:11:25 AM
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Re: Ferrite beads
Thanx Jay, you keep good comment here, yes it can be added to an inductor to improve, in two ways, its ability to block unwanted high frequencies which are considered to be noise.

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amrutah
amrutah
11/25/2013 3:38:16 PM
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Re: Vibration
@DaeJ:"wonder what type application require for vibration in the passive component. Did any passive component define the vibration requirement?"

I think the MEMS capacitors are one good example where a mechanical stress (or vibrations) is used to generate equivalent electrical signal which can be further processe.

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JAYARAMAN KIRUTHI VASAN
JAYARAMAN KIRUTHI VASAN
11/25/2013 2:37:39 AM
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Master
Ferrite beads
Bill,

Nice post.

We had the problem of high frequency signal creeping in in a Electro-surgical Cautery. The activation switch is in the handpiece and the device is supposed to only sense the switch closure and not the high frequency itself (one arm of switch is high frequency signal). We used appropriate Ferrite beads from Wurthe to suppress this interference.

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eafpres1
eafpres1
11/25/2013 12:15:23 AM
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Blogger
Extreme cabling
I have had many, many problems with coaxial cable & connectors.  In my work with antennas for various in-building applications, as well as some consumer electronics, there were severable classes of issues.  Many times the cable connected to the antenna was soldered to a PCB or metal element or both.  It was easy to damage small RG-174 etc. coax when soldering.  The next class of issues was around the connector.  Many times it was hard to control the crimp of the ferrule, which mechanically holds the connector by crimping the braided shield against the connector body.  This was such a problem that in many cases we had to do continuous sampling and pull testing.  

Another class of issues was that in many cases, the cable entry to an antenna housing had to be sealed.  The cable jackets are frequently not conducive to sealing, either they aren't bondable with common adhesives and things like O-rings often could not create a good enough seal..  

Temperature extremes are also a common challenge for cable.  In one project we had all these problems together.  It was automotive, and the antenna, used to communicate to tire pressure sensors.  The customer mounted the antenna very near the exhaust pipe on the undercarriage of a car.  The specs were -40C to +125C, IP67 water resistance.  We had to use a PTFE jacket on the cable to meet the temperature spcs.  The PTFE would not seal, even using an RTV silicone.  Eventually we had to treat the jacket with an acid to prime it so the silicone would bond.

 

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