Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 10uF 
capacitor.
Results:
Capacitor other end biased to 2V => 126 Hz out
At 36 V bias 2470 Hz out
That means 1:19 change in capacitance!
Maybe I can build some low frequency VCO out of these...
Amazing things.

-ek 

E wrote:
> Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 10uF 
> capacitor.
> Results:
> Capacitor other end biased to 2V => 126 Hz out
> At 36 V bias 2470 Hz out
> That means 1:19 change in capacitance!
> Maybe I can build some low frequency VCO out of these...
> Amazing things.
> 

Shhhhht! Don't let out all the secret tricks :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Mon, 14 Sep 2009 18:27:59 +0000, E wrote:

> Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 10uF
> capacitor.
> Results:
> Capacitor other end biased to 2V => 126 Hz out At 36 V bias 2470 Hz out
> That means 1:19 change in capacitance! Maybe I can build some low
> frequency VCO out of these... Amazing things.
> 
> -ek

Did you verify that the 2V and 36V supplies were effective shorts to 
ground for AC?

Inneresting results -- makes me want to go check Digi-Key to see if that 
mix is available for lower capacitance ranges, too.

-- 
www.wescottdesign.com

> Did you verify that the 2V and 36V supplies were effective shorts to
> ground for AC?
>

There were one film cap + 100u electrolytic to ground + whatever is in lab 
supply

Tim Wescott wrote:
> On Mon, 14 Sep 2009 18:27:59 +0000, E wrote:
> 
>> Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 10uF
>> capacitor.
>> Results:
>> Capacitor other end biased to 2V => 126 Hz out At 36 V bias 2470 Hz out
>> That means 1:19 change in capacitance! Maybe I can build some low
>> frequency VCO out of these... Amazing things.
>>
>> -ek
> 
> Did you verify that the 2V and 36V supplies were effective shorts to 
> ground for AC?
> 
> Inneresting results -- makes me want to go check Digi-Key to see if that 
> mix is available for lower capacitance ranges, too.
> 

Yup:

http://www.avx.com/docs/Catalogs/class2-gp.pdf

Many younger engineers consider Y5V and Z5U junk. Little do they know ...

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg wrote:
> E wrote:
>> Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 
>> 10uF capacitor.
>> Results:
>> Capacitor other end biased to 2V => 126 Hz out
>> At 36 V bias 2470 Hz out
>> That means 1:19 change in capacitance!
>> Maybe I can build some low frequency VCO out of these...
>> Amazing things.
>>
> 
> Shhhhht! Don't let out all the secret tricks :-)
> 

That's another point.  I have an application (an AC tweak on an improved 
laser noise canceller)that is crying out for a MVAM109 varactor (500 
pF), except that they don't make them anymore...   I'm looking at 
alternatives, e.g. a 100 pF cap with an inverting op amp driving the 
other end, with gain set by a dpot.  Unfortunately, getting good noise 
performance requires low resistance feedback, which in an inverting 
configuration requires a BF862 buffer in front, which needs AC 
coupling,... about a dozen parts and 30 mA of supply current when it's 
done. (Blech.)

Jameco has some 2200 pF Y5Vs made by "Prosperity Dielectric Co", but 
that isn't too confidence inspiring from either a quality or supply 
perspective.

I need it to be a pretty good adjustable bypass cap (one end grounded), 
nice and capacitive from about 10 kHz to 10 MHz, ballpark 100-500 pF.
Keeping the excess phase shift low at high frequencies is the key to this.

Any suggestions?

Thanks

Phil Hobbs





-- 
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

Phil Hobbs wrote:
> Joerg wrote:
>> E wrote:
>>> Just made oscillator from 74HC14, 1k resistor and  Taiyo Yuden Y5V 
>>> 10uF capacitor.
>>> Results:
>>> Capacitor other end biased to 2V => 126 Hz out
>>> At 36 V bias 2470 Hz out
>>> That means 1:19 change in capacitance!
>>> Maybe I can build some low frequency VCO out of these...
>>> Amazing things.
>>>
>>
>> Shhhhht! Don't let out all the secret tricks :-)
>>
> 
> That's another point.  I have an application (an AC tweak on an improved 
> laser noise canceller)that is crying out for a MVAM109 varactor (500 
> pF), except that they don't make them anymore...   I'm looking at 
> alternatives, e.g. a 100 pF cap with an inverting op amp driving the 
> other end, with gain set by a dpot.  Unfortunately, getting good noise 
> performance requires low resistance feedback, which in an inverting 
> configuration requires a BF862 buffer in front, which needs AC 
> coupling,... about a dozen parts and 30 mA of supply current when it's 
> done. (Blech.)
> 
> Jameco has some 2200 pF Y5Vs made by "Prosperity Dielectric Co", but 
> that isn't too confidence inspiring from either a quality or supply 
> perspective.
> 
> I need it to be a pretty good adjustable bypass cap (one end grounded), 
> nice and capacitive from about 10 kHz to 10 MHz, ballpark 100-500 pF.
> Keeping the excess phase shift low at high frequencies is the key to this.
> 
> Any suggestions?
> 

Yes, check out these:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=478-4238-ND

Datasheet:
http://www.avx.com/docs/Catalogs/class2-gp.pdf

But they only come in through-hole.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

> 
> Many younger engineers consider Y5V and Z5U junk. Little do they know ...
> 
Well, I'm not a young engineer any longer and tend to consider Y5V and 
Z5U as junk.
I don't even regard this as "secret trick". Sure you can build a VCO 
this way, but then you also have to add a thermostat, which will turn 
the secret trick into an expensive trick. Not to mention that the 
thermostat won't cure the thermal hysteresis problem.

Klaus

Klaus Bahner wrote:
>>
>> Many younger engineers consider Y5V and Z5U junk. Little do they know ...
>>
> Well, I'm not a young engineer any longer and tend to consider Y5V and 
> Z5U as junk.
> I don't even regard this as "secret trick". Sure you can build a VCO 
> this way, but then you also have to add a thermostat, which will turn 
> the secret trick into an expensive trick. Not to mention that the 
> thermostat won't cure the thermal hysteresis problem.
> 

It's the same with varicaps, FETs and whatever else you want to use in 
this function. A good designer designs out those dependencies or makes 
the circuitry live with them :-))

It is not trivial to build a variable resonant circuit in the kHz range 
where the varying element is supposed to cost no more than five cents, 
other than with Z5U and such. I've also done super-cheap spectrum 
spreaders that way for EMI mitigation. There, a temperature-dependency 
doesn't matter at all.

Of course, in Phil's case he needs to watch out where he puts the 
capacitor. It should not be in a path where there would be large signal 
amplitudes across it, else the whole thing will become uncomfortably 
non-linear.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg wrote:
> Klaus Bahner wrote:
>>>
>>> Many younger engineers consider Y5V and Z5U junk. Little do they know 
>>> ...
>>>
>> Well, I'm not a young engineer any longer and tend to consider Y5V and 
>> Z5U as junk.
>> I don't even regard this as "secret trick". Sure you can build a VCO 
>> this way, but then you also have to add a thermostat, which will turn 
>> the secret trick into an expensive trick. Not to mention that the 
>> thermostat won't cure the thermal hysteresis problem.
>>
> 
> It's the same with varicaps, FETs and whatever else you want to use in 
> this function. A good designer designs out those dependencies or makes 
> the circuitry live with them :-))
> 
> It is not trivial to build a variable resonant circuit in the kHz range 
> where the varying element is supposed to cost no more than five cents, 
> other than with Z5U and such. I've also done super-cheap spectrum 
> spreaders that way for EMI mitigation. There, a temperature-dependency 
> doesn't matter at all.
> 
> Of course, in Phil's case he needs to watch out where he puts the 
> capacitor. It should not be in a path where there would be large signal 
> amplitudes across it, else the whole thing will become uncomfortably 
> non-linear.
> 

It's going across a current mirror, so the maximum swing should be less 
than 50 mV even if everything is going nuts.


Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net