CGW glass-dielectric capacitors

[Winfield Hill]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

 

[Baron]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

Yes I still have boxes of them!

 

[John Larkin]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

Several people make mos capacitors, up to a couple hundred pF. They
are amazing, near zero da, huge q's, low tc, low voltage coeff.

Metelics, Vishay, maybe others.

John

 

[Damon Hill]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

AVX makes glass capacitors, up to 2400 pF. Possibly the
best capacitors made, within their capacitance range.

Not cheap.

--Damon

 

[Uncle Monster]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

Corning Glass Works capacitor division was sold
to AVX in 1987 according to this article.

http://query.nytimes.com/gst/fullpage.html?res=9B0DE0DB103FF93AA3575AC0A961948260

http://tinyurl.com/2g3ysn

[8~{} Uncle Monster

 

[Robert Baer]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

I fondly remember them, and Corning Glass Works for some unknown
reason stopped making them.
Far better than most precision, selected Micas.

 

[Robert Baer]

Several people make mos capacitors, up to a couple hundred pF. They
are amazing, near zero da, huge q's, low tc, low voltage coeff.

Metelics, Vishay, maybe others.

John

But those damn things are eXpen$ive!

 

[Winfield]

Yes I still have boxes of them!

Hey, Baron, do you want to sell any of those?

 

[Baron]

Hey, Baron, do you want to sell any of those?

Er ! What do you have in mind ? These have been stored in my loft for
a number of years now. They were originally purchased when I was doing
development work.

 

[Tom Bruhns]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

Have you checked the dielectric absorption? I understand that's
pretty bad.

Do you happen to know the temperature coefficient?

Cheers,
Tom

 

[John Larkin]

But those damn things are eXpen$ive!

Well, quality costs. More significantly, they're really hard to mount.
They are usually either leadless parallel-plate things, or the Vishay
parts have bump pads on the bottom, impossible to solder by hand.

Oh, sorta off the topic, but this is cute:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2450

One of my products uses this to coarse-tune an LC oscillator at every
powerup, to get within varicap range. That eliminates a trimmer cap
and associated labor, and takes care of longterm drift. It was a pita
to program.

John

 

[Tom Bruhns]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

OK, I just answered at least part of the questions I just posted, via
the AVX website. I suppose with a high (+140ppm/C) but stable
temperature coefficient, they could be useful in thermal compensation,
but unfortunately, it's more often that a negative temperature
coefficient is appropriate for that (esp. in an LC circuit).

I'm scratching my head, wondering why I'd want to use a glass cap
instead of a C0G ceramic. Though I don't see a voltage coefficient
listed in the AVX data sheet for C0G caps, my distortion measurements
tell me that it cannot be very large; I suppose even in the glass
caps, it's not truly zero, just vanishingly small.

Cheers,
Tom

 

[John Larkin]

OK, I just answered at least part of the questions I just posted, via
the AVX website. I suppose with a high (+140ppm/C) but stable
temperature coefficient, they could be useful in thermal compensation,
but unfortunately, it's more often that a negative temperature
coefficient is appropriate for that (esp. in an LC circuit).

I'm scratching my head, wondering why I'd want to use a glass cap
instead of a C0G ceramic. Though I don't see a voltage coefficient
listed in the AVX data sheet for C0G caps, my distortion measurements
tell me that it cannot be very large; I suppose even in the glass
caps, it's not truly zero, just vanishingly small.

Consider a 7-pole 40 MHz lowpass filter, 50 ohms or so, running at
levels up to maybe 2 volts RMS. Using C0G caps, do you have any guess
as to how much THD the caps might generate on their own?

We're doing a new DDS synthesizer/arb: lookup table, 14-bit
diff-current-out dac, diffamp, lowpass filter, output amp. It's
clocked at 128 MHz and max output will be half Nyquist, 32 MHz.

We're seeing complex patterns of harmonic distortion versus frequency
and amplitude, but I hadn't thought about the caps as culprits. We'd
like to hold -60 dB to 10 volts p-p, which is optimistic. Commercial
RF signal generators and arbs seem to have distortion specs above
-40dB, some as bad as -20.

John

 

[Winfield]

Does anybody remember the CGW capacitor company -
and what happened to them? I have some CGW CY06C
glass-dielectric caps -- amazing performance, no voltage
coefficient, etc. I think AVX also makes CY06C caps.

Corning Glass Works capacitor division was sold
to AVX in 1987 according to this article.

http://query.nytimes.com/gst/fullpage.html?res=9B0DE0DB103FF93AA3575A...

http://tinyurl.com/2g3ysn

[8~{} Uncle Monster

Thank You, I had forgotten Corning Glass Works capacitors.

 

[Winfield]

Have you checked the dielectric absorption? I understand
that's pretty bad.

Datasheet says low, about 0.012% per MIL-C-19978,
similar to polystyrene, but thanks, I'll measure that.

Do you happen to know the temperature coefficient?

The datasheet says about +125ppm from -55 to +45C,
increasing to +165ppm at +125C. They say it's VERY
stable at these values, with 5ppm retraceability.

 

[Winfield]

I'm scratching my head, wondering why I'd want to use
a glass cap instead of a C0G ceramic. Though I don't
see a voltage coefficient listed in the AVX data sheet
for C0G caps, my distortion measurements tell me that
it cannot be very large; I suppose even in the glass
caps, it's not truly zero, just vanishingly small.

One big difference: "glass capacitors exhibit
zero piezoelectric noise." (Quoting from the
AVX spec page.)

Piezoelectric effects are easy to miss with
conventional capacitor-testing equipment, like
I have, because they show up very strongly at
discrete resonance frequencies. Yes my hp4192
has a 0.1 to 1ppm frequency resolution, good
for measuring crystal parameters, etc., but
one could take forever looking for capacitor
resonances that way. I imagine a new test
jig with a sweep generator is required.

Or one stays away from C0G parts in critical
signal applications like John's filters (next
post). But, they sure are inexpensive!

 

[Tom Bruhns]

Consider a 7-pole 40 MHz lowpass filter, 50 ohms or so, running at
levels up to maybe 2 volts RMS. Using C0G caps, do you have any guess
as to how much THD the caps might generate on their own?

We're doing a new DDS synthesizer/arb: lookup table, 14-bit
diff-current-out dac, diffamp, lowpass filter, output amp. It's
clocked at 128 MHz and max output will be half Nyquist, 32 MHz.

We're seeing complex patterns of harmonic distortion versus frequency
and amplitude, but I hadn't thought about the caps as culprits. We'd
like to hold -60 dB to 10 volts p-p, which is optimistic. Commercial
RF signal generators and arbs seem to have distortion specs above
-40dB, some as bad as -20.

John

So, I can tell you that I'm doing tests at +20dBm much of the time,
from about 1MHz to 100MHz. I use common SMT and axial-leaded C0G
MLCCs in various filters; some are filters I'm testing, and some are
filters I use to clean the generator output or kill the fundamental.
They range from 5th order to 11th order, typically, and generally have
zeros at specific frequencies; though I've also tested common
Butterworth and Chebychev designs too. If I assume simple second and
third order models, I can assure you that these capacitors won't even
come close to giving you trouble at your +30dBm level, down to well
below -60dBc. As far as I know, nothing goes suddenly bad between
+20dBm and +30dBm with them.

Cheers,
Tom

 

[Tom Bruhns]

One big difference: "glass capacitors exhibit
zero piezoelectric noise." (Quoting from the
AVX spec page.)

Piezoelectric effects are easy to miss with
conventional capacitor-testing equipment, like
I have, because they show up very strongly at
discrete resonance frequencies. Yes my hp4192
has a 0.1 to 1ppm frequency resolution, good
for measuring crystal parameters, etc., but
one could take forever looking for capacitor
resonances that way. I imagine a new test
jig with a sweep generator is required.

Or one stays away from C0G parts in critical
signal applications like John's filters (next
post). But, they sure are inexpensive!

Hmmm... I'm interested in distortion levels well below what John's
talking about, at levels up to +20dBm (only 10dB lower than his), and
I've never seen a hint of problem from C0G's.

Based on the low Q (relative to a crystal resonator) of ceramic
filters, I'd be really surprised if MLCCs showed all that narrow a
mechnical resonance bandwidth. Could be wrong, but it would be a
serious surprise. Actually it should be easy to see if it's there. I
can excite with random noise and look at 20kHz to 45MHz or so easily,
with 300Hz RBW or lower, and invoke a whole lot of averaging. I'm
well aware of high-K dielectrics exhibiting piezo effects, but my
impression is that C0G shows very low piezo.

Cheers,
Tom

 

[Robert Baer]

One big difference: "glass capacitors exhibit
zero piezoelectric noise." (Quoting from the
AVX spec page.)

Piezoelectric effects are easy to miss with
conventional capacitor-testing equipment, like
I have, because they show up very strongly at
discrete resonance frequencies. Yes my hp4192
has a 0.1 to 1ppm frequency resolution, good
for measuring crystal parameters, etc., but
one could take forever looking for capacitor
resonances that way. I imagine a new test
jig with a sweep generator is required.

Or one stays away from C0G parts in critical
signal applications like John's filters (next
post). But, they sure are inexpensive!

Why not try a step function?

 

[John Larkin]

So, I can tell you that I'm doing tests at +20dBm much of the time,
from about 1MHz to 100MHz. I use common SMT and axial-leaded C0G
MLCCs in various filters; some are filters I'm testing, and some are
filters I use to clean the generator output or kill the fundamental.
They range from 5th order to 11th order, typically, and generally have
zeros at specific frequencies; though I've also tested common
Butterworth and Chebychev designs too. If I assume simple second and
third order models, I can assure you that these capacitors won't even
come close to giving you trouble at your +30dBm level, down to well
below -60dBc. As far as I know, nothing goes suddenly bad between
+20dBm and +30dBm with them.

Cheers,
Tom

That's good to know. We have waveform table quantization errors (with
digital interpolation!), DAC errors, diffamp errors [1], then the
filter, and then the output amps. Distortion versus frequency and
amplitude is looking very complex, but at least the filter's caps
shouldn't be a big contributor.

John

[1] so everybody is making great "TX" dacs, 12 to 16 bits, clocks in
the hundreds of MHz, great stuff. But the outputs are differential
currents. So why don't they make compatible diff-to-single ended amps?
They make lots of them for diff-in adc's, but none for diff-out dacs.

If you make your own out of opamps, it gets messy.

Do they assume that everybody will just use transformers?

John