Multilayer ceramic chip capacitor for op amp active fiter

[Steve]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

 

[PeteS]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

MLCC device capacitance varies quite widely with applied voltage. A X5R
will typically be at 50% nominal capacitance at 90% rated voltage. I
somewhere have a graph of such things.

My rule for MLCC devices [1] is never to run them above 50% rated
voltage and not use anything worse than X5R except where I can live
with +20/-80% variations across temperature and -80% across the applied
voltage range (typical Y5V).

[1]. As with all rules, I break it on occasion

Cheers

PeteS

 

[Gareth]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ?

Capacitance change with voltage will result in distortion of your signal.

There are different types of ceramic capacitor - basically, you can have
low capacitance values and high quality, or large values and low quality.

NP0 and C0G are the most stable and will cause the least distortion to
your signal (compared to other ceramic types, I'm not sure how they
compare to polyester etc.). Unfortunately, these are not usually
available in large values, and if they are, they will be physically
larger than the other types of ceramic cap of the same value. You could
put a few in parallel , but that will obviously increase size and cost.

X7R is not as stable, but you can get higher capacitance than C0G for a
fixed size. X5R and X8R are very similar, but the max operating temp is
lower for X5R and higher for X8R. If you are not too worried about
distortion, these could be ok. I expect that the 10uF +/- 10% caps you
mention are X5R or X7R.

Y5V is not very stable but does offer large values in small sizes. I
would NOT use these in a filter (or anything else).

It is the usual compromise between size, cost and performance.

The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

--

 

[John Popelish]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

If the tolerance is good enough, it will probably work, The
very high K types (Y5V, Z5U, F) will change capacitance a
lot with both temperature and voltage, but show this as a
wide tolerance. The X5R and X7R are pretty good, especially
if you can find units that handle a bit more voltage than
your circuit will apply.

Read the data sheet and look for graphs of capacitance
versus both voltage and temperature.

Take a look at the Panasonic ECJ-3YB1E106K, 10 uF, 1206
size, X5R, 25 V 10%, $0.55 each from Digikey.
http://www.panasonic.com/industrial/components/pdf/abj0000ce4.pdf

 

[Eeyore]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ?
Yes.

Is capacitance change with voltage an
issue ?
Yes.

The filters will be used at room temperature with little
temperature variation.

Hi-K ceramic caps are norotiously non-linear.

See http://members.aol.com/sbench102/caps.html
http://members.aol.com/sbench102/caps2.html

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Film caps are fine. Polyester will do the jon nicely. The above link is
incorrectly critical of polyester btw - the test method is slightly flawed.

Graham

 

[Tom Bruhns]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

Can you use higher resistor values, so you can use lower capacitor
values? If so, C0G ceramics may become possible. You can get them in
excess of 0.1uF these days. They tend to be pricey.

Beware that capacitors with dielectric absorption will add to the
non-ideal behaviour at low frequencies. AFAIK, C0G are low dielectric
absorption, as are polypropylene. I came across another dielectric
that I'm not remembering right now that's also good--not one of the
"usual suspects." Mylar/polyester are not particularly good. The
non-ideal behaviour in this case is that the capacitors will look
smaller in value to high frequencies than to low; it's still generally
a linear effect, at least, unlike the voltage-dependence of the high-K
ceramics.

In the distant past, I inherited a partially-done (barely begun) design
requiring some low-frequency filtering, four channels of 8 poles each
on a business-card size board, and the filters had to have selectable
cutoff frequencies. I soon discovered that the required parts would
NOT fit, and the performance using those parts would be disappointing
at best. Instead, I ended up digitizing the input and passing it
through a small DSP, and back out to ADCs. That was before the days of
codecs; now the parts are so good and small, it seems it would be a
very reasonable way to do it if you want to keep things small. Power
might be an issue for you, though; narrow bandwidth op amps are pretty
low power compared with DSPs.

Cheers,
Tom

 

[[email protected]]

Hi-K ceramic caps are norotiously non-linear.

See http://members.aol.com/sbench102/caps.html
http://members.aol.com/sbench102/caps2.html



Film caps are fine. Polyester will do the jon nicely. The above link is
incorrectly critical of polyester btw - the test method is slightly flawed.

Graham

I'm surprised no one has mentioned that hi-k ceramic caps are
microphonic[1], which may be undesirable depending on the filter's
application. Mechanical vibration, for example, could manifest as
electrical noise.

[1] Besides making decent 'varactors,' they're microphonic enough that
I've considered using them as cheapie transducers.

Best,
James Arthur

 

[Steve]

Can you use higher resistor values, so you can use lower capacitor
values? If so, C0G ceramics may become possible. You can get them in
excess of 0.1uF these days. They tend to be pricey.

Beware that capacitors with dielectric absorption will add to the
non-ideal behaviour at low frequencies. AFAIK, C0G are low dielectric
absorption, as are polypropylene. I came across another dielectric
that I'm not remembering right now that's also good--not one of the
"usual suspects." Mylar/polyester are not particularly good. The
non-ideal behaviour in this case is that the capacitors will look
smaller in value to high frequencies than to low; it's still generally
a linear effect, at least, unlike the voltage-dependence of the high-K
ceramics.

Tom,

I am using Texas Instrument's Filter Pro software and designing a 4
pole high pass MFB filter. With R1 seed at 100 k, it generates
capacitance values of 15 uF. and feedback R1 values of 174 k and 412
k. WIth R1 seed as 1 M, the generated capacitance values drop to 1.5
uF and the R1 increases to 1.74 M and 4.12 M. I am using a quad OPA
4277 op amp. Any sugestions on op am parameters to watch out for when
dealing with such high feedback resistor values ?

How high a frequency is needed before capacitors with dielectric
absorption begin to show lower capacitance ? i.e. If I am working
with 1 Hz filter frequencies, are the offending frequencies always so
high that they will always be beyond the filter's cutoff frequency
even if the capacitance value changes and effects the actual cutoff
frequency ?

Steve

 

[joseph2k]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

MLCC device capacitance varies quite widely with applied voltage. A X5R
will typically be at 50% nominal capacitance at 90% rated voltage. I
somewhere have a graph of such things.

My rule for MLCC devices [1] is never to run them above 50% rated
voltage and not use anything worse than X5R except where I can live
with +20/-80% variations across temperature and -80% across the applied
voltage range (typical Y5V).

[1]. As with all rules, I break it on occasion

Cheers

PeteS

Yeow, that is a lot of detuning versus voltage. That is reason enough for
me to skip MLC for this purpose.

 

[John Popelish]

I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve

MLCC device capacitance varies quite widely with applied voltage. A X5R
will typically be at 50% nominal capacitance at 90% rated voltage. I
somewhere have a graph of such things.

My rule for MLCC devices [1] is never to run them above 50% rated
voltage and not use anything worse than X5R except where I can live
with +20/-80% variations across temperature and -80% across the applied
voltage range (typical Y5V).

[1]. As with all rules, I break it on occasion

Cheers

PeteS

Yeow, that is a lot of detuning versus voltage. That is reason enough for
me to skip MLC for this purpose.

Except that it isn't true. An X5R capacitor speced for 10%
tolerance will have within 10% of its rated capacitance over
its voltage and temperature range. Only Y5V or Z5U and
other very high K types will show such extreme capacitance
variations with applied voltage. And if you want to keep
the voltage effects low with the X5R or X7R types, just get
capacitors that have at least twice the voltage rating
needed. i.e. 25 volt capacitor for 10 volt operation.

 

[PeteS]

Steve wrote:
I am designing low and high pass op amp (+/- 15V) based active filters
near 1 Hz that require capacitor values between 1 and 10 uF. Are
there any reasons to not use surface mount multilayer ceramic chip
capacitors in such a design ? Is capacitance change with voltage an
issue ? The filters will be used at room temperature with little
temperature variation.

Multilayer ceramic chip capacitors are available in values to 10 uF or
higher with +/- 10% tolerances and lead spacings of a few millimeters
for $1. Is it better to use metalized polypropylene or metalized
polyester even though they are more expensive and have much larger
lead spacing (up to 1 inch) ? Examples inlcude Panasonic ECQ-E(B) or
ECQ-E(F) series and Epcos MKT series, available at 5% or even better
tolerance.

Thanks,

Steve
MLCC device capacitance varies quite widely with applied voltage. A X5R
will typically be at 50% nominal capacitance at 90% rated voltage. I
somewhere have a graph of such things.

My rule for MLCC devices [1] is never to run them above 50% rated
voltage and not use anything worse than X5R except where I can live
with +20/-80% variations across temperature and -80% across the applied
voltage range (typical Y5V).

[1]. As with all rules, I break it on occasion

Cheers

PeteS

Yeow, that is a lot of detuning versus voltage. That is reason enough
for
me to skip MLC for this purpose.

Except that it isn't true.

Um - it is.

A capacitor is tolerance rated separately for capacitance across
temperature and across voltage.

I have some really nice Murata, Kemet and Panasonic datasheets and they
show clearly the variation of capacitance of the various types across
rated voltage.

C0G (as one might expect) does best, with no more than 10% decrease
(typically) of capacitance across the working voltage range. Y5V / Z5U
do pretty horrendously, with a typical 70% - 90% decrease in capacitance
at rated voltage. Note that this is independent of the temperature spec.

I noted that I overspec by a factor of 2 on DCWV for this very reason.

Cheers

PeteS


An X5R capacitor speced for 10% tolerance

 

[John Popelish]

A capacitor is tolerance rated separately for capacitance across
temperature and across voltage.

(snip)
Thanks for correcting my misunderstanding.

I found a rough graph of the effect on page 3 of this Kemet
application note:
http://www.kemet.com/kemet/web/home...C36CF87BBCCA2570A50016092B/$file/F3102_CE.pdf

According to this, the X7R types do pretty well as long as
you stay below about 30% of rated voltage.

 

[John Popelish]

(snip)
Thanks for correcting my misunderstanding.

I found a rough graph of the effect on page 3 of this Kemet application
note:
http://www.kemet.com/kemet/web/home...C36CF87BBCCA2570A50016092B/$file/F3102_CE.pdf


According to this, the X7R types do pretty well as long as you stay
below about 30% of rated voltage.

.... and more details of ceramic capacitor dielectric properties:

http://www.vishay.com/docs/45156/elecdata.pdf

 

[Al]

... and more details of ceramic capacitor dielectric properties:

http://www.vishay.com/docs/45156/elecdata.pdf

Also you should know that ceramic caps. are piezoelectric devices. They
will generate noise when flexed. If your application will be subjected
to vibration, noise may be induced into your circuit by flexing of the
board on which the ceramics are mounted. If they are lead mounted, not
to worry.

I worked on a program that had this problem a number of years ago. The
noise from the caps. was sufficient to cause noise in a modulation
circuit. The application was shipboard....on a carrier.

Al

 

[Tom Bruhns]

I am using Texas Instrument's Filter Pro software and designing a 4
pole high pass MFB filter. With R1 seed at 100 k, it generates
capacitance values of 15 uF. and feedback R1 values of 174 k and 412
k. WIth R1 seed as 1 M, the generated capacitance values drop to 1.5
uF and the R1 increases to 1.74 M and 4.12 M. I am using a quad OPA
4277 op amp. Any sugestions on op am parameters to watch out for when
dealing with such high feedback resistor values ?

How high a frequency is needed before capacitors with dielectric
absorption begin to show lower capacitance ? i.e. If I am working
with 1 Hz filter frequencies, are the offending frequencies always so
high that they will always be beyond the filter's cutoff frequency
even if the capacitance value changes and effects the actual cutoff
frequency ?

(Sorry for the delayed reply...I missed seeing your followup before.)

When you go to higher resistances, voltage noise gets worse. If that's
an issue, you'll need to put some amplification ahead of the filter
stage, to get the signal far enough above the noise. Op amps with
extremely low current noise help: those will generally be JFET-input
op amps. There's also the advantage that input bias current is low, so
that higher resistance values won't cause too much additional DC offset
voltage. Look out, too, for 1/f noise corner frequencies that are too
high. If offsets and very low frequency noise are issues for you, you
could consider chopper-stabilized CMOS amplifiers, but they get
expensive I suppose. In laying out the circuit, work to keep circuit
areas small so that noise has less chance to be picked up. Some sort
of electrostatic shielding may be in order. You mentioned it's a HPF,
so of course, you need to maintain bandwidth out to whatever your
application dictates.

Dielectric absorption can be modelled as an ideal capacitor in parallel
with several copies of a series R-C, where each C is small compared
with the ideal cap, and the R-C time constants of each vary over a
range generally from milliseconds to many seconds. So the effect is
seen as a gradually changing capacitance versus frequency, if you look
at it in the frequency domain.

I'm not sure what topology your filter software is using, but you may
find some advantage to using a state variable topology. The
integrators can be high impedance, and their low-pass characteristic
will keep noise out of the feedback path. The feedback path itself can
be kept low impedance, to keep wideband noise down and to make the
circuit less sensitive to electrostatic coupling from outside. The
higher parts count may be worth it! It will take four integrators to
get your four poles: four capacitors, four op amps. Add to that the
amps to sum the feedback with the stage's input signal, for two stages.

Cheers,
Tom