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Alternatives to capacitors from American Technical Ceramics

Started by Darol Klawetter December 15, 2014
I need a broadband chip capacitor (0.01uf) that has nearly ideal performanc=
e up to 3 GHz. I'm using it to AC couple the RF input of a receiver. Americ=
an Technical Ceramics manufactures capacitors (e.g., the 550 series) that h=
ave excellent performance up to 40 GHz. Of course, this comes at a cost: th=
ey are about 100 times more expensive than a standard x7r cap. I would like=
 to find something that is less expensive but would have similar performanc=
e up to 3 GHz.

Any suggestions?

Darol Klawetter
On Monday, December 15, 2014 4:28:28 PM UTC-5, Darol Klawetter wrote:
> I need a broadband chip capacitor (0.01uf) that has nearly ideal performance up to 3 GHz.
the non-idealities of the cap, inductance etc are almost all caused by the physical size. An 0402 SMT 100pF cap will be close to ideal and a 0.01uF 0402 SMT cap will actually not be that much worse because the inducatance is about the same. Are you working from below 1MHz up to 3 GHz and that is why you need 0.01uF Mark
On Mon, 15 Dec 2014 13:28:23 -0800 (PST), Darol Klawetter
<darol.klawetter@gmail.com> wrote:

>I need a broadband chip capacitor (0.01uf) that has nearly ideal performance up to 3 GHz. I'm using it to AC couple the RF input of a receiver. American Technical Ceramics manufactures capacitors (e.g., the 550 series) that have excellent performance up to 40 GHz. Of course, this comes at a cost: they are about 100 times more expensive than a standard x7r cap. I would like to find something that is less expensive but would have similar performance up to 3 GHz. > >Any suggestions? > >Darol Klawetter
3 GHz is easy. Make a controlled-impedance microstrip trace with a small gap, and bridge the gap with a regular surface-mount cap about the same width as the trace. Or use two small caps side-by-side if that fits. I've tried the expensive DiLabs super-wideband caps and they don't seem to be different from a cheapie, at least in my TDR measurement bandwidth, about 15 GHz. The rotated (0306 type) caps are even better in low-impedance, higher-speed situations. https://dl.dropboxusercontent.com/u/53724080/Parts/0306_Caps.JPG These are 2.2 uF caps, 6 cents each from Digikey. An 0306 or 0508 might bridge a 50 ohm trace nicely. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Monday, December 15, 2014 3:39:06 PM UTC-6, mako...@yahoo.com wrote:
> On Monday, December 15, 2014 4:28:28 PM UTC-5, Darol Klawetter wrote: > > I need a broadband chip capacitor (0.01uf) that has nearly ideal performance up to 3 GHz. > > > the non-idealities of the cap, inductance etc are almost all caused by the physical size. An 0402 SMT 100pF cap will be close to ideal and a 0.01uF 0402 SMT cap will actually not be that much worse because the inducatance is about the same. > > Are you working from below 1MHz up to 3 GHz and that is why you need 0.01uF > > Mark
Yes, my frequency range requires 0.01uf to 0.02uf. Anyway, the manufacturers' impedance plots I've seen indicate that the impedance of the standard chip cap can exceed 10 ohms at over 1 GHz - I want to avoid that.
On Monday, December 15, 2014 4:22:28 PM UTC-6, John Larkin wrote:
> On Mon, 15 Dec 2014 13:28:23 -0800 (PST), Darol Klawetter > <darol klawetter> wrote: >=20 > >I need a broadband chip capacitor (0.01uf) that has nearly ideal perform=
ance up to 3 GHz. I'm using it to AC couple the RF input of a receiver. Ame= rican Technical Ceramics manufactures capacitors (e.g., the 550 series) tha= t have excellent performance up to 40 GHz. Of course, this comes at a cost:= they are about 100 times more expensive than a standard x7r cap. I would l= ike to find something that is less expensive but would have similar perform= ance up to 3 GHz.
> > > >Any suggestions? > > > >Darol Klawetter >=20 > 3 GHz is easy. Make a controlled-impedance microstrip trace with a > small gap, and bridge the gap with a regular surface-mount cap about > the same width as the trace. Or use two small caps side-by-side if > that fits. >=20 > I've tried the expensive DiLabs super-wideband caps and they don't > seem to be different from a cheapie, at least in my TDR measurement > bandwidth, about 15 GHz. >=20 > The rotated (0306 type) caps are even better in low-impedance, > higher-speed situations. >=20 > https://dl.dropboxusercontent.com/u/53724080/Parts/0306_Caps.JPG >=20 > These are 2.2 uF caps, 6 cents each from Digikey. An 0306 or 0508 > might bridge a 50 ohm trace nicely. >=20 >=20 >=20 >=20 > --=20 >=20 > John Larkin Highland Technology, Inc > picosecond timing precision measurement=20 >=20 > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Thanks for the input. I'll do some bench testing to see how a standard 0402= x7r cap behaves in my application. I may also look into the rotated, low i= nductance caps you mention, though my microstrip width may not accommodate = them.
On Mon, 15 Dec 2014 15:22:42 -0800 (PST), Darol Klawetter
<darol.klawetter@gmail.com> wrote:

>On Monday, December 15, 2014 4:22:28 PM UTC-6, John Larkin wrote: >> On Mon, 15 Dec 2014 13:28:23 -0800 (PST), Darol Klawetter >> <darol klawetter> wrote: >> >> >I need a broadband chip capacitor (0.01uf) that has nearly ideal performance up to 3 GHz. I'm using it to AC couple the RF input of a receiver. American Technical Ceramics manufactures capacitors (e.g., the 550 series) that have excellent performance up to 40 GHz. Of course, this comes at a cost: they are about 100 times more expensive than a standard x7r cap. I would like to find something that is less expensive but would have similar performance up to 3 GHz. >> > >> >Any suggestions? >> > >> >Darol Klawetter >> >> 3 GHz is easy. Make a controlled-impedance microstrip trace with a >> small gap, and bridge the gap with a regular surface-mount cap about >> the same width as the trace. Or use two small caps side-by-side if >> that fits. >> >> I've tried the expensive DiLabs super-wideband caps and they don't >> seem to be different from a cheapie, at least in my TDR measurement >> bandwidth, about 15 GHz. >> >> The rotated (0306 type) caps are even better in low-impedance, >> higher-speed situations. >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/0306_Caps.JPG >> >> These are 2.2 uF caps, 6 cents each from Digikey. An 0306 or 0508 >> might bridge a 50 ohm trace nicely. >> >> >> >> >> -- >> >> John Larkin Highland Technology, Inc >> picosecond timing precision measurement >> >> jlarkin att highlandtechnology dott com >> http://www.highlandtechnology.com > >Thanks for the input. I'll do some bench testing to see how a standard 0402 x7r cap behaves in my application. I may also look into the rotated, low inductance caps you mention, though my microstrip width may not accommodate them.
It seems good to not have the cap much narrower than the trace, so the current doesn't have to crowd down into the skinny cap. But, as noted, 3 GHz isn't super fast. The "wall in the sky" here (term borrowed from Chuck Yeager's breaking the sound barrier) is around 100 ps, which is 3.5 GHz. Things are fairly easy at 100 ps, but get harder fast. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Darol Klawetter wrote:
> I need a broadband chip capacitor (0.01uf) that has nearly ideal performance up to 3 GHz. I'm using it to AC couple the RF input of a receiver. American Technical Ceramics manufactures capacitors (e.g., the 550 series) that have excellent performance up to 40 GHz. Of course, this comes at a cost: they are about 100 times more expensive than a standard x7r cap. I would like to find something that is less expensive but would have similar performance up to 3 GHz. > > Any suggestions? > > Darol Klawetter
Depends on capacitance you need. Take a ceramic cap and partly wrap copper foil around it "C-shape,cap in middle) and solder one lead to foil. The copper foil acts like a shorted turn to the internal "U"-shaped inductance of leads and capacitor.
"Darol Klawetter" <darol.klawetter@gmail.com> wrote in message 
news:ca908d35-3b94-4f2a-abf2-caf0f86f0ff2@googlegroups.com...
> > Yes, my frequency range requires 0.01uf to 0.02uf. Anyway, the > manufacturers' impedance plots I've seen indicate that the impedance of > the standard chip cap can exceed 10 ohms at over 1 GHz - I want to avoid > that. >
It's not a property of the capacitor, it's a transmission line property. As long as it's going over ground plane with the correct trace width, it should be fine. Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
On Tuesday, December 16, 2014 7:01:40 AM UTC-6, Tim Williams wrote:
> "Darol Klawetter" wrote in message > news:ca908d35-3b94-4f2a-abf2-caf0f86f0ff2@googlegroups.com... > > > > Yes, my frequency range requires 0.01uf to 0.02uf. Anyway, the > > manufacturers' impedance plots I've seen indicate that the impedance of > > the standard chip cap can exceed 10 ohms at over 1 GHz - I want to avoid > > that. > > > > It's not a property of the capacitor, it's a transmission line property. > As long as it's going over ground plane with the correct trace width, it > should be fine. > > Tim > > -- > Seven Transistor Labs > Electrical Engineering Consultation > Website: http://seventransistorlabs.com
Tim, you'll need to elaborate on your statement. ESL is capacitor dependent.
Darol Klawetter wrote:
> On Tuesday, December 16, 2014 7:01:40 AM UTC-6, Tim Williams wrote: >> "Darol Klawetter" wrote in message >> news:ca908d35-3b94-4f2a-abf2-caf0f86f0ff2@googlegroups.com... >>> Yes, my frequency range requires 0.01uf to 0.02uf. Anyway, the >>> manufacturers' impedance plots I've seen indicate that the impedance of >>> the standard chip cap can exceed 10 ohms at over 1 GHz - I want to avoid >>> that. >>> >> It's not a property of the capacitor, it's a transmission line property. >> As long as it's going over ground plane with the correct trace width, it >> should be fine. >> >> Tim >> >> -- >> Seven Transistor Labs >> Electrical Engineering Consultation >> Website: http://seventransistorlabs.com > > Tim, you'll need to elaborate on your statement. ESL is capacitor dependent.
ESL depends on size and shape, not on price and application domain, despite what some manufacturers would want us to believe. If your capacitor sits over a gap in a transmission line and has the same width as that transmission line, chances are that its ESL is nearly invisible. That got said several times over, by now. Jeroen Belleman