On Mon, 5 Sep 2022 10:00:15 +1000, Clifford Heath <no_spam@please.net> wrote:>On 4/9/22 06:29, jlarkin@highlandsniptechnology.com wrote: >> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" >> <jmiles@gmail.com> wrote: >>> One of the things I've learned fairly recently is that discrete LC filters are a >>> bag of hurt when it comes to production. I used to use a lot of packaged >>> Mini-Circuits elliptic filters until the last project, when I got tired of paying >>> for them. I can run a filter design program just as well as they can, right? >> >> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I >> want a 15 MHz filter so I'll have to make it. >> >> It's strange that nobody makes a series of lp filters aimed at the DDS >> market. > >It's difficult to build good LC filters in SMD for HF. The multi-layer >inductors that work fine at UHF just don't have the required Q at lower >frequencies. > >I designed a nice-looking 7th order bandpass filter for 50MHz, then >started looking for SMD parts to realise it. Stick the actual Q values >into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really >quickly. > >Coilcraft make suitable small inductors that are wound, not multi-layer, >but you pay a lot more for that.Well, 20 cents in quantity for a 0805, 30 cents for the midi springs. They do great stuff and are generous with samples.> >Clifford HeathThere are lowpass filters that are designed around finite-Q parts; Williams has tables for some. The math is even nastier than ideal filters. But a DDS filter doesn't need a beautifully flat frequency response graph. It drives a comparator.
DDS differential filter
Started by ●September 1, 2022
Reply by ●September 14, 20222022-09-14
Reply by ●September 18, 20222022-09-18
On 14/9/22 14:35, Simon S Aysdie wrote:> On Sunday, September 4, 2022 at 5:00:24 PM UTC-7, Clifford Heath wrote: >> On 4/9/22 06:29, jla...@highlandsniptechnology.com wrote: >>> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" >>> <jmi...@gmail.com> wrote: >>>> One of the things I've learned fairly recently is that discrete LC filters are a >>>> bag of hurt when it comes to production. I used to use a lot of packaged >>>> Mini-Circuits elliptic filters until the last project, when I got tired of paying >>>> for them. I can run a filter design program just as well as they can, right? >>> >>> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I >>> want a 15 MHz filter so I'll have to make it. >>> >>> It's strange that nobody makes a series of lp filters aimed at the DDS >>> market. >> It's difficult to build good LC filters in SMD for HF. The multi-layer >> inductors that work fine at UHF just don't have the required Q at lower >> frequencies. >> >> I designed a nice-looking 7th order bandpass filter for 50MHz, then >> started looking for SMD parts to realise it. Stick the actual Q values >> into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really >> quickly. >> >> Coilcraft make suitable small inductors that are wound, not multi-layer, >> but you pay a lot more for that. > > By "7th order bandpass" I'll guess you mean 7 resonators. BPF are usually even order. Anyway, you're right that wirewound CCI will be more expensive than multilayer. Multilyers are rarely good enough for bandpass filters. > > Just to experiment, I hacked out a 5-coil 10% 50 MHz BPF using 82 nH MIDI (1812SMS-82NGL_) coils, just to experiment. > > features > * 50 MHz center freq > * 10% nominal BW (b4 non-idealities) > * 20 dB nominal return loss > * all 5 coils coerced to 82 nH > (coercion "paid for" with additional caps) > * 5 finite transmission zeros > * Coil Q: guess 80 (midi spring) > * Cap Q: guess 250 > * All internal nodes have design capacitance to ground > (enable absorbtion of parasitic capacitance; costs caps)I didn't respond previously because that LTSpice doesn't work for me. It displays and appears to run the sim, but then I can't probe anywhere to view a trace. Has anyone else seen this behaviour or knows how to fix it? CH
Reply by ●September 18, 20222022-09-18
On Sunday, September 18, 2022 at 8:19:42 PM UTC-4, Clifford Heath wrote:> On 14/9/22 14:35, Simon S Aysdie wrote: > > On Sunday, September 4, 2022 at 5:00:24 PM UTC-7, Clifford Heath wrote: > >> On 4/9/22 06:29, jla...@highlandsniptechnology.com wrote: > >>> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" > >>> <jmi...@gmail.com> wrote: > >>>> One of the things I've learned fairly recently is that discrete LC filters are a > >>>> bag of hurt when it comes to production. I used to use a lot of packaged > >>>> Mini-Circuits elliptic filters until the last project, when I got tired of paying > >>>> for them. I can run a filter design program just as well as they can, right? > >>> > >>> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I > >>> want a 15 MHz filter so I'll have to make it. > >>> > >>> It's strange that nobody makes a series of lp filters aimed at the DDS > >>> market. > >> It's difficult to build good LC filters in SMD for HF. The multi-layer > >> inductors that work fine at UHF just don't have the required Q at lower > >> frequencies. > >> > >> I designed a nice-looking 7th order bandpass filter for 50MHz, then > >> started looking for SMD parts to realise it. Stick the actual Q values > >> into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really > >> quickly. > >> > >> Coilcraft make suitable small inductors that are wound, not multi-layer, > >> but you pay a lot more for that. > > > > By "7th order bandpass" I'll guess you mean 7 resonators. BPF are usually even order. Anyway, you're right that wirewound CCI will be more expensive than multilayer. Multilyers are rarely good enough for bandpass filters. > > > > Just to experiment, I hacked out a 5-coil 10% 50 MHz BPF using 82 nH MIDI (1812SMS-82NGL_) coils, just to experiment. > > > > features > > * 50 MHz center freq > > * 10% nominal BW (b4 non-idealities) > > * 20 dB nominal return loss > > * all 5 coils coerced to 82 nH > > (coercion "paid for" with additional caps) > > * 5 finite transmission zeros > > * Coil Q: guess 80 (midi spring) > > * Cap Q: guess 250 > > * All internal nodes have design capacitance to ground > > (enable absorbtion of parasitic capacitance; costs caps) > I didn't respond previously because that LTSpice doesn't work for me. It > displays and appears to run the sim, but then I can't probe anywhere to > view a trace. > > Has anyone else seen this behaviour or knows how to fix it?Why not use the excellent tool debugging features in LTspice? Oh, that's right, they don't have any. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
Reply by ●September 19, 20222022-09-19
On Sunday, September 18, 2022 at 5:19:42 PM UTC-7, Clifford Heath wrote:> On 14/9/22 14:35, Simon S Aysdie wrote: > > On Sunday, September 4, 2022 at 5:00:24 PM UTC-7, Clifford Heath wrote: > >> On 4/9/22 06:29, jla...@highlandsniptechnology.com wrote: > >>> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" > >>> <jmi...@gmail.com> wrote: > >>>> One of the things I've learned fairly recently is that discrete LC filters are a > >>>> bag of hurt when it comes to production. I used to use a lot of packaged > >>>> Mini-Circuits elliptic filters until the last project, when I got tired of paying > >>>> for them. I can run a filter design program just as well as they can, right? > >>> > >>> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I > >>> want a 15 MHz filter so I'll have to make it. > >>> > >>> It's strange that nobody makes a series of lp filters aimed at the DDS > >>> market. > >> It's difficult to build good LC filters in SMD for HF. The multi-layer > >> inductors that work fine at UHF just don't have the required Q at lower > >> frequencies. > >> > >> I designed a nice-looking 7th order bandpass filter for 50MHz, then > >> started looking for SMD parts to realise it. Stick the actual Q values > >> into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really > >> quickly. > >> > >> Coilcraft make suitable small inductors that are wound, not multi-layer, > >> but you pay a lot more for that. > > > > By "7th order bandpass" I'll guess you mean 7 resonators. BPF are usually even order. Anyway, you're right that wirewound CCI will be more expensive than multilayer. Multilyers are rarely good enough for bandpass filters. > > > > Just to experiment, I hacked out a 5-coil 10% 50 MHz BPF using 82 nH MIDI (1812SMS-82NGL_) coils, just to experiment. > > > > features > > * 50 MHz center freq > > * 10% nominal BW (b4 non-idealities) > > * 20 dB nominal return loss > > * all 5 coils coerced to 82 nH > > (coercion "paid for" with additional caps) > > * 5 finite transmission zeros > > * Coil Q: guess 80 (midi spring) > > * Cap Q: guess 250 > > * All internal nodes have design capacitance to ground > > (enable absorbtion of parasitic capacitance; costs caps) > I didn't respond previously because that LTSpice doesn't work for me. It > displays and appears to run the sim, but then I can't probe anywhere to > view a trace. > > Has anyone else seen this behaviour or knows how to fix it?Hi Clifford, Only s11 and s21 are saved via .SAVE .... Simply comment it away (or delete) if you want all the nets. I rarely use the rest of the nets for this sort of thing. Sorry--habit!
Reply by ●September 19, 20222022-09-19
On Sunday, September 18, 2022 at 6:48:38 PM UTC-7, Ricky wrote:> On Sunday, September 18, 2022 at 8:19:42 PM UTC-4, Clifford Heath wrote:> > Has anyone else seen this behaviour or knows how to fix it? > Why not use the excellent tool debugging features in LTspice? Oh, that's right, they don't have any.It isn't a bug--a debugger would not help.
Reply by ●September 21, 20222022-09-21
On 14/9/22 14:35, Simon S Aysdie wrote:> On Sunday, September 4, 2022 at 5:00:24 PM UTC-7, Clifford Heath wrote: >> On 4/9/22 06:29, jla...@highlandsniptechnology.com wrote: >>> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" >>> <jmi...@gmail.com> wrote: >>>> One of the things I've learned fairly recently is that discrete LC filters are a >>>> bag of hurt when it comes to production. I used to use a lot of packaged >>>> Mini-Circuits elliptic filters until the last project, when I got tired of paying >>>> for them. I can run a filter design program just as well as they can, right? >>> >>> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I >>> want a 15 MHz filter so I'll have to make it. >>> >>> It's strange that nobody makes a series of lp filters aimed at the DDS >>> market. >> It's difficult to build good LC filters in SMD for HF. The multi-layer >> inductors that work fine at UHF just don't have the required Q at lower >> frequencies. >> >> I designed a nice-looking 7th order bandpass filter for 50MHz, then >> started looking for SMD parts to realise it. Stick the actual Q values >> into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really >> quickly. >> >> Coilcraft make suitable small inductors that are wound, not multi-layer, >> but you pay a lot more for that. > > By "7th order bandpass" I'll guess you mean 7 resonators. BPF are usually even order. Anyway, you're right that wirewound CCI will be more expensive than multilayer. Multilyers are rarely good enough for bandpass filters. > > Just to experiment, I hacked out a 5-coil 10% 50 MHz BPF using 82 nH MIDI (1812SMS-82NGL_) coils, just to experiment. > > features > * 50 MHz center freq > * 10% nominal BW (b4 non-idealities) > * 20 dB nominal return loss > * all 5 coils coerced to 82 nH > (coercion "paid for" with additional caps) > * 5 finite transmission zeros > * Coil Q: guess 80 (midi spring) > * Cap Q: guess 250 > * All internal nodes have design capacitance to ground > (enable absorbtion of parasitic capacitance; costs caps)Just got back to this now. Thanks for pointing out the .SAVE thing I'd overlooked. And you're right, I meant 7 resonators. That does work nicely Simon. I haven't played with the capacitor tolerances, to see what standard values (or pairs, paralleled) would be usable. I'm curious what you used to design this? Clifford Heath.
Reply by ●September 22, 20222022-09-22
On Wednesday, September 21, 2022 at 4:37:01 PM UTC-7, Clifford Heath wrote:> On 14/9/22 14:35, Simon S Aysdie wrote: > > On Sunday, September 4, 2022 at 5:00:24 PM UTC-7, Clifford Heath wrote: > >> On 4/9/22 06:29, jla...@highlandsniptechnology.com wrote: > >>> On Sat, 3 Sep 2022 12:47:45 -0700 (PDT), "John Miles, KE5FX" > >>> <jmi...@gmail.com> wrote: > >>>> One of the things I've learned fairly recently is that discrete LC filters are a > >>>> bag of hurt when it comes to production. I used to use a lot of packaged > >>>> Mini-Circuits elliptic filters until the last project, when I got tired of paying > >>>> for them. I can run a filter design program just as well as they can, right? > >>> > >>> The mini-ckts mlcc flters are great, but start around 1 GHz or so. I > >>> want a 15 MHz filter so I'll have to make it. > >>> > >>> It's strange that nobody makes a series of lp filters aimed at the DDS > >>> market. > >> It's difficult to build good LC filters in SMD for HF. The multi-layer > >> inductors that work fine at UHF just don't have the required Q at lower > >> frequencies. > >> > >> I designed a nice-looking 7th order bandpass filter for 50MHz, then > >> started looking for SMD parts to realise it. Stick the actual Q values > >> into LTSpice and weep. 1dB pass-band loss turns into 60dB loss really > >> quickly. > >> > >> Coilcraft make suitable small inductors that are wound, not multi-layer, > >> but you pay a lot more for that. > > > > By "7th order bandpass" I'll guess you mean 7 resonators. BPF are usually even order. Anyway, you're right that wirewound CCI will be more expensive than multilayer. Multilyers are rarely good enough for bandpass filters. > > > > Just to experiment, I hacked out a 5-coil 10% 50 MHz BPF using 82 nH MIDI (1812SMS-82NGL_) coils, just to experiment. > > > > features > > * 50 MHz center freq > > * 10% nominal BW (b4 non-idealities) > > * 20 dB nominal return loss > > * all 5 coils coerced to 82 nH > > (coercion "paid for" with additional caps) > > * 5 finite transmission zeros > > * Coil Q: guess 80 (midi spring) > > * Cap Q: guess 250 > > * All internal nodes have design capacitance to ground > > (enable absorbtion of parasitic capacitance; costs caps) > Just got back to this now. Thanks for pointing out the .SAVE thing I'd > overlooked. And you're right, I meant 7 resonators. > > That does work nicely Simon. I haven't played with the capacitor > tolerances, to see what standard values (or pairs, paralleled) would be > usable.Yeah, to get serious about it, that would need to be done. But it is doable. As a play-thing w/ arbitrary specs, I did not do any sensitivity work. A premium was placed on getting all coils identical, and using as few as possible. Caps are the price. Some may need "doubling," as you say.> I'm curious what you used to design this?filsyn ---------------------------- This is the same, but with very hi Q -- the "native" design Version 4 SHEET 1 6120 3588 WIRE 496 -736 432 -736 WIRE 624 -736 560 -736 WIRE 1488 -736 1424 -736 WIRE 1616 -736 1552 -736 WIRE 2352 -736 2288 -736 WIRE 2480 -736 2416 -736 WIRE 208 -672 -240 -672 WIRE 368 -672 272 -672 WIRE 432 -672 432 -736 WIRE 432 -672 368 -672 WIRE 624 -672 624 -736 WIRE 688 -672 624 -672 WIRE 784 -672 688 -672 WIRE 960 -672 848 -672 WIRE 1168 -672 960 -672 WIRE 1232 -672 1168 -672 WIRE 1360 -672 1296 -672 WIRE 1424 -672 1424 -736 WIRE 1424 -672 1360 -672 WIRE 1616 -672 1616 -736 WIRE 1712 -672 1616 -672 WIRE 2032 -672 1712 -672 WIRE 2096 -672 2032 -672 WIRE 2224 -672 2160 -672 WIRE 2288 -672 2288 -736 WIRE 2288 -672 2224 -672 WIRE 2480 -672 2480 -736 WIRE 2544 -672 2480 -672 WIRE 2592 -672 2544 -672 WIRE 3056 -672 2656 -672 WIRE 432 -608 432 -672 WIRE 480 -608 432 -608 WIRE 624 -608 624 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45.940816p SYMATTR SpiceLine Rser=1e-12 SYMBOL cap 2560 -480 M0 SYMATTR InstName C17 SYMATTR Value 70.752997p SYMATTR SpiceLine Rser=1e-12 SYMBOL cap 2656 -688 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C18 SYMATTR Value 104.602713p SYMATTR SpiceLine Rser=1e-12 TEXT -1312 -2784 Left 2 ;o TEXT 5416 1528 Left 2 ;o TEXT -232 -856 Left 2 !.net I(R_load00) Vsrc00 TEXT -240 -792 Left 2 !.SAVE S11(vsrc00) S21(vsrc00) TEXT -216 -912 Left 2 !.ac lin 3801 10e6 200e6 TEXT 448 -1024 Left 2 ;"10% BW" 50 MHz BPF\nQL = very hi\nQC = very hi
