I entered an LC filter, with parameters F and Z which are my actual desired frequency and impedance. I use .param to calculate the L and C scaling factors, and state component values as the normalized (w=1, z=1) values times those scaling factors.
So I fiddle F and Z until I get the system response that looks good. Now the component values are right, but they are not obviously visible. To figure out what actual value I need for, say, L3, I need to pull out a calculator and reproduce the math that Spice just did.
Is there any way to see the actual, calculated parts values? Or to see the calculated values of .PARAM things?
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John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
On Wed, 06 Jan 2016 14:37:41 -0800, John Larkin wrote:
OK, I cranked it out manually, not really hard for a small filter, and then picked the closest part values that we have in stock. I got lucky on that... the response looks great.
I added a 50 ohm transmission line and mis-terminated that, to demonstrate how this filter absorbs reflections. It's pretty impressive.
Version 4 SHEET 1 1380 680 WIRE -272 96 -320 96 WIRE -224 96 -272 96 WIRE -96 96 -144 96 WIRE -64 96 -96 96 WIRE 112 96 16 96 WIRE 224 96 112 96 WIRE 448 96 304 96 WIRE 640 96 448 96 WIRE 704 96 640 96 WIRE 912 96 704 96 WIRE 1104 96 1008 96 WIRE 1168 96 1104 96 WIRE 912 128 832 128 WIRE 1088 128 1008 128 WIRE -320 144 -320 96 WIRE 448 144 448 96 WIRE 640 144 640 96 WIRE 112 160 112 96 WIRE 1168 160 1168 96 WIRE 832 192 832 128 WIRE 1088 192 1088 128 WIRE 448 256 448 208 WIRE 640 256 640 208 WIRE -320 288 -320 224 WIRE 112 288 112 224 WIRE 1168 288 1168 240 WIRE 448 384 448 336 WIRE 640 400 640 336 WIRE 448 512 448 464 FLAG -320 288 0 FLAG 1168 288 0 FLAG 112 288 0 FLAG 640 400 0 FLAG 832 192 0 FLAG 1088 192 0 FLAG 448 512 0 FLAG -272 96 GEN FLAG -96 96 IN FLAG 704 96 OUT FLAG 1104 96 LOAD SYMBOL cap 96 160 R0 WINDOW 0 70 29 Left 2 WINDOW 3 73 60 Left 2 SYMATTR InstName C2 SYMATTR Value 9p SYMBOL cap 432 144 R0 WINDOW 0 65 23 Left 2 WINDOW 3 66 60 Left 2 SYMATTR InstName Cb SYMATTR Value 3p SYMBOL ind 208 112 R270 WINDOW 0 43 61 VTop 2 WINDOW 3 -9 61 VBottom 2 SYMATTR InstName L1 SYMATTR Value 33n SYMATTR SpiceLine Rser=0 Cpar=0 SYMBOL res 1184 256 R180 WINDOW 0 -52 67 Left 2 WINDOW 3 -60 34 Left 2 SYMATTR InstName R2 SYMATTR Value 100 SYMBOL voltage -320 128 R0 WINDOW 0 68 81 Left 2 WINDOW 3 27 116 Left 2 WINDOW 123 55 153 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 1 10n 200p 200p 10n) SYMATTR Value2 AC 1 SYMATTR SpiceLine Rser=0 Cpar=0 SYMBOL tline 960 112 R0 WINDOW 0 -1 -32 Bottom 2 WINDOW 3 6 37 Top 2 SYMATTR InstName T1 SYMATTR Value Td=15n Z0=50 SYMBOL cap 624 144 R0 WINDOW 0 69 23 Left 2 WINDOW 3 70 59 Left 2 SYMATTR InstName Ca SYMATTR Value 5p SYMBOL res 624 240 R0 WINDOW 0 71 50 Left 2 WINDOW 3 72 84 Left 2 SYMATTR InstName Ra SYMATTR Value 50 SYMBOL ind 432 240 R0 WINDOW 0 68 42 Left 2 WINDOW 3 66 77 Left 2 SYMATTR InstName Lb SYMATTR Value 22n SYMATTR SpiceLine Rser=0 Cpar=0 SYMBOL res 432 368 R0 WINDOW 0 69 46 Left 2 WINDOW 3 66 80 Left 2 SYMATTR InstName Rb SYMATTR Value 121 SYMBOL res -128 80 R90 WINDOW 0 -12 56 VBottom 2 WINDOW 3 43 57 VTop 2 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL ind -80 112 R270 WINDOW 0 42 57 VTop 2 WINDOW 3 -7 59 VBottom 2 SYMATTR InstName L3 SYMATTR Value 8.2n SYMATTR SpiceLine Rser=0 Cpar=0 TEXT -328 352 Left 2 ;3-pole Reflectionless Lin-Phase EquiRipple Lowpass TEXT 832 328 Left 2 !.tran 0 100n 0 10p TEXT -208 400 Left 2 ;(Jeroen Belleman's design) TEXT -248 448 Left 2 ;JL Jan 6, 2016 MAX stock parts TEXT 832 368 Left 2 !;ac dec 100 20Meg 2G TEXT -296 488 Left 2 ;350 MHz 50R Tr 1.0ns -28 dB at 1 GHz
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John Larkin Highland Technology, Inc
lunatic fringe electronics
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