C-multiplier again
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From: Mike on 25 May 2010 10:54 George Herold <gherold(a)teachspin.com> wrote: [...] > Hi Mike, Would you mind telling me how I dump this into LT spice. > I�m not a spice virgin.... but I am still a newlywed. > > Thanks, > > George H. Hi George - here's how: 1. Select the listing with your mouse. 2. Press Ctrl-C to copy the selected block to the clipboard. 3. Open any plain ascii text editor such as NotePad or EditPad. 4. Paste the selected text into the word processor with Ctrl-V. 5. Use "Save As" to save the file to a suitable folder. Use the file extension ".asc" to run it in LTspice. 6. Repeat if there is a plot file, using the ".plt" extension. If you have installed LTspice and associated the ASC file extension, all you need to do is select the file in MS Explorer and it will load the file into LTspice. If you have not associated the file extensions, then load LTspice and use the Open File command to locate and run the file. Please repost if you have any problems. Mike
From: Mike on 25 May 2010 11:30 == Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: [...] > The Early effect causes problems at higher currents, because it > adds a conductance that's more or less proportional to the emitter > current. > That makes a difference, especially if the base resistor is too > big, so that the base current change causes an output voltage > change. > Lots of Spice models don't handle it well IME. Slower, bigger, > higher voltage transistors have higher Early voltages. Big fat > ceramics (10 uF) are good for the output cap. > I've used MPSA14s to cut 50 mV of 10 kHz ripple down to a nanovolt > or two in real circuits. I couldn't do a lot of what I do without > cap multipliers. > Cheers > Phil Hobbs Thanks, that new info makes a big difference. When you said to use a BFC capacitor on the emitter, I thought you meant a big capacitor, so I looked at electrolytics above 1000uF. These have a series resonance somewhere around 100KHz, and it made the C-E capacitance only affect the high side of the bathtub curve. There was no capacitance ratio effect that you mentioned earlier. However, a 10uF ceramic has a much higher series resonance frequency, and this changes the entire picture. I'm including a fairly long LTspice file that describes it. Here's a description of the output signals: Vout1 : This uses the Fairchild spice model for the MPSA14. It shows that spice cannot model the conductance properly in a bjt series pass element, as you stated. Vout2 : Using the numbers from your previous posts, the attenuation is 20*log(2e-9/50e-3) = -147.95 dB. Using a 10uF emitter capacitor, the MPSA14 can be modeled as a simple 60 megohm resistor in parallel with a 400 femtofarad capacitor. This produces a shelf at -146.95 dB from about 10KHz to just over 1 MHz. The attenuation is the ratio of the two capacitors, just as you said earlier. Vout3 : Now that we have a more realistic model for the MPSA14, it is useful to try it with a large electrolytic. Low ESR caps are now very common. I used a Nic Components Corp. aluminum electrolytic NRE-HL332M16V12.5x35F, 3300uf, 0.020 Ohm @ 100KHz, listed in page 3 of http://www.niccomp.com/Catalog/nrehl.pdf. This shows a dramatic improvement of about 50 dB for frequencies below 10KHz. (Ignore the -190dB at 6KHz:) Vout4: The 10uF ceramic works well for the higher frequencies, but it doesn't do much for frequencies below 10KHz. Here's the effect of using a large electrolytic in parallel with the 10uF ceramic. There is a huge reduction below 10KHz, and a significant reduction all the way up to 300KHz. So for the price of a plain electrolytic you can probably find in your junkbox, you can get a major improvement in attenuation. This might also apply to the reference filter. Of course, as Joerg always recommends, add diodes to protect against hard shorts. Regards, Mike Here's the file. There might be prolems due to line wrap: Version 4 SHEET 1 1140 1108 WIRE -256 -416 -272 -416 WIRE 16 -416 -176 -416 WIRE 112 -416 16 -416 WIRE 144 -416 112 -416 WIRE 384 -416 144 -416 WIRE 480 -416 384 -416 WIRE 576 -416 480 -416 WIRE 672 -416 576 -416 WIRE 768 -416 672 -416 WIRE 864 -416 768 -416 WIRE 16 -384 16 -416 WIRE 384 -352 384 -416 WIRE 576 -352 576 -416 WIRE 768 -352 768 -416 WIRE -48 -336 -112 -336 WIRE 144 -336 144 -416 WIRE 480 -336 480 -416 WIRE 672 -336 672 -416 WIRE 864 -336 864 -416 WIRE -272 -304 -272 -416 WIRE -112 -304 -112 -336 WIRE 32 -288 16 -288 WIRE 80 -288 32 -288 WIRE 32 -224 32 -288 WIRE 48 -224 32 -224 WIRE 144 -224 144 -240 WIRE 144 -224 128 -224 WIRE 240 -224 144 -224 WIRE 256 -224 240 -224 WIRE 384 -224 384 -272 WIRE 432 -224 384 -224 WIRE 480 -224 480 -272 WIRE 480 -224 432 -224 WIRE 576 -224 576 -272 WIRE 624 -224 576 -224 WIRE 672 -224 672 -272 WIRE 672 -224 624 -224 WIRE 768 -224 768 -272 WIRE 816 -224 768 -224 WIRE 864 -224 864 -272 WIRE 864 -224 816 -224 WIRE -272 -208 -272 -224 WIRE -112 -208 -112 -224 WIRE 256 -208 256 -224 WIRE 384 -208 384 -224 WIRE 576 -208 576 -224 WIRE 768 -208 768 -224 WIRE 864 -208 864 -224 WIRE 144 -160 144 -224 WIRE 256 -128 256 -144 WIRE 384 -128 384 -144 WIRE 576 -128 576 -144 WIRE 768 -128 768 -144 WIRE 864 -128 864 -144 WIRE 144 -64 144 -80 WIRE 256 -32 256 -48 WIRE 384 -32 384 -48 WIRE 576 -32 576 -48 WIRE 768 -32 768 -48 WIRE 864 -32 864 -48 WIRE 256 64 256 48 WIRE 384 64 384 48 WIRE 576 64 576 48 WIRE 768 64 768 48 WIRE 864 64 864 48 FLAG -112 -208 0 FLAG -272 -208 0 FLAG 144 -64 0 FLAG 112 -416 Vin FLAG 240 -224 Vout1 FLAG 256 64 0 FLAG 432 -224 Vout2 FLAG 384 64 0 FLAG 624 -224 Vout3 FLAG 576 64 0 FLAG 816 -224 Vout4 FLAG 768 64 0 FLAG 864 64 0 SYMBOL npn 80 -336 R0 SYMATTR InstName Q1 SYMATTR Value q1model SYMBOL voltage -272 -320 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -112 -320 R0 WINDOW 123 0 0 Left 0 WINDOW 39 36 57 Left 0 SYMATTR SpiceLine Rser=10 SYMATTR InstName V2 SYMATTR Value 10 SYMBOL current 144 -160 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 31 14 Left 0 WINDOW 3 27 60 Left 0 SYMATTR InstName I1 SYMATTR Value 1ma SYMBOL voltage -160 -416 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value2 AC 1 SYMATTR Value "" SYMBOL npn -48 -384 R0 SYMATTR InstName Q2 SYMATTR Value q1model SYMBOL res 368 -368 R0 SYMATTR InstName R4 SYMATTR Value 80e6 SYMBOL cap 240 -208 R0 SYMATTR InstName C1 SYMATTR Value 10�f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 240 -48 R0 SYMATTR InstName R2 SYMATTR Value 3m SYMBOL ind 240 -144 R0 SYMATTR InstName L1 SYMATTR Value 2.5nh SYMBOL cap 368 -208 R0 SYMATTR InstName C2 SYMATTR Value 10�f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 368 -48 R0 SYMATTR InstName R3 SYMATTR Value 3m SYMBOL ind 368 -144 R0 SYMATTR InstName L2 SYMATTR Value 2.5nh SYMBOL res 144 -240 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 200e6 SYMBOL cap 464 -336 R0 SYMATTR InstName C3 SYMATTR Value 400f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 560 -368 R0 SYMATTR InstName R5 SYMATTR Value 80e6 SYMBOL cap 560 -208 R0 SYMATTR InstName C4 SYMATTR Value 3300�f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 560 -48 R0 SYMATTR InstName R6 SYMATTR Value 20m SYMBOL ind 560 -144 R0 SYMATTR InstName L3 SYMATTR Value 10nh SYMBOL cap 656 -336 R0 SYMATTR InstName C5 SYMATTR Value 400f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 752 -368 R0 SYMATTR InstName R7 SYMATTR Value 80e6 SYMBOL cap 752 -208 R0 SYMATTR InstName C6 SYMATTR Value 3300�f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 752 -48 R0 SYMATTR InstName R8 SYMATTR Value 20m SYMBOL ind 752 -144 R0 SYMATTR InstName L4 SYMATTR Value 10nh SYMBOL cap 848 -336 R0 SYMATTR InstName C7 SYMATTR Value 400f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL cap 848 -208 R0 SYMATTR InstName C8 SYMATTR Value 10�f SYMATTR SpiceLine Rser=1u Lser=1n SYMBOL res 848 -48 R0 SYMATTR InstName R9 SYMATTR Value 3m SYMBOL ind 848 -144 R0 SYMATTR InstName L5 SYMATTR Value 2.5nh TEXT 8 -512 Left 0 ;'MPSA14 Darlington vs passive models TEXT 48 -472 Left 0 !.ac oct 100 1 4e6 TEXT -264 144 Left 0 !.MODEL Q1model NPN(IS=1.34E-14 BF=340 NF=1 VAF= 136.7 IKF=0.38 ISE=7.84E-14 NE=1.5 BR=0.657 NR=1 VAR=92 IKR=1.87\n+ ISC= 9.0E-13 NC=2.0 RB=86.610 RE=0.08 NK=0.9 RE=0.58 RC=0.25 EG=1.180 FC=0.5 CJE=1.19288E-11 VJE=1.12097\n+ MJE=0.301248 CJC=1.25659E-11 VJC=0.70336 MJC=0.325457 XCJC=0.9 TF=1.27E-9 XTB=2.12 XTI=3) TEXT 40 -376 Left 0 ;MPSA14 TEXT -264 64 Left 0 ;C4 :Nic Components Corp. NRE-HL332M16V12.5x35F, \n3300uf, 0.020 Ohm @ 100KHz\nhttp://www.niccomp.com/Catalog/nrehl.pdf RECTANGLE Normal 208 -176 -160 -400
From: Mike on 25 May 2010 11:55 Sorry, the model statement is too long and it wraps. LTspice won't load. I posted the zip file in abse under the title "MPSA14 Ripple Filter Model" I checked and it works fine. Mike
From: John Larkin on 25 May 2010 11:57 On Mon, 24 May 2010 21:04:19 GMT, Mike <spam(a)me.not> wrote: >Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> On 5/24/2010 8:09 AM, Mike wrote: > >[...] > >> Like I said, it's basically C_CE/C_BFC. You pick a transistor with >> reasonable characteristics at frequencies you care about, drive its >> base from a really really filtered version of V_CC--with a resistor in >> series to make sure it doesn't oscillate and doesn't blow up if the >> input or output gets shorted--and put a BFC at the output. If the >> transistor has 10 pF C_CB and the BFC is 100 uF, that's 140 dB, >> provided you look after other stuff such as the Early voltage and the >> ESR of the output cap. Generally if your application needs more than >> 100 dB of ripple rejection, you have to be pretty careful. >> >> Cheers >> >> Phil Hobbs > >Is that spiceable? I made a simple circuit with a voltage source driving >the base and a cap on the emitter. I tried various transistors such as >2N2222 and 2N2369, and various ESR and ESL values for the cap. > >The capacitance had little effect on the attenuation floor, but mainly >moved the low frequency corner. No reasonable combination of transistors >or cap values got below -120dB. The base resistance had little effect. >Here's the file if you'd like to show me how it should work: > >Version 4 >SHEET 1 1140 1108 >WIRE -304 -448 -384 -448 >WIRE -160 -448 -224 -448 >WIRE -128 -448 -160 -448 >WIRE -128 -400 -128 -448 >WIRE -192 -352 -256 -352 >WIRE -384 -320 -384 -448 >WIRE -256 -320 -256 -352 >WIRE -128 -288 -128 -304 >WIRE -32 -288 -128 -288 >WIRE 16 -288 -32 -288 >WIRE -128 -256 -128 -288 >WIRE -32 -256 -32 -288 >WIRE -384 -224 -384 -240 >WIRE -256 -224 -256 -240 >WIRE -32 -176 -32 -192 >WIRE -128 -160 -128 -176 >WIRE -32 -80 -32 -96 >WIRE -32 16 -32 0 >FLAG -256 -224 0 >FLAG -384 -224 0 >FLAG -128 -160 0 >FLAG -160 -448 Vin >FLAG -32 -288 Vout >FLAG -32 16 0 >SYMBOL npn -192 -400 R0 >SYMATTR InstName Q1 >SYMATTR Value 2N2369 >SYMBOL voltage -384 -336 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V1 >SYMATTR Value 15 >SYMBOL voltage -256 -336 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 24 38 Left 0 >SYMATTR SpiceLine Rser=1 >SYMATTR InstName V2 >SYMATTR Value 10 >SYMBOL current -128 -256 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName I1 >SYMATTR Value 20ma >SYMBOL voltage -208 -448 R90 >WINDOW 0 49 39 VRight 0 >WINDOW 123 -48 40 VRight 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V3 >SYMATTR Value2 AC 1 >SYMATTR Value "" >SYMBOL cap -48 -256 R0 >SYMATTR InstName C1 >SYMATTR Value 1000�f >SYMATTR SpiceLine Rser=1u Lser=1n >SYMBOL res -48 -96 R0 >SYMATTR InstName R1 >SYMATTR Value 100m >SYMBOL ind -48 -192 R0 >SYMATTR InstName L1 >SYMATTR Value 10n >TEXT -216 -536 Left 0 ;'BJT Ripple Filter >TEXT -224 -504 Left 0 !.ac oct 100 1 1e7 I did about the same, similar results. ftp://jjlarkin.lmi.net/C-multiplier.gif The lf rejection was about 3000:1. The hf rolloff corner corresponds to a 2 ohm Re and the 15u load cap. The load is only 14 mA, so Re is relatively high. My opamp circuit starts with the opamp's roughly 100 dB PSRR and then hits a 15 ohm + 120 uF lowpass, about 88 Hz corner frequency. That RC rolloff gets pretty far down before the opamp's PSRR starts to get bad. And I don't lose the 0.7 volts (or twice that for a darlington) which happens to matter in my immediate case. Neither circuit is perfect. There's probably something really good lurking out in circuit space. John
From: George Herold on 25 May 2010 12:18
On May 25, 10:54 am, Mike <s...(a)me.not> wrote: > George Herold <gher...(a)teachspin.com> wrote: > > [...] > > > Hi Mike, Would you mind telling me how I dump this into LT spice. > > Im not a spice virgin.... but I am still a newlywed. > > > Thanks, > > > George H. > > Hi George - here's how: > > 1. Select the listing with your mouse. > 2. Press Ctrl-C to copy the selected block to the clipboard. > 3. Open any plain ascii text editor such as NotePad or EditPad. > 4. Paste the selected text into the word processor with Ctrl-V. > 5. Use "Save As" to save the file to a suitable folder. Use the file > extension ".asc" to run it in LTspice. > 6. Repeat if there is a plot file, using the ".plt" extension. > > If you have installed LTspice and associated the ASC file extension, all > you need to do is select the file in MS Explorer and it will load the > file into LTspice. > > If you have not associated the file extensions, then load LTspice and use > the Open File command to locate and run the file. > > Please repost if you have any problems. > > Mike Thanks Mike that was easy.... pretty soon Ill be ready for the spice Karma Sutra. George H. |