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Posted to sci.electronics.design,sci.electronics.basics,rec.audio.tech
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Filtering ideas
John Jardine. wrote:
wrote in message oups.com... w2aew wrote: Depending on "what" you need to measure on your signal, it might be a good application for a lock-in amplifier. This technique is often used to measure very small signals buried in noise. Anyone have any thoughts on this Elliptic filter - http://www.filter-solutions.com/active.htg/pos3.gif It's the highest order Elliptic active filter I could find. It's not bad, but would need at least 4 stages. Paul Opamp elliptics are a bit of a waste of time unless you have a particular frequency to notch out. Certainly useless if you want that 1MHz break frequency. I'd guess a 30kHz filter might be appropriate. Would suggest just stacking some simple 2nd or 3rd order Butterworth designs. john Thanks for input. I see that you're 100% correct. Have you tried a program called "Filter Solutions 2006?" It's a dream program. I'm very disappointed in the Elliptic filters. The best bandpass filter I found using a Pos SAB active implementation with lower & higher corner freq. = 1KHz & 10KHz is a Chebyshev I. It requires only 4 op-amps for a 7th order bandpass. Even after entering LM741 amp parameters I still get -208db at 60Hz and -89db at 25KHz. Nearly 1db at 1KHz and 10KHz. It's unbelievable! I'm curious what the disadvantages to a Pos SAB active implementation since it uses less than half the parts-- 4 op-amps compared to 10. Here's the Spice Net List: MULTIPLE ANALYSES * V1 1 0 AC 1 *V1 1 0 PULSE 0 1 0 5.033E-08 0 R111 1 2 4E+04 C112 2 7 1.069E-08 R113 2 0 2500 R109 2 3 1E+04 C101 3 4 1.504E-08 C102 4 5 1.828E-09 R103 5 0 5.737E+05 R104 4 7 2500 R106 6 0 1E+04 R107 6 7 1795 C108 4 0 2.183E-09 X101 5 6 7 OPAMP PARAMS: A=3E+11 B=4E+06 R211 7 8 2E+04 C212 8 13 6.06E-09 R213 8 0 5000 R209 8 9 1E+04 C201 9 10 1.001E-08 C202 10 11 7.2E-09 R203 11 0 1.051E+05 R204 10 13 5000 R206 12 0 1E+04 R207 12 13 2821 C208 10 0 1.469E-09 X201 11 12 13 OPAMP PARAMS: A=3E+11 B=4E+06 R311 13 14 2E+04 C312 14 19 6.288E-09 R313 14 0 5000 R309 14 15 1E+04 C301 15 16 7.512E-09 C302 16 17 1.434E-08 R303 17 0 7.002E+04 R304 16 19 5000 R306 18 0 1E+04 R307 18 19 2269 C308 16 0 9.47E-10 X301 17 18 19 OPAMP PARAMS: A=3E+11 B=4E+06 R401 19 20 1E+04 C402 20 21 1.451E-09 R403 21 0 1.557E+04 R404 20 23 3.513E+04 R406 22 0 1E+04 R407 22 23 7.787E+04 C408 20 0 1.451E-09 X401 21 22 23 OPAMP PARAMS: A=3E+11 B=4E+06 ..AC DEC 200 0.1 2.5E+04 ..PLOT AC VDB(23) -200 0 ..PLOT AC VP(23) -200 200 ..PLOT AC VG(23) 0 0.005 ..TRAN 0.05 10 0 ..PLOT TRAN V(23) -0.5 0.3 ..END *OpAmp Complex Model 1=+in 2=-in 10=Vo A=G*Bw Product(Hz) B=Bw(Hz) ..SUBCKT OPAMP 1 2 10 +PARAMS: A=1.E+12 B=1.E+06 Rin 1 2 2.e+06 Cin 1 2 5.e-12 E1 3 0 1 2 1.0 Rp 3 4 1.0 Cp 4 0 {1/(2*PI*B)} E2 5 0 4 0 {A/B} Rout 5 10 500. ..ENDS OPAMP |
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#3
Posted to sci.electronics.design,sci.electronics.basics,rec.audio.tech
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Filtering ideas
wrote in message
oups.com... Even after entering LM741 amp parameters I still get -208db at 60Hz and -89db at 25KHz. Nearly 1db at 1KHz and 10KHz. It's unbelievable! It sure is! Unless you're cooling the with, e.g., liquid helium, thermal noise alone is well above -208dB in any reasonable bandwidth! :-) I'm curious what the disadvantages to a Pos SAB active implementation since it uses less than half the parts-- 4 op-amps compared to 10. Most likely sensitivity to component value variations -- run a Monte Carlo simulation on each and see. |
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#4
Posted to sci.electronics.design,sci.electronics.basics,rec.audio.tech
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Filtering ideas
wrote in message oups.com... John Jardine. wrote: wrote in message oups.com... w2aew wrote: Depending on "what" you need to measure on your signal, it might be a good application for a lock-in amplifier. This technique is often used to measure very small signals buried in noise. Anyone have any thoughts on this Elliptic filter - http://www.filter-solutions.com/active.htg/pos3.gif It's the highest order Elliptic active filter I could find. It's not bad, but would need at least 4 stages. Paul Opamp elliptics are a bit of a waste of time unless you have a particular frequency to notch out. Certainly useless if you want that 1MHz break frequency. I'd guess a 30kHz filter might be appropriate. Would suggest just stacking some simple 2nd or 3rd order Butterworth designs. john Thanks for input. I see that you're 100% correct. Have you tried a program called "Filter Solutions 2006?" It's a dream program. I'm very disappointed in the Elliptic filters. The best bandpass filter I found using a Pos SAB active implementation with lower & higher corner freq. = 1KHz & 10KHz is a Chebyshev I. It requires only 4 op-amps for a 7th order bandpass. Even after entering LM741 amp parameters I still get -208db at 60Hz and -89db at 25KHz. Nearly 1db at 1KHz and 10KHz. It's unbelievable! I'm curious what the disadvantages to a Pos SAB active implementation since it uses less than half the parts-- 4 op-amps compared to 10. Here's the Spice Net List: Yes, the prog is excellent. I recognised the circuit drawing. Don't believe those incredible dB figures. In normal practice you're lucky to get anything down to -80. To spot those filter differences, initially pick a SAB type circuit design, select a component on it, then on the drop down box go for a multiple run Monte-Carlo analysis using random values for all the R's and C's. You'll see some -really- ugly spreads on that original pristine response. Then do the same using leapfrog and GIC implementations. john |
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