Low Pass Reconstruction Filter

Started by dacrow June 2, 2006
I'm trying to build a Low Pass Reconstruction Filter for use after a DAC .

The thing is it has to be a Zi = 300 Ohm input and the fc has to be 37 MHz


and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be < 1dB.


Already tried the Butterworth but the coils were to large in fuction of
the 

self resonant frequency of it .

The Chebyshev filter has a too large ripple in the passband .

All of it was simulated with Filter Solutions ..

Anybody has a solution ?


>I'm trying to build a Low Pass Reconstruction Filter for use after a DAC
.
> >The thing is it has to be a Zi = 600 Ohm input and the fc has to be 37
MHz
> > >and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be <
1dB.
> > >Already tried the Butterworth but the coils were to large in fuction of >the > >self resonant frequency of it . > >The Chebyshev filter has a too large ripple in the passband . > >All of it was simulated with Filter Solutions .. > >Anybody has a solution ? > > >
dacrow wrote:
> I'm trying to build a Low Pass Reconstruction Filter for use after a DAC . > > The thing is it has to be a Zi = 300 Ohm input and the fc has to be 37 MHz > > > and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be < 1dB. > > > Already tried the Butterworth but the coils were to large in fuction of > the > > self resonant frequency of it . > > The Chebyshev filter has a too large ripple in the passband . > > All of it was simulated with Filter Solutions .. > > Anybody has a solution ? > >
Do you mean the coil values were inconveniently large, or that you can only get coils that are physically too large? Granted, you can't seem to get 1uH inductors in 0603 packages, but sometimes that's how the cookie crumbles. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
dacrow wrote:

> I'm trying to build a Low Pass Reconstruction Filter for use after a DAC . > The thing is it has to be a Zi = 300 Ohm input and the fc has to be 37 MHz > and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be < 1dB. > Already tried the Butterworth but the coils were to large in fuction of > the self resonant frequency of it . > > The Chebyshev filter has a too large ripple in the passband . > All of it was simulated with Filter Solutions .. > > Anybody has a solution ?
Chebyshev Type II? Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
>dacrow wrote: >> I'm trying to build a Low Pass Reconstruction Filter for use after a
DAC .
>> >> The thing is it has to be a Zi = 300 Ohm input and the fc has to be 37
MHz
>> >> >> and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be <
1dB.
>> >> >> Already tried the Butterworth but the coils were to large in fuction
of
>> the >> >> self resonant frequency of it . >> >> The Chebyshev filter has a too large ripple in the passband . >> >> All of it was simulated with Filter Solutions .. >> >> Anybody has a solution ? >> >> >Do you mean the coil values were inconveniently large, or that you can >only get coils that are physically too large? Granted, you can't seem >to get 1uH inductors in 0603 packages, but sometimes that's how the >cookie crumbles. > >-- > >Tim Wescott >Wescott Design Services >http://www.wescottdesign.com > >Posting from Google? See http://cfaj.freeshell.org/google/ > >"Applied Control Theory for Embedded Systems" came out in April. >See details at http://www.wescottdesign.com/actfes/actfes.html >
Yes , the coils values were too large ,the min. self resonant frequency of a 3.9 uH (MLF1608 Smd) for example is 35 Mhz , the cutoff of the YPbPr filter is 37 MHZ .
"dacrow" <affligem@gmail.com> wrote in message 
news:0OmdnQM2H_sT3RjZnZ2dnUVZ_tGdnZ2d@giganews.com...
> >dacrow wrote: >>> I'm trying to build a Low Pass Reconstruction Filter for use after a > DAC . >>> >>> The thing is it has to be a Zi = 300 Ohm input and the fc has to be 37 > MHz >>> >>> >>> and 50 dB attuenuation @ 118 Mhz and the passband ripple has to be < > 1dB. >>> >>> >>> Already tried the Butterworth but the coils were to large in fuction > of >>> the >>> >>> self resonant frequency of it . >>> >>> The Chebyshev filter has a too large ripple in the passband . >>> >>> All of it was simulated with Filter Solutions .. >>> >>> Anybody has a solution ? >>> >>> >>Do you mean the coil values were inconveniently large, or that you can >>only get coils that are physically too large? Granted, you can't seem >>to get 1uH inductors in 0603 packages, but sometimes that's how the >>cookie crumbles. >> >>-- >> >>Tim Wescott >>Wescott Design Services >>http://www.wescottdesign.com >> >>Posting from Google? See http://cfaj.freeshell.org/google/ >> >>"Applied Control Theory for Embedded Systems" came out in April. >>See details at http://www.wescottdesign.com/actfes/actfes.html >> > > > > Yes , the coils values were too large ,the min. self resonant frequency of > a 3.9 uH (MLF1608 Smd) for example is 35 Mhz , the cutoff of the YPbPr > filter is 37 MHZ . > >
In Filter Solutions select Elliptic as the filter type, set the passband ripple to be what you need, set 5th order and your required pass and stop frequencies. A quick trial suggests L values of <1.8uH. You may want to move the cutoff frequency up to improve group delay and component sensitivity. The Coilcraft 1008CS inductors of that value have SRF >160MHz, the 3.9uH >120MHz. http://www.coilcraft.com/1008cs.cfm Regards Ian
> >"dacrow" <affligem@gmail.com> wrote in message >news:0OmdnQM2H_sT3RjZnZ2dnUVZ_tGdnZ2d@giganews.com...
>> >> >In Filter Solutions select Elliptic as the filter type, set the passband
>ripple >to be what you need, set 5th order and your required pass and stop >frequencies. A quick trial suggests L values of <1.8uH. >You may want to move the cutoff frequency up to improve group >delay and component sensitivity. > >The Coilcraft 1008CS inductors of that value have SRF >160MHz, >the 3.9uH >120MHz. >http://www.coilcraft.com/1008cs.cfm > >Regards > Ian > >
Hi , It ain't gonna work with the 600 Zi , I placed an emitter follower between the DAC and the filter , next problem is to find suited transistors ,I came up with the next one : NPN 9 GHz wideband transistor BFS540 When I tested just the emiiter follower it gives a distorted signal above 39 MHz ?! Isn't the transition frequency {9 Ghz}the parameter to work with?
>
"dacrow" <affligem@gmail.com> wrote in message 
news:bPSdnQVjVZP4kxXZnZ2dnUVZ_qudnZ2d@giganews.com...
> > >>"dacrow" <affligem@gmail.com> wrote in message >>news:0OmdnQM2H_sT3RjZnZ2dnUVZ_tGdnZ2d@giganews.com... > >>> >>> >>In Filter Solutions select Elliptic as the filter type, set the passband > >>ripple >>to be what you need, set 5th order and your required pass and stop >>frequencies. A quick trial suggests L values of <1.8uH. >>You may want to move the cutoff frequency up to improve group >>delay and component sensitivity. >> >>The Coilcraft 1008CS inductors of that value have SRF >160MHz, >>the 3.9uH >120MHz. >>http://www.coilcraft.com/1008cs.cfm >> >>Regards >> Ian >> >> > > Hi , It ain't gonna work with the 600 Zi , I placed an emitter follower > between the DAC and the filter , next problem is to find suited > transistors ,I came up with the next one : NPN 9 GHz wideband transistor > BFS540 > When I tested just the emiiter follower it gives a distorted signal above > 39 MHz ?! > Isn't the transition frequency {9 Ghz}the parameter to work with? >> >
What "ain't gonna work"? If I recall, you originally wanted 300 ohms source and load, which seems rather high. What DAC, what specs, what are you trying to do? Regards Ian