Has anyone heard of a method to convert a digital FIR filter back into an analog filter? Can you perform a bilinear or impulse invariant transform backwards? Thanks Brett Emsley
Converting a Digital Filter to an Analog Filter
Started by ●March 3, 2004
Reply by ●March 3, 20042004-03-03
In article 65422a2a.0403030825.41cc6192@posting.google.com, Brett at bemsley@yahoo.com wrote on 03/03/2004 11:25:> Has anyone heard of a method to convert a digital FIR filter back into > an analog filter? Can you perform a bilinear or impulse invariant > transform backwards?the quick answer is yes to both.> Thanks1. BLT: invert s = 2/T * (1-z^-1)/(1+z^-1) 2. IIT: convert to parallel and replace each h[n] = a^-n to h(t) = a^(t/T) where t = n*T r b-j
Reply by ●March 3, 20042004-03-03
Hi Brett! You can use a Analogue Laguerre Network to do this. It is important to notice that this filter is an IIR filter with FIR filter structure where each digital delay elements is replaced by 1:st order analogue all-pass filters. Se T. Oliviera "On Determination of the Optimal Pole Position of Laguerra Filters", for more information about that. All the best, Michael Numminen, M.Sc.E.E. "Brett" <bemsley@yahoo.com> skrev i meddelandet news:65422a2a.0403030825.41cc6192@posting.google.com...> Has anyone heard of a method to convert a digital FIR filter back into > an analog filter? Can you perform a bilinear or impulse invariant > transform backwards? > > Thanks > Brett Emsley
Reply by ●March 3, 20042004-03-03
> > 1. BLT: invert s = 2/T * (1-z^-1)/(1+z^-1) > > 2. IIT: convert to parallel and replace each h[n] = a^-n to > h(t) = a^(t/T) where t = n*T > > r b-j >Hello, I understand that methods like BLT, IT etc assist us to design digital filter from analog design. Why would people interested in the other way round? What design application would need this approach? Regards, FD
Reply by ●March 3, 20042004-03-03
"Michael Numminen" <michael.numminen@comhem.se> wrote in message news:sss1c.51137$mU6.207815@newsb.telia.net...> Hi Brett! > > You can use a Analogue Laguerre Network to do this. It is important to > notice that this filter is an IIR filter with FIR filter structure where > each digital delay elements is replaced by 1:st order analogue all-pass > filters. Se T. Oliviera "On Determination of the Optimal Pole Position of > Laguerra Filters", for more information about that.Perhaps this addresses the "next step" after R B-J's response. Anyway, I was going to say that after you do the mapping then you need to figure out how to change the rational function into a real filter of R's, L's, C's, op amps, etc. I'm sure there are ways but that's a necessary step to get to an analog filter design from a digital filter design. Fred
Reply by ●March 4, 20042004-03-04
In article rEu1c.69764$aH3.2126163@bgtnsc04-news.ops.worldnet.att.net, flipdog at john.lai@worldnet.att.net wrote on 03/03/2004 19:21:>> >> 1. BLT: invert s = 2/T * (1-z^-1)/(1+z^-1) >> >> 2. IIT: convert to parallel and replace each h[n] = a^-n to >> h(t) = a^(t/T) where t = n*T >> >> r b-j >> > Hello, > I understand that methods like BLT, IT etc assist us to design digital > filter from analog design. Why would people interested in the other way > round?beats me. maybe their using some optimized IIR design program and they wanna design some op-amp filter. i dunno.> What design application would need this approach?well, there will continue to be the need for analog filters in some contexts. whatever comes before the A/D or after the D/A or in some manufactured products, it might just be less expensive to delete the DSP step and do it all in the continuous-time domain. again, i dunno. r b-j
Reply by ●March 4, 20042004-03-04
Thank you everyone for your responses. I hope to start working on them today. Perhaps I should I have described our motivation for wanted to go from digital to analog. What we have is an RF front end that has a less than flat response, mostly in group delay. My boss konws that I had, in another project, taken the response of a distorted IF from a network analyzer and created a digital filter that had the inverse response. So with that information my boss wondered if I could take that experience a step further and create an analog filter with the inverse response of the RF front endo that they could place that filter on the RF board. It seems to be that there must be a better way to fix the problems of an RF chain, but I'm just the DSP guy. Thanks again Brett
Reply by ●March 4, 20042004-03-04
Brett wrote:> Thank you everyone for your responses. I hope to start working on > them today. > > Perhaps I should I have described our motivation for wanted to go from > digital to analog. What we have is an RF front end that has a less > than flat response, mostly in group delay. My boss konws that I had, > in another project, taken the response of a distorted IF from a > network analyzer and created a digital filter that had the inverse > response. So with that information my boss wondered if I could take > that experience a step further and create an analog filter with the > inverse response of the RF front endo that they could place that > filter on the RF board. It seems to be that there must be a better > way to fix the problems of an RF chain, but I'm just the DSP guy. > > Thanks again > BrettHow about a frontal attack on the problem? Guillemin "Synthesis of Passive Networks"; John Wiley " "The Mathematics of Circuit Analysis"; MIT Press Weinberg "Network Analysis and Synthesis"; McGraw-Hill Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������