Cascaded integrator-comb (CIC) filter question

Started by Rick Lyons August 17, 2003
Hi Guys,

  I've been trying to learn about those darned cascaded 
integrator-comb (CIC) filters and have reviewed 
Hogenaurer's original paper 

  Hogenauer, E. "An Economical Class of Digital Filters 
  For Decimation and Interpolation," IEEE Trans. Acoust. 
  Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, 
  April 1981.

and Matt Donadio's CIC write-up (on www.dspguru.com).

But I ran into something concerning CIC interpolators 
that I don't understand and hope you folk might help 
me out.

Hogenauer says (on pp. 160) that there will be bit growth 
(gain) through the interpolator's comb filter(s) 
(differentiators) comprising the initial stage(s) 
of a CIC interpolation filter.  He says the bit 
growth will be a factor of 2 
for each comb filter used in the implementation.
Because a comb (differentiator) merely outputs 
the difference between successive inputs, I don't see 
how there can be bit growth (gain) through the comb 
stages.

My MATLAB modeling shows no gain (bit growth) in the 
interpolator's comb filters.  They have a gain of zero 
at DC.  (My modeling agrees with what Ray Andraka has 
stated here, for the gain of a CIC interpolator, 
several times on this newsgroup.)

Anyway, my questions are: is there really bit 
growth (gain) in the initial comb stages of a CIC 
interpolation filter?  Am I missing something simple 
here?  Do I need to increase the dosage of my medication?

Thanks for any help,
[-Rick-]



Rick Lyons wrote:
> > Hi Guys, > > I've been trying to learn about those darned cascaded > integrator-comb (CIC) filters and have reviewed > Hogenaurer's original paper > > Hogenauer, E. "An Economical Class of Digital Filters > For Decimation and Interpolation," IEEE Trans. Acoust. > Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, > April 1981. > > and Matt Donadio's CIC write-up (on www.dspguru.com). > > But I ran into something concerning CIC interpolators > that I don't understand and hope you folk might help > me out. > > Hogenauer says (on pp. 160) that there will be bit growth > (gain) through the interpolator's comb filter(s) > (differentiators) comprising the initial stage(s) > of a CIC interpolation filter. He says the bit > growth will be a factor of 2 > for each comb filter used in the implementation. > Because a comb (differentiator) merely outputs > the difference between successive inputs, I don't see > how there can be bit growth (gain) through the comb > stages.
The frequency response for a filter [1 -1] is a sin function with a gain of 2 at fs/2 (i.e. Pi/2). Consider the sequence 1 -1 1 -1 1 -1 ...... What would be the output after putting that thru the differentiator. Of course in real life a signal usually won't have that much energy near fs/2, so the issue of 'bit growth' (or overflow) may not be observed. -jim -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =-----
I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised
everything, and used an example from literature to test the design. I am not
an expert in choosing the bit widths.
The comb filters just keeps accumulating samples. The accumulation result
gets bigger and bigger. If you subsample with a factor 16, the accumulation
register should not overflow within that period. I chose a wrong width ones
and did notice wrong results at the output.
regards,
--
Peter Beukelman
senior ASIC designer
http://www.eonic.com
"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message
news:3f402ef6.115258812@news.west.earthlink.net...
> > Hi Guys, > > I've been trying to learn about those darned cascaded > integrator-comb (CIC) filters and have reviewed > Hogenaurer's original paper > > Hogenauer, E. "An Economical Class of Digital Filters > For Decimation and Interpolation," IEEE Trans. Acoust. > Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, > April 1981. > > and Matt Donadio's CIC write-up (on www.dspguru.com). > > But I ran into something concerning CIC interpolators > that I don't understand and hope you folk might help > me out. > > Hogenauer says (on pp. 160) that there will be bit growth > (gain) through the interpolator's comb filter(s) > (differentiators) comprising the initial stage(s) > of a CIC interpolation filter. He says the bit > growth will be a factor of 2 > for each comb filter used in the implementation. > Because a comb (differentiator) merely outputs > the difference between successive inputs, I don't see > how there can be bit growth (gain) through the comb > stages. > > My MATLAB modeling shows no gain (bit growth) in the > interpolator's comb filters. They have a gain of zero > at DC. (My modeling agrees with what Ray Andraka has > stated here, for the gain of a CIC interpolator, > several times on this newsgroup.) > > Anyway, my questions are: is there really bit > growth (gain) in the initial comb stages of a CIC > interpolation filter? Am I missing something simple > here? Do I need to increase the dosage of my medication? > > Thanks for any help, > [-Rick-] > >
On Mon, 18 Aug 2003 06:20:25 -0500, jim <sjedging@mwt.net> wrote:

> > >Rick Lyons wrote: >> >> Hi Guys, >> >> I've been trying to learn about those darned cascaded >> integrator-comb (CIC) filters and have reviewed >> Hogenaurer's original paper >> >> Hogenauer, E. "An Economical Class of Digital Filters >> For Decimation and Interpolation," IEEE Trans. Acoust. >> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, >> April 1981. >> >> and Matt Donadio's CIC write-up (on www.dspguru.com). >> >> But I ran into something concerning CIC interpolators >> that I don't understand and hope you folk might help >> me out. >> >> Hogenauer says (on pp. 160) that there will be bit growth >> (gain) through the interpolator's comb filter(s) >> (differentiators) comprising the initial stage(s) >> of a CIC interpolation filter. He says the bit >> growth will be a factor of 2 >> for each comb filter used in the implementation. >> Because a comb (differentiator) merely outputs >> the difference between successive inputs, I don't see >> how there can be bit growth (gain) through the comb >> stages. > >The frequency response for a filter [1 -1] is a sin function with a gain >of 2 at fs/2 (i.e. Pi/2). Consider the sequence 1 -1 1 -1 1 -1 ...... What >would be the output after putting that thru the differentiator. > Of course in real life a signal usually won't have that much energy near >fs/2, so the issue of 'bit growth' (or overflow) may not be observed. > >-jim
Hi Jim, Yes, yes. The peak freq mag response of a comb is two. Darn. Thanks for reminding me. I agree with what you wrote. If the comb has a delay of 2 samples, the gain peak (two) will occur at fs/4. [-Rick-]
Hi Peter,
  did you really build a 1 Gsample/sec A/D converter?(!!)

I don't even want to *think* about it.
I mean, how do you 'breadboard' a circuit that 
runs at 1 GHz.   How do you inject test signals?
How do you monitor voltages at different nodes?
I checked my Radio Shack catalog and they don't 
even sell test equipment that operates at 1 GHz.

[-Rick-]

-------------------------------------------
On Mon, 18 Aug 2003 13:32:28 +0200, "John Smith" <piet@bel.com> wrote:

>I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised >everything, and used an example from literature to test the design. I am not >an expert in choosing the bit widths. >The comb filters just keeps accumulating samples. The accumulation result >gets bigger and bigger. If you subsample with a factor 16, the accumulation >register should not overflow within that period. I chose a wrong width ones >and did notice wrong results at the output. >regards, >-- >Peter Beukelman >senior ASIC designer >http://www.eonic.com >"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message >news:3f402ef6.115258812@news.west.earthlink.net... >> >> Hi Guys, >> >> I've been trying to learn about those darned cascaded >> integrator-comb (CIC) filters and have reviewed >> Hogenaurer's original paper >> >> Hogenauer, E. "An Economical Class of Digital Filters >> For Decimation and Interpolation," IEEE Trans. Acoust. >> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, >> April 1981. >> >> and Matt Donadio's CIC write-up (on www.dspguru.com). >> >> But I ran into something concerning CIC interpolators >> that I don't understand and hope you folk might help >> me out. >> >> Hogenauer says (on pp. 160) that there will be bit growth >> (gain) through the interpolator's comb filter(s) >> (differentiators) comprising the initial stage(s) >> of a CIC interpolation filter. He says the bit >> growth will be a factor of 2 >> for each comb filter used in the implementation. >> Because a comb (differentiator) merely outputs >> the difference between successive inputs, I don't see >> how there can be bit growth (gain) through the comb >> stages. >> >> My MATLAB modeling shows no gain (bit growth) in the >> interpolator's comb filters. They have a gain of zero >> at DC. (My modeling agrees with what Ray Andraka has >> stated here, for the gain of a CIC interpolator, >> several times on this newsgroup.) >> >> Anyway, my questions are: is there really bit >> growth (gain) in the initial comb stages of a CIC >> interpolation filter? Am I missing something simple >> here? Do I need to increase the dosage of my medication? >> >> Thanks for any help, >> [-Rick-] >> >> > >
Rick,

Hotrod ADCs with samples rate >=1Gsps are not unusual these days, at
least in labs.  I know of at least one 4-bit, 1Gsps monolithic ADC in
a lab, and they're working to add two more bits.  There are
non-monolithic converters that operate in those ranges as well that
are commercialized.   There may be monolothic converters on the market
in that range, too...


On Wed, 20 Aug 2003 05:47:57 GMT, ricklyon@REMOVE.onemain.com (Rick
Lyons) wrote:

> >Hi Peter, > did you really build a 1 Gsample/sec A/D converter?(!!) > >I don't even want to *think* about it. >I mean, how do you 'breadboard' a circuit that >runs at 1 GHz. How do you inject test signals? >How do you monitor voltages at different nodes? >I checked my Radio Shack catalog and they don't >even sell test equipment that operates at 1 GHz. > >[-Rick-] > >------------------------------------------- >On Mon, 18 Aug 2003 13:32:28 +0200, "John Smith" <piet@bel.com> wrote: > >>I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised >>everything, and used an example from literature to test the design. I am not >>an expert in choosing the bit widths. >>The comb filters just keeps accumulating samples. The accumulation result >>gets bigger and bigger. If you subsample with a factor 16, the accumulation >>register should not overflow within that period. I chose a wrong width ones >>and did notice wrong results at the output. >>regards, >>-- >>Peter Beukelman >>senior ASIC designer >>http://www.eonic.com >>"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message >>news:3f402ef6.115258812@news.west.earthlink.net... >>> >>> Hi Guys, >>> >>> I've been trying to learn about those darned cascaded >>> integrator-comb (CIC) filters and have reviewed >>> Hogenaurer's original paper >>> >>> Hogenauer, E. "An Economical Class of Digital Filters >>> For Decimation and Interpolation," IEEE Trans. Acoust. >>> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, >>> April 1981. >>> >>> and Matt Donadio's CIC write-up (on www.dspguru.com). >>> >>> But I ran into something concerning CIC interpolators >>> that I don't understand and hope you folk might help >>> me out. >>> >>> Hogenauer says (on pp. 160) that there will be bit growth >>> (gain) through the interpolator's comb filter(s) >>> (differentiators) comprising the initial stage(s) >>> of a CIC interpolation filter. He says the bit >>> growth will be a factor of 2 >>> for each comb filter used in the implementation. >>> Because a comb (differentiator) merely outputs >>> the difference between successive inputs, I don't see >>> how there can be bit growth (gain) through the comb >>> stages. >>> >>> My MATLAB modeling shows no gain (bit growth) in the >>> interpolator's comb filters. They have a gain of zero >>> at DC. (My modeling agrees with what Ray Andraka has >>> stated here, for the gain of a CIC interpolator, >>> several times on this newsgroup.) >>> >>> Anyway, my questions are: is there really bit >>> growth (gain) in the initial comb stages of a CIC >>> interpolation filter? Am I missing something simple >>> here? Do I need to increase the dosage of my medication? >>> >>> Thanks for any help, >>> [-Rick-] >>> >>> >> >> >
Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
I did an FFT that worked at 960 MHz a year and a half ago in an FPGA.  The
application had an Atmel 1GHz 8 bit ADC coupled to the FPGA, and the FPGA did
overlapped FFTs on the data in real time.

Eric Jacobsen wrote:

> Rick, > > Hotrod ADCs with samples rate >=1Gsps are not unusual these days, at > least in labs. I know of at least one 4-bit, 1Gsps monolithic ADC in > a lab, and they're working to add two more bits. There are > non-monolithic converters that operate in those ranges as well that > are commercialized. There may be monolothic converters on the market > in that range, too... > > On Wed, 20 Aug 2003 05:47:57 GMT, ricklyon@REMOVE.onemain.com (Rick > Lyons) wrote: > > > > >Hi Peter, > > did you really build a 1 Gsample/sec A/D converter?(!!) > > > >I don't even want to *think* about it. > >I mean, how do you 'breadboard' a circuit that > >runs at 1 GHz. How do you inject test signals? > >How do you monitor voltages at different nodes? > >I checked my Radio Shack catalog and they don't > >even sell test equipment that operates at 1 GHz. > > > >[-Rick-] > > > >------------------------------------------- > >On Mon, 18 Aug 2003 13:32:28 +0200, "John Smith" <piet@bel.com> wrote: > > > >>I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised > >>everything, and used an example from literature to test the design. I am not > >>an expert in choosing the bit widths. > >>The comb filters just keeps accumulating samples. The accumulation result > >>gets bigger and bigger. If you subsample with a factor 16, the accumulation > >>register should not overflow within that period. I chose a wrong width ones > >>and did notice wrong results at the output. > >>regards, > >>-- > >>Peter Beukelman > >>senior ASIC designer > >>http://www.eonic.com > >>"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message > >>news:3f402ef6.115258812@news.west.earthlink.net... > >>> > >>> Hi Guys, > >>> > >>> I've been trying to learn about those darned cascaded > >>> integrator-comb (CIC) filters and have reviewed > >>> Hogenaurer's original paper > >>> > >>> Hogenauer, E. "An Economical Class of Digital Filters > >>> For Decimation and Interpolation," IEEE Trans. Acoust. > >>> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, > >>> April 1981. > >>> > >>> and Matt Donadio's CIC write-up (on www.dspguru.com). > >>> > >>> But I ran into something concerning CIC interpolators > >>> that I don't understand and hope you folk might help > >>> me out. > >>> > >>> Hogenauer says (on pp. 160) that there will be bit growth > >>> (gain) through the interpolator's comb filter(s) > >>> (differentiators) comprising the initial stage(s) > >>> of a CIC interpolation filter. He says the bit > >>> growth will be a factor of 2 > >>> for each comb filter used in the implementation. > >>> Because a comb (differentiator) merely outputs > >>> the difference between successive inputs, I don't see > >>> how there can be bit growth (gain) through the comb > >>> stages. > >>> > >>> My MATLAB modeling shows no gain (bit growth) in the > >>> interpolator's comb filters. They have a gain of zero > >>> at DC. (My modeling agrees with what Ray Andraka has > >>> stated here, for the gain of a CIC interpolator, > >>> several times on this newsgroup.) > >>> > >>> Anyway, my questions are: is there really bit > >>> growth (gain) in the initial comb stages of a CIC > >>> interpolation filter? Am I missing something simple > >>> here? Do I need to increase the dosage of my medication? > >>> > >>> Thanks for any help, > >>> [-Rick-] > >>> > >>> > >> > >> > > > > Eric Jacobsen > Minister of Algorithms, Intel Corp. > My opinions may not be Intel's opinions. > http://www.ericjacobsen.org
-- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 email ray@andraka.com http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759
Rick, the growth in a decimating CIC is in the integrator.
The comb can drop one LSB per stage if you don't need the
full precision without loss of function.   In the
interpolating filter, the combs come first, and in that case
there is a growth of one bit in each layer of the comb.  The
comb can't have any overflow or the differences would not
accumulate properly in the integrator.  An extra bit at each
level of the comb ensures that you will never have an
overflow in the comb sections.

Rick Lyons wrote:

> Hi Guys, > > I've been trying to learn about those darned cascaded > integrator-comb (CIC) filters and have reviewed > Hogenaurer's original paper > > Hogenauer, E. "An Economical Class of Digital Filters > For Decimation and Interpolation," IEEE Trans. Acoust. > Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, > April 1981. > > and Matt Donadio's CIC write-up (on www.dspguru.com). > > But I ran into something concerning CIC interpolators > that I don't understand and hope you folk might help > me out. > > Hogenauer says (on pp. 160) that there will be bit growth > (gain) through the interpolator's comb filter(s) > (differentiators) comprising the initial stage(s) > of a CIC interpolation filter. He says the bit > growth will be a factor of 2 > for each comb filter used in the implementation. > Because a comb (differentiator) merely outputs > the difference between successive inputs, I don't see > how there can be bit growth (gain) through the comb > stages. > > My MATLAB modeling shows no gain (bit growth) in the > interpolator's comb filters. They have a gain of zero > at DC. (My modeling agrees with what Ray Andraka has > stated here, for the gain of a CIC interpolator, > several times on this newsgroup.) > > Anyway, my questions are: is there really bit > growth (gain) in the initial comb stages of a CIC > interpolation filter? Am I missing something simple > here? Do I need to increase the dosage of my medication? > > Thanks for any help, > [-Rick-]
-- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 email ray@andraka.com http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759
Ray,

Gnarly.   Do you recall how expensive that ADC was or how much power
it used?   Both parameters are improving quickly these days...

On Wed, 27 Aug 2003 20:29:37 -0400, Ray Andraka <ray@andraka.com>
wrote:

>I did an FFT that worked at 960 MHz a year and a half ago in an FPGA. The >application had an Atmel 1GHz 8 bit ADC coupled to the FPGA, and the FPGA did >overlapped FFTs on the data in real time. > >Eric Jacobsen wrote: > >> Rick, >> >> Hotrod ADCs with samples rate >=1Gsps are not unusual these days, at >> least in labs. I know of at least one 4-bit, 1Gsps monolithic ADC in >> a lab, and they're working to add two more bits. There are >> non-monolithic converters that operate in those ranges as well that >> are commercialized. There may be monolothic converters on the market >> in that range, too... >> >> On Wed, 20 Aug 2003 05:47:57 GMT, ricklyon@REMOVE.onemain.com (Rick >> Lyons) wrote: >> >> > >> >Hi Peter, >> > did you really build a 1 Gsample/sec A/D converter?(!!) >> > >> >I don't even want to *think* about it. >> >I mean, how do you 'breadboard' a circuit that >> >runs at 1 GHz. How do you inject test signals? >> >How do you monitor voltages at different nodes? >> >I checked my Radio Shack catalog and they don't >> >even sell test equipment that operates at 1 GHz. >> > >> >[-Rick-] >> > >> >------------------------------------------- >> >On Mon, 18 Aug 2003 13:32:28 +0200, "John Smith" <piet@bel.com> wrote: >> > >> >>I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised >> >>everything, and used an example from literature to test the design. I am not >> >>an expert in choosing the bit widths. >> >>The comb filters just keeps accumulating samples. The accumulation result >> >>gets bigger and bigger. If you subsample with a factor 16, the accumulation >> >>register should not overflow within that period. I chose a wrong width ones >> >>and did notice wrong results at the output. >> >>regards, >> >>-- >> >>Peter Beukelman >> >>senior ASIC designer >> >>http://www.eonic.com >> >>"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message >> >>news:3f402ef6.115258812@news.west.earthlink.net... >> >>> >> >>> Hi Guys, >> >>> >> >>> I've been trying to learn about those darned cascaded >> >>> integrator-comb (CIC) filters and have reviewed >> >>> Hogenaurer's original paper >> >>> >> >>> Hogenauer, E. "An Economical Class of Digital Filters >> >>> For Decimation and Interpolation," IEEE Trans. Acoust. >> >>> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, >> >>> April 1981. >> >>> >> >>> and Matt Donadio's CIC write-up (on www.dspguru.com). >> >>> >> >>> But I ran into something concerning CIC interpolators >> >>> that I don't understand and hope you folk might help >> >>> me out. >> >>> >> >>> Hogenauer says (on pp. 160) that there will be bit growth >> >>> (gain) through the interpolator's comb filter(s) >> >>> (differentiators) comprising the initial stage(s) >> >>> of a CIC interpolation filter. He says the bit >> >>> growth will be a factor of 2 >> >>> for each comb filter used in the implementation. >> >>> Because a comb (differentiator) merely outputs >> >>> the difference between successive inputs, I don't see >> >>> how there can be bit growth (gain) through the comb >> >>> stages. >> >>> >> >>> My MATLAB modeling shows no gain (bit growth) in the >> >>> interpolator's comb filters. They have a gain of zero >> >>> at DC. (My modeling agrees with what Ray Andraka has >> >>> stated here, for the gain of a CIC interpolator, >> >>> several times on this newsgroup.) >> >>> >> >>> Anyway, my questions are: is there really bit >> >>> growth (gain) in the initial comb stages of a CIC >> >>> interpolation filter? Am I missing something simple >> >>> here? Do I need to increase the dosage of my medication? >> >>> >> >>> Thanks for any help, >> >>> [-Rick-] >> >>> >> >>> >> >> >> >> >> > >> >> Eric Jacobsen >> Minister of Algorithms, Intel Corp. >> My opinions may not be Intel's opinions. >> http://www.ericjacobsen.org > >-- >--Ray Andraka, P.E. >President, the Andraka Consulting Group, Inc. >401/884-7930 Fax 401/884-7950 >email ray@andraka.com >http://www.andraka.com > > "They that give up essential liberty to obtain a little > temporary safety deserve neither liberty nor safety." > -Benjamin Franklin, 1759 > >
Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
I didn't do the board design or procurement, so I wasn't privy to the cost of the
components.  The ADC was an Atmel TS8388. It was a brand new part, we had first
been
slated to use another ADC and separate mux chip when this was announced.

Eric Jacobsen wrote:

> Ray, > > Gnarly. Do you recall how expensive that ADC was or how much power > it used? Both parameters are improving quickly these days... > > On Wed, 27 Aug 2003 20:29:37 -0400, Ray Andraka <ray@andraka.com> > wrote: > > >I did an FFT that worked at 960 MHz a year and a half ago in an FPGA. The > >application had an Atmel 1GHz 8 bit ADC coupled to the FPGA, and the FPGA did > >overlapped FFTs on the data in real time. > > > >Eric Jacobsen wrote: > > > >> Rick, > >> > >> Hotrod ADCs with samples rate >=1Gsps are not unusual these days, at > >> least in labs. I know of at least one 4-bit, 1Gsps monolithic ADC in > >> a lab, and they're working to add two more bits. There are > >> non-monolithic converters that operate in those ranges as well that > >> are commercialized. There may be monolothic converters on the market > >> in that range, too... > >> > >> On Wed, 20 Aug 2003 05:47:57 GMT, ricklyon@REMOVE.onemain.com (Rick > >> Lyons) wrote: > >> > >> > > >> >Hi Peter, > >> > did you really build a 1 Gsample/sec A/D converter?(!!) > >> > > >> >I don't even want to *think* about it. > >> >I mean, how do you 'breadboard' a circuit that > >> >runs at 1 GHz. How do you inject test signals? > >> >How do you monitor voltages at different nodes? > >> >I checked my Radio Shack catalog and they don't > >> >even sell test equipment that operates at 1 GHz. > >> > > >> >[-Rick-] > >> > > >> >------------------------------------------- > >> >On Mon, 18 Aug 2003 13:32:28 +0200, "John Smith" <piet@bel.com> wrote: > >> > > >> >>I designed a CIC in VHDL for Altera for our 1 Gs/s ADC. I just parameterised > >> >>everything, and used an example from literature to test the design. I am not > >> >>an expert in choosing the bit widths. > >> >>The comb filters just keeps accumulating samples. The accumulation result > >> >>gets bigger and bigger. If you subsample with a factor 16, the accumulation > >> >>register should not overflow within that period. I chose a wrong width ones > >> >>and did notice wrong results at the output. > >> >>regards, > >> >>-- > >> >>Peter Beukelman > >> >>senior ASIC designer > >> >>http://www.eonic.com > >> >>"Rick Lyons" <ricklyon@REMOVE.onemain.com> wrote in message > >> >>news:3f402ef6.115258812@news.west.earthlink.net... > >> >>> > >> >>> Hi Guys, > >> >>> > >> >>> I've been trying to learn about those darned cascaded > >> >>> integrator-comb (CIC) filters and have reviewed > >> >>> Hogenaurer's original paper > >> >>> > >> >>> Hogenauer, E. "An Economical Class of Digital Filters > >> >>> For Decimation and Interpolation," IEEE Trans. Acoust. > >> >>> Speech and Signal Proc., Vol. ASSP?29, pp. 155-162, > >> >>> April 1981. > >> >>> > >> >>> and Matt Donadio's CIC write-up (on www.dspguru.com). > >> >>> > >> >>> But I ran into something concerning CIC interpolators > >> >>> that I don't understand and hope you folk might help > >> >>> me out. > >> >>> > >> >>> Hogenauer says (on pp. 160) that there will be bit growth > >> >>> (gain) through the interpolator's comb filter(s) > >> >>> (differentiators) comprising the initial stage(s) > >> >>> of a CIC interpolation filter. He says the bit > >> >>> growth will be a factor of 2 > >> >>> for each comb filter used in the implementation. > >> >>> Because a comb (differentiator) merely outputs > >> >>> the difference between successive inputs, I don't see > >> >>> how there can be bit growth (gain) through the comb > >> >>> stages. > >> >>> > >> >>> My MATLAB modeling shows no gain (bit growth) in the > >> >>> interpolator's comb filters. They have a gain of zero > >> >>> at DC. (My modeling agrees with what Ray Andraka has > >> >>> stated here, for the gain of a CIC interpolator, > >> >>> several times on this newsgroup.) > >> >>> > >> >>> Anyway, my questions are: is there really bit > >> >>> growth (gain) in the initial comb stages of a CIC > >> >>> interpolation filter? Am I missing something simple > >> >>> here? Do I need to increase the dosage of my medication? > >> >>> > >> >>> Thanks for any help, > >> >>> [-Rick-] > >> >>> > >> >>> > >> >> > >> >> > >> > > >> > >> Eric Jacobsen > >> Minister of Algorithms, Intel Corp. > >> My opinions may not be Intel's opinions. > >> http://www.ericjacobsen.org > > > >-- > >--Ray Andraka, P.E. > >President, the Andraka Consulting Group, Inc. > >401/884-7930 Fax 401/884-7950 > >email ray@andraka.com > >http://www.andraka.com > > > > "They that give up essential liberty to obtain a little > > temporary safety deserve neither liberty nor safety." > > -Benjamin Franklin, 1759 > > > > > > Eric Jacobsen > Minister of Algorithms, Intel Corp. > My opinions may not be Intel's opinions. > http://www.ericjacobsen.org
-- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 email ray@andraka.com http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759