Better FM demodulator

Started by chris1911 January 14, 2006
Currently, I have a project that uses the Blackfin DSP.  A 8-bit A/D will
do undersampling (at 1.6384MHz) of an IF signal which is down-converter
from standard stereo FM broadcast. There are quite a few standard FM
demodulators, e.g. baseband delay, phase-adapter, mixed type and PLL
demodulator.  It seems the mixed demodulator should have the best
performance among those four.  Is there any other better performance (i.e.
S/N, distortion) demodulator available?  




chris1911 wrote:

> Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will > do undersampling (at 1.6384MHz) of an IF signal which is down-converter > from standard stereo FM broadcast.
This is pointless because the complete analog FM receiver IC costs about 50c and the DSP solution is not going to be any better.
> There are quite a few standard FM > demodulators, e.g. baseband delay, phase-adapter, mixed type and PLL > demodulator. It seems the mixed demodulator should have the best > performance among those four. Is there any other better performance (i.e. > S/N, distortion) demodulator available?
There are many ways to build a discriminator. However if you do the things right the performance will be identical, because it is still a discriminator by operation. It does not matter which way you built it. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Vladimir Vassilevsky wrote:

   ...

> There are many ways to build a discriminator. ...
Personally, I'm partial to the Avins-Seely ratio detector. Not me; my cousin. He had over fifty patents, many of them FM detectors. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
in some applications, a  THRESHOLD EXTENSION demodulator can work
better comapred to a standard discriminator...

but an FM  broadcast receiver is not one of those applications...

Mark

Vladimir Vassilevsky wrote:
> chris1911 wrote: > > > Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will > > do undersampling (at 1.6384MHz) of an IF signal which is down-converter > > from standard stereo FM broadcast. > > This is pointless because the complete analog FM receiver IC costs about > 50c and the DSP solution is not going to be any better.
I know you're a jerk but perhaps "project" means something to do for school, for learning, for fun? Tom
Tom St Denis wrote:
> Vladimir Vassilevsky wrote: > >>chris1911 wrote: >> >> >>>Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will >>>do undersampling (at 1.6384MHz) of an IF signal which is down-converter >>>from standard stereo FM broadcast. >> >>This is pointless because the complete analog FM receiver IC costs about >>50c and the DSP solution is not going to be any better. > > > I know you're a jerk but perhaps "project" means something to do for > school, for learning, for fun?
Perhaps project means for professional use too. A digital radio already has a powerful DSP. When the radio is switched to receiving analogue FM it makes perfect sense to use the DSP. It is cheaper, technically as good, and "fully digital receiver" has immense marketing power. Steve
Steve Underwood wrote:
> Tom St Denis wrote: > > Vladimir Vassilevsky wrote: > > > >>chris1911 wrote: > >> > >> > >>>Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will > >>>do undersampling (at 1.6384MHz) of an IF signal which is down-converter > >>>from standard stereo FM broadcast. > >> > >>This is pointless because the complete analog FM receiver IC costs about > >>50c and the DSP solution is not going to be any better. > > > > > > I know you're a jerk but perhaps "project" means something to do for > > school, for learning, for fun? > > Perhaps project means for professional use too. A digital radio already > has a powerful DSP. When the radio is switched to receiving analogue FM > it makes perfect sense to use the DSP. It is cheaper, technically as > good, and "fully digital receiver" has immense marketing power.
That's what the DAB radios getting popular here in the UK do. My BT Aviator radio has a Blackfin DSP and can process analogue FM as well as the digital broadcasts. Leon

Steve Underwood wrote:


>>>> Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D >>>> will >>>> do undersampling (at 1.6384MHz) of an IF signal which is down-converter >>>> from standard stereo FM broadcast. >>> >>> This is pointless because the complete analog FM receiver IC costs about >>> 50c and the DSP solution is not going to be any better. >> >> I know you're a jerk but perhaps "project" means something to do for >> school, for learning, for fun? > > Perhaps project means for professional use too. A digital radio already > has a powerful DSP. When the radio is switched to receiving analogue FM > it makes perfect sense to use the DSP. It is cheaper, technically as > good, and "fully digital receiver" has immense marketing power. >
Instead of continuation of bullshit, here is the formula: Vfm = (I*dQ/dt - Q*dI/dt)/(I^2 + Q^2) Behold the FM discriminator. It is a bit more complicated then 2+2 = 4. However don't expect the great result. The experience tells that the extra knowledge only hurts the idiots. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Leon wrote:
> Steve Underwood wrote: > >>Tom St Denis wrote: >> >>>Vladimir Vassilevsky wrote: >>> >>> >>>>chris1911 wrote: >>>> >>>> >>>> >>>>>Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will >>>>>do undersampling (at 1.6384MHz) of an IF signal which is down-converter >>>> >>>>>from standard stereo FM broadcast. >>>> >>>>This is pointless because the complete analog FM receiver IC costs about >>>>50c and the DSP solution is not going to be any better. >>> >>> >>>I know you're a jerk but perhaps "project" means something to do for >>>school, for learning, for fun? >> >>Perhaps project means for professional use too. A digital radio already >>has a powerful DSP. When the radio is switched to receiving analogue FM >>it makes perfect sense to use the DSP. It is cheaper, technically as >>good, and "fully digital receiver" has immense marketing power. > > > That's what the DAB radios getting popular here in the UK do. My BT > Aviator radio has a Blackfin DSP and can process analogue FM as well as > the digital broadcasts. > > Leon >
I think all the DAB solutions do this. I believe some cell phones with FM radio features are doing it too. It seems to make less sense in that case, since the FM front end must be completely separate from the cellular front end. Steve
"chris1911" <chris@omnicomm.com.hk> wrote in message
news:MqadnQb6e8WWPFTenZ2dnUVZ_vydnZ2d@giganews.com...
> Currently, I have a project that uses the Blackfin DSP. A 8-bit A/D will > do undersampling (at 1.6384MHz) of an IF signal which is down-converter > from standard stereo FM broadcast. There are quite a few standard FM > demodulators, e.g. baseband delay, phase-adapter, mixed type and PLL > demodulator. It seems the mixed demodulator should have the best > performance among those four. Is there any other better performance (i.e. > S/N, distortion) demodulator available? > > >
You will not outdo a standard analogue PLL with low phase noise in the VCO in a hurry.Why go digital when there is a perfectly cheap analogue solution? Naebad