VCO in a PLL

On Wed, 11 May 2016 10:44:52 -0700, mariam876am wrote:

> HowtodemodulatedtheFMsignalwithhighfrequencysuchas1GHZ,

1: If you have a new question, ask it in a new thread.

2: use spaces.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

On 1/12/2014 3:27 PM, robert bristow-johnson wrote:
> On 1/12/14 3:05 PM, gyansorova@gmail.com wrote:
>> An old engineer told me that although in theory you get improvements
>> in demodulating FM via a PLL,
>
> dunno what that theory is.  but i *do* remember that "PLL front end" or
> something like that was a selling point for stereo receivers back in the
> 70s.  i think the PLL was also part of the AFC function.
>
>> in practice you cannot make a VCO which has low enough phase noise to
>> compete with say a Quadrature Detector.
>
> dunno.  have to see the specific circuit, system, and specs on the
> parts.  i dunno what phase noise is in a VCO.  i think of "phase noise"
> as a term applied to roundoff applied to the index to a table-lookup
> wavetable oscillator.

Doesn't phase noise also apply to analog components?


>> This is also the feeling in industry. I would have thought that a VCO
>> could be made near perfect with an FPGA nowadays - or am I missing
>> something?
>
> do FPGAs have analog components inside?  i generally think of them as
> all-digital parts.  or do you mean the digital counterpart to a VCO,
> usually called an "NCO"?

FPGAs have internal PLLs, but they are intended for clock generation and 
I don't think would be suitable for an FM receiver, unless it was a SDR, 
all digital receiver.

A digital PLL can be designed with as low phase noise as required by the 
application.  Ultimately the limit will be the phase noise of the 
reference oscillator or if the output is analog, the DAC.

-- 

Rick C

On Thu, 12 May 2016 23:05:39 -0400, rickman wrote:

> On 1/12/2014 3:27 PM, robert bristow-johnson wrote:
>> On 1/12/14 3:05 PM, gyansorova@gmail.com wrote:
>>> An old engineer told me that although in theory you get improvements
>>> in demodulating FM via a PLL,
>>
>> dunno what that theory is.  but i *do* remember that "PLL front end" or
>> something like that was a selling point for stereo receivers back in
>> the 70s.  i think the PLL was also part of the AFC function.
>>
>>> in practice you cannot make a VCO which has low enough phase noise to
>>> compete with say a Quadrature Detector.
>>
>> dunno.  have to see the specific circuit, system, and specs on the
>> parts.  i dunno what phase noise is in a VCO.  i think of "phase noise"
>> as a term applied to roundoff applied to the index to a table-lookup
>> wavetable oscillator.
> 
> Doesn't phase noise also apply to analog components?
> 

<snip>

Indeed it does, and analog PLL's both reduce it in places and increase it 
in places, which makes the design challenging.


-- 
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work!  See my website if you're interested
http://www.wescottdesign.com

On 5/13/2016 11:44 AM, Tim Wescott wrote:
> On Thu, 12 May 2016 23:05:39 -0400, rickman wrote:
>
>> On 1/12/2014 3:27 PM, robert bristow-johnson wrote:
>>> On 1/12/14 3:05 PM, gyansorova@gmail.com wrote:
>>>> An old engineer told me that although in theory you get improvements
>>>> in demodulating FM via a PLL,
>>>
>>> dunno what that theory is.  but i *do* remember that "PLL front end" or
>>> something like that was a selling point for stereo receivers back in
>>> the 70s.  i think the PLL was also part of the AFC function.
>>>
>>>> in practice you cannot make a VCO which has low enough phase noise to
>>>> compete with say a Quadrature Detector.
>>>
>>> dunno.  have to see the specific circuit, system, and specs on the
>>> parts.  i dunno what phase noise is in a VCO.  i think of "phase noise"
>>> as a term applied to roundoff applied to the index to a table-lookup
>>> wavetable oscillator.
>>
>> Doesn't phase noise also apply to analog components?
>>
>
> <snip>
>
> Indeed it does, and analog PLL's both reduce it in places and increase it
> in places, which makes the design challenging.

Indeed...

-- 

Rick C

On Tuesday, May 17, 2016 at 3:12:58 AM UTC+12, rickman wrote:
> On 5/13/2016 11:44 AM, Tim Wescott wrote:
> > On Thu, 12 May 2016 23:05:39 -0400, rickman wrote:
> >
> >> On 1/12/2014 3:27 PM, robert bristow-johnson wrote:
> >>> On 1/12/14 3:05 PM, gyansorova@gmail.com wrote:
> >>>> An old engineer told me that although in theory you get improvements
> >>>> in demodulating FM via a PLL,
> >>>
> >>> dunno what that theory is.  but i *do* remember that "PLL front end" or
> >>> something like that was a selling point for stereo receivers back in
> >>> the 70s.  i think the PLL was also part of the AFC function.
> >>>
> >>>> in practice you cannot make a VCO which has low enough phase noise to
> >>>> compete with say a Quadrature Detector.
> >>>
> >>> dunno.  have to see the specific circuit, system, and specs on the
> >>> parts.  i dunno what phase noise is in a VCO.  i think of "phase noise"
> >>> as a term applied to roundoff applied to the index to a table-lookup
> >>> wavetable oscillator.
> >>
> >> Doesn't phase noise also apply to analog components?
> >>
> >
> > <snip>
> >
> > Indeed it does, and analog PLL's both reduce it in places and increase it
> > in places, which makes the design challenging.
> 
> Indeed...
> 
> -- 
> 
> Rick C

That's why PLLs are out of fashion in many FM receivers. They use Quad detectors instead.