Hi all,
I use the LPC2365 micro with SMSC LAN8700 as Ethernet PHY.
In order to reduce the EMI emissions, I would like to use this spread
spectrum oscillator:
http://www.digikey.com/product-search/en?x=15&y=17&lang=en&site=us&KeyWords=ASSVP-R-C01-ND
The Spread Spectrum Bandwidth is 0.125% that corresponds to 50ps
maximum jitter (the frequency is 50MHz with a stability of 25ppm).
The Ethernet PHY accepts clock jitter up to 150ps but unfortunately
the board works fine at 10Mbit/s but doesn't work at 100Mbit/s.
Has someone tried to use spread spectrum oscillators with ethernet?
Thanks in advance,
Giuseppe
Ethernet PHY and spread spectrum oscillator
Started by ●March 21, 2013
Reply by ●March 21, 20132013-03-21
Is the network clock in of the LPC connected to the clk out of the phy or
directly to the oscillator?
Because I had a similar problem with a different phy and a different oscillator. Because the delay in the clock through the phy was too big. Both the phy and the lpc need to be directly connected to the oscillator.
10mbit works because the timing is less critical.
--
Kevin
--- In l..., Geppo wrote:
>
> Hi all,
> I use the LPC2365 micro with SMSC LAN8700 as Ethernet PHY.
> In order to reduce the EMI emissions, I would like to use this spread
> spectrum oscillator:
> http://www.digikey.com/product-search/en?x=15&y=17&lang=en&site=us&KeyWords=ASSVP-R-C01-ND
> The Spread Spectrum Bandwidth is 0.125% that corresponds to 50ps
> maximum jitter (the frequency is 50MHz with a stability of 25ppm).
> The Ethernet PHY accepts clock jitter up to 150ps but unfortunately
> the board works fine at 10Mbit/s but doesn't work at 100Mbit/s.
> Has someone tried to use spread spectrum oscillators with ethernet?
> Thanks in advance,
> Giuseppe
>
Because I had a similar problem with a different phy and a different oscillator. Because the delay in the clock through the phy was too big. Both the phy and the lpc need to be directly connected to the oscillator.
10mbit works because the timing is less critical.
--
Kevin
--- In l..., Geppo wrote:
>
> Hi all,
> I use the LPC2365 micro with SMSC LAN8700 as Ethernet PHY.
> In order to reduce the EMI emissions, I would like to use this spread
> spectrum oscillator:
> http://www.digikey.com/product-search/en?x=15&y=17&lang=en&site=us&KeyWords=ASSVP-R-C01-ND
> The Spread Spectrum Bandwidth is 0.125% that corresponds to 50ps
> maximum jitter (the frequency is 50MHz with a stability of 25ppm).
> The Ethernet PHY accepts clock jitter up to 150ps but unfortunately
> the board works fine at 10Mbit/s but doesn't work at 100Mbit/s.
> Has someone tried to use spread spectrum oscillators with ethernet?
> Thanks in advance,
> Giuseppe
>
Reply by ●March 22, 20132013-03-22
Thanks Kevin,
the output of oscillator is directly connected to both CLKIN of PHY and ENET_REF_CLK of LPC2365.
--- In l..., "Kevin" wrote:
>
> Is the network clock in of the LPC connected to the clk out of the phy or directly to the oscillator?
>
> Because I had a similar problem with a different phy and a different oscillator. Because the delay in the clock through the phy was too big. Both the phy and the lpc need to be directly connected to the oscillator.
>
> 10mbit works because the timing is less critical.
>
> --
> Kevin
>
>
> --- In l..., Geppo wrote:
> >
> > Hi all,
> > I use the LPC2365 micro with SMSC LAN8700 as Ethernet PHY.
> > In order to reduce the EMI emissions, I would like to use this spread
> > spectrum oscillator:
> > http://www.digikey.com/product-search/en?x=15&y=17&lang=en&site=us&KeyWords=ASSVP-R-C01-ND
> > The Spread Spectrum Bandwidth is 0.125% that corresponds to 50ps
> > maximum jitter (the frequency is 50MHz with a stability of 25ppm).
> > The Ethernet PHY accepts clock jitter up to 150ps but unfortunately
> > the board works fine at 10Mbit/s but doesn't work at 100Mbit/s.
> > Has someone tried to use spread spectrum oscillators with ethernet?
> > Thanks in advance,
> > Giuseppe
>
the output of oscillator is directly connected to both CLKIN of PHY and ENET_REF_CLK of LPC2365.
--- In l..., "Kevin" wrote:
>
> Is the network clock in of the LPC connected to the clk out of the phy or directly to the oscillator?
>
> Because I had a similar problem with a different phy and a different oscillator. Because the delay in the clock through the phy was too big. Both the phy and the lpc need to be directly connected to the oscillator.
>
> 10mbit works because the timing is less critical.
>
> --
> Kevin
>
>
> --- In l..., Geppo wrote:
> >
> > Hi all,
> > I use the LPC2365 micro with SMSC LAN8700 as Ethernet PHY.
> > In order to reduce the EMI emissions, I would like to use this spread
> > spectrum oscillator:
> > http://www.digikey.com/product-search/en?x=15&y=17&lang=en&site=us&KeyWords=ASSVP-R-C01-ND
> > The Spread Spectrum Bandwidth is 0.125% that corresponds to 50ps
> > maximum jitter (the frequency is 50MHz with a stability of 25ppm).
> > The Ethernet PHY accepts clock jitter up to 150ps but unfortunately
> > the board works fine at 10Mbit/s but doesn't work at 100Mbit/s.
> > Has someone tried to use spread spectrum oscillators with ethernet?
> > Thanks in advance,
> > Giuseppe
>
