25 Mhz Crystal And Associated Rc Components - Intel Quark SoC X1000 Design Manual

Platform Clocks Design Guidelines—Intel
Table 42. iClock (Single-ended Clocks)
For the Intel
RMII_REF_CLK_OUT clock, is used as a reference to the RMII. This clock is routed to
the PHY and also back the SoC integrated MAC.
RMII_REF_CLK_OUT
PCB Routing Layer(s) optional
Transmission Line Segment
Routing Layer (Microstrip /
Stripline / Dual Stripline)
Characteristic Impedance
(Single-ended)
Trace Width (w)
Trace Spacing(S2): Between
Single-ended Clocks
Trace Spacing(S3): Between
Clock and other signals
Trace Segment Length
Length Matching between Single-ended Clocks
Rs
Number of vias
Reference Plane
The single ended clocks are driven via clock drivers. The package and board routes
should be treated similarly to differential clock routes. They should be fully shielded on
both sides with VSS that is applicable to the driver, and with spacing equal to or greater
than the standard clock routes should be maintained. They should not be routed over
the XTAL_IN and XTAL_OUT traces.
10.4

25 MHz Crystal and Associated RC Components

Platforms are required to use the 25 MHz crystal to generate all platform clocks. This
requires that on board the following components should be stuffed:
• A 25 MHz crystal
• 2 External Load Capacitors Ce1 and Ce2
• A 1-M bias resistor
Refer to
June 2014
Order Number: 330258-002US
®
Quark™ SoC X1000
®
Quark™ SoC X1000 use case, one of the flex clocks,
Figure 38 below for illustration of the 25 MHz crystal connectivity.
Breakout
4 Layer 4 Layer
L L
A1 A2
MS MS
50 Ω +/- 15%
4.2 mil 4.2 mil
4.2 mil 20 mil
4.2 mil 20 mil
0.5" max 0.8" max
L + L <= 500 mil
A A2
Total trace length from SoC output
(RMII_REF_CLK_OUT) to external PHY must match
the trace length from SoC Output
(RMII_REF_CLK_OUT) to SoC input
(RMII_REF_CLK) within 10mils.
22 ohm +/- 5%
max 2
Continuous Ground only
4 Layer 4 Layer
L L
B C
MS MS
4.2 mil 4.2 mil
20 mil 20 mil
20 mil 20 mil
0.2" max 6" max
®
Intel Quark™ SoC X1000
4 Layer
L
D
MS
4.2 mil
20 mil
20 mil
1" max
PDG
77