cn8237 Mindspeed Technologies, cn8237 Datasheet - Page 359

• Manufacturer Part Number: cn8237
• Description: Atm Oc-12 Servicesar Plus With Xbr Traffic Management
• Manufacturer: Mindspeed Technologies

CN8237
ATM OC-12 ServiceSAR Plus with xBR Traffic Management
Figure 16-10. Add a Delay Line
28237-DSH-001-C
ADDR/CNTRL/DATA Hold
Step 2 – Calculating the
Time to the SSRAMs
NOTE(S):
Not shown are series terminators located close to the source on all signals.
SAR
speed, the minimum set-up time is reduced) for set-up time. This design therefore
requires that a delay of at least 2.0 ns be added to the clock lines. An initial
approach was to adjust the series terminators for the clocks upwards to achieve
the equivalent of a 2 ns delay. This yielded a Set-up Time of 2.0 ns for the
SSRAMs. Eighteen ohm resistors were used on all signals except the clock lines
which had 70 ohm resistors. The large series (70 ohm) terminators on the clock
lines cause the signal fidelity to degrade (i.e., rounding of the square wave, slow
rise and fall times, and a voltage shift above ground). A better solution is to use
18 ohm series terminators on the clock lines and then add a Delay Line (DL) on
the output of the series terminator which needs to provide an absolute minimum
delay of 2.0 ns. (See
DS1L5DJ250S was selected which has a tolerance of +/- 5% (DL range is
2.375 ns to 2.625 ns) and an impedance of 50 ohms.
Calculate the ADDR/CNTRL/DATA hold time to the SSRAM using the SAR’s
absolute minimum signal propagation delay(s):
1.625 ns. This gives a margin of 1.125 ns.
CNTRL are held longer on the bus 3/4T + 1.25 ns)
The synchronous SRAMs require a minimum of 2.0 ns (as devices increase in
T/4 + 0.25 ns – DL = HOLD TIME (this applies to the DATA; ADDR and
15/4 + 0.25 ns – 2.375 ns = 1.625 ns
The hold time for the SSRAMs is 0.5 ns (or less) and this design provides for
CLK
Mindspeed Technologies
ADDR/CNTRL/DATA
DL
Figure
16-10.) To accomplish a 2.5 ns Delay Line, Thin-Film
16.0 Electrical and Mechanical Specifications
™
SSRAM
by_16
(4X)
8237_162
16.1 Timing
16-11