ds0026 National Semiconductor Corporation, ds0026 Datasheet - Page 5

• Manufacturer Part Number: ds0026
• Description: Dual High-speed Mos Driver
• Manufacturer: National Semiconductor Corporation

AC Test Circuits and Switching Time Waveforms
Typical Applications
DC Coupled RAM Memory Address or Precharge
AC Coupled MOS Clock Driver
Driver (Positive Supply Only)
DS005853-17
DS005853-16
FIGURE 1.
FIGURE 2.
5
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Application Hints
DRIVING THE MM5262 WITH THE
DS0026 CLOCK DRIVER
The clock signals for the MM5262 have three requirements
which have the potential of generating problems for the user.
These requirements, high speed, large voltage swing and
large capacitive loads, combine to provide ample opportunity
for inductive ringing on clock lines, coupling clock signals to
other clocks and/or inputs and outputs and generating noise
on the power supplies. All of these problems have the poten-
tial of causing the memory system to malfunction. Recogniz-
ing the source and potential of these problems early in the
design of a memory system is the most critical step. The ob-
ject here is to point out the source of these problems and
give a quantitative feel for their magnitude.
Line ringing comes from the fact that at a high enough fre-
quency any line must be considered as a transmission line
with distributed inductance and capacitance. To see how
much ringing can be tolerated we must examine the clock
voltage specification. Figure 3 shows the clock specification,
in diagram form, with idealized ringing sketched in. The ring-
ing of the clock about the V
the V
tion stored in the memory could be altered. Referring to Fig-
ure 1 , if the threshold voltage of a transistor were −1.3V, the
clock going to V
whose gates are tied to that clock, would be only 300 mV
from turning on. The internal circuitry needs this noise mar-
gin and from the functional description of the RAM it is easy
to see that turning a clock on at the wrong time can have di-
sastrous results.
DS005853-14
SS
− 1 V
OH
is not maintained, at all times, the informa-
SS
− 1 would mean that all the devices,
SS
level is particularly critical. If
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