MC912DG128ACPVE Datasheet, PDF (202/478 Pages) Freescale Semiconductor, Inc – Upward compatible with M68HC11 instruction set

Oscillator
Freescale Semiconductor, Inc.
yield an unacceptable NRM for a worst-case situation (the slope of the
NRM vs. capacitance curve is very steep, indicating severe sensitivity to
small variations). If the NRM optimization happened to be performed on
a best-case sample set, there could be unexpected sensitivity at worst-
case.
Negative Resistance Margin vs. Capacitance
1000
WCS
TYP
100
TYP
BCS
10
8 10 13 15 18 22 27 33 39 47 56 68
Capacitance
NRM measurement techniques can also generate misleading results
when applied to Automatic Level Control (ALC) style oscillator circuits
such as the D60x/Dx128x. Many NRM methods slowly increase series
resistance until oscillation stops. ALC-style oscillators reduce the gain of
the oscillator circuit after start-up to reduce current, so if the oscillator
tends to have more gain than optimum it will be more tolerant of
additional resistance after start-up than it will during the start-up process.
This means that NRM figures may be optimistic unless the method
verifies the NRM value by attempting to start the oscillator with the
additional resistance in-place. Worse, this phenomenon exaggerates
the difference between best- and worst-case NRM curves.
Technical Data
202
MC68HC912DT128A — Rev 4.0
Oscillator
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