AM7968 AMD [Advanced Micro Devices], AM7968 Datasheet - Page 17

• Manufacturer Part Number: AM7968
• Description: TAXIchip Integrated Circuits(Transparent Asynchronous Xmitter-Receiver Interface)
• Manufacturer: AMD [Advanced Micro Devices]

Oscillator
The Am7968 and Am7969 contain an inverting amplifier
intended to form the basis of a parallel mode oscillator.
The design of this oscillator considered several factors
related to its application.
The first consideration is the desired frequency accu-
racy. This may be subdivided into several areas. An os-
cillator is considered stable if it is insensitive to
variations in temperature and supply voltage, and if it is
unaffected by individual component changes and aging.
The design of the TAXIchip set is such that the degree to
which these goals are met is determined primarily by the
choice of external components. Various types of crystal
are available and the manufacturers’ literature should
be consulted to determine the appropriate type. For
good temperature stability, zero temperature coefficient
capacitors should be used (Type NPO).
The mechanism by which a crystal resonates is electro-
mechanical. This resonance occurs at a fundamental
C* = 220 pF for 4.0–12.5 MHz crystal, 150 pF for a 12.5–17.5 MHz Crystal.
*C determined by crystal specifications and trace capacities. Values shown are typical.
Figure 1. Connections for 4.0 MHz–17.5 MHz
X1
Am7968 or, Am7969
C
Am7968/Am7969
frequency (1st harmonic) and at all odd harmonics of
this frequency (even harmonic resonance is not me-
chanically possible). Unless otherwise constrained,
crystal oscillators operate at their fundamental
frequencies.
A typical crystal specification for use in this circuit is:
Fundamental Frequency 3.3 MHz–17.5 MHz
Resonance: Mode
Load Capacitor (Correlation)
Operating Temperature Range
Temperature Stability
Drive Level (Correlation)
Effective Series Resistance
Holder Type
Aging for 10 years
It is good practice to ground the case of the crystal to
eliminate stray pick-up and keep all connections as
short as possible.
X2
C
RESET
Power On RESET (Optional)
07370F-10
0 C to 70 C
25
Low profile
100 ppm
AMD
Parallel
10 ppm
2 mW
30 pF
(max)
0.1%
13