AM7968-125JC datasheet(17/127 Pages) AMD

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AMD

Am7968/Am7969

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

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

their

fundamental

frequencies.

A typical crystal specification for use in this circuit is:

Fundamental Frequency 3.3 MHz–17.5 MHz

± 0.1%

Resonance: Mode

Parallel

Load Capacitor (Correlation)

30 pF

Operating Temperature Range

°C to 70°C

Temperature Stability

±100 ppm

Drive Level (Correlation)

2 mW

Effective Series Resistance

Ω (max)

Holder Type

Low profile

Aging for 10 years

±10 ppm

It is good practice to ground the case of the crystal to

eliminate stray pick-up and keep all connections as

short as possible.

RESET

Am7968 or, Am7969

Power On RESET (Optional)

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.

07370F-10

Figure 1. Connections for 4.0 MHz–17.5 MHz

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