AM7992B datasheet(7/27 Pages) AMD

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Am7992B

Figure 3.

TTL Clock Driver Circuit for X

SIA Oscillator

Speciﬁcation for External Crystal

When using a crystal to drive the Am7992B oscillator,

the following crystal speciﬁcation should be used to en-

sure a transmit accuracy of 0.01%:

Some crystal manufacturers have generated crystals

to this speciﬁcation. One such manufacturer is Reeves-

Hoffman. Their ordering part number for this crystal is

RH#04-20423-312. Another manufacturer is Epson—

Par t #MA 506-200M-50 pF, which is a surface-

mounted crystal.

Speciﬁcation for External TTL Level

When driving the oscillator from an external clock

source, X

2 must be left ﬂoating (unconnected). An

external clock having the following characteristics

must be used to ensure less than +0.5 ns jitter at

Transmit+ (see the X

1 Driven from External Source

waveform diagram and the TTL Clock Driver Circuit

for X

1, Figure 3):

s Clock Frequency: 20 MHz

±0.01%

s Rise/Fall Time (t

R/tF): <4 ns, monotonic

s X

1 HIGH/LOW Time (t

HlGH/tLOW): > 20 ns

s X

1 Falling Edge-to-Falling Edge Jitter: < ±0.2 ns at

1.5 V input

Receiver Path

The principle functions of the receiver are to signal the

LANCE that there is information on the receive pair and

to separate the incoming Manchester-encoded data

stream into clock and NRZ data.

The receiver section (see Figures 4 and 5) consists of

two parallel paths. The receive data path is a zero

threshold, wide bandwidth line receiver. The carrier

path is an offset threshold bandpass-detecting line re-

ceiver. Both receivers share common bias networks to

allow operation over an input common mode range of

0 V to 5.5V.

Limit

Unit

Min

Nominal

Max

Resonant Frequency

Error with C

L = 50 pF

–50

+50

PPM

Change in Resonant

Frequency Temperature

with C

L = 50 pF

–40

+40

PPM

Parallel Resonant

Frequency with

L = 50 pF

MHz

Motional Crystal

Capacitance, C

0.022

ALS Driver or

Equivalent

03378I-7

Manchester

Decoder

Data

Receiver

Noise

Reject

Filter

Carrier

Detect

RCLK

RENA

03378I-8

Figure 4.

Receiver

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