1055497-1 Datasheet, PDF (273/320 Pages) Tyco Electronics – RF Coax Products

Inches
1000
100
10
RF Coax Connectors
Appendix A - Theory and Application (Continued)
Notice that rise time is the time required for the pulse to
rise from 10% to 90% of its amplitude - not from zero to
maximum. Rise and fall time is perhaps the single most
important characteristic of a pulse in today’s high-speed
digital equipment. Figure 11 shows that the faster the rise
and fall time, the more pulses will fit in a given time frame.
A
1
0.1
Time
.001 GHz .01 GHz .1 GHz
1 GHz
10 GHz 100 GHz
B
FREFQrUeqEuNeCncYy ((MMHZ)
TEFLON (E=2.03)
Figure 9
AIR (E=1.00)
Table 1.
Properties of Insulating Materials
Dielectric
__^M_^a_^t_^e_^ri_^a_^l_
TFE
Polyethylene
Nylon
TPX
Polypropylene
Acetal
Dielectric
_^C_^o__ⁿ_^s_^ta_ⁿ_^t_
2.03
2.3
4.6-4.0
2.12
2.25
3.7
Operating
_^T_^e_^m__^p_^e_^ra_^t_^u_^r_^e_^R__^a_ⁿ_^g_^e_
-70 +250°C
-60 +80°C
-40 +120°C
-65 +85°C
-40 +105°C
-65 +85°C
Time
Figure 11
Pulse Rise and Fall Time
Pulses
The sine wave is most often used for communication
purposes where intelligence is imposed on the wave by a
variation in amplitude (amplitude modulation, AM) or by a
variation in frequency (frequency modulation, FM).
Pulses, on the other hand, are primarily used in computers
and digital instrumentation. Since pulses are generally used
for triggering purposes, the pulse rise/fall time, amplitude
and width are the most important. Figure 10 shows a pulse
and identifies these characteristics.
Width
90%
90%
Amplitude
10%
10%
Repetition
Rate
Rise
Time
Figure 10
Pulse Characteristics
Fall Time
The bit rate for a system is the maximum rate of pulses per
second that a system can process without causing data
errors. The maximum performance can also be specified
in terms of baud rate. The baud rate is defined as the
number of characters (bytes) that are transmitted per sec-
ond. Generally a character represents 10 bits (7 bits for
the information, one parity bit, and two for start and stop,
totalling 10).
Now that we know why fast pulses are required, the next
problem is how to obtain faster rise times. A pulse is
made up of a great number of different frequencies, and
the more high frequencies a pulse contains, the faster will
be its rise time and the flatter will be its peak. To better
understand this, refer to Figure 12. At A, you will see a
fundamental frequency (1), its third harmonic (3), and the
resultant waveform (S3), which is a combination of 1 and
3. Although this does not yet resemble a square wave,
you will note that the rise time is decreased, and a dip
appears at the peak. At B of Figure 12, we have added
the fifth harmonic. Rise time is further decreased, and the
peak is beginning to flatten out. At C the seventh har-
monic has been included, and the resultant wave S7
begins to resemble a square wave. As more high fre-
quency harmonics are added to the waveform, it will more
closely resemble a square wave, and the squarer it
becomes, the faster will be the rise time.
TPX is a trademark of Mitsui Chemicals America, Inc.
273
Catalog 1307191
Revised 3-07
www.tycoelectronics.com
Dimensions are in millimeters
and inches unless otherwise
specified. Values in brackets
are standard equivalents.
Dimensions are shown for
reference purposes only.
Specifications subject
to change.
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