Digital Signal Processing Reference
In-Depth Information
Signal energy is lost to the trace resistance and to leakage currents in the
dielectric.
•
At low frequencies the conductor loss outweighs dielectric loss, but this re-
verses at high frequency.
•
High-impedance traces have lower conductor loss than low-impedance
traces.
•
Surface roughness of the trace and the return planes increase the conductor
loss, especially at high frequency.
•
Dielectric loss increases with frequency and is determined by the laminate's
loss tangent value.
•
Changes in temperature alter the conductor and dielectric losses, and the
dielectric loss is also affected by moisture.
•
Traces are usually not rectangular in shape. This alters the transmission line's
electrical characteristics.
•
Problems
Answers to these problems are available on the Artech House Web site at http://
www.artechhouse.com/static/reslib/thierauf/thierauf1.html.
8.1
A serial interface requires a minimum signal of 175 mV peak to peak at
the receiver. Assuming that the transmitter launches 800 mV peak to peak,
what is the maximum loss allowed in the interconnect?
8.2
Transmission line loss is a concern in a design linking two custom-designed
integrated circuits. What impedance and trace width should be selected to
minimize loss?
8.3
Estimate the conductor loss of a 15.75-inch (40-cm)-long, 8-mil (0.20-mm)-
wide, 50
Ω
half-ounce stripline on FR4 at 1.25 GHz.
8.4
In a particular application, 50
controlled impedance stripline traces on
FR4 have too much loss. The signal integrity engineer states that although it
will cost more to manufacture, both the dielectric and conductor losses can
be reduced by changing to a low
Dk
laminate. Is this true, and if so, why?
Ω
8.5
To reduce cost and current consumption, a gate array manufacture has
moved an old product line to a new process technology. A side effect is that
the I/O signal rise time that was 1 nS becomes 700 pS. According to the
manufacturer, this is advantageous because it results in more setup time for
downstream logic. Considering only signal integrity, what must be consid-
ered before you can decide if it is safe to use this new version of the chip in
place of the older chip in existing designs?
8.6
A 50
stripline has a dielectric loss of 3 dB at 2 GHz. What is the dielectric
loss at 1 GHz for a 100
Ω
Ω
stripline that is fabricated on the same circuit
board?
8.7
What the dielectric loss for a 40-cm-long stripline trace at 1 GHz when
fabricated on IS410?
