Digital Signal Processing Reference
In-Depth Information
Near-end crosstalk (discussed in Chapter 10) between traces 1 and 5 (
Kb
1,5)
causes trace 1 to induce a small voltage on trace 5 and a larger voltage on trace
2 from (
Kb
1,2). This coupling is shown as occurring on trace 3 because here the
vertical connecting strap is assumed to be short enough to be ignored. The
Kb
1,5
signal arrives at the serpentine output
tpd
seconds after traveling the length of
trace 5, and the stronger
Kb
1,2 signal arrives 2
tpd
seconds later, after traveling
the entire length of traces 3 and 4. This voltage adds to the crosstalk already pres-
ent, causing the output to increase. The output reaches the full value at 5
tpd
with
the arrival of the launched signal. A ladder-like waveform [13] has been created at
the serpentine output, as illustrated in Figure 14.5(a). The expected waveform is
shown in Figure 14.5(b).
Laddering can occur with either stripline or microstrip because each are sus-
ceptible to near end crosstalk.
V
tpd
2 tpd
2 tpd
(a)
V
5 tpd
Voltage
Time
(b)
Figure 14.5
(a) Ladder-like waveform created by crosstalk appearing at the output of a fi ve-seg-
ment serpentine delay line contrasts with (b) the expected waveform.
