IEEE Solid-States Circuits Magazine - Fall 2020 - 27

to meet target SNR and BER requirements, thus degrading energy efficiency. The authors of [14] evaluated
the effects of crosstalk on channels
separated physically and by frequencies. In [30], the authors provided a
further detailed analysis of multichannel effects, with the assumption of a Chebyshev filter profile.

To mitigate dispersion effects, techniques in
the optical and electrical domains have been
investigated through the decades.
based tuning methods have been
im--plemented to adjust the dispersion
profile, range, and compensation frequency [62], [63]. However, grating
structures normally have a large size;
therefore, the techniques cannot be
used in interconnect applications,
where the channel size is one critical
specification for bandwidth density.
Although optical dispersion compensation techniques have long been
deployed, the approaches in the electrical domain are more versatile, agile,
and cost effective due to the almostfree transistors and unlimited signal
processing capabilities provided by
the semiconductor process's dramatic
advancement. Example techniques
include narrow-bandwidth and dispersionless sensitive modulation/demodulation schemes [64] and predistortion
and pulse shaping [65]. Most signal
processing for dispersion compensation is performed through filtering and
equalization techniques. Filtering has
two implementation formats: finite
impulse response and infinite impulse
response [66], [67]. Equalization can be
conducted through feedforward and
feedback equalization for precursor
and postcursor processing techniques

Dispersion Compensation
Techniques
To mitigate dispersion effects, techniques in the optical and -electrical
domains have been investigated
through the decades. In the optical
domain, dispersion compensation techniques are required to overcome the
fiber dispersion effect for long-distance
communication because fiber attention
is negligible and does not form the limit.
With dispersion-compensation fiber,
an opposite group delay profile is used
to offset fiber dispersion effects, at
the cost of a high loss. Another technique is to use a zero-dispersion wavelength (roughly 1.3 µm) in silica-based
optical fibers [59]. This approach is
constrained to only one frequency,
prohibiting its use in wideband and
wavelength-division multiplexing scenarios. Chirped delay lines and periodic grating structures [60], [61] are
widely adopted to generate a reverse
dispersion profile to compensate for
the original channel dispersion. Furthermore, strain- and temperature-

[68]-[77]. The incomparable signal processing capabilities in the electrical
domain do come with the hefty prices
of power consumption and latency,
which are exacerbated as processing
speed and complexity grow.
Figure 8 gives the dispersion compensation results for a silicon DWG
frequency-dependent dielectric constant through two fitting profiles:
linear and second order. The secondorder fitting generates results that are
clearly better. However, to completely
remove dispersion effects, existing solutions face challenges, such as bandwidth
limitations and profile approximation.
Besides, mismatch-caused group delay
ringing effects and nonmonotonic frequency dependency further challenge
dispersion compensation [78]. Nonconventional approaches may hold significant potential to advance this field.
For example, non-Foster techniques
[79], [80], which provide negative inductance and capacitance, can potentially
completely cancel frequency-dependent characteristics by offering the
same profile but with the opposite
sign [81]-[84]. However, non-Foster schemes have their own design
difficulties and drawbacks. First,

(mm)

SIW
Duplexer

Tapered
Slot Antenna
(a)

Electric Dipole
RO6006, εr = 6.15
HDPE, εr = 2.25

tal

flec

tor

Reflector

10
9
8
7
6
5
4
3
2
1
0

Slot Dipole
RO6006, εr = 6.15

(b)

HRS
400 µm
Trench

Overpass

Dummy
Overpass
(c)

FIGURE 7: (a) The SIW-based OMT for bidirectional links on the same physical channel [111]. (b) The dipole/slot-coupling structures [58].
(c) A silicon-based orthomode DWG channel [39] to provide polarization-orthogonal channels. SIW: substrate integrated waveguide; HRS:
high-resistivity silicon.

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IEEE Solid-States Circuits Magazine - Fall 2020

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