IEEE Solid-State Circuits Magazine - Fall 2017 - 89

topology. Figure 10 shows the core
differential circuit incorporating the
capacitive neutralization technique.
Capacitive neutralization of differential amplifiers is a wideband technique that insures the stability of the
amplifier. Conse quently, differential front-end mm-wave power amplifiers on the transmitter side and
low-noise amplifiers on the receiver
side use this technique to achieve
wideband performance improvement. In addition, this technique can
be used at near-fmax frequencies to
boost the amplifier's power gain.
One important observation is that,
besides stabilizing the amplifier, neutralization essentially increases the
maximum allowable matching bandwidth of the amplifier, predicted by
the Bode-Fano limit [1]. This notion
will be used in wideband RF or mmwave applications.
For a better performance comparison,
consider two amplifiers in the same
180 -n m CMOS pr o cess, bot h de signed to operate at 28-GHz center frequency. In Figure 11, (a) shows a source
degenerated cascode amplifier, and (b)
indicates a common-source stage with
neutralization. For the sake of simplicity,
the input and output matching circuits
are realized with transformers. From
the simulated gain plots indicated in
Figure 12(a), the neutralized commonsource stage exhibits higher peak gain
and wider frequency response, which
is to be expected. Since the operation

frequency is close to fmax of the device
in this process, which is around 55 GHz,
the common-gate transistor contributes considerably to the overall
noise figure. The noise figure of the cascode amplifier is higher than that of the
neutralized common-source amplifier, which is also verified with noise figure simulation of these two stages [see
Figure 12(b)].

Conclusions
The general concept of amplifier
neutralization to overcome amplifier
instability has been around for many
years, dating back to the early part of the
20th century. This article provided an
overview of neutralization techniques
for high frequency amplifiers. First, the
problem of instability in non-unilateral
amplifiers driving tuned RLC tank circuits was studied. This discussion was
followed by revisiting RF cascode amplifiers. The issues associated with cascode topology at high frequencies were
briefly explained, which paved the way
for introducing the neutralization techniques in both single-ended and differential high-frequency amplifiers. Two
examples, a cascode amplifier with
source degeneration and a neutralized

Neutralized

6
5.5

6.5

5
4.5
4
3.5
3
2.5
2

5.5

6
Gain (dB)

Gain (dB)

Cascode

The general concept of amplifier neutralization
to overcome amplifier instability has been
around for many years, dating back to the
early part of the 20th century.

2.7 2.8 2.9
3
Frequency (Hz) × 1010
(a)

4
3

Acknowledgments
This work was supported in part by
a grant from the Samsung Advanced
Institute of Technology (SAIT) Global
Research Outreach (GRO) Program
and NSF Award ECCS-1611575.

References

[1] T. H. Lee, Planar Microwave Engineering:
A Practical Guide to Theory, Measurement,
and Circuits. Cambridge, U.K. Cambridge
Univ. Press, 2004.
[2] B. Razavi, Design of Analog CMOS Integrated Circuits, 2nd ed. New York: McGraw-Hill, 2016.
[3] P. Heydari, "Design and analysis of a performance-optimized CMOS UWB distributed LNA," IEEE J. Solid-State Circuits, vol.
42, no. 9, pp. 1892-1905, Sept. 2007.
[4] M. Zargari, M. Terrovitis, S. H. M. Jen, B. J.
Kaczynski, M. Lee, M. P. Mack, S. S. Mehta,
S. Mendis, K. Onodera, H. Samavati, W.
W. Si, K. Singh, A. Tabatabaei, D. Weber,
D. K. Su, and B. A. Wooley, "A single-chip
dual-band tri-mode CMOS transceiver
for IEEE 802.11a/b/g wireless LAN," IEEE
J. Solid-State Circuits, vol. 39, no. 12, pp.
2239-2249, Dec. 2004.
[5] V. Jain, S. Sundararaman, and P. Heydari,
"A CMOS 22-29GHz receiver front-end for
UWB automotive pulse-radars," in Proc.
IEEE Custom Integrated Circuits Conf.,
Sept. 2007, pp. 757-760.
[6] A. Shameli and P. Heydari, "A novel ultralow power (ULP) low noise amplifier using
differential inductor feedback," in Proc.
32nd European Solid-State Circuits Conf.,
Sept. 2006, pp. 352-355.
[7] K. K. Clarke and D. T. Hess, Communication Circuits: Analysis and Design, 2nd ed.
Florida: Krieger Publishing, 1994.

About the Authors

4.5
3.5

2.6

common-source amplifier, in a 180-nm
CMOS process and for carrier frequency
of 28 GHz were presented. The commonsource amplifier shows higher power
gain and lower noise figure compared to
the cascode amplifier, as was anticipated
from the study of this article.

2.6

2.7 2.8 2.9
3
Frequency (Hz) × 1010
(b)

FIGURE 12: (a) Simulated gain versus frequency. (b) Simulated noise figure versus frequency
for both cascode and common-source amplifiers in Figure 11(a) and (b).

Payam Heydari is a full professor of
electrical engineering at the University of California, Irvine. He is noted
for his pioneering work on siliconbased millimeter-wave and terahertz
IC design. He is the author or coauthor
of two books, one book chapter, and
more than 130 journal and conference
papers. He is a Fellow of the IEEE.

IEEE SOLID-STATE CIRCUITS MAGAZINE

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