MWE 2018 FR4A-4

0.18μm CMOS 技術における DGS 構造による実現される仮想インダクタンスの比較検討
Comparative Study of Virtual Inductors Realized by Defected GroundStructures for VCO Applications in 0.18 µm CMOS Technology
Ramesh K. Pokharel, Nusrat Jahan, Adel Barakat
Graduate School of Information Science and Electrical Engineering (ISEE), Kyushu University, Motooka 744, NishiKu, Fukuoka 819-0395, Japan
Abstract
We analyze the quality factor of three different types of defected ground structure (DGS) resonators including a series
resonance in addition to the parallel one. Then, we implement the resonators to design high-performance K-band VCOs
in 0.18 μm CMOS Technology and finally, a low phase noise VCO at K-band is introduced.
Index Terms—Defected Ground structure, CMOS, on-chip, phase noise, series resonance, VCO.

1.

2.

DESIGN AND ANALYSIS OF HIGH Q-FACTOR DGS
A DGS etched on the ground plane below a 50-Ohms
microstrip line (MSL) interrupts the electromagnetic field(EM) producing notches [3], and this can be interpreted asa virtual series inductor of high Q-factor [4]. To
investigate this, two types of DGS on 1-poly 6-metal(1P6M) 0.18 μm CMOS technology as shown in Fig. 1 isanalyzed. An H-shape DGS consists of two current loops
in parallel which makes the equivalent inductance (LEQ) of
the DGS to be half of the inductance of each loop so thatthe unloaded Q-factor (QU) is degraded. To mitigate thisproblem, we designed a square-shaped DGS as shown inFig. 1(b) where H-shape DGS is first halved and then areaof the square-shaped DGS is made equal to the original Hshape DGS. As shown, the square-shape DGS has only
one current loop, and LEQ will be the same as theinductance of each loop of an H-shape DGS. Both of these
DGS can be modeled using the equivalent circuit shownin Fig. 1(b). The square-shape DGS resonator has a higher

50Ω MSL(M6)
gH-shape
DGS on M1

50Ω MSL(M6)(a)

gSquare-shape
DGS on M1

k2p
2p

kpp
t

2p

(b)

t
Groundplane(M1)

2p

SiO2

Groundplane(M1)

SiO2

P1

20P2

RDGS LDGS

CDGS

Quality factor (QU)

INTRODUCTION
Design of spiral-inductors based Complementary
Metal-Oxide-Semiconductor (CMOS) circuit elements atKu-band and higher encounters difficulty due to thesudden deterioration of the quality (Q-) factor and the selfresonance of spiral inductors. To mitigate this problem
particularly of a voltage controlled oscillator (VCO)
design, various types of high Q-factor inductor [1-3], highresistivity substrate [4], proton bombardment techniques[4], and substrate removal by post micromachining [4]were proposed. However, all of these techniques requirecomplicated post-processing of the CMOS wafer which
may increase the cost. In this abstract, we discuss three
DGS structures to realize a high Q-factor virtual
inductance in 0.18 μm CMOS technology and theiremployment in the design of low phase-noise K/Ku-bandVCOs.

(c)

H-shaped DGS
Square-shaped DGS15(d)1050010203040

Frequency (GHz)
Fig 1. (a) H-shape DGS (b) Square-shape DGS (c) Equivalent circuit(d) Comparison of QU.

inductance and QU than that of the H-shape DGS ascompaed on Fig 1(d). The optimized value of p,g, t, and k
are 50 µm, 15 µm, 14 µm, and 25 µm, respectively.
When the feeding MSL is cut from the middle, the DGS
can produce both the resonance/series resonance and anti-