Super-Regenerative Detection 241
Figure 1 0.8: Schematic of CMOS 96 GHz SRX with DTL-CSRR.
SRRs are closely coupled to the same host T-line implemented in the to pmost
metal layer (M8). The overall size of the proposed DTL-SRR is 35 × 34 µm
2
.
For the purpose of comparison, a traditional LC-tank resonator is designed in
the M8 metal layer as shown in Figure 10 .9(b), which has the same resonance
frequency of 135GHz. The S-parameters of both structur es are also verified by
EMX with the same parasitic capacitance of 16fF. As shown in Figur e 10 .10, a t
the vicinity of 140-GHz resonanc e, ε > 0 and µ < 0, and a magnetic plasmonic
medium is formed. As a re sult, a stop-band is formed at 140 GHz within a
narrow bandwidth of 3.5 GHz. The Q factor of the DTL-SRR resonator is 40,
which is more than 2 times the Q of the LC-tank re sonator. Moreover, the
DTL-SRR resonator layout area (1190 µm
2
) is less than half of the LC-tank
resonator (2500 µm
2
).
Such a Q factor enhancement effect can also be explained by the strong
phase non-linearity in the freq ue nc y range closed to SRRs resonance. Note
that the Q factor c an also be obtained by phase-based method:
Q =
ω
0
2
· |
d∠Z(jω)
dω
|, (10.15)
where ∠Z(jω) is the phase of resonator impedance. Figure 10.11(a) shows
the impedance dia gram of both DTL-SRR and LC-Tank witho ut any capac-
itor loading. A resonance generated by the SRR loadings is observed at 167
GHz for DTL-SRR. Such res onance causes non-linear phase shift at 140 GHz.
Figure 10.11(b) shows that DTL-SRR has much s tronger pha se non-linearity
than that of LC-Tank around 140 GHz. As shown in Figure 10.11(c), both
242 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
Figure 10.9: Layout for CMOS on-chi p implementation of DTL-SRR
for 135 GHz SRX.
Figure 10.10: EM-simulation-based comparison of DTL-SR R and LC-
tank resonator for CMOS 135 GHz SRX design.
structures have the same resonance frequency of 140 GHz after inc luding the
ideal capacitance (C = 1 6 fF). The phase non-linearity in DTL-SRRs increases
the phase gradie nt of Z
Dif f
at 140 GHz, resulting in a higher Q according to
(10.15).
10.3.3.2 1 35-GHz DTL-SRR-Based S RX
Figure 10.12 depicts the s chematic of 135-GHz DTL-SRR- based SRX. Firstly,
a transformer-based matching network is applied to the input matching for
Super-Regenerative Detection 243
(a)
(b)
(c)
Figure 10.11: Impedance diagram of DT L-S RR and LC-tank in Global
Foundries 65-n m CMOS process. (a) real and imaginary parts of
Z
Diff
, (b) phase of Z
Diff
, (c) p hase of Z
Diff
when the ideal 16-fF
capacitor is included.
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