Chapter 10
Super-Regenerative
Detection
10.1 Introduction
Recently, CMOS-based THz detectors have been developed [250, 89, 31, 32,
33, 251]. One can thereby develop a low-cost, portable and large-arrayed THz
imaging system in CMOS. One transmission-type design is shown in Figure
10.1, where each THz image pixel consists o f a receiver and an antenna. How-
ever, the THz radiation signal strength is usually weak when generated by
CMOS and it will be further attenuated by absorption and diffraction during
the propagation. The main challenge is to design a high-sensitivity rece iver
that can compensate the weak signal source and the path propagation loss
with both narrow-band or wide-band approaches. Moreover, a large-arrayed
receiver is desired with improved spatial resolution and also image capturing
sp eed, requiring a compact design of each THz image pixel [252].
The re cent super-regenerative receiver (SRX) [89, 90] topology can achieve
high sensitivity within a narrow band, which is desired for a THz imager that
has a relatively low data rate. As depicted in Figure 10.2(a), the core of
a SRX is a quench-controlled oscillator, which consists of a r esonator with
a positive feedback network to realize an oscillatory amplification. When a
periodic quench-control signal is applied, the avera ge of detected signal en-
velope is amplified for the injected RF signa l from LNA. One compact and
high-sensitivity SRX for a THz imager requires a compact and high quality
factor (Q) res onator. Note that the Q of the traditional LC-tank-based re s-
onator [253] ha s significant performance degr adation with large area at THz
frequency region.
231
232 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
Figure 1 0.1: CMOS THz imager array.
Figure 10.2: (a) Block diagram of super-regenerative receiver; (b)
impact of resonator Q-factor to receiver sensi tivity.
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