IEEE Circuits and Systems Magazine - Q1 2021 - 52

Mini-Circuits
ZHL-42 PA

Tx Vivaldi

Hittite HMC213
Mixer
700 ps Gaussion
Pulse Generator

Equivalent Time Sampling

Mini-Circuits
ZX95-3360 VCO
3 GHz

Power
Divider

Sample CLK
Quadrature
90°
0°

Rx Vivaldi Array
SP8T
Switch

10 MHz Driving CLK

Hitite
HMC753 LNA

DC-1.5 GHz
Low Pass

IN
Q
D[0-9]

150 MHz

Data I

ADC
Power
Divider

Delay Line

Data Q

FPGA

ADC

Figure 7. Block diagram of the UWB radar prototype [21] © 2013 IEEE.

The experimental validation included a subject imitating
chest vibration to ensure repeatability and reproducibility
of the data. Next, an analysis on the extraction of human
vital signs in the presence of noise was presented in [48].
The heart rate and respiration rate were obtained after
phase demodulation of the received signal. The results
show that monitoring of heart rate and respiration rate
can be achieved even at 10 m distance from the radar.
As summarized in Table 5, various frequency bands
have been used for UWB impulse radars. Several examples are the one used by [50] operating from 0.5 to
5.5 GHz, the radar in [45] with center frequencies ranging
from 1 GHz to 18 GHz, and bandwidth ranging from 7.3 to
12.7 GHz; and the radar in [21] with a center frequency of
3 GHz and a bandwidth of 1.5 GHz. Other reported UWB
impulse radars operated in a single frequency such as in
[48] using 5.4 GHz, the radar in [40] using 5.75 GHz, and
the radar in [36] using 6 GHz. In literature, the highest
center frequency reported for such type of radar is at
7.3 GHz, operating with a bandwidth of 1.4 GHz [46].

C. FMCW Radar
FMCW radars are designed to overcome the disadvantages of CW and UWB radars. Operation of the FMCW
radar includes the linear frequency sweeping of the
transmit signal over time for repeated periods. The resulting frequency modulated signal is called a " chirp " .
The radar then measures the frequency differences
between the transmitted signal (which is linearly frequency modulated) and the received signal from which
information about the range and velocity can be obtained [2], [8]. In a recent work in [7], an FMCW radar is
used to obtain the RR and HR of a patient in a bedroom
environment. A signal-processing algorithm featuring
advanced phase unwrapping manipulation was used.
Meanwhile, the work in [51] prototyped a 60 GHz FMCW

27 MHz

1.8-3.3 V

XOSC and
243 MHz PLL
Rx R (t )

Amp.

Loop
Filter

Phase
Detector

G
Integrator 1/s

F (t )
Tx T(t )

Frequency
Output
b (t )

PLL
PM

Multiphase PLL
1,215/1,458 MHz

Multiphase PLL
1,944 MHz

Transmitter
B(t )
Phase Output

LO

Control
Logic

PMU

LNA

Sampler

SPI

PLL CW
Figure 8. Phase detection [33] © 2018 IEEE.

52

IEEE CIRCUITS AND SYSTEMS MAGAZINE

Figure 9. Block diagram of SoC radar in [4]. licensed under
Creative Commons attribution license.

FIRST QUARTER 2021



IEEE Circuits and Systems Magazine - Q1 2021

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