We present a low-noise small-area 24 GHz CMOS radar sensor for automotive collision avoidance. This sensor is based on direct-conversion pulsed-radar architecture. The proposed circuit is implemented using TSMC 0.13
The rapid evolution of wireless communications has resulted in a strong motivation toward building high performance SoC (System-on-a-Chip) in silicon. Particularly CMOS-based circuit is realizing its low cost and high level of integration. Thanks to these advantages, the growing demand for larger bandwidth also pursues CMOS-based circuits to move toward higher frequencies [
In this paper, we propose a low-noise and small-area 24 GHz receiver for the automotive radar. The proposed circuit is fabricated using TSMC 0.13
Thanks to the higher positioning accuracy and its narrow bandwidth, frequency-modulated continuous wave (FMCW) radar based on positioning techniques is often used in automotive radar systems [
FMCW radar principle.
For these cases related equations are expressed as (
If there is another radar operation with the same modulation scheme and the same frequency band, mutual interference will occur.
The proposed sensor is based on the direct-conversion pulsed-radar architecture shown in Figure
The proposed direct-conversion sensor.
Figure
Low-noise amplifier for 24 GHz radar sensor.
The input impedance expressed in (
Equation (
Considering only the drain current noise, the NF (noise figure) of the neutralized LNA can be shown as
In a cascade LNA, the extra common-gate transistor contributes additional noise, resulting in an overall NF of
The core of the mixer shown in Figure
Gilbert-cell downconversion mixer.
The chopping function is accomplished by the mixing cells of
Figure
Voltage-controlled oscillator.
Choosing the method to control a gain is essential at PGA design. The proposed PGA with source degeneration resistor is shown in Figure
Programmable gain amplifier.
The proposed SC (switched-capacitor) integrator contains some basic building blocks such as operational transconductance amplifier, capacitors, switches, and nonoverlapping clocks as shown in Figure
Fully differential switched-capacitor integrator.
At least one pair of nonoverlapping clocks is essential in SC circuits. These clocks determine when charge transfers occurs and they must be nonoverlapping to reduce inadvertent charge lost. As seen in Figure
Nonoverlapping clocks: (a) clock signals and (b) possible circuit implementation of nonoverlapping clocks from a single clock.
The circuits are designed and fabricated using TSMC 0.13
Table
Comparison of each component area of radar sensor.
Proposed circuit | Conventional circuit | |||
---|---|---|---|---|
Transmission lines | Area ( |
Inductors | Area ( | |
LNA |
|
20 |
|
70 |
|
30 |
|
80 |
|
|
10 |
|
50 |
|
Total TL area | 180 |
Total inductor area | 140 |
|
Total LNA area | 200 |
Total LNA area | 250 |
|
|
||||
Mixer |
|
10 |
|
50 |
|
20 |
|
70 |
|
|
30 |
|
100 |
|
Total TL area | 120 |
Total inductor area | 100 |
|
Total mixer area | 180 |
Total mixer area | 220 |
|
|
||||
VCO |
|
20 |
|
70 |
|
70 |
|
80 |
|
Total TL area | 110 |
Total inductor area | 150 |
|
Total VCO area | 160 |
Total LNA area | 180 |
|
|
||||
PGA + integrator | Total area | 12 |
Total area | 13 |
|
||||
Die | Total area | 800 |
Total area | 1,500 |
The die photograph is shown in Figure
Die photograph.
The input and output pads are laid out in GSG configuration with a pitch of 150
The radar sensor is tested by probing the input, output, and LO ports. The input, output, and power supply pads are laid out in GPG (ground-power-ground) and GSG (ground-signal-ground) configurations with a pitch of 50
Figure
Performance results as a function of frequency: (a) input impedance, (b) voltage gain, and (c) noise figure.
Table
Comparison results for two different measurements.
Test | Frequency [GHz] | ||||||
---|---|---|---|---|---|---|---|
23.0 | 23.5 | 24.0 | 24.5 | 25.0 | 25.5 | ||
Measurement |
|
38.5 | 42.2 | 46.0 | 50.1 | 55.2 | 59.4 |
|
37.4 | 38.8 | 39.0 | 38.2 | 36.9 | 35.6 | |
NF [dB] | 2.70 | 2.76 | 2.86 | 3.00 | 3.12 | 3.31 | |
|
|
|
|
|
|
|
|
|
97.2 | 96.8 | 95.6 | 97.8 | 99.1 | 101.1 | |
|
|||||||
Calculation |
|
44.3 | 47.2 | 50.2 | 53.5 | 56.2 | 58.1 |
|
37.2 | 38.5 | 38.9 | 38.1 | 36.8 | 35.0 | |
NF [dB] | 2.71 | 2.77 | 2.87 | 3.01 | 3.13 | 3.35 | |
|
|
|
|
|
|
|
|
|
96.8 | 95.6 | 95.5 | 96.7 | 98.8 | 99.9 |
Figure
Performance of mixer: (a) conversion gain and (b) noise figure.
The tuning voltage characteristics, transient voltage, Fourier spectrum, and phase noise of the voltage-controlled oscillator are shown in Figure
Performance of VCO: (a) tuning voltage characteristics, (b) transient voltage, (c) Fourier spectrum, and (d) phase noise.
Figure
Transient voltage of PGA.
The sensor chip performance is measured using a coaxial setup for 24 GHz. In addition to circuit breakouts, in situ probing is also enabled using pads that are absorbed as part of the design. The measured pulse width at the input is chosen for full bandwidth of 7 GHz operation, and the PLL output frequency is set at the center frequency of the 24 GHz band. The 24 GHz output is directly measured on a sampling oscillator. The spectrum corresponding to pulse width of about 300 ps for the 24 GHz pulse is readily measured.
The complete measured performance comparison of the sensor is summarized in Table
Performance comparison of 24 GHz radar sensor.
Performance | This work | [ |
[ |
[ |
[ |
[ |
[ |
---|---|---|---|---|---|---|---|
Conversion gain (dB) |
|
16.5 | 35 | 27.5 | 16 | 31.5 | 37.7 |
DSB noise figure (dB) |
|
5.3 | 4.5 | 7.7 | 5 | 6.7 | 5.8 |
Input return loss ( |
|
NA | <−10 |
|
NA |
|
<−14.5 |
Output return loss ( |
|
NA | <−15 |
|
NA | NA | <−15 |
LO-to-RF leakage (dB) |
|
<−45 | <−70 | NA |
|
NA | <−30 |
LO-to-IF leakage (dB) |
|
<−45 | <−38 | NA |
|
NA | <−23 |
Input P |
|
−26 | −33.2 |
|
|
|
|
Technology ( |
0.13 CMOS | 0.13 CMOS | 0.18 BiCMOS | 0.18 CMOS | 0.13 CMOS | 0.065 CMOS | 0.18 CMOS |
Size (mm × mm) |
|
1.4 × 0.5 | 3.9 × 1.9 | 0.4 × 0.5 | 0.86 × 0.59 | 1.6 × 1.2 | 3.0 × 1.0 |
Power dissipation (mW) | 39.5 | 18 | 107.5 | 64.5 | 22.2 | 78 | 131 |
Operating temperature (°C) | −40~125 | — | — | — | −40~125 | — | — |
This paper presented low-noise small-area 24 GHz CMOS radar sensor based on direct-conversion pulsed-radar architecture. The proposed sensor was fabricated using TSMC 0.13
The authors declare that they have no competing interests.
This research was conducted under the Pukyong National University Research Park (PK-URP) for Industry-Academic Convergence R&D support program, which is funded by the Busan Metropolitan City, Korea, and this research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2015R1D1A3A01015753).