TIDUFB9 April   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Reference Design Features
      2. 2.2.2 Switch Settings
    3. 2.3 Highlighted Products
      1. 2.3.1 IWRL6432W
      2. 2.3.2 Crystal
      3. 2.3.3 TPS6285020M – 1.8V DC/DC Regulator
      4. 2.3.4 QSPI Flash Memory
  9. 3System Design Theory
    1. 3.1 Antenna
      1. 3.1.1 Range and Phase Compensation
      2. 3.1.2 Chirp Configuration
    2. 3.2 PCB
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 Reference Design
      2. 4.1.2 Small Form-Factor Reference Design
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 Human Detection at 15 Meters in Boresight
      2. 4.4.2 Antenna Radiation Plots
      3. 4.4.3 Angle Estimation Accuracy
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Authors

3.2 PCB

The reference design uses a four-layer stack-up for the PCB. The antenna resides on the bottom layer (Lyr 4) of the PCB. The top layer along with the bottom layer has FR408HR dielectric material. Because both the layers contribute in the grounded coplanar waveguide (GCPW) transmission lines, the stack-up, especially the dielectric for both of these layers is critical for good antenna performance. The following are a few critical properties of the dielectric for both of these layers:

  1. The dielectric has 2 × 1067 (dual ply) spread glass construction
  2. The thickness of the dielectric is 5mils (127μm), this thickness value is adjusted for impedance matching
  3. The Dk value of the dielectric is 3.3 at 60GHz
  4. This is core material
Note:
  • The dielectric thickness must not be altered because this can cause impedance mismatch and more reflection of the radiated power.
  • Prepreg material must not be used for the antenna layers.

TIDEP-01040 Antenna on the Bottom Layer

Figure 3-3 Antenna on the Bottom Layer

Grounded coplanar waveguide (GCPW) transmission lines are used to carry the RF signals to the antenna. Following are some critical considerations for the antenna layer and the ground layer followed by the antenna layer:

  1. Finished copper thickness on the antenna layer is 40μm
  2. Ground plane (below the antenna plane, Layer 2) thickness is 1oz (0.5oz can also be used if 1oz is not available).
  3. The copper is very low profile (VLP) or better for reduced surface roughness
  4. PCB surface finish is OSP or immersion silver
    Note: Electroless Nickel Immersion Gold (ENIG) surface finish is not recommended because this can potentially cause higher insertion losses for the mmWave frequency range.

The overall PCB thickness of the reference design is 1.17mm.

Figure 3-4 shows the stack-up details.


TIDEP-01040 Design Stack-Up

Figure 3-4 Design Stack-Up
Note:
  1. Use the TI stack-up as manufactured. If a different stack-up is desired, 3D electromagnetic solvers are recommended and antenna optimization needs to be done.
  2. The Er values mentioned in the stack-up are of lower frequency and are not optimized for 60GHz. Also, depending on different types of construction, the value can alter a little.