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Radar sensor Forum Discussions

ielopez
Level 1
5 sign-ins First reply posted First question asked
Level 1

Dear Infineon Community,

I am a researcher at the Universidad Politecnica de Madrid. I am currently uing the radar sensors BGT24MTR11. I have designed some PCBs with a radar system based on the chip BGT24MTR11. I have encountered a problem measuring the output power at the TX, TXX outputs. I measure -15 dBm, in stead of the 10 dBm written in the datasheet and application notes. I explain below the techniques followed to carry out the measurements.

To measure the putput power at TX and TXX ports of BGT24MTR11, the TX and TXX outputs of one of these PCBs are not connected to an antenna. They are connected to an spectrum analyzer (using microstrip line, a connector and a cable). In more detail, the connection is TX output - matching network presented in pag 20 of the datasheet of BGT24MTR11 - 50 Ohm microstrip line (2 cm long) - 50 Ohm southwest connector - Cable - Spectrum Analyzer.

-The stack-up of the PCB is the same as the one presented in pag 20 of the datasheet of BGT24 MTR11 (0.254 mm layer of Ro4350B).

-The 50 Ohm transmission line is simulated. The losses introduced are around 0.2 dB in the frequency band.

-The connector is measured. The losses introduced are smaller than 1 dB in the frequency band.

-The cable is measured. The losses introduced are smaller than 0.5 dB in the frequency band.

-The complete system (including matching network, transmission lines and connectors) is simulated. The losses are smaller than 1.5 dB in the frequency band.

-The resolution bandwidth of the spectrum analyzer is set to 8 MHz.

Using this configuration,

-I bias the BGT24MTR11 with 3.3 V.

-I configure the chip through SPI according to pag 17 of the datasheet. I use the configuration word 0x0008.  I observe that the current consumption changes from 130 mA to 170 mA (approximately).

-At the input of the VCO (fine and coarse pins) I insert a DC voltage generated with an external source. I observe a power of approximately -15 dBm in the spectrum analyzer. The output frequency varies with the  voltage at the input of the VCO (from 21.8 GHz at 0.5 V to 26.8 GHz at 5 V).  There is no frequency where the output exeeds -10 dBm.

I have tried to configure the chip with different words. For instance, using 0x000F I observe that the output is reduced 9 dB (I measure approximately -25 dBm). I have also tried in the switch off configuration, measuring a power of approximately -50 dBm. Thus, it seems that the chip is being programmed correctly.

I have tried to read the output power sensor as explained in pag 18 of the datasheet. For this measurement I use the configuration words 0x00C8 and 0x0048. I read Vreftx = 1.87 V. Vptx = 2.3 V. Thus, DeltaV = 0.43 V. Thus, Pout ~9 dBm. It seems that the chip is providing the correct output power.

Can someone provide any hints about what can be going on? Has anyone encountered the same problem? Any other information I should provide, I will be happy to.

Thanks for the help.

Ignacio

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1 Solution
Deepa_V
Moderator
Moderator 50 solutions authored 100 replies posted 100 sign-ins
Moderator

Hi @ielopez ,

The reason for missing output power is the wrong matching in the RF section because of NO solid device RF grounding. The ONLY GND of all BGT24MTR11 Vee pins and the center bottom plane is done via the thin connection to pin26 (TXoff). This pin is grounded via a long line. GND via is not a solid RF GND via, because of cross connection to GND plane L2. A solid connection is mandatory. In BGT24MTR11 data sheet page 23 minimum GND vias (L1=>L2) is shown.
https://www.infineon.com/dgdl/Infineon-BGT24MTR11-DS-v03_01-EN.pdf?fileId=db3a304339dcf4b10139def491...

More GND vias are better.  In our Distance2Go board we use various blind vias, but through vias should be possible too.
Attached below is a picture of BGT24MTR11 vicinity in the Distance2Go.

Deepa_V_0-1661831334143.jpeg

In single ended configuration loss is min 3dB. Be aware of cable RF loss to spectrum analyser.

Hope this helps !

Best regards,

Deepa

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5 Replies
Deepa_V
Moderator
Moderator 50 solutions authored 100 replies posted 100 sign-ins
Moderator

Hi @ielopez ,

Thank you for your detailed query ! It explains a lot of attributes at your end but we need a bit more clarity of your setup to understand your issue better. 

1. Since you are stating that 'I have tried to read the output power sensor as explained in pag 18 of the datasheet. For this measurement I use the configuration words 0x00C8 and 0x0048. I read Vreftx = 1.87 V. Vptx = 2.3 V. Thus, DeltaV = 0.43 V. Thus, Pout ~9 dBm. It seems that the chip is providing the correct output power.' , this would mean that MMIC is actually working fine at your end as it matches the expected graph as shown in Figure 7 of https://www.infineon.com/dgdl/Infineon-AN305%20User's%20Guide%20to%20BGT24MTR11-ApplicationNotes-v01... . 

2. We would suggest you to please verify the TxOFF pin requirements as stated in https://www.infineon.com/dgdl/Infineon-AN305%20User's%20Guide%20to%20BGT24MTR11-ApplicationNotes-v01... . 

Deepa_V_0-1659528501532.png

3. Since you mention that 'I have also tried in the switch off configuration, measuring a power of approximately -50 dBm. Thus, it seems that the chip is being programmed correctly.', please note that ideally the PTXOFF should be -30dBm as stated in Table 7  https://www.infineon.com/dgdl/Infineon-BGT24MTR11-DS-v03_01-EN.pdf?fileId=db3a304339dcf4b10139def491... but you are having ~20dB loss in this measurement as well. 

We recommend you to check your setup and PCB one more time and also, verify the second point and do let us know if you are still facing issues !

Best regards,

Deepa

 

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ielopez
Level 1
5 sign-ins First reply posted First question asked
Level 1

Hi @Deepa_V ,

Thank you very much for your reply.

I have verified the TxOFF pin. The TxOFF pin is grounded.

I have also verified the setup and the PCB. I attach 4 pictures of the PCB layout I am using. I would be very grateful if you could take a look at them to check if there is anything wrong.

1. bgt24mtr11_schematic Screenshot of the schematic used. I include some comments below.

-Pin 1 and 31 are connected to the PFD ADF4159 with a 100 pF capacitor in between (R23, R25, L1 and L2 are not placed).

-Pin 4 and 5 are connected to the output of the PLL filter using the sturcture in fig 2, pag 15 of the datasheet of bgt24mtr11.

-The SPI signals are in the range 0-3.3 V. It is used SPI 1.

2. bgt24mtr11_layout_nozoom 2D layout where the footprint and transition lines can be observed.

3. bgt24mtr11_layout_zoom 2D layout where the footprint and the connection nets can be observed.

4. 3. bgt24mtr11_layout_3d 3D layout.

Again, I am very grateful for your help.

Bets regards, 

Ignacio

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Deepa_V
Moderator
Moderator 50 solutions authored 100 replies posted 100 sign-ins
Moderator

Hi @ielopez ,

Thank you for the layout and additional info. We are looking into the issue at our end. Will soon get back to you !! In the meantime, can you please verify the connector side as well as there is high chance there might be power loss due to the connections at the connector side too. 

Best regards,

Deepa

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Deepa_V
Moderator
Moderator 50 solutions authored 100 replies posted 100 sign-ins
Moderator

Hi @ielopez ,

The reason for missing output power is the wrong matching in the RF section because of NO solid device RF grounding. The ONLY GND of all BGT24MTR11 Vee pins and the center bottom plane is done via the thin connection to pin26 (TXoff). This pin is grounded via a long line. GND via is not a solid RF GND via, because of cross connection to GND plane L2. A solid connection is mandatory. In BGT24MTR11 data sheet page 23 minimum GND vias (L1=>L2) is shown.
https://www.infineon.com/dgdl/Infineon-BGT24MTR11-DS-v03_01-EN.pdf?fileId=db3a304339dcf4b10139def491...

More GND vias are better.  In our Distance2Go board we use various blind vias, but through vias should be possible too.
Attached below is a picture of BGT24MTR11 vicinity in the Distance2Go.

Deepa_V_0-1661831334143.jpeg

In single ended configuration loss is min 3dB. Be aware of cable RF loss to spectrum analyser.

Hope this helps !

Best regards,

Deepa

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ielopez
Level 1
5 sign-ins First reply posted First question asked
Level 1

Hi @Deepa_V ,

Thank you for the information. We will implement a new version with more GND vias. We will also keep the attached layout in mind. Again, I am very grateful for your help.

Best regards,

Ignacio

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