Antenna questions on nRF7002 - nRF5340

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Fri, 01 Sep 2023 07:54:54 GMT

The RF switch is controlled by the nRF7002, it will be set high when WIFI is transmitting or receiving. The state of the CTRL pin must match the input of the RF switch the nRF7002 is connected to. Using the DK as a example, if the nRF7002 was connected to RF2, the SW_CTRL0 pin could be connected directly to the CTRL pin of the RF switch.

RE: Antenna questions on nRF7002 - nRF5340

dario.sortino — Wed, 30 Aug 2023 15:17:33 GMT

Sorry for the late reply.

So I assume that I can connect directly SW_CTRL0 to the CTRL pin of the RF switch, and have a devicetree overlay with

	nrf_radio_coex: nrf7002-coex {
		....
		....
		
		swctrl1-gpios = <&gpio0 29 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
		...
		...
		
	};

Am I correct?

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Tue, 01 Aug 2023 14:34:33 GMT

It's used for inverting the control signal from the nRF7002. The pull-up resistor R62 configures the RF switch to connect RF2 to RF by default. This is done to eliminate the need for crossing the RF traces. Which would be needed if the SW_CTRL0 pin of the nRF7002 is connected directly to the CTRL pin of the RF switch, as the switch would by default connect RF1 to RF.

RE: Antenna questions on nRF7002 - nRF5340

dario.sortino — Tue, 01 Aug 2023 08:28:52 GMT

Do you have an explanation for the Q10 transistor used to control the RF Swtich in the 7002 part of schematic (image in your first comment)

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Mon, 31 Jul 2023 13:49:50 GMT

[quote user="dario.sortino"]Does this mean that in "regular" applications like normal BT, without having WiFi, let's say by default I should have a 2.4Ghz antenna that can interface directly with the 5340?[/quote]

Yes, for boards without WiFI you would just connect the antenna directly to the nRF5340, with only the required radio and antenna matching networks in the RF path. Here is the nRF5340DK as a reference point:

J1 is just a test connector it can be ignored.

[quote user="dario.sortino"]Also, If I want to make my matching+patch antenna instead of using A2 as a chip antenna, should I control the impedance of the traces (inside the blue pen drawing) to be 50 ohms?[/quote]

Yes, all transmission lines should have a controlled impedance of 50 Ohm.

RE: Antenna questions on nRF7002 - nRF5340

dario.sortino — Thu, 27 Jul 2023 09:24:53 GMT

I have one more question about this topic.

The component U16 is the switch between the 5340 own antenna and the shared one with the 7002. This is controlled by GPIO 1 10 that in the devicetree I see its the btrf-switch-gpios field under the coex interface.

Does this mean that in "regular" applications like normal BT, without having WiFi, let's say by default I should have a 2.4Ghz antenna that can interface directly with the 5340?

Also, If I want to make my matching+patch antenna instead of using A2 as a chip antenna, should I control the impedance of the traces (inside the blue pen drawing) to be 50 ohms?

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Fri, 21 Jul 2023 14:28:40 GMT

Yes, it should be possible to make WiFi coexist with ESB,

RE: Antenna questions on nRF7002 - nRF5340

dario.sortino — Fri, 21 Jul 2023 14:27:09 GMT

Super clear. Just one last question: even if the example works with BLE, is it possible to make WiFi coexist with ESB?

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Fri, 21 Jul 2023 14:23:16 GMT

Since both ESB and WiFi uses the 2.4GHz band the two antennas will be optimized for the same frequency band, this means a good amount of power will be coupled from one antenna to the other. WiFi can transmit at a higher power than the nRF5340, leading to the nRF5340 being deafened by the nRF7002. If the nRF5340 is in RX mode it may not be able to receive the anything as the receiver may be saturated by the TX power of the nRF7002.

This is solved by using coexistence, which ensures only one device is using the radio, most protocols allows for this as there isn't continuously radio activity. We have a sample that demonstrates this with WiFi and BLE coexistence:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/wifi/sr_coex/README.html

This also allows the nRF7002 and nRF5340 to share a 2.4GHz antenna as both won't be using it at the same time. The nRF7002 have dedicated pins for coexistence which must be connected to the nRF5340, as well as a dedicated pin for controlling the RF switch when sharing antenna with the nRF5340.

RE: Antenna questions on nRF7002 - nRF5340

dario.sortino — Fri, 21 Jul 2023 14:09:46 GMT

Thank you for your answer.

What do you mean that both can't be transmitting simultaneously even if I have different antennas? I thought it was not a problem since the antennas are different. I was planning to collect data from a set of devices via ESB (hence running in the network core) and forward them via WiFi (in the application core). Is there any problem with this?

RE: Antenna questions on nRF7002 - nRF5340

Bendik Heiskel — Fri, 21 Jul 2023 13:58:49 GMT

Hi,

There are some designs for dual band PCB antennas, but they would require simulation to optimize the shape for both bands simultaneously. Using just one antenna is OK, but if you just want to use the 2.4GHz band it would be simplest just to share the antenna between the nRF5340 and the nRF7002. Both radios can't be transmitting simultaneously anyways so sharing the antenna is not a problem. If you want to try this you can use parts of the nRF7002 DK design files as reference, as the DK have a option to use the same 2.4GHz antenna for both radios:

just remove the diplexter and connect the output of the RF switch to the antenna matching network directly.

[quote user=""]Do I need matching circuitry? If not, it's correct to assume that my antenna start directly from the PIN?[/quote]

You don't need a matching network for the nRF7002 side as the TXRF0 pin already have an impedance of 50 Ohm, but the antenna will require a matching network. The type of matching network is dependent on the type of antenna.

The TXRF1 pin can just be left floating when not using 5GHz.

Best regards,

Bendik