nRF52840 ANT matching circuit

[Balu Varkala]

Hi

we are using the nRF52840 and antenna signal i connected ceramic chip antenna(ACAG020-2450-T).

 

The above attached schematic of ant signal matching circuit schematic.

The below is the antenna datasheet link.

https://abracon.com/datasheets/ACAG0201-2450-T.pdf

Kindly check the antenna area matching circuit.

Please suggest if any changes/modifications required ASAP.

Regards

Bala

[ketiljo]

C3, L2 and C8 belongs to the radio and takes care of impedance transformation and some harmonic attenuation. 

So L1 and C3 remains as antenna tuning components. I recommend either adding a shunt component in parallel with C3 to make a PI-network for the antenna or a series component between L1 and the antenna for  T-network. A PI-network is easier as it requires only one series component.

[Balu Varkala]

Hi,

Thank you for the replay.

As per above i will add the component in parallel with C3. Should i add resistor or capacitor and what is the value for the same.

Kindly suggest the same.

[ketiljo]

Take a look at this white paper: https://infocenter.nordicsemi.com/pdf/nwp_017.pdf

[Balu Varkala]

Hi,

Thank you for replay. I attached the schematic and layout.

The below is the Antenna link of ceramic antenna which is used in layout.

https://abracon.com/datasheets/ACAG0201-2450-T.pdf

Kindly review the same.

Thanks and Regards

Bala

[ketiljo]

That won't work well. You need a ground plane on the top layer. Using tracks to connect ground is not going to work at these frequencies. Take a look at  the reference layout to see how it's done. 

C3, C8 and L7 shall be placed like this: 

Note how C3 here is grounded only to the VDD_PA pin and the center pad.

It's _very_ important that you follow the antenna manufacturers reference layout: 

(from the antenna datasheet)

Every dimension must be correct!

[Balu Varkala]

Hi,

Thank you for the replay. I modified the the layout and added ground plane on the top layer. Attached below is the layout

Maintained as per antenna datasheet distance keep out and Ground plane.

Kindly review and suggest and comments please.

Thanks 

Bala

[ketiljo]

Take a closer look at the pictures in my last post

[Balu Varkala]

Hi,

Thank you for the replay.

I modified the layout as trail replay.

Please find the attached below layout of the same.

[ketiljo]

Your're getting closer. But I think you need to have some ground on the left hand side of the antenna as well. And make sure C3 (reference schematic) is connected only to the VDD_PA pin (and the center pad) and not to the ground plane.

[Balu Varkala]

Hello,

Thank you for the replay. I changed the C3(reference schematic) is connected only to the VSS_PA(and the center pad). And this board is 4 layer top and bottom as routing layer and 2 layer as Ground and 3rd layer as power.

The below is the snapshot for the same.