BT840X Low Transmit Power with Skyworks FEM

RE: BT840X Low Transmit Power with Skyworks FEM

Susheel Nuguru — Mon, 15 Jan 2024 07:06:56 GMT

Pablo, I was assuming that you were using NCS as well. Is this for the nRF5SDK based solution? If it is, then I think the support of FEM in our softdevice was very limited. We know that nRF5 based SDK solution might not be working with Skyworks FEM as we only supported generic gpio based solution in that.

Regarding the NCS support, Currently released support for (simple GPIO) Skyworks FEM does not allow run-time control. Decision to use PA or bypass is taken at compile-time.

RE: BT840X Low Transmit Power with Skyworks FEM

PabloL — Thu, 11 Jan 2024 14:39:31 GMT

Hello Susheel,

It would be a great help for developers.
Unfortunately the documentation is a bit confusing.
I'm using a Fanstel EV-BT40X board (nRF52840 + SKY66112).

I was able to make the example ble_app_uart_c work successfully with the Softdevice S140, using the control codes from Fanstel (https://www.fanstel.com/s/BT840X_SKY66112-Codes.zip), but not for Zephyr with NCS 2.5.0.

// BT840X SKY66112 FEM ble_app_uart_c example
// main.c
...
#include "pa_lna.h"

#define APP_PA_LAN

#ifdef APP_PA_LAN
#define APP_PA_PIN      17      // CTX pin
#define APP_LNA_PIN     19      // CRX pin
#define APP_CHL_PIN		8       // CHL pin (0: TX low pwer, 1: TX high power)
#define APP_CPS_PIN		6       // CPS pin (0: LNA/PA On, 1: Bypass)
#endif
...

int main(void)
{
...
#ifdef APP_PA_LAN
	nrf_gpio_cfg_output(APP_CPS_PIN);
	nrf_gpio_cfg_output(APP_CHL_PIN);
	nrf_gpio_pin_clear(APP_CPS_PIN);    // LNA/PA On
	nrf_gpio_pin_set(APP_CHL_PIN);      // TX High Power
	pa_lna_init(APP_PA_PIN,APP_LNA_PIN);    
#endif
...
}

Please let us know any news.

Thank you.

Pablo

RE: BT840X Low Transmit Power with Skyworks FEM

Susheel Nuguru — Thu, 11 Jan 2024 06:32:24 GMT

OK, it looks like something is clearly wrong then if it is more than one who is seeing the same thing. I will try to find Skyworkorks FEM Module or order it to test this myself.

RE: BT840X Low Transmit Power with Skyworks FEM

PabloL — Wed, 10 Jan 2024 14:29:57 GMT

Hi,

Same for me. I could not get it to work.

If you see the nrf52840dk_nrf52840.dts, in the included file nrf52840dk_nrf52840-pinctrl.dtsi

uart0_default: uart0_default {
    group1 {
            psels = <NRF_PSEL(UART_TX, 0, 6)>,
            <NRF_PSEL(UART_RTS, 0, 5)>;
        };
    group2 {
            psels = <NRF_PSEL(UART_RX, 0, 8)>,
            <NRF_PSEL(UART_CTS, 0, 7)>;
            bias-pull-up;
        };
};

uart0_sleep: uart0_sleep {
    group1 {
            psels = <NRF_PSEL(UART_TX, 0, 6)>,
                    <NRF_PSEL(UART_RX, 0, 8)>,
                    <NRF_PSEL(UART_RTS, 0, 5)>,
                    <NRF_PSEL(UART_CTS, 0, 7)>;
            low-power-enable;
    };
};

The uart0 uses pins P0.6 and P0.8 as TX and RX.
Does the new definitions in the device tree override the pin functions?

RE: BT840X Low Transmit Power with Skyworks FEM

edmcnicholas — Fri, 05 Jan 2024 16:24:49 GMT

If you review the post you will see that they are set in software. What I am stating is that your gain settings for the driver are incorrect. I expect a setting of 8db to have the same rssi with clear line of sight with or without a FEM.

RE: BT840X Low Transmit Power with Skyworks FEM

Susheel Nuguru — Fri, 05 Jan 2024 16:19:54 GMT

If the other pins are not controlled by the gpio and are set to default float then the behavior of the default value SKYWorks FEM is unpredictable.

RE: BT840X Low Transmit Power with Skyworks FEM

edmcnicholas — Fri, 05 Jan 2024 15:04:07 GMT

Yes that is what I explained to the other engineer but i think the gain setup is incorrect by default

RE: BT840X Low Transmit Power with Skyworks FEM

Susheel Nuguru — Wed, 03 Jan 2024 11:31:47 GMT

It looks like SKYWorks have other pins CSD/CPS/CHL other than CTX and CRX that needs to be controlled for proper functionality. We provide FEM support for skyworks through simple_gpio. We control crx and ctx pins automatically.Other pins whatever they are, are to be controlled by the user application, as gpios.

RE: BT840X Low Transmit Power with Skyworks FEM

Hieu — Sun, 31 Dec 2023 19:12:11 GMT

edmcnicolas,

[quote user="edmcnicholas"]I am using 2.5.0 as I have not seen 2.5.1 on the toolchain manager.[/quote]

I checked the Toolchain Manager, and it is as you said. My apologize. I saw that the documentation was already release and repository already tagged for v2.5.1 and thought it was released. Perhaps the process was interrupted due to the holiday.

Thank you for the details of your tests. I will have someone with better knowledge on this topic look at this and we will get back to you soon.

RE: BT840X Low Transmit Power with Skyworks FEM

edmcnicholas — Thu, 28 Dec 2023 15:34:48 GMT

Hieu,

I am using 2.5.0 as I have not seen 2.5.1 on the toolchain manager.

What I was saying is that when i set the power to 8db dynamically the unit with FEM is being received at a lower level than the unit without fem when connecting wither to the same board mounted antenna so there is obviously a difference in power through the FEM unit with the the current config at defaults.

As for using the default settings and setting the "CONFIG_BT_CTLR_TX_PWR_ANTENNA=22" that only shows 10mA on the power profiler so that is not the correct setup. As per the data sheet for the SKY66112-11 the fact that fem control is only 2 pin and not 4 pin CHL and CPS need to be set so that the FEM uses high power mode as only CRX and CTX are controlled by MPSL from what I can see and have read.

If i set the CHL and CPS then I do get higher output but i only see peaks of 75ma when the fanstel example has peaks up to 200mA. WIth this setting I see rssi best rssi of -32 on a nrf52833 dk at 40". By lowering the tx-db-gain in the device tree to -12 i get a peak of -28 dbm with peaks of 225mA and can manipulate it up and down from there. What I see is that the dynamic power control seems a bit confused with the default settings and is not using 1db increments like the data sheet would indicate it is able to. I have use dynamic power controls repeatedly with non-fem modules with no issue.

My though is that with the fem settings and the default device tree set at 22db i dont think the output power is be set correctly in the tx. I tried reading the txpower register but it was always at 0. For full power on the Skyworks part I need an input of -1db from the radio.

RE: BT840X Low Transmit Power with Skyworks FEM

Hieu — Thu, 28 Dec 2023 13:59:58 GMT

Hello edmcnicolas,

[quote user=""]The unit with the FEM is about 6-10 DB low so I am going to say something is being left on the table for link budget.[/quote]

By this, do you mean that the device with FEM output at 6-10dB lower than you expected, or 6-10dB lower than the device without FEM?

In NCS, MPSL takes care of FEM control completely, so you shouldn't need to toggle the CHL and CPS line like you are doing.

I unfortunately haven't tried to control TX power dynamically with FEM before, and unfortunately have neither a Skyworks nor a nRF21540 with me to test at the moment.

For the time being, could you please try to build a simple project (such as the beacon sample) with the TX Power set only in Kconfig, without any additional code controlling it? This is a setup I have tested before and confirmed to be working. We can use it as a starting point to rule out any other factors that could be wrong.

Please also share:

What version of the nRF Connect SDK (NCS) you are using. If possible, please use the latest version. At the time of writing, it's 2.5.1.
Your compiled DTS file, <build folder>/zephyr/zephyr.dts
Your compiled Kconfig file, <build folder>/zephyr/.config

Hieu

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RE: BT840X Low Transmit Power with Skyworks FEM

edmcnicholas — Wed, 27 Dec 2023 21:35:11 GMT

I enabled the response from the command and I am not getting the power expected int the response my actual tx power is lower and I cant use every power level. I am also wondering if this takes into account the return loss in the chip as the data sheet states that is needs -1 db input for 20db output? What looks suspicious to me is that i am seeing numbers that are down 12db.

[00:00:00.024,963] <wrn> bleCommon: Actual Tx Power: 18
[00:00:00.025,146] <wrn> bleCommon: Actual Tx Power: 18
[00:00:00.025,329] <wrn> bleCommon: Actual Tx Power: 6
[00:00:00.025,512] <wrn> bleCommon: Actual Tx Power: 6