Fitbit Luxe
Fitbit launched Fitbit Luxe in April 2021. The fitness tracker has an AMOLED display, touch screen, optical Heart rate monitor, red and infrared sensor for Spo2 monitoring, Device temperature sensor, and 3-axis accelerometer. Fitbit Luxe does not have a GPS and NFC.
Ambiq Apollo4 Inside Fitbit Luxe
Fitbit Luxe uses Ambiq Apollo4 Blue. Apollo4 Blue is a multi-die IC package with 131 pins and a package area of 22m2. Ambiq manufactured Apollo4 SOC series in TSMC 22nm ULL (ultra low leakage) process.
Ambiq is the first mover to 22nm BLE SOC
Ambiq launched Apollo4 SOC in H2–2020. To my knowledge, Ambiq is the first mover to the 22nm in the short-range MCU wireless (Bluetooth, Zigbee) MCU industry.
Most advanced BLE SOC in 2022
The application processor Cortex-M4 can run up to 192 MHz, core processing currents are sub 5uA/MHz, and contains 2 Mbyte of MRAM and 1MByte of SRAM.
Multi-die package
My hunch is that the second die in Apollo4 Blue package is a radio die in 40nm TSMC process. The reason is that the predecessor of Apollo4 (i.e. Apollo3) is implemented in 40nm TSMC.
Ambiq likely ported Apollo3 SOC to 22nm except for the radio. The reason would be to reduce the development time to market. Further, I did not spot any inductors in the Apollo4 Blue MCU die photo. In contrast, a typical radio transceiver utilizes a few inductors (VCO, LNA, Power-Amplifier) in the design.
The MRAM is part of the Apollo 4 Blue MCU die. The blue rectangle box highlights the MRAM on this die.
Other Fitbit products also use Ambiq
Fitbit has also designed Ambiq Bluetooth SOC in Fitbit Charge 5. Fitbit has recently launched three new products (Fitbit Sense 2, Inspire 3, and Versa 4) in Q3–2022. I have not found any teardown information on the internet for these latest products. My hunch is that Fitbit will continue to use the Apollo4 SOC series in some of its fitness trackers. The reason is that Apollo4 SOC is the most high-end BLE SOC currently on the market.