An initial implementation of the Bluetooth radio was made of three pieces of silicon bonded onto a small fibreglass substrate with overall area of 4 square centimetres.
The module was partitioned into three pieces of silicon partly because the overall area required would give a low yield, but mainly because the three sections used widely different types of circuit structure.
The analog integrated circuit contained amplifiers, oscillators, filters and mixers that operate in the 2.4 GHz band. This was too fast for CMOS transistors and so bipolar transistors with thin bases were used. The module amplifies the radio signals and converts them using the mixers down to an intermediate frequency of a few MHz that can be processed by the ADC and DAC components on the digital circuit.
The digital circuit had a small amount of low-frequency analog circuitry in its ADC and DACs and perhaps in its line drivers if these are analog (e.g. HiFi). However, it was mostly digital, with random logic implementations of the modem functions and a microcontroller with local RAM. The local RAM holds a system stack, local variables and temporary buffers for data being sent or received.
The FLASH chip is a standard part, non-volatile memory array that can hold firmware for the microcontroller, parameters for the modem and encryption keys and other end application functions. The flash memory is a standard 29LV800BE (Fujitsu) - 8m (1m X 8/512 K X 16) Bit
Today, the complete Bluetooth module can be implemented on one piece of silicon, but this still presents a major technical challenge owing to the diverse requirements of each of the sub-components.