When considering the implementation cost of Bluetooth, the choice of process technology and the number of required components are often debated. Many Bluetooth chip vendors adopt a multi-chip approach: the baseband DSP and microcontroller are produced in CMOS, while the RF functions are implemented in bipolar technology. This simplifies chip design but has drawbacks, especially regarding the number of components, PCB space, and system integration, all of which increase implementation cost.
Single-Chip CMOS Architecture
Each chip contains the baseband DSP, the RF section, and a multifunction 16-bit processor for fully integrated units. This protected "RF in the chip" architecture offers clear advantages beyond simply reducing the number of discrete components. Its main technical and economic benefits fall into four areas: 1) voltage-controlled oscillator (VCO); 2) intermediate-frequency (IF) receiver; 3) RF front-end between antenna and transmitter/receiver; and 4) integration and production.
1. Voltage-Controlled Oscillator (VCO)
In single-chip Bluetooth solutions, the synthesizer integrates all VCO elements, including the resonator and capacitors. These modules require no external tuning during manufacturing. Self-test functions and analog calibration routines can run when the chip is operating at high speed, handling trimming and matching automatically. Adjustment during assembly is unnecessary. Drift caused by operation is compensated by corresponding parameter adjustments, ensuring reliable Bluetooth connections.
2. RF Receiver Advantages
Many traditional Bluetooth systems use a relatively high 100 MHz IF, which forces designers to use SAW (surface acoustic wave) channel filters. The radio sections integrated on single-chip Bluetooth cores operate at much lower IF, allowing filtering to be implemented on-chip and eliminating the need for external filter components. In addition, these receivers use a fully digital detector that, in combination with the analog front-end design, delivers improved adjacent-channel suppression.
3. RF Front-End Advantages
In current Bluetooth systems, the high-frequency front-end elements between the antenna and the transceiver are typically off-chip. The BlueCore approach is similar in that regard, but because the entire chip is manufactured in CMOS, the receiver achieves much higher linearity than comparable bipolar implementations, which simplifies requirements for external filtering.
4. Integration and Manufacturing Advantages
Almost all Bluetooth systems require shielding for some or all components. A single-chip Bluetooth solution reduces or eliminates the need for shielding, and the product family can be designed directly on FR4 printed circuit boards. The choice of FR4 takes dielectric properties and resulting losses into account, which helps lower manufacturing cost.
