Building a Bluetooth System with Kaben's Products and Technology Bluetooth has evolved over the past ten years from a low throughput rate (723 Kbps) short range wireless link operating in the 2.4 to 2.4835 GHz IMS band, and transmitting a simple frequency hopped, Gaussian FSK modulated signal. In this version of Bluetooth, (Bluetooth 1.2), the carrier is shifted by +/- 160 kHz representing the data bit, and hopped 1600 times per second onto one of 79 channels, each spaced by 1 MHz.
In “Bluetooth 2+EDR” (Enhanced Data Rate), the throughput rate available for the payload packets has increased to 2 Mbps for a mandatory differential QPSK modulated signal, and to 3 Mbps for an optional differential 8PSK modulated signal. To maintain backward compatibility, the Access Code, used by a receiving device to recognize an incoming transmission, and the Header packets, used to describe the packet type and length, still use Gaussian FSK modulation. The higher throughput rates available in the payload packets are useful mainly to establish a variety of links simultaneously.
In order to minimize interference with other wireless links operating in the 2.4 GHz band, it is desirable to provide an analog IF filter having excellent filtering performance. This is normally done with an external SAW (Surface Acoustic Wave) RF filter. In addition, the digital functions of the Bluetooth back-end are typically realized in dedicated digital hardware, and are not able to reconfigure their parameters to optimize their reception in a congested or strongly fading channel.
Kaben has invented a wholly new type of RF filter based on RF sampling techniques. This SIF (Sampled IF Filter) can be integrated with the other blocks of the Bluetooth transceiver onto a single silicon die, thereby removing the need for, and extra cost of, external components. This filter not only achieves excellent (SAW like) filtering performance, it is exceedingly robust to semiconductor process variations, and temperature changes. Further, the filter is programmable in adjacent channel suppression, bandwidth, and center frequency, enabling adaptive reception to different congested channels. In highly congested environments, 60 dB of adjacent channel suppression can be selected, while for benign environments, a “One Half Power Consumption” savings mode can be selected having 30 dB adjacent channel suppression. Inclusion of this novel RF filter into a Bluetooth transceiver significantly reduces the cost of the BOM (Bill of Materials). Further, for the first time, it enables a Bluetooth transceiver to be integrated as a secondary function onto a CMOS die, with the host function being, for example, an MP3 player.
Kaben's end-to-end system design of a Bluetooth transceiver has culminated in the design of the programmable Sampled IF Filter (dependent on the deviation measured), an equalizer (to compensate for the sin x / x roll-off of the filter), a digital AGC (Automatic Gain Control), and a complex phase-locked loop demodulator for the receiver. The transmitter design consists of a PSK modulated and frequency hopped, synthesizer having extremely low phase noise and spur levels.
All key RF blocks, including the RF filters and frequency synthesizer, are implemented in CMOS technology, and all key back-end blocks are implemented in real-time code running on a commercial CMOS processor. This yields a Bluetooth transceiver providing either Bluetooth 2+EDR or Bluetooth 1.2 with a reduced product cost (due to the integrated RF filter) and an increase in performance (through its flexible response to channel congestion or fading). 
|
