System Overview

The design above was developed during the first half of the semester as students learned background material needed for implementating the detailed circuit designs needed for realization.  Unlike direct-conversion and low-IF architectures being applied elsewhere, this design is based on the classic superhet approach.  Thus, it retains many of the desirable features of superhet receiver implementations.  However, it is unique in several ways.  A brief walk-through of the design is given below.  Please contact Dr. Kuhn for further information on the project.

• Unlike many commercial products, our receiver is designed to be a fully-integrated solution, with no external components.  Indeed, two students in the class even looked at the possibility of implementing the antenna on-chip (see below).
• The design relies on unusual RF filtering technology being studied at K-State in which the traditional preselect filter, LNA, and image filter combination is replaced by a single "Q-enhanced LNA" with a bandwidth of 20 MHz, followed by an image reject mixer downconverting to a 1IF of 120.5 MHz (nominal).  Total image rejection is expected to exceed 50 dB, and attenuation of out-of-band inteferrers is superior to direct-conversion designs that do not provide preselect filtering in fully-integrated implementations.
• Frequency selection is implemented in two stages. The Q-enhanced LNA is tuned in 16 MHz steps.  The final channel selection is then done at the 1IF to 2IF downconversion (from 120.5 MHz to 5.5 MHz) using a low-power synthesizer at 128 MHz (nominal).  An AFC loop is provided in the demodulator to provide accurate tuning needed to meet sensitivity, selectivity, and error-rate performance specifications.
• The 1IF to 2IF downconversion relies on a second IR mixer and no image reject filtering is provided at this stage.  While generally unwise, considering the limited rejection of IR mixers, the Bluetooth spec allows for low attenuation of in-band images, making such cost/power savings strategies possible.
• Finally, the receiver architecture employs simple, classical, robust channel select filtering and demodulation techniques.  A 5.5 MHz 2IF frequency combined with the 1 MHz Bluetooth channel allows a 2 pole bandpass gm-C filter to be implemented at low power with straightforward master-slave tuning of frequency only.  A quadrature phase-shift FM demod employs a third copy of the gm-C resonator used in the filter, and is followed by a 3-pole LPF for 11 MHz product attenuation and noise attenuation prior to bit decisions.  An accurate RSSI completes the design.