User Manual

4) Description of Functional Blocks
Radio Transceiver and Synthesiser
The receiver features a near-zero IF architecture that allows the channel filters to be
integrated on to the die. Sufficient out-of-band blocking specification at the LNA input
allows the radio to be used in close proximity to GSM and W-CDMA cellular phone
transmitters without being de-sensitised. The use of a digital FSK discriminator means
that no discriminator tank is needed and its excellent performance in the presence of
noise allows BlueCore2-External to exceed the Bluetooth requirements for co-channel
and adjacent channel rejection. Fast AGC is implemented by measuring the RSSI on
a slot-by-slot basis and adjusting the front-end LNA gain to keep the first mixer input
signal within a limited range. This improves the dynamic range of the receiver in
interference-limited environments.
The transmitter features a direct IQ modulator to minimise the frequency drift during a
transmit timeslot and results in a well controlled modulation index. A digital baseband
transmit filter provides the required spectral shaping.
The maximum transmit power of +7dBm allows BlueCore2-External to be used in
Class 2 and Class 3 radios and its support for transmit power control allows a simple
implementation for Class 1 with an external RF power amplifier.
The radio synthesiser is fully integrated with no requirement for an external VCO
screening can, varactor tuning diodes or LC resonators.
The radio has several built-in automatic calibration routines to maintain the radio
performance within specification across temperature and ageing. No LNA, PA or
TX/RX switch is required for Class 2 operation across the device’s full operating
temperature range.
Auxiliary Features
The device contains two clock sources: one reference oscillator for the RF carrier
frequency and one low frequency clock oscillator that is used as an interval timer
during sleep modes, i.e., Sniff, Hold or Park.
The reference oscillator requires an external crystal. Alternatively, the crystal
terminals can be driven from an external reference clock.The reference frequency can
be in the range of 8-32MHz in multiples of 250kHz.
The low frequency clock oscillator requires no external components. It is calibrated
automatically and maintains an accuracy of better than 250ppm. This oscillator
consumes less than 2µA and is permanently enabled.