STA2500D datasheet(18/57 Pages) STMICROELECTRONICS

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Functional description

STA2500D

18/57

Doc ID 16067 Rev 1

Functional description

5.1

Transmitter

The transmitter uses the serial transmit data from the Bluetooth Controller. The transmitter

modulator converts this data into GFSK,

π/4-DQPSK or 8-DPSK modulated I and Q digital

signals for respectively 1, 2 and 3 Mbps transmission speed. These signals are then

converted to analog signals that are low pass filtered before up-conversion. The carrier

frequency drift is limited by a closed loop PLL.

5.2

Receiver

The STA2500D implements a low-IF receiver for Bluetooth modulated input signals. The

radio signal is taken from a balanced RF input and amplified by an LNA. The mixers are

driven by two quadrature LO signals, which are locally generated from a VCO signal running

at twice the frequency. The I and Q mixer output signals are band pass filtered by a poly-

phase filter for channel filtering and image rejection. The output of the band pass filter is

amplified by a VGA to the optimal input range for the A/D converter. Further channel filtering

is done in the digital part. The digital part demodulates the GFSK, π/4-DQPSK or 8-DPSK

coded bit stream by evaluating the phase information. RSSI data is extracted. Overall

automatic gain amplification in the receive path is controlled digitally. The RC time constants

for the analog filters are automatically calibrated on chip.

5.3

PLL

The on-chip VCO is part of a PLL. The tank resonator circuitry for the VCO is completely

integrated without need of external components. Variations in the VCO centre frequency are

calibrated out automatically.

STA2500D 데이터시트(PDF) 18 Page - STMicroelectronics