STA2500DTR STMICROELECTRONICS [STMicroelectronics], STA2500DTR Datasheet - Page 18

• Manufacturer Part Number: STA2500DTR
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Functional description
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5.1
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Functional description
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.
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,
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.
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.
Doc ID 16067 Rev 1
π
/4-DQPSK or 8-DPSK
STA2500D