2
Bluetooth Modem
2.1
RF Ports
2.1.1
BT_RF
CSR8640 BGA contains an on-chip balun which combines the balanced outputs of the PA on transmit and produces
the balanced input signals for the LNA required on receive. No matching components are needed as the receive
mode impedance is 50Ω and the transmitter has been optimised to deliver power in a 50Ω load.
G-
T
W
-00
05523.2.2
+
_
PA
+
_
LNA
BT_RF
On-chip Balun
VDD
VSS_BT_RF
Figure 2.1: Simplified Circuit BT_RF
2.2
RF Receiver
The receiver features a near-zero IF architecture that enables the channel filters to be integrated onto the die.
Sufficient out-of-band blocking specification at the LNA input enables the receiver to operate in close proximity to
GSM and W‑CDMA cellular phone transmitters without being desensitised. A digital FSK discriminator means that
no discriminator tank is needed and its excellent performance in the presence of noise enables CSR8640 BGA to
exceed the Bluetooth requirements for co‑channel and adjacent channel rejection.
For EDR, the demodulator contains an ADC which digitises the IF received signal. This information is then passed
to the EDR modem.
2.2.1
Low Noise Amplifier
The LNA operates in differential mode and takes its input from the balanced port of the on-chip balun.
2.2.2
RSSI Analogue to Digital Converter
The ADC implements fast AGC. The ADC samples the RSSI voltage on a slot-by-slot basis. The front-end LNA gain
is changed according to the measured RSSI value, keeping the first mixer input signal within a limited range. This
improves the dynamic range of the receiver, improving performance in interference-limited environments.
Advance Information
This material is subject to CSR's non-disclosure agreement
© Cambridge Silicon Radio Limited 2011
Page 23 of 110
CS-209182-DSP1
CSR8640 BGA
Data Sheet
