1-18 (No.RA015<Rev.001>)
2.4.9 Bluetooth/GPS Circuit
The main component of the BT/GPS circuit is BT/GPS IC (IC850).
The clocks of BT/GPS IC require 19.2MHz for core and 32.768kHz slow clock (X850) for UART.
19.2MHz clock (X700) is shared with MPU/DSP (IC702), and is supplied through the clock buffer IC (IC700).
The BT/GPS IC communicates to the MPU/DSP (IC702) on the HCI UART. Interface of UART & Digital audio (PCM) between the
MPU/DSP (IC702) and the BT/GPS IC (IC850), have level conversion at the level conversion IC (IC852, IC853).
The BT/GPS IC is powered by 1.8V and 3.3V which are supplied from two discrete external regulators (IC38 and IC37). The input of
these regulators is sourced from a switching regulator (IC33) which regulates the battery voltage to 3.8V.
Fig.5 Bluetooth/GPS circuit
2.4.9.1
Bluetooth Circuit
The BT/GPS IC (IC850) support Bluetooth 3.0 up to HCI level.
The TX/RX frequency is 2400-2483.5MHz (79ch Hopping, 2402-2480MHz, 1MHz step). The transmit power is +2dBm at Bluetooth
antenna input.
The Bluetooth antenna is made of sheet metal, and connected to the BT/GPS IC (IC850) through the LC filter (L855).
Frequency configuration for Bluetooth is following:
There are two LO modes: 2X and Offset LO (OSLO). 2X where LO is 2*RF_FREQ (e.g. when transmitting at 2441MHz it is at
4882MHz). OSLO where LO is at 2/3*RF_FREQ (e.g. when transmitting at 2441MHz it is at 1627.333MHz).
In RX the 2X is always used.
In GFSK TX if power is 10dBm or more then OSLO is used.
In EDR2 TX if power is -12dBm or more then OSLO is used.
In EDR3 TX if power is -12dBm or more then OSLO is used.
Otherwise 2X is used for TX as well.
Fig.6 Bluetooth circuit
HPF
Pre-SAW
Post-SAW
LNA
GPS antenna
Attenuator
GPS IC(IC850)
LNA Supply
LNA Enable
TCXO
19.2MHz
1.8V
3.3V
GPS_LNA_IN(L2)
GPS_EXT_LNA_EN(H6)
VDD_TCXO(G1)
TCXO_CLK_LV(F1)
BT_HCI_UART_TX(A4)
BT_HCI_UART_RX(B5)
RTC_CLK(H9)
OSCILLATOR
32.768kHz
BTFM_nSHUTDOWN(A6)
GPS PA EN(G3)
VBAT1(A2)
Level
Conversion
TCXO_LDO_IN(H1)
Clock
Buffer
Matching
GPS_TX
GPS_RX
BT antenna
LC filter
BT_RF
VDDS
MPU/DSP
IC702
IC850
BT/GPS IC
IC700
IC702
IC852
IC850
UART
UART
L855
IC853
PCM
PCM
Sheet metal
X700
IC700
X850
MPU/DSP
BT/GPS
IC
TCXO
19.2MH
32.768kHz
Clock
Filter
LC
Anttena
Bluetooth
Clock
Buffer
Level
Conversion
Level
Conversion