Antenna Circuit - Motorola A920 Service Manual

A920:

Antenna Circuit

Description
All cellular receive bands are fed into either the internal antenna or external antenna. M001 is a mechanical switch which has the internal antenna path connected when a
no insertion condition exists. The RF path will switch to external antenna upon insertion of a male SMA connector to M001. The internal antenna path is fed to the
FEM(Front End Module) through antenna matching components. The FEM provides band selection and filtering between the EGSM, DCS, PCS and WCDMA receive
and transmit bands to a single antenna port. GSM band selection is done by control lines N_BAND_1 and N_BAND_0_G. Mode selection is done by control lines
HL_TX_EN, RX_EN_LIFE, N_GSM_EXC_EN, and GSM_EXC_EN. The diplexing arrangement permits reception of WCDMA signals in any FEM switch position.
This allows the phone, while in a GSM call in any band, to detect signals from a WCDMA base station. The decision may then be made to hand over to the WCDMA
system. Similarly, EGSM base station signals can be detected while the phone is in a WCDMA call to permit a handover decision from WCDMA to EGSM (This is not
possible for base station signals in the DCS and PCS bands.).
Signals received at the antenna between 2110 - 2170MHz will see the RF switch as an open circuit at any position. Consequently WCDMA Rx signals will go through
FL2 to the WCDMA receiver. FL2 should have a maximum insertion loss of ~0.5dB. Outside of the WCDMA Rx band, FL2 behaves as an open circuit, preventing out-
of-band signals from reaching the WCDMA receiver.
GSM, DCS, and PCS receive signals from the antenna port through the FEM should have a maximum insertion loss of -4.4dB. The FEM EGSM transmit path should
have a maximum insertion loss of -2.5dB. The FEM DCS transmit path should have a maximum insertion loss of -3.1dB. The FEM PCS transmit path should have a
maximum insertion loss of -3.7dB.
Q902 is a dual FET package that's being used to multiplex function of the N_BAND_0 control signal coming from the Magic LV. With the use of Q902,
N_GSM_EXC_EN will follow N_BAND_0. GSM_EXC_EN will be the inverted level of N_BAND_0. Q906 is another dual FET package that's used to prevent simulta-
neous GSM and WCDMA transmission conditions. During WCDMA transmission conditions, HL_TX_EN will be in a high state. This will open both FETs in Q906,
thus, disabling any signal functions from control lines NB_EXC_EN and N_BAND_0. Q901 is used to invert the control signal coming from Q906.
Ext Antenna
GSM_RX
DCS_RX
GSM PCS_RX
RF SECTION
GSM_TX
DCS_PCS_TX
RX_EN_LIFE
N_BAND_1
MAGIC
LV
N_BAND_0
GSM TX VCO
VRF_TX_2_775V
Q901
NB_EXC_EN
POG
Int Antenna
M001
Ant
Match
WCDMA_RX
WCDMA_TX
FL001
FEM
CMOS level shifter
Decoder ASIC
HL_TX_EN
Q902
Q906
FL010
WCDMA
RF SECTION
FL030
HARMONY
LITE
N_BAND_0
MAGIC LV