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6.1 Block Diagram - Radio Frequency (RF)
Rx frontend filter
DCS
Ceramic Filter
1805..1880 MHz
GSM
SAW Filter
925..960 MHz
RX
Antenna
Antenna
Switch
RF Connector with
mechanical switch
TX
Detector and
APC loop
Level control
Directional
PA
coupler + LPF
Directional
PA
coupler
DET_EN
IC 1
Digital
DET_TX
signals
TXP_OFS_EN
IC 2
Analog
AUX_DAC
signals
6.1.1 General RF Indications
The radio part of the CMD-J5/J16 handles the air interface according to the GSM specifications.
It is the main contributor for the dualband functionality for E-GSM 900 and DCS 1800.
Receiver
The receiver consists of two separated RF paths for GSM and DCS 1800 each.
On the transmission line between the antenna switch of the RF part and the antenna there is the RF connector
including a mechanical switch to connect an external antenna for accessory use. The integrated mechanical
switch switches between the helix antenna and the external RF antenna connection. As long as a plug is
connected the antenna is deactivated and all RF signals go across the connector.
The GMSK (Gaussian-filtered minimum shift keying) modulated 900 MHz / 1800 MHz signal received by the
antenna is filtered, gained and downconverted into the baseband via an intermediate frequency of 440 MHz.
The 440 MHz filter is followed by a tuneable amplifier and IQ demodulator. Behind the demodulator there are
additional base band amplifiers and low pass filters.
The In Phase (I) and Quadrature (Q) signal outputs are balanced each.
A 13 MHz voltage-controlled-temperature-compensated crystal oscillator (VCTCXO) generates the clock
frequency for the PLL and baseband part.
Transmitter
In the transmit direction the digitally GMSK-modulated baseband signal is upconverted to the transmit frequency
in the 900 MHz / 1800 MHz band via an intermediate frequency of 195 MHz (GSM) / 325 MHz (DCS 1800) by
means of an IQ modulator and the subsequenting sum loop.
All RF and IQ signals are balanced signals in order to suppress crosstalk effects. According to GSM
recommendations transmitter and receiver are never active at the same time.
(TDMA system "Time Division Multiple Access").
Rx interstage filter
1st Rx mixer
LNA
RF
IF
SAW Filter
LO
1805..1880 MHz
LNA
RF
IF
SAW Filter
LO
925..960 MHz
LNA Bias
control
GSM
Tx GSM VCO
Pin diode
880..915 MHz
880..915 MHz
switch
LP Filter
DCS1800
Tx DCS VCO
Pin diode
1710..1785 MHz
1710..1785 MHz
switch
Loop
Filter
LP Filter
TX_SW_EN
GSM_TX_EN
GSM_VCO_EN
APC_DOWN
DCS_TX_EN
DCS_VCO_EN
TXP
SECTION 6
DIAGRAMS
IQ Demodulator
IF
SAW Filter
440 MHz
IF Amplifier (PGC)
I
90°
∑
0
°
Q
RX:
GSM 1365..1400 MHz
DCS 1365..1440 MHz
440 MHz
1
2
Transceiver
TX:
GSM 1370..1440 MHz
DCS 1385..1460 MHz
2
DCS
GSM
1
5
TX:
1
GSM 685..720 MHz
DCS 1385..1460 MHz
3/5
GSM :5
DCS :3
1
Down
LP Filter
Converter
Sum loop
ϕ
90°
∑
Phase
detector
GSM 195 MHz
DCS 325 MHz
17
VCC_RF
VCC_SYNTH
BB amplifier and
low pass filter
LO1 (RF) PLL:
- RX -
GSM 1365..1400 MHz
N+1
DCS 1365..1440 MHz
- TX -
Total VCO Range:
GSM 1370..1440 MHz
1365 to 1460 MHz
DCS 1385..1460 MHz
LO1
Loop
Filter
VCO
PLL
LO2 (IF) PLL
RX 880 MHz
TX 975 MHz
LO2
Loop
Filter
VCO
Total VCO Range:
880 to 975 MHz
I
0
°
Q
RF_IC_EN
LDO
RF_EN
LDO
RXIP
RXIN
RXQP
RXQN
AFC
VCTCXO
CLK13M
13 MHz
LO1 (RF) PLL
N
200 kHz step
1
ϕ
N
1
ϕ
N
1
M
LO2 (IF) PLL
1 MHz step
1
SERCK
SERDA
SERLE1
SERLE2
TXIP
TXIN
TXQP
TXQN
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