Motorola Internal Use
2
V2288 – Circuit Description
V2288 Level 3 Product Guide
RF:
Receive
1)
The RF Signal from the base station is received through the Antenna
A100
and is fed
to
J300
, which is a purely mechanical switch which is operated when an cable is
plugged into the Aux RF socket of the phone. This connects RF to the Aux RF port or
the antenna.
2)
The RX signal is then fed directly into
U100
RF Switch, the switch acts as an
isolation between TX and RX, this is controlled via the signals
VA
and
VB
which are
previously created by
TX_EN
and
RX_EN
respectively through
Q110.
3)
Provided
VB
is high, then the received signal will be passed to the band pass filter
FL470
, where the selected frequency band (GSM 1800 or GSM900) will be filtered
through, *Note. The front-end filter has a bandwidth that is capable of working with
the American GSM standard 1900Mhz. This gives the option of creating a PCS unit
without the need to change many components.
4)
The appropriate signal is then fed onto
FL472
(For GSM 1800) or
FL480
(For 900)
where any existing harmonics or other unwanted frequencies are removed.
5)
Our received RF frequency is now fed into the
Front End IC
(
U432
). This IC is new
to the T2288 and has several main purposes; reduce discreet part count and therefore
cost as it replaces the mixer stage and also the two other front end filters from
previous products and also the main RX VCO buffer. (Refer to Front End IC
Document for internal block diagram interpretation). The IC’s power is maintained by
RF_V2
(MAGIC), and is controlled with the aid of
RVCO_250
(created by
SF_OUT
(MAGIC) and
GPO4
(MAGIC) through
Q172
),
RX_EN
(Whitecap) and
DCS_SEL
(MAGIC). The GSM 900 signal is fed in through
Pin 13
, back out through
Pin 12
to
matching circuitry, then returns to the IC on
Pin 9
, where the signal is internally
mixed with the RX VCO signal to produce a ba and – 400 MHz IF Signal.
The main reason for using the balanced IF output is to provide cancelling of the 3
rd
harmonic. This is then fed out on
Pins 3 and 4.
The GSM 1800 route is of the same
description but uses the
Pins 18-20-23-3 and 4
.
6)
The
RX VCO U253
is now an integrated circuit and is controlled firstly from the
Whitecap using the
MQ SPI
bus to program the MAGIC and then MAGIC drives the
RX VCO IC using the
CP_RX
signal
Pin B1
. The power is supplied by
RVCO_250
(
SF_OUT
+
GPO4
through
Q172
).
7)
The + and – IF, is now fed to the
SAW FL490
filter (Surface Acoustic Wave), this
filter is the same as was used in previous 400MHz products, and is balanced to accept
the new + and – IF.
8)
The signal is then passed to the
MAGIC IC U200
PRE IN
Pin A7
9)
The signal is then demodulated internally using an external Varactor diode RX Local
Oscillator set up
CR249
, which is driven by
PLL CP
Pin A9
of
MAGIC U200
.
10)
Where in earlier products, we used to have
RX I
and
RXQ
, these signals are now
only used in digital form within the MAGIC and cannot be measured. The
demodulated signal is now converted internally to digital form to be passed along an
RX SPI bus to the Whitecap.
