CD P7689 A4 C L3 V1.0, Nieposegregowane
[ Pobierz całość w formacie PDF ]
P7689
Level 3
Circuit Description
25 / 03 / 2000
V1.0
P7689 – Circuit Description
P7689 Level 3 Product Guide
RF:
Receive
1)
The RF Signal from the base station is received through the Antenna
A1
or from the
Accessory Connector
J600
and is fed to
Pin 10
or
Pin 3
respectively
of the
RF Switch
U150
, the switch acts as an isolation between TX and RX. The
RF Switch control
is
provided by
U151
.This decides whether the Switch is opened for TX or RX and if the
RF is passed to the Aux RF port or the Antenna. This is managed by the following
signals:
TX_EN
RX_EN
SW_RF (50W Load)
Result
H
L
Loaded
TX through J600
L
H
Loaded
RX through J600
H
L
Not Loaded
TX through Antenna
L
H
Not Loaded
RX through Antenna
2)
TX_EN
and
RX_EN
are produced by
Whitecap U800,
Pins C1
and
E3
respectively.
U151
is supported by the voltages
FILTERED –5V
(From
–5V
(
U903
))
and
RF_V1
(
Q201
)
3)
Once the received signal is present (using GSM 900 as the example) in the RF switch.
Provided
RX275_GSM_PCS
(
Q2101
) is high, then the received signal will be passed
to the band pass filter
FL400
, GSM900received frequency will be filtered through,
*Note
RX275_GSM_PCS
also selects the PCS 1900 frequency passed through
FL2400
. The DCS 1800 frequency is selected by
RX275_DCS
(
Q110
) and passed
through
FL1400
4)
For the PCS 1900 and DCS 1800 frequencies the signal is then fed onto the
DCS/PCS
Select switch U400.
The signal
RVCO_PCS
and
RVCO_DCS
(
Q1100
) will then
select the appropriate signal; with output tuning being provided by
L1411
and
C1411
for DCS and
C2411
for PCS.
5)
Once selected the signal will be fed into a Low noise Amplifier Circuit, this part of
the circuit is critical in the achievement of a very low signal to noise ratio, therefore
as can be seen around the actual amplifiers
Q400
for GSM (supported by
RX275_GSM
(
Q110
)) and
Q1400
for DCS / PCS (supported by
RX275_DPCS
(
Q2102
)), a large amount of external frequency matching and noise reduction
circuitry is involved.
6)
The appropriate signal is then fed onto
FL1401
(For GSM 1800 / 1900) or
FL401
(For GSM 900) where any existing harmonics or other unwanted frequencies are
removed.
Motorola Internal Use
2
P7689 – Circuit Description
7)
The amplified signal is now injected to the base of the dual transistor mixer
Q450
.
Both mixers are supported by
RX275
(
Q112
).The tuned emitter biasing voltage is
provided by
RX275_GSM
(
Q110
) and
RX275_DPCS
(
Q2102
)
8)
The
RX VCO U250
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 A1
. The power is supplied by
RVCO_275
(
SF_OUT
+
GPO4
through
Q1102
).
9)
The generated RX VCO signal is then split, with a part going back to the
MAGIC IC
– U200.
Pin A3
to serve as the feedback for the RX VCO Phase lock loop. The other
part is firstly amplified through a
Tuned Transistor Amplifier Q252,
before being
used to mix with the received frequencies through the emitters of the dual mixer
transistor
Q450.
10)
The mixer will produce sum and difference signals i.e. RX’ed frequency + RX VCO
frequency and RX’ed frequency - RX VCO frequency. It will be the difference signal
that is now fed to the
SAW Filter FL457
(Surface Acoustic Wave), this filter is the
same as was used in previous 400MHz products. The purpose of the SAW filter is to
provide comprehensive removal of harmonics created during the mixing process.
11)
The IF signal fed to the SAW filter will be 400Mhz. The reason for the change to
400Mhz from 215Mhz is to limit the span of the RX VCO e.g.
Description
IF
Channel
Received
Frequency
RX VCO
Frequency
Difference
EGSM L Channel 400Mhz
975
925.2Mhz
1325.2Mhz
264.6Mhz
PCS H Channel
400Mhz
810
1989.8Mhz
1589.8Mhz
EGSM L Channel 215Mhz
975
925.2Mhz
1140.5Mhz
634.6Mhz
PCS H Channel
215Mhz
810
1989.8Mhz
1774.8Mhz
As can be seen if the IF was kept at 215Mhz, the frequency span would have to be an
extra
370Mhz
.
This is turn assists in reducing the part count.
12)
The 400Mhz IF signal is then passed to the Isolation Amplifier Q480
The purpose of an Isolation Amp is to couple an analogue signal to adjoining parts of
a circuit with 2 different grounds. Also to protect the base band signals from any stray
RF. The Isolation Amp is supported by
SW_VCC
(
MAGIC U200
Pin C7
)
Isolation
Amp
MAGIC
IC
U200
Base-band
Signal
101001010100
Motorola Internal Use
3
P7689 – Circuit Description
13)
The signal is then passed to the
MAGIC IC U200
PRE IN
Pin A7
14)
The signal is then demodulated internally using an external 800 MHz Varactor diode
CR249
,
RX Local Oscillator set up, which is driven by
PLL CP
Pin A9
of
MAGIC
U200
.
15)
Where in earlier products, we used to have
RX RXQ, and I
these signals are now
only used in digital form within the MAGIC and can only be measured using a
specific set up. The demodulated signal is now converted internally to a base band
digital form to be passed along an RX SPI bus to the Whitecap.
16)
The
RX SPI
signal is made up of
BDR
(Base band Data Receive),
BFSR
(Base band
Frame Synch Receive) and
BCLKR
(Base band Clock Receive, fed from MAGIC
Pins G8, G9 and F7
respectively.
17)
The
Whitecap U800
receives these signals on
Pins A3, D4 and B4,
within the
Whitecap the signal is digitally processed. Baud rate reduced, Error correction bits
removed, etc…
18)
The digital signal is now being fed down the
DIG_AUD_SPI
bus to the
GCAP II
U900
, internally to the GCAP, the digital signal is converted to analogue and
distributed to the correct outputs:
19)
For Earpiece speaker, from GCAP II
Pins H6 and H7
to speaker pads
J502
and
J503
20)
The Alert is generated within the Whitecap, given the appropriate data from the
incoming signal, SMS, call etc… and is fed to the alert pads
J003
and
J5004
. This
signal is supported by the signal
ALRT_VCC
, which is generated from B+ through
Q903
.
21)
For the headset only the
SPKR-
signal is used from GCAP II
Pin H6
.The output is
then fed out to the
Headset Jack socket J504.
Pin 3.
RF:
Transmit
1)
There are 2 Mic inputs, firstly from the
Xcvr Mic J900
, where the analogue input is
fed to the
GCAP II U900
Pin J2.
2)
Secondly the analogue voice can be fed from the Aux Mic attached to the headset and
will be routed from
connection 1
of the
Headset Jack J504
, through to GCAP II,
Pin
H3
.
3)
Within the GCAP II the analogue audio will be converted to digital and clocked out
onto the
DIG_AUD
SPI bus to the
Whitecap U800
.
Motorola Internal Use
4
P7689 – Circuit Description
4)
It is within the Whitecap that all information about the transmission burst is
formulated i.e. The timing of the burst / The channel to transmit on / The error
correction protocol / In which frame the information will be carried to the base
station, etc, etc…
5)
All this information is then added to the digitised audio and is transferred to the
MAGIC U200
along a TX SPI bus. The bus is made up of
BCLKX
(Base band Clock
Transmit)
Pin B3
and
BDX
(Base band Data Transmit)
Pin B6
. The timing for this
data is already decided for the transmission burst, and therefore a frame synch is not
required.
6)
The SPI comes into the MAGIC at
Pin G7
(
BCLKX
) and
Pin J2
(
BDX
)
7)
The operation of the MAGIC is very complex and with respect to the transmit path,
integrates the functions of the Modem and its function of performing GMSK
(Gaussian Minimum Shift Keying) and also the functions of the TIC (Translational
Integrated Circuit).
8)
A very basic block view of how the transmit path works within the MAGIC is
demonstrated in: Fig 8.1
Internal MAGIC Operation
Fig 8.1
BDX
AFC
Look
Up
ROM
S
Channel
Info
CLK
Digital
representation
of RX VCO
Digital
r
e
presentation
of TX VCO
F/B
TX_CP
CLK
9)
The data is transmitted from Whitecap to MAGIC on TX SPI bus
BDX
, within the
MAGIC each bit of data is clocked into a register. The clocked bit and the 3
preceding bits on the register are then clocked into the look up ROM, which looks at
the digital word and from that information downloads the appropriate GSMK digital
representation. Channel information and AFC information from MAGIC SPI is then
Motorola Internal Use
5
[ Pobierz całość w formacie PDF ]