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A008 / A6188+ – Circuit Description
RF:
Receive
1) The RF Signal from the base station is received through the Antenna
RF Switch
U101, This connects RF to the Aux RF port or the antenna, and isolates
TX from RX. The switch is controlled primarily by the following signals
This is a 50Ω load signal from Pin 2 of the
device is attached. RX / TX isolation is achieved using the negatively biased signals
from
Q101
and Q102. These devices use the signals
through Q340) and
produce the Transmit and Receive switching signals. The negative bias is produced
using
-5V
through
with the correct switching voltages (for RX Mode 0 – 2.7V, for TX Mode –5V to
2.7V) and
Q106
is used to change the output path between Antenna and Buttplug.
The control signals from
switch. These 3 signals, supported by the voltages
GSM_SEL) and
DCS_LNAS275 (DCS_SEL and
select whether the signal is Transmitted or Received.
2) Provided
MIX_275
filter FL460, for GSM 900 and to
frequency range (GSM 1800 or GSM900), and remove any existing harmonics or
other unwanted frequencies.
3) The signal will be fed into the appropriate
GSM 900 and
Q451
a very low signal to noise ratio, therefore as can be seen around the actual amplifiers,
a large amount of external frequency matching and noise reduction circuitry is
involved. The LNA's are supported by
GSM_LNA275
for Q461and
4) The appropriate signal is then fed onto
1800) where any harmonics created during amplification are removed.
5) The amplified signal is now injected to the base of the dual transistor mixer Q1254.
Both mixers are supported by
provided by
GSM_LNA275
6) The
RX VCO Varactor CR250.
basically a Varactor diode works in the following way:
When a reverse voltage is applid to a PN junction , the holes in the p-region are
attracted to the anode terminal and electrons in the n-region are attracted to the
cathode terminal creating a region where there is little current.This region ,the
depletion region, is essentially devoid of carriers and behaves as the dielectric of a
capacitor.
The depletion region increases as reverse voltage across it increases; and since
capacitance varies inversely as dielectic thickness, the junction capacitance will
Motorola Internal Use
A6188 Level 3 Product Guide
PAC_275 (TX_EN + RF_V2
Q104, Q105,
these 2 transistors are used to provide the RF Switch
Q101
and
Q102
is high, then the received signal will be passed to the band pass
FL450
for DCS. This part of the circuit is critical in the achievement of
MIX_275
DCS_LNAS275
FL470
MIX_275
(Q342) and
Is the active component used within the RX VCO,
Accessory Socket
J600, when an external
MIX_275 (RX_EN + RF_V2
through Q321
are then fed to Pins 2 and 9 of the RF
GSM_LNA275 (MIX_275 +
MIX_275) both through
for GSM 1800. The filters will then pass the
Low noise Amplifier Circuit, Q461
and are biased on or off by
for
Q451.
(For GSM 900 or
(Q340).The tuned emitter biasing voltage is
DCS_LNA275
(Q342)
2
A1
and is fed to
SW_RF:
and Q320) to
Q342
for
FL465
(For GSM
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