Topaz T2688/T200, T2988/T205 L3 Circuit Description
8
Motorola Proprietary Information
TRANSMIT
30.
There are 2 sources of input audio:
31.
Auxiliary Microphone is fed in through
J40 External Connector
Pin1
and is fed
through
Jumper Connector J8
(JTAG Use), and is amplified through the BQ5 circuit,
supported by the voltage
DVCC
. The input signal is fed onto the base of
Audio
AmpBQ5
, amplified, and fed out of the collector as
AUXI
.
32.
The
Internal Microphone X1
, uses the circuit
R14 / R15 / C22 / C23 / R17 / R18
to
provide microphone biasing, the biasing support voltage being fed from the
VEGA IC
from
Pin 26
. (Gain approximately 27dBm)
Voltage suppressers U48
and
U49
provide
ESD protection to the circuit.
33.
If both inputs are active then, output signal from the internal microphone will be used.
34.
The input analogue audio is then routed to the
VEGA IC
Pins 28 & 29
. Within the
VEGA the analogue signal will be driven through a PGA with a gain of between –
12dB to +12dB in 1dB steps.
35.
A Sigma-Delta Modulator converts the signal from analogue to Digital, sampled at
1Mhz. The signal is the decimated and the sampling rate taken down to signal
samples at 8Khz.
36.
Once again, as in
RECEIVE
, the loop between the
VEGA IC
and the
GEMINI IC
is
put in place for standard data processing.
37.
The transmitted signal is sent to the
Gemini IC
over the Voice-band
VDR
Line
VEGA
Pin 14
and is clocked by
VCLKRX
Pin 16
. The signals are then received by
the
Gemini IC
on
Pins 97 & 98
respectively. Synchronisation is achieved using the
frame synch signal
VFSRX
(
VEGA
Pin 13
/
GEMINI
Pin 96
.
38.
After processing, the Base-band signal information is transferred back to
the VEGA
IC
using the base-band lines,
BFSR / BDR / BCLKR
/ (
VEGA
Pins 6, 4 & 5
and
GEMINI
Pins 74 / 75 / 76
respectively)
39.
Within the
VEGA IC
, the received information will now be modulated by GMSK.
MICBIAS
MICIP
AUXI
PGA
Sigma -Delta
Modulator
Decimation
Band-pass
Filters
Bias
Generator
Microphone
Amp
Auxiliary
Amp
MICIN
To Voice
Serial
Interface
Summary of Contents for TALKABOUT T2688
Page 1: ...T200 T2688 Level 1 2 Service Manual Rev 1 2 ...
Page 4: ...of 51 GSM Field Service Support iv T200 T2688 SECTION 1 GENERAL ...
Page 8: ...of 51 GSM Field Service Support 1 T200 T2688 SECTION 2 T200 DESCRIPTION ...
Page 15: ...of 51 GSM Field Service Support 8 T200 T2688 SECTION 3 FEATURE LIST ...
Page 22: ...of 51 GSM Field Service Support 15 T200 T2688 SECTION 4 DISASSEMBLY PARTS ...
Page 26: ...of 51 GSM Field Service Support 19 T200 T2688 4 5 Exploded Parts Diagram ...
Page 28: ...of 51 GSM Field Service Support 21 T200 T2688 SECTION 5 SIM CARDS AND SECURITY ...
Page 32: ...of 51 GSM Field Service Support 25 T200 T2688 SECTION 6 REPAIR AND TEST PROCEDURES ...
Page 40: ...of 51 GSM Field Service Support 33 T200 T2688 SECTION 7 ACCESSORIES ...
Page 42: ...of 51 GSM Field Service Support 35 T200 T2688 SECTION 8 SALES MODEL NUMBERS ...
Page 46: ...of 51 GSM Field Service Support 39 T200 T2688 SECTION 9 GLOSSARY OF TERMS ...
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