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20.1 DESCRIPTION
Cellular telephones can
be
tested
using
the Cellu-
lar-Telephone Test
board. By
selecting tests
from a
menu
on the screen, the operator
can
use
the board to
provide the data and generate
the tones
necessary to
communicate
with
a
Cellular
telephone. This board
also contains
circuitry
to
test
a
Cellular
telephone
in
the
Manual Mode
and to send the
results
of an
Auto-
Test
to a
printer.
A
block diagram
of the Cellular-Telephone
Test
board
is
shown
at the
end
of
the
section
in Figure
20-1,
a
schematic in
Figure
20-2, and the
printed wir-
ing board assembly and
parts
list
in
Figure
20-3.
20.2
THEORY OF OPERATION
20.2.1 TRANSMITIED
DATA
The
system
microprocessor
generates
all data
trans-
mitted
to
the
Cellular
telephone under
test.
A
syn-
chronous serial-data
adapter
(SSDA)
(U8)
on the
Cellular-Telephone
Test board
transforms
the
data
from a parallel
to a serial
format. The transmitted data
is then Manchester-encoded
at U1
and filtered
by U24.
T he transmit
clock
is divided
down to 10 kHz from
the
3.84-MHz master
oscillator
by
U3 and
U7.
20.2.2
RECEIVED DATA
The data received
from
the
Cellular
telephone under
test
is filtered
by
U40. A
hard
limiter (U17) shapes the
Manchester-encoded data
to CMOS
levels.
The data enters a
synchronizer IC
(U3)
where
a
bit-
sync
detector
derives
the
receive
clock.
The received
data
is then Manchester
decoded,
and
the
synchro-
nizer looks for
word
sync,
which
is
an
11-bit
sequence.
When it
detects
word
sync,
U3
signals the
SSDA that
valid
data is available.
The
data
is
then clocked into
the SSDA and
read
by the microprocessor.
20.2.3
CONTROL
The
microprocessor
controls all data and
signal
paths
through U9, an on-board peripheral-interface
adapter (PIA). This PIA
disables
all analog signals
when data is
being
transmitted, and disables the
data
path when data is not
being
transmitted.
20.2.4
MODULATION
The audio-modulation paths are enabled
or
dis-
abled,
depending
on
whether
or
not a Cellular test is
in
progress.
As
long as there is no Cellular test, the
SECTION
20.
CELLULAR TELEPHONE
TEST
OPTION
EXT MOD RTN
(0),
INT MOD
RTN (0), and
1KHz
SINE
RTN
(0)
paths are enabled. During a Cellular
test, whenever data is not being
t ransmitted,
MIC
IN,
EXT MOD INPUT,
INT
MOD
(I)
and
1 KHz SINE
RTN
(0)
are enabled.
During
a Cellular test, the System Analyzer trans-
mits
a supervisory audio tone (SAT) with
a
frequency
of 5970
Hz, 6000 Hz,
or 6030
Hz.
This
tone comes to
the board
via the
INT MOD
(I)
line. The SAT
passes
through an automatic gain control (AGC) circuit
(U23
and U25). U25B full-wave
rectifies
the
SAT, and
amplifier U23A
sets
the output level. U23B then com-
pares
the
average
voltage of
the
rectified
signal
with
2.5
V
de.
The output of U23B drives the gate of
Q2,
which
acts as a voltage-variable
resistor
to attenuate the
input
SAT.
The
microphone
input port
(Mic)
on the front panel
allows voice to be transmitted to the Cellular
tele-
phone
under
test. The
incoming
signal
is
amplified
and
filtered
before it
enters compressor U21, which
con-
denses
amplitude variations by attenuating high-level
signals
and
amplifying low-level ones.
The
signal enters
a
pre-emphasis
circuit, and then, to limit
the
FM
deviation to
a
specified
level,
an instantaneous devia-
tion
control
(IDC) circuit.
To
attenuate harmonics
created
by
the
IDC,
a
splatter
filter follows.
The 1
KHz
SINE
RTN
(0)
line
can
be used
to
measure receiver
distortion and
sensitivity.
EXT MOD
INPUT can be used to add an
external
modulation
source.
20.2.5
10-KHz
DETECTION
Detect circuitry measures
the
duration
of
the
Cel-
lular
telephone's 10-kHz
signaling
tone. The received
signaling
tone comes in
via
DEMOD CAL AUDIO,
where
it is
filtered
to
eliminate
noise
and
unwanted
signals
before
becoming
an input for a 10-kHz detec-
tor
(U12).
The
output of this
detector is normally
a
logic
1.
However,
when
it detects
a
10-kHz
signal,
U12
outputs
a
logic 0
for the duration of the 10-kHz
signal.
A timer
IC
(U10) measures
the
duration
of
the
logic
0.
20.2.6
MANUAL-MODE
CONTROL
With the Manual-Mode Test,
the
transceiver por-
tion
of
the
Cellular telephone can
be manually tested.
The Manual-Mode Test
connector
(CELL
BUS) is
located
on the back
of the System
Analyzer.
A handshaking
(asynchronous)
process
transfers
data
to
and from
the
transceiver. The microprocessor
controls
the
signals and their
direction
through a
PIA
(Ul5).
All
control and
data lines
are
buffered
by
GPIB
transceivers
U35 and 036.
20-1/20-2 blank
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