MC33215
Table 3. Logic Table for Switch–Over
TSE > RSE
TSE > TBN + 13 mV
RSE > V
RSE > RBN + 13 mV
Mode
DDT
1
1
0
0
0
1
0
X
X
1
0
0
X
X
X
1
Transmit
Idle
X
X
X
Receive
Receive
Idle
0
The resistors for the sensitivity setting have to be coupled
capacitively to the pins for dc decoupling, and also to create
a high pass filter to suppress low frequent background noises
like footsteps and 50 Hz.
The switch–over timing is performed by charging and
discharging the CSWT capacitor. The switch–over from
transmit to receive or vice versa is fast, on the order of
milliseconds, and is proportional to the value of CSWT. The
switch–over to idle mode is slow, in the order of a few
seconds, and is proportional to the product of the values of
RSWT and CSWT. Figure 16 depicts a typical switch–over
behavior when applying transmit and receive stimuli.
The electrical characteristics and the behavior of the
MC33215 are not the only factor in designing a handsfree
speakerphone. During the design the acoustics have to be
taken into account from the beginning. The choice of the
transducers and the design of the cabinet are of great
influence on the speakerphone performance. Also, to
achieve a proper handsfree operation, the fine tuning of the
components around the duplex controller have to be done
with the final choice of the cabinet and the transducers.
Figure 15. Compression Range of the Signal Monitors
100.0E–3
10.0E–3
1.0E–3
100.0E–3
Upper Limit of
Compression
Upper Limit of
Compression
Dial Tone
Threshold
10.0E–3
Lower Limit of
Compression
Lower Limit of
Compression
1.0E–3
100.0E–6
10.0E–6
100.0E–6
1000
10000
100000
1000
10000
100000
100
100
R
(Ω)
R
(Ω)
RSA
TSA
A. Receive Monitor
B. Transmit Monitor
Figure 16. Switch–Over Behavior
Receive
Transmit
VMC + 0.5
VMC – 0.5
SWT
16
MOTOROLA ANALOG IC DEVICE DATA
MOTOROLA [ MOTOROLA ]
