MC33218ADWR2 Freescale Semiconductor, MC33218ADWR2 Datasheet - Page 21

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MC33218ADWR2

Manufacturer Part Number
MC33218ADWR2
Description
IC VOICE SWITCH SPKPHONE 24-SOIC
Manufacturer
Freescale Semiconductor
Datasheet

Specifications of MC33218ADWR2

Function
Voice-Switched Speakerphone
Interface
SPI Serial
Voltage - Supply
2.7 V ~ 6.5 V
Current - Supply
4.6mA
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
*
Includes
Chip Disable
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power (watts)
-
Number Of Circuits
-
Other names
MC33218ADWTR
Switching and Response Time Theory
by the components at C T (Pin 7, refer to Figure 3), and
second by the capacitors at the level detector outputs (RLO,
TLO).
idle, or from the other mode, is determined by the capacitor at
C T , together with the internal current sources (refer to
Figure 29). The switching time is:
I = 42 A, the C T capacitor is 15 F, and T calculates to
I = 42 A, the C T capacitor is 15 F, and T calculates to
sources are shut “off”, and the time constant is determined by
the C T capacitor and RT, the external resistor (see
Figure 29). With C T = 15
constant is
(for 95% change). The switching period to idle begins when
both speakers have stopped talking. The switching time back
to the original mode will depend on how soon that speaker
begins speaking again. The sooner the speaking starts
during the “decay to idle” period, the quicker the switching
time since a smaller voltage excursion is required. That
switching time is determined by the internal current sources
as described above.
(or vice–versa), the total switching time depends not only on
the components and currents at the C T pin, but also on the
response of the level detectors, the relative amplitude of the
two speech signals, and the mode of the circuit, since the two
level detectors are connected differently to the two
attenuators.
not significant since it is so short. The decay time, however,
provides a significant part of the “hold time” necessary to hold
the circuit (in transmit or receive) during the normal pauses in
speech. The capacitors at the two outputs must be equal
value ( 10%) to prevent
response.
TLI) do not affect the switching time, but rather affect the
relative signal levels required to switch the circuit, as well as
the frequency response of the detectors. They must be
adjusted for proper switching response as described later in
this document.
Switching and Response Time Measurements
switch among its modes, the timing results were measured
and are indicated in Figures 21–25.
attenuator only (normally via the microphone and the
microphone amplifier), the transmit background noise
monitor immediately indicates the “presence of speech” as
evidenced by the fact that CPT begins rising. The slope of the
rising CPT signal is determined by the external resistor and
capacitor on that pin. Even though the transmit attenuator is
initially in the idle mode (–16 dB), there is sufficient signal at
MOTOROLA ANALOG IC DEVICE DATA
36 ms.
53 ms. When switching from idle to transmit, V = 100 mV,
The switching time of the MC33218A circuit is dominated
The transition time to receive or to transmit mode from
When switching from idle to receive,
When the circuit switches to idle, the internal current
When the circuit switches directly from receive to transmit
The rise time of the level detector’s outputs (RLO, TLO) is
The components at the inputs of the level detectors (RLI,
Using burst of 1.0 kHz sine waves to force the circuit to
a) In Figure 21, when a signal is applied to the transmit
225 ms, giving a total switching time of
D
T
+
D
problems in timing and signal
V
F, and RT = 15 k , the time
I
Freescale Semiconductor, Inc.
C
T
For More Information On This Product,
APPLICATIONS INFORMATION
V = 150 mV,
Go to: www.freescale.com
0.68 s
MC33218A
its output to cause TLO to increase. The attenuator control
circuit then forces the circuit to the transmit mode, evidenced
by the change at the C T pin. The attenuator output signal is
then 6.7 dB above the input.
the circuit will stay in the transmit mode until the CPT pin gets
to within 36 mV of its final value. At that point the internal
comparator (see Figure 32) switches, indicating to the
attenuator control circuit that the signal is not speech, but
rather it is background noise. The circuit now begins to decay
to idle, as evidenced by the change at C T and TLO, and the
change in amplitude at TAO.
the CPT pin drops quickly, allowing the CPT to quickly
respond to any new speech which may appear afterwards.
The voltage at C T decays according to the time constant of its
external components, if not already at idle.
input signal’s amplitude, and the components at XDI and TLI.
The change at C T is internally fixed at the level shown. The
timing numbers shown depend both on the signal amplitudes
and the components at the C T and CPT pins.
signal is applied to the receive side only. RLO and CPR react
similarly to TLO and CPT. However, the circuit does not
switch to idle when CPR finishes transitioning since the dial
tone detector disables the background noise monitor,
allowing the circuit to stay in the receive mode as long as
there is a signal present. If the input signal amplitude had
been less than the dial tone detector’s threshold, the circuit
response would have been similar to that shown in Figure 21.
The voltage change at C T depends on the setting of the
volume control (bits B3–B0). The +150 mV represent
maximum volume.
and receive signals are alternately applied, with relatively
short cycle times (300 ms each) so that neither attenuator will
begin to go to idle during its “on” time. Figure 24 indicates the
circuit response with longer cycle times (1 s each), where the
transmit side is allowed to go to idle. Figure 25 is the same as
Figure 24, except the capacitor at CT has been reduced from
15
reactions at the various pins are shown. The response times
at TAO and RAO are different, and typically slightly longer
than what is shown in Figures 21 and 22 due to:
to the positions of the attenuators, as well as their decay time,
and
The timing responses shown in these three figures are
representative for those input signal amplitudes, and burst
durations. Actual response time will vary for different signal
conditions.
switching time between modes by reducing the capacitor at
CT, this should be done with caution for two reasons:
may appear to be “too quick” to the user, who may consider
its operation erratic. The recommended values in this data
sheet, along with the accompanying timings, provide what
With the steady sine wave applied to the transmit input,
When the transmit signal at MCO is removed (or reduced),
The voltage change at CP2, CPT, and TAO depend on the
b) Figure 22 indicates what happens when the same
c) Figure 23 indicates the circuit response when transmit
– The larger transition required at CT pin,
– The greater difference in the levels at RLO and TLO due
– Response time of background noise monitors.
NOTE: While it may seem desirable to decrease the
1) If the switching time is too short, the circuit response
F to 6.8
F, providing a quicker switching time. The
21

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