MC33218ADWR2 Freescale Semiconductor, MC33218ADWR2 Datasheet - Page 22

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

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

experience has shown to be a “comfortable response“ by the
circuit.
the CT capacitor value is decreased. The extra THD will be
most noticeable at the lower frequencies, and at the lower
amplitudes. Table 1 provides a guideline for this issue.
Considerations in the Design of a Speakerphone
human interfaces issues, as well as proper signal levels.
Because of this fact, it is not practical to do all of the design
mathematically. Certain parts of the design must be done by
trial and error, most notably the switching response and the
“How does it sound?” part of the testing. Among the
recommendations for a successful design are:
electronics. Do not leave the case design to the end as its
properties are just as important (just as equally important) as
the electronics. One of the major issues involved in a
speakerphone design is the acoustic coupling of the speaker
to the microphone, which must be minimized. This parameter
is dependent entirely on the design of the enclosure, the
mounting of the speaker and the microphone, and their
characteristics.
alone can make a difference of several dB in the sound level
from the speaker, as well as the sound quality. The speaker
manufacturer should be consulted for this information.
speaker hanging out in midair. It will not work. The speaker
and microphone must be in a suitable enclosure, preferably
one resembling the end product. If this is not feasible,
temporarily use some other properly designed enclosure,
such as one of the many speakerphones on the market.
or a plug–in prototyping board. Use a PC board, preferably
with a ground plane. Proper filtering of the supply voltage, at
the V CC pin, is essential.
hybrid, and connected to a phone line, or phone line
simulator. The performance of the hybrid is just as important
as the enclosure and the speakerphone IC.
Capacitor
22
2) The distortion in the receive attenuator will increase as
The design and adjustment of a speakerphone involves
1) Design the enclosure concurrently with the
2) Ensure the speaker is optimally mounted. This fact
3) Do not breadboard the circuit with the microphone and
4) Do not breadboard the circuit on a wirewrapped board
5) The speakerphone must be tested with the intended
6.8 F
3.3 F
15 F
CT
Table 1. THD versus CT Capacitor
Transition
Idle–R x
53 ms
24 ms
12 ms
100 mVrms
100 mVrms
100 mVrms
20 mVrms
20 mVrms
20 mVrms
@ RAI
Input
Freescale Semiconductor, Inc.
For More Information On This Product,
1.0 kHz
1.0 kHz
1.0 kHz
1.0 kHz
1.0 kHz
1.0 kHz
300 Hz
300 Hz
300 Hz
300 Hz
300 Hz
300 Hz
Freq.
Go to: www.freescale.com
@ RAO
0.12%
1.5%
0.3%
0.6%
3.6%
1.0%
1.4%
0.4%
7.0%
1.9%
2.8%
0.7%
THD
MC33218A
environment. If the speakerphone is in a room with large
windows and tile floors, it will sound different than if it is in a
carpeted room with drapes. Additionally, be conscious of the
background noise in a room.
sure the person at the other end of the phone line is not in the
same room as the speakerphone.
Design and Adjustment Procedure
intended production microphone and speaker installed, and
the PC boards installed (or temporary substitutes for the PC
boards) a recommended sequence is as follows (refer to
Figure 35):
the phone line for both DC and AC characteristics. The return
loss must be adjusted so as to comply with the appropriate
regulatory agency. The sidetone should then be adjusted
according to the intent of the product. If the product is a
speakerphone only, without a handset, the sidetone gain
(GST) should be adjusted for maximum loss. If a handset is
part of the end product, the sidetone must be adjusted for the
minimum acceptable sidetone levels in the handset.
Generally, for the speakerphone, 10–20 dB sidetone loss is
preferred for GST.
Figure 35). With a steady sound coming out of the speaker,
measure the rms voltage on the speaker terminals, and the
rms voltage out of the microphone. Experience has shown
that the loss should be at least 40 dB, preferably 50 dB. This
should be checked over the frequency range of 20 Hz to
10 kHz.
on the lowest speech levels as well as the loudest. Based on
the typical levels from commonly available microphones, a
gain of about 35–45 dB is required from the microphone
terminals to Tip and Ring. Most of that gain should be in the
microphone amplifier so as to make best use of the transmit
attenuator, but make sure the maximum attenuator input
level at MCO is not exceeded. If a signal generator is used
instead of a microphone for testing, the circuit can be locked
into the transmit mode by grounding CPT (Pin 3), or using
bits B7 and B6 (set to 11). Frequency response can generally
be tailored with capacitors at the microphone amplifier.
on the lowest speech levels as well as the loudest. A gain of
about 30 dB is required from Tip and Ring to the speaker
terminals for most applications (at max. volume). Most of that
gain should be in the receive amplifier (at RXI, RXO) so as to
make best use of the receive attenuator, but make sure the
max. attenuator input level at RXO is not exceeded. If a
signal generator is used for signal injection during testing, the
circuit can be locked into the receive mode by grounding
CPR (Pin 10), although this is usually not necessary since
the dial tone detector will keep the circuit in the receive mode.
As an alternate, bits B7 and B6 can be set to 01. Frequency
response can generally be tailored with capacitors at the
receive amplifier.
acoustic coupling gain + transmit path gain + sidetone gain)
is less than 0 dB over all frequencies. If not, “singing” will
occur – a steady oscillation at some audible frequency.
detector inputs (RLI and TLI) for proper switching response
6) When testing the speakerphone, be conscious of the
7) When testing the speakerphone on a phone line, make
Assuming the end product enclosure is available, with the
1) Design the hybrid, ensuring it interfaces properly with
2) Check the acoustic coupling of the enclosure (GAC in
3) Adjust the transmit path for proper signal levels, based
4) Adjust the receive path for proper signal levels, based
5) Check that the loop gain (i.e., the receive path gain +
6) a) The final step is to adjust the resistors at the level
MOTOROLA ANALOG IC DEVICE DATA