MC33215B Freescale Semiconductor, MC33215B Datasheet - Page 15

• Manufacturer Part Number: MC33215B
• Manufacturer: Freescale Semiconductor

Specifications of MC33215B

• Max Transmitter Gain: 58dB
• Receiver Gain (max): 27dB
• Operating Temp Range: -20C to 70C
• Package Type: SDIP
• Pin Count: 42
• Operating Current: 15mA
• Operating Temperature Classification: Commercial
• Mounting: Through Hole
• Lead Free Status / Rohs Status: Not Compliant

be below 0 dB and preferably below –10 dB for comfort. In a
practical telephone design, both the A
A
50 dB will give a loop gain of less than –10 dB. An optimized
sidetone network is of high importance for handsfree
operation. The better the network matches with the
telephone line the less local feedback and the smaller the
switching range can be.
duplex controller is set via resistor R
other, they have to be monitored. This is done by making a
signal envelope and a background noise envelope via the
C
C
a schematic behavior of the envelopes is depicted which is
equal for both transmit and receive.
current via the sensitivity adjust network. Then this current is
led through a diode which gives a logarithmic compression in
voltage. It is this voltage from which the signal envelope is
created by means of asymmetric charge and discharge of the
signal envelope capacitor. The noise envelope voltage then
follows in a similar way. Based on the envelope levels, the
MC33215 will switch to transmit, receive or idle mode
following Table 3. The fact that in receive mode the signal on
the base microphone is greater than it is in case of transmit
MOTOROLA ANALOG IC DEVICE DATA
RXBM(max)
TSE
RSE
To avoid howling, the maximum possible loop gain should
The amount of gain reduction A
In the typical application the gain reduction will be 50 dB.
To compare the transmit and receive signals with each
The voltage signal at the input is first transferred to a
, C
, C
A
attenuators
SWD
TBN
RBN
A
SWD
will be less than 20 dB thus a switching depth of
capacitors for the receive channel. In Figure 14,
capacitors for the transmit channel and via the
= Switching depth as performed in the
+
20 log
Microphone
Input Signal
3.6 x R
R
REF
Freescale Semiconductor, Inc.
SWD
SWD
For More Information On This Product,
SWD
BMRX(max)
according:
Figure 14. Signal and Noise Envelopes
Internal
1.8 V
obtained by the
2
(dB)
TSA
R
Go to: www.freescale.com
C
TSA
TSA
and the
MC33215
20 log R
mode, due to the coupling of the high loudspeaker signal, is
automatically taken into account.
will go to idle mode if the signals are not at least 4.5 dB
greater then the noise floor, which calculates as a 13 mV
voltage difference in envelopes. This avoids continuous
switching over between the modes under slight variations of
the background noise due to, for instance, typing on a
keyboard. Second, a dial tone detector threshold is
implemented to avoid that the set goes to idle mode in
presence of a continuous strong receive signal like a dial
tone. The dial tone detector threshold is proportional to the
R
the threshold is at 1.26 mVrms at the input RXI or 20 mVrms
at the line. Line length AGC is of influence on the dial tone
detector threshold, increasing the level depending on the line
current with a maximum of 6.0 dB.
signal strengths, the sensitivity of the envelope detectors can
be adjusted via the resistors connected to TSA and RSA.
Based on the above, and on the fact that there is an effective
gain of 20 dB in the transmit monitor, it can be derived that for
stable operation the following two relations are valid:
for R
completely free. The logarithmic compressors and the
amplifier stages have a certain range of operation and, on the
receive side, the choice for R
tone detector threshold. Figure 15 indicates the available
dynamic range for the selected value of the sensitivity
resistors.
RSA
In the table, two particulars can be found. At first, the set
In order to perform a correct comparison between the
By measuring the gains and choosing the R
TSA
20 log R
VHF
resistor. In the typical application with R
TSA
TSE
follow. The choice for the sensitivity resistors is not
C
TSE
TSA
t
20 log R
u
– A
20 log R
SW
RSA
)
RSA
RSA
20 (dB)
VHF
– A
is given by the desired dial
TBN
C
BMRX(max)
TBN
– A
RXBM(max)
RSA
RSA
)
, the limits
= 3.3 k ,
20 (dB)
15