MT8843 查看數據表（PDF） - Zarlink Semiconductor Inc
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MT8843 Datasheet PDF : 23 Pages
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MT8843
IN+
C
RIN
IN-
RF
GS
Voltage Gain
(AV) = RF / RIN
VRef
Figure 6 - Single-Ended Input
Configuration
C1 R1
IN+
IN-
C2 R4
R5
GS
R3
R2
VRef
Differential Input Amplifier
C1 = C2
R1 = R4 (For unity gain R5= R4)
R3 = (R2R5) / (R2 + R5)
Voltage Gain
(AVdiff) = R5/R1
Input Impedance
(ZINdiff) = 2 R12 + (1/ωC)2
Figure 7 - Differential Input Configuration
FSK Demodulation
CNIC2 first bandpass filters and then demodulates
the incoming FSK signal. The device’s carrier
detector provides an indication of the presence of
signal at the bandpass filter output. The CNIC2’s
dual mode 3-wire interface allows convenient
extraction of the 8-bit data words in the demodulated
FSK bit stream.
Note that signals such as dual tone alert signal,
speech and DTMF tones lie in the same frequency
band as FSK. They will, therefore, be demodulated
and as a result, false data will be generated. To
avoid demodulation of false data, an FSKen pin is
provided so that the FSK demodulator may be
disabled when FSK signal is not expected. There
are two events that if either is true, should be used to
disable FSKen. The events are CD returning high or
receiving all the data indicated by the message
length word.
Item
BT
Bellcore
Mark
frequency
(logic 1)
1300Hz
±± 1.5%
1200Hz
±± 1%
Space
frequency
(logic 0)
Received
signal level -
mark
2100Hz
±± 1.5%
-8dBV to
-40dBV
(-5.78dBm to
-37.78dBm)
2200Hz
±± 1%
-12dBma to
-32dBm
Received
signal level -
space
Signal level
differential
(twist)
-8dBV to
-40dBV
up to 6dB
-12dBm to
-36dBm
up to 10dBb
Unwanted
signals
<= -20dB
(300-3400Hz)
<= -25dB
(0-4kHz)c
Transmission
rate
1200 baud
±± 1%
1200 baud
±± 1%
Word format
1 start bit (logic
0), 8 bit word
(LSB first), 1 to
10 stop bits
(logic 1)
1 start bit (logic
0), 8 bit word
(LSB first),
1 stop bit
(logic 1)d
Table 2 - FSK Characteristics
a. The signal power is expressed in dBm referenced to 600 ohm
at the CPE tip/ring (A/B) interface.
b. SR-3004,Issue 2, January 1995.
c. The frequency range is specified in GR-30-CORE.
d. Up to 20 marks may be inserted in specific places in a single
or multiple data message.
The FSK characteristics described in Table 2 are listed
in BT and Bellcore specifications. The BT signal
frequencies correspond to CCITT V.23. The Bellcore
frequencies correspond to Bell 202. The U.K.’s CCA
requires that the TE be able to receive both CCITT
V.23 and Bell 202, as specified in the BT and Bellcore
specifications. CNIC2 is compatible with both formats
without any adjustment.
CNIC2 will meet these characteristics with its input
opamp at unity gain.
• 3-wire User Interface
The MT8843 provides a powerful dual mode 3-wire
interface so that the 8-bit data words in the
demodulated FSK bit stream can be extracted
without the need either for an external UART or for
the TE/CPE’s microcontroller to perform the UART
function in software. The interface is specifically
5-37
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