73K324L
CCITT V.22bis,V.23,V.22,V.21, Bell 212A
Single-Chip Modem
DATA SHEET
DESCRIPTION
(continued)
The 73K324L offers full hardware and software
compatibility with other products in TERIDIAN
Semiconductor's K-Series family of single-chip
modems, allowing system upgrades with a single
component change. The 73K324L is ideal for use in
free-standing or integral system modem products
where full-duplex 2400 bit/s operation with Alternate
mode capability is required. Its high functionality, low
power consumption, and efficient packaging simplify
design requirements and increase system reliability.
A complete modem requires only the addition of the
phone line interface, a control microprocessor, and
RS-232 level converters for a typical system.
The 73K324L is designed to provide a complete
V.22bis, V.22, Bell 212A, V.21, and V.23 compatible
modem on a chip. Many functions were included to
simplify implementation in typical modem designs. In
addition to the basic 2400 bit/s QAM, 1200/600 bit/s
DPSK
and
1200/300/75
bit/s
FSK
modulator/demodulator sections, the device also
includes synch/asynch buffering, DTMF, answer,
soft carrier, guard, and calling tone generator
capabilities. Handshake pattern detectors simplify
control of connect sequences, and precise tone
detectors allow accurate detection of call progress,
answer, calling, and soft carrier turn off tones. All
Operating modes defined by the incorporated
standards are included, and Test modes are
provided. Most functions are selectable as options,
and logical defaults are provided. The device can be
directly interfaced to a microprocessor via its 8-bit
multiplexed address/data bus for control and status
monitoring. Data communications takes place
through a separate serial port. Data may also be
sent and received through the control registers. This
simplifies designs requiring speed buffering, error
control and compression.
incoming signal. Adaptive equalization corrects for
varying line conditions by automatically changing
filter parameters to compensate for line
characteristics.
DPSK MODULATOR/DEMODULATOR
The 73K324L modulates a serial bit stream into
di-bit pairs that are represented by four possible
phase shifts as prescribed by the Bell 212A/V.22
standards. The baseband signal is then filtered to
reduce intersymbol interference on the bandlimited
2-wire PSTN line. Transmission occurs on either a
1200 Hz (Originate mode) or 2400 Hz carrier
(Answer mode). Demodulation is the reverse of the
modulation process, with the incoming analog signal
eventually decoded into di-bits and converted back
to a serial bit stream. The demodulator also recovers
the clock, which was encoded into the analog signal
during modulation. Demodulation occurs using either
a 1200 Hz carrier (Answer mode or ALB Originate
mode) or a 2400 Hz carrier (Originate mode or ALB
Answer mode). The 73K324L use a phase locked
loop coherent demodulation technique that offers
excellent performance. Adaptive equalization is also
used in DPSK modes for optimum operation with
varying lines.
FSK MODULATOR/DEMODULATOR
The FSK modulator/demodulator produces a
frequency modulated analog output signal using two
discrete frequencies to represent the binary data.
V.21 frequencies of 980 and 1180 Hz (originate
mark and space), or 1650 and 1850 Hz (answer
mark and space) are used in V.21 mode. V.23 mode
uses 1300 and 2100 Hz for the main channel or 390
and 450 Hz for the back channel. Demodulation
involves detecting the received frequencies and
decoding them into the appropriate binary value.
The rate converter and scrambler/descrambler are
automatically bypassed in the FSK modes.
PASSBAND FILTERS AND EQUALIZERS
High and low band filters are included to shape the
amplitude and phase response of the transmit and
receive signals and to provide compromise delay
equalization as well as rejection of out-of-band
signals. The transmit signal filtering corresponds to a
√&%%
raised
cosine
frequency
response
characteristic.
FUNCTIONAL DESCRIPTION
QAM MODULATOR/DEMODULATOR
The 73K324L encodes incoming data into quad-bits
represented by 16 possible signal points with
specific phase and amplitude levels. The baseband
signal is then filtered to reduce intersymbol
interference on the bandlimited telephone network.
The modulator transmits this encoded data using
either a 1200 Hz (Originate mode) or 2400 Hz
(Answer mode) carrier. The demodulator, although
more complex, essentially reverses this procedure
while also recovering the data clock from the
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©
2005, 2008 TERIDIAN Semiconductor Corporation
Rev 7.1
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
