73K224L-28IH TDK [TDK Electronics], 73K224L-28IH Datasheet - Page 26

• Manufacturer Part Number: 73K224L-28IH
• Description: V.22bis/V.22/V.21/ Bell 212A/Bell 103 Single-Chip Modem
• Manufacturer: TDK [TDK Electronics]

73K224L
V.22bis/V.22/V.21/Bell 212A/Bell 103
Single-Chip Modem
DIRECT ACCESS ARRANGEMENT (DAA)
The telephone line interfaces show two examples of
how the “hybrid” may be implemented. The split supply
design (Figure 1) is a typical two op-amp hybrid. The
receive op-amp serves two purposes. It supplies gain
to amplify the receive signal to the proper level for the
modem’s detectors and demodulator, and it removes
the transmitted signal from the receive signal present
at the transformer. This is done by supplying a portion
of the transmitted signal to the non-inverting input of
the receive op-amp at the same amplitude as the
signal appearing at the transformer, making the
transmit signal common mode.
The single-supply hybrid is more complex than the
dual-supply version described above, but its use
eliminates the need for a second power supply. This
circuit (Figure 2) uses a bridged drive to allow
undistorted signals to be sent with a single 5 volt
supply.
amplitude than data, these signals will clip if a single-
ended drive approach is used. The bridged driver uses
an extra op-amp (U1A) to invert the signal coming
from the gain setting op-amp (U1B)
Because
DTMF
REFERENCE
VOLTAGE
RXA
TXA
HOOK
RING
tones
0.1 µF
0.1 µF
C6
R11
C3
*
+5V
20K 1%
R10
utilize
R7
FIGURE 2: Single 5V Hybrid Version
*
0.0047 µF
0.1 µF
C4
C7
5
6
2
3
8
*
+
-
+
37.4K 1%
-
20K 1%
20K 1%
750 pF
U1C
22.1K
390 pF
R5 3.3K
*
+
R6
C5
R9
R8
C1
R4
10 µF
U1A
11
C8
a
+5V
4
+
-
*
U1B
10
7
1
9
higher
R14
10K
IN914
D2
D3
D4
20K 1%
20K 1%
ZENERS
475 1%
0.033 µF
3.3V
R1
R2
R3
C2
+5V
Q1
2N2222A
26
MIDCOM
671-8005
K1
T1
IN4004
D1
before sending it to the other leg of the
transformer. Each op-amp then supplies half the
drive signal to the transformer. The receive
amplifier (U1C) picks off its signal at the junction of
the
transformer. Because the bottom leg of the
transformer is being driven in one direction by U1A
and the resistor is driven in the opposite direction
at the same time by U1B, the junction of the
transformer
constant and the receive signal is unaffected.
DESIGN CONSIDERATIONS
TDK Semiconductor's 1-chip modem products
include all basic modem functions. This makes
these devices adaptable for use in a variety of
applications,
conventional digital bus peripherals. Unlike digital
logic circuitry, modem designs must properly
contend with precise frequency tolerances and
very
acceptable
circuit design practices will generally result in a
sound
recommendations which should be taken into
consideration when starting new designs.
0.47 µF
R12
22K
250V
C10
4N35
U2
impedance
Note: Op-amp U1
must be rated for
single 5V
operation. R10 &
R11 values depend
on Op-amp used.
low
R13
22K
design.
+5V
level
performance.
and
and
V250L20
MOV
VR1
T
R
matching
analog
resistor
Following
as
easy
Using
signals,
resistor
remains
to
are
good
control
to
and
additional
relatively
ensure
analog
the
as