tca3388 Freescale Semiconductor, Inc, tca3388 Datasheet - Page 10

• Manufacturer Part Number: tca3388
• Description: Advance Information Telephone Line Interface
• Manufacturer: Freescale Semiconductor, Inc

RECEIVE
HYL/HYS inputs. These are the same amplifiers present in
the dc loop of Figure 5. The signal is first converted to current
by the transconductance amplifier with transfer G e . The
multiplier placed after performs the line length AGC. It
switches over between the 2 signals at HYS and HYL
according to the line current via a modulation factor m.
Afterwards, the current is converted back to voltage via the
external feedback network Z Load . The resulting voltage is
available at output RXO1, and inverted at RXO2.
be derived as:
be found under the sidetone characteristics.
as a differential load. The above calculated gain is valid for the
single ended case. When connecting as a differential load, the
gain is increased by 6.0 dB. The TCA3388 offers the
possibility to mute the signal coming from the line to the
earpiece. This can be useful during pulse– and DTMF–dialing.
With:
A
10
The receive part of the TCA3388 is shown in Figure 10.
The receive signal is picked up by the amplifiers at the
From the diagram of Figure 10 the receive gain (A RX ) can
More information on Z H and the modulation factor m can
The earpiece can either be connected as a single ended or
RX
+
HYS connected to HYL, or
2 sidetone networks
Z
Z
1
1
H
H
V
V
+
+
RXO
Line
Line +
Line –
m x
R1 x Z1
R20
+
R1 x Z1
Ge x R1 x Z
R20
HYS
Z2
in case of 1 sidetone network and
SAI
Z1
2V
BE + V01
)
(m –1)
Load
HYL
R20
R19
G e
G e
Figure 10. Receive Part of the TCA3388
R1 x Z2 in case of
x
R1
R19
Z
1
H
Line Mute
AGC
C17
)
Z
1
in
TCA3388
Gnd
IMP
1.6 V
V ref
SIDETONE
the signal is returned to the receive channel due to the
architecture of the 2 to 4 wire conversion of the hybrid. During
transmit, the signal on the line will be –I Line x Z Line . During
receive, the signal on the line will be I Line x Z in . When
replacing Z in in the formula for the receive gain, it follows that
the signal on the earpiece output due to a sending signal on
the line will be:
connected to HYL, it follows:
impedance, and the average linelength of the countries
involved in the application. A complex sidetone network can
be made via a complex Z1 which is preferred above making
R20 complex. The coupling capacitor C17 in series with R20
is meant only to block dc.
currents and as Z HS for short lines with high line currents.
This can be useful in applications such as DECT and
handsfree where the sidetone has to be minimized to reduce
the effect of delayed echoing and howling respectively. The
TCA3388 will automatically switch over between the 2 hybrid
networks as a function of line current. This is expressed in the
TCA3388
V
When a transmit signal is transmitted to the line, a part of
Line (transmit)
In applications with 1 sidetone network where HYS is
Z H has to be chosen according the average line
For applications with 2 sidetone networks it follows:
The Z H thus exists as Z HL for long lines with low line
V ear
Z
1
H
RXO1
RXI
+
m
MOTOROLA ANALOG IC DEVICE DATA
Z
R1 x Z1
+
m
1
H
R20
R Load
G e x R1 x Z
Z
+
HL
1
R1 x Z1
–1X
)
R20
)
(m – 1)
C
(m –1)
Load
RXO2
C
+
ear
Load
R1 x Z2
Z
Z
HS
1
HL
1
R19
x
Z
1
+
H
Handset
Earpiece
–
Z
Line
1