Preliminary Data Sheet
September 2001
L9216B/H
High-Voltage Ringing SLIC with Ground Start
Using R
EQ
, calculate the desired transmit gain, taking
into account the impedance transformation:
600
T
X
(dB) = T
X (specified[dB])
+ 20log ----------
-
R
EQ
T
X (specified[dB])
is the specified transmit gain. 600
Ω
is
the impedance at the PCM, and R
EQ
is the impedance
at
600
tip and ring. 20log ---------- represents the power
-
R
EQ
loss/gain due to the impedance transformation.
Note that in the case of a 600
Ω
pure resistive termina-
tion
600
600
at T/R 20log ---------- = 20log --------- = 0.
-
-
R
EQ
600
Thus, there is no power loss/gain due to impedance
transformation and T
X
(dB) = T
X (specified[dB])
.
Finally, convert T
X
(dB) to a ratio, g
TX
:
ac Applications
(continued)
Design Examples
(continued)
ac Interface Using First-Generation Codec
(contin-
ued)
Transmit Gain
Transmit gain will be specified as a gain from T/R to
PCM, T
X
(dB). Since PCM is referenced to 600
Ω
and
assumed to be 0 dB, and in the case of T/R being refer-
enced to some complex impedance other than 600
Ω
resistive, the effects of the impedance transformation
must be taken into account.
Again, specified complex termination impedance at T/R
is of the form:
R
2
R
1
C
5-6396(F)
T
X
(dB) = 20log g
TX
The ratio of R
X
/R
T6
is used to set the transmit gain:
First, calculate the equivalent resistance of this network
at the midband frequency of 1000 Hz.
R
EQ
=
2
2
2
2
2
πf
R
2 2
C
1
-
2
(
2
πf )
C
1
R
1
R
2
+
R
1
+
R
2
+
--------------------------------------------------
----------------------------------------------------------------------------
-
1
+
(
2
πf )
2
R
2 2
C
1 2
1
+
(
2
πf )
2
R
2 2
C
1 2
R
X
R
T6
----------
= g
TX
•
-----------------
-
318.25
20
1
•
---- with a quad Agere codec
-
M
such as T7504:
R
X
< 200 kΩ
R
TGS
C
GS
R
x
–I
T/R
318.25
R
GX
= 4750
Ω
0.1
µF
20
V
TX
T
XI
V
ITR
R
T6
–
+
CODEC
OP AMP
C
N
R
N1
RCVN
RCVP
R
N2
R
RCV
R
GP
R
T3
R
HB
CODEC
OUTPUT
DRIVE
AMP
5-6400.P (F)
Figure 23. Interface Circuit Using First-Generation Codec (Blocking Capacitors Not Shown)
Agere Systems Inc.
37
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
