Preliminary Data Sheet
October 2001
Low-Cost Ringing SLIC
L9214A/G
34
Agere Systems Inc.
ac Applications
(continued)
Design Examples
(continued)
First-Generation Codec ac Interface Network
—
Complex Termination
The following reference circuit shows the complete
SLIC schematic for interface to the Agere T7504 first-
generation codec for the German complex termination
impedance. For this example, the ac interface was
designed for a 220
+ (820
|| 115 nF) complex ter-
mination and hybrid balance with transmit gain and
receive gain set to 0 dBm.
Complex Termination Impedance Design Example
The gain shaping necessary for a complex termination
impedance may be done by shaping across the Ax
amplifier at nodes ITR and VTX.
Complex termination is specified in the form:
5-6396(F)
To work with this application, convert termination to the
form:
5-6398(F)
where:
R
1
′
= R
1
+ R
2
1
R
2
R
2
′
=
(R
1
+ R
2
)
C
′
=
C
ac Interface Using First-Generation Codec
R
GX
/R
TGS
/C
GS
(Z
TG
): These components give gain
shaping to get good gain flatness. These components
are a scaled version of the specified complex termina-
tion impedance.
Note for pure (600
) resistive terminations, compo-
nents R
TGS
and C
GS
are not used. Resistor R
GX
is used
and is still 4750
.
R
X
/R
T6
: With other components set, the transmit gain
(for complex and resistive terminations) R
X
and R
T6
are
varied to give specified transmit gain.
R
T3
/R
RCV
/R
GP
: For both complex and resistive termina-
tions, the ratio of these resistors sets the receive gain.
For resistive terminations, the ratio of these resistors
sets the return loss characteristic. For complex termi-
nations, the ratio of these resistors sets the low-fre-
quency return loss characteristic.
C
N
/R
N1
/R
N2
: For complex terminations, these compo-
nents provide high-frequency compensation to the
return loss characteristic.
For resistive terminations, these components are not
used and RCVN is connected to ground via a resistor.
R
HB
: Sets hybrid balance for all terminations.
Set Z
TG
—
gain shaping:
Z
TG
= R
GX
|| R
TGS
+ C
GS
which is a scaled version of
Z
T/R
(the specified termination resistance) in the
R
1
′
|| R
2
′
+ C
′
form.
R
GX
must be 4750
to set SLIC transconductance to
300 V/A.
R
GX
= 4750
At dc, C
GS
and C
′
are open.
R
GX
= M x R
1
′
where M is the scale factor.
R
1
′
M =
It can be shown:
R
TGS
= M x R
2
′
and
C
TGS
=
R
2
C
R
1
R
1
′
C
′
R
2
′
-------
+
R
1
R
2
---------------------
2
--------------
′
M
------