L9214A/G
Low-Cost Ringing SLIC
Preliminary Data Sheet
October 2001
Transmit Gain:
ac Applications (continued)
Design Examples (continued)
Example 1, Real Termination
VGSX
gtx = ----------
VT/R
–RX 300
-------- --------
gtx =
×
RT2
ZT/R
The following design equations refer to the circuit in
Figure 13. Use these to synthesize real termination
impedance.
Hybrid Balance:
hbal = 20log
RX
RHB
Termination Impedance:
-----------
– gtx × grcv
VT/R
–IT/R
------------
zT =
VGSX
--------------
hbal = 20log
2400
zT = 36 Ω + 2RP +
VFR
----------------------------------
1 +
RT1
RT1
+
-------- -----------
RGP RRCV
To optimize the hybrid balance, the sum of the currents
at the VFX input of the codec op amp should be set to
0. The expression for ZHB becomes the following:
Receive Gain:
VT/R
-----------
grcv =
RX
VFR
-------------------
RHB(kΩ) =
gtx × grcv
8
grcv =
------------------------------------------------------------------
RRCV RRCV
ZT
1 +
+
1 +
--------
----------- -----------
RT1
RGP
ZT/R
RX
VGSX
–0.300 V/mA
RT2
VFXIN
VFXIP
–
VITR
+
RT1
RCVN
RCVP
RHB1
–
–
18 Ω
+2.4 V
ZT/R
RP
TIP
AV = 4
+
AV = 1
RRCV
VFR
IT/R
+
+
CURRENT
SENSE
VS
ZT
VT/R
–
RP
RGP
+
AV = –1
RING
18 Ω
–
L9214
1/4 T7504 CODEC
12-3569 (F)
Figure 13. ac Equivalent Circuit
Agere Systems Inc.
31
AGERE [ AGERE SYSTEMS ]
