Data Sheet
May 2001
L8576B Dual Ringing SLIC
RX/RT2: With other components set, the transmit gain
(for complex and resistive terminations) RX and RT2 are
varied to give specified transmit gain.
Applications (continued)
ac Design (continued)
RT1/RRCV/RGP: For both complex and resistive termina-
tions, the ratio of these resistors set the receive gain.
For resistive terminations, the ratio of these resistors
set the return loss characteristic. For complex termina-
tions, the ratio of these resistors set the low-frequency
return loss characteristic.
Example 2, Complex Termination
The gain shaping required of a complex termination
impedance can be synthesized using the internal AX
amplifier. The following discussion and equations
present a method for selecting proper component val-
ues for the SLIC/codec interface when using a complex
termination.
CN/RN1/RN2: For complex terminations, these compo-
nents provide high-frequency compensation to the
return loss characteristic. For resistive terminations,
these components are not used. RCVN is connected to
ground via a resistor.
Complex termination is usually of the form:
R2
RHB: Sets hybrid balance for all terminations.
R1
C
Set ZTG — gain shaping:
5-6396(F)
ZTG = RTGP || RTGS + CTGS which is a scaled version of
ZT/R (the specified termination resistance) in the
R1´ || R2´ + C´ form.
To work with this application, convert termination to the
form:
R1´
RTGP must be 24.4 kΩ to set SLIC transconductance to
125 V/A.
RTGP = 24.4 kΩ
R2´ C´
5-6397(F)
At dc, CTGS and C´ are open.
RTGP = M x R1´
where:
R1´ = R1 + R2
where M is the scale factor.
R1
R2´ = ------- (R1 + R2)
R2
24.4 kΩ
M = -----------------------
R1′
C´ = --------------------- 2 C
R2
R1 + R2
It can be shown:
RTGS = M x R2´
and
For the following discussion, refer to Figure 21.
RTGP/RTGS/CTGS (ZTG): 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 Ω) resistive termi-
nations, components RTGS and CTGS are not used.
Resistor RTGP is used and is the series resistance com-
bination of RGX1 and RGX2 or 24.4 kΩ.
C′
CTGS = ------
M
Agere Systems Inc.
21
AGERE [ AGERE SYSTEMS ]
