HC5513 View Datasheet(PDF) - Harris Semiconductor
Part Name
Description
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HC5513 Datasheet PDF : 20 Pages
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HC5513
IM
TIP
RF
ZL
VTR
+
-
ZTR
+
EG
-
+
VTX
-
IM
RING RF
+-
1
HC5513
A = 250
A = 250
A=4
VTX
+
VTX
-
ZT
RSN
IM
1000
ZRX
+
VRX
-
FIGURE 16. SIMPLIFIED AC TRANSMISSION CIRCUIT
ZTR is defined as:
ZTR = V---I--TM---R---
Substituting in Equation 9 for VTR
ZTR
=
V-----T---X-- + 2----R-----F-----•----I--M---
IM
IM
Substituting in Equation 12 for VTX
ZTR = 1----Z0---0-T---0- + 2RF
(EQ. 13)
(EQ. 14)
(EQ. 15)
Therefore
ZT = 1000 • (ZTR – 2RF)
(EQ. 16)
Equation 16 can now be used to match the SLIC’s imped-
ance to any known line impedance (ZTR).
EXAMPLE:
Calculate ZT to make ZTR = 600Ω in series with 2.16µF.
RF = 20Ω.
ZT
=
1000
•
600
+
--------------------1---------------------
jω • 2.16 • 10–6
–
2
•
20
ZT = 560kΩ in series with 2.16nF
(AC) 2-Wire to 4-Wire Gain
The 2-wire to 4-wire gain is equal to VTX/ VTR
From Equations 9 and 10 with VRX = 0
A2 – 4 = V-V----TT---R-X-- = -Z---T-----⁄-Z--1-T--0---⁄0---1-0--0---+0----02----R-----F-
(EQ. 17)
(AC) 4-Wire to 2-Wire Gain
The 4-wire to 2-wire gain is equal to VTR/VRX
From Equations 9, 10 and 11 with EG = 0
A4 – 2 = V-V----RT----RX-- = –Z---Z-R---T--X- • -1-------Z0------0--T------0------+----Z-2--L-R-----F-----+-----Z---L--
(EQ. 18)
For applications where the 2-wire impedance (ZTR,
Equation 15) is chosen to equal the line impedance (ZL), the
expression for A4-2 simplifies to:
A4 – 2 = –Z---Z-R---T--X- • 12--
(EQ. 19)
(AC) 4-Wire to 4-Wire Gain
The 4-wire to 4-wire gain is equal to VTX/VRX
From Equations 9, 10 and 11 with EG = 0
A4 – 4 = V-V----RT----XX-- = –Z---Z-R---T--X- • -1-------Z0------0--T-----Z-0----L--+---+--2---2R----R-F---F--+-----Z---L--
(EQ. 20)
Transhybrid Circuit
The purpose of the transhybrid circuit is to remove the
receive signal (VRX) from the transmit signal (VTX), thereby
preventing an echo on the transmit side. This is
accomplished by using an external op amp (usually part of
the CODEC) and by the inversion of the signal from the
4-wire receive port (RSN) to the 4-wire transmit port (VTX).
Figure 17 shows the transhybrid circuit. The input signal will
be subtracted from the output signal if I1 equals I2. Node
analysis yields the following equation:
-V----T----X-- + -V----R----X-- = 0
RTX ZB
(EQ. 21)
The value of ZB is then
ZB = –RTX • V-V----RT----XX--
(EQ. 22)
Where VRX/VTX equals 1/ A4-4
10
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