Application Note August 2001 AN9872.1 Authors: LaFontaine, Chris
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HC5503PRC SLIC Texas Instruments TP3057A Combined CODEC Filter
Application Note August 2001 AN9872.1
Authors: LaFontaine, Chris Ludeman
Reference Design using HC5503PRC SLIC Texas Instruments TP3057A Combined CODEC Filter
network requirements many countries require Analog Subscriber Line Circuit (SLIC) terminate subscriber line with impedance voiceband frequencies which complex, rather than resistive (e.g., 600). This requires that physical resistance that situated between SLIC subscriber line, comprised protection and/or sensing resistors, output resistance SLIC itself, adapted present impedance subscriber line that varies with frequency. This accomplished using feedback around SLIC. purpose this application note show means accomplishing this task HC5503PRC Texas Instruments TP3057A Combo. Discussed this application note following: 2-wire impedance matching 2-wire complex impedance matching Receive gain (4-wire 2-wire) transmit gain (2-wire 4-wire) calculations Transhybrid balance calculations Reference design 2-wire load Reference design China complex 2-wire load
2*Rp
2*Rs
FEED AMPS ZSLIC
FROM COMBO
f(Z0) TRANSMIT COMBO
FIGURE IMPEDANCE MATCHING BLOCK DIAGRAM
circuitry inside dotted representative SLIC feed transmit amplifiers. feed transmit amplifiers pass voice signals receive transmit directions respectively. Without feedback block f(Z0), termination resistance would equal protection resistors (RP) sense resistors (RS), feed amplifiers present very output impedance subscriber line. desired termination impedance feedback block f(Z0) matches SLICs output impedance (ZSLIC) plus protection resistors (RP) sense resistors (RS) load (Z0). Impedance matching HC5503PRC accomplished making SLIC's impedance (ZSLIC, Figure equal desired terminating impedance minus value protection sense resistors. desired impedance input SLIC given Equation
ZSLIC (EQ.
Impedance Matching
Impedance matching HC5503PRC subscriber load important optimization wire return loss, which turn cuts down echoes voice communication path. also important maintaining voice signal levels long loops. Consider equivalent circuit shown Figure
ZSLIC R*4RS RP+RS VFXI+ INTERSIL HC5503PRC VFXI+ 0.47µ 4RSIL RZ01= VGSX 0.47µ VFRO TEXAS INSTRUMENTS TP3057A
FIGURE IMPEDANCE MATCHING
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AN9872
loop current required satisfy this condition given Equation
matching (EQ.
current calculated Equation used feedback match impedance SLIC both protection sense resistors load output voltage SLIC (VTX) defined design given Equation
(EQ.
Analysis Equation yields feedback network. first term phase inversion. This requires path flow through amps makes matching different complex loads easy. (i.e., feedback network equal want match). second term phase inversion requires only feedback path. Figure shows circuit required achieve matching SLIC's impedance load voltage function VTX, (VTXRZO1/Ra2) voltage determined superposition. circuit equation feedback network given Equation
Substituting from Equation into Equation results voltage output that will used generate required feedback.
(EQ.
(EQ.
impedance matching wire side, equal zero. This reduces Equation that shown Equation
design, equal times voltage receive input (RX) Figure
(EQ.
(EQ.
Substituting Equation into Equation
(EQ.
achieve desired matching circuit line impedance design Equation equal circuit Equation inspection correct phase Equations have Equations
(EQ.
Solving Equation voltage function (when matching ZSLIC protection resistors (RP) sense resistors load given Equation
-VTX (EQ.
(EQ.
Equation gain feedback circuit (output/input VRX/VTX) used match impedance SLIC both protection sense resistors. Note: Equation seemed logical simplify numerator trying combine subsequent terms together. practice however, impedance network want match (Z0) cannot easily have 2*Rp 2*Rs subtracted from since these resistors often larger than value series resistance complex network. Equation therefore rewritten Equation
-VTX (EQ.
Given: RZO1 Note: making 2Rf, value becomes (Equation 13). This results 2-wire 4-wire gain being equal (Equation Equation From Equation
(EQ.
From Equation
(EQ.
AN9872 Receive Gain (VIN V2W)
4-wire 2-wire gain equal divided input voltage reference Figure gains through CODEC considered this point.
(EQ.
Ohms defines being equal 2W/ZO Substituting 2W/ZO Equation gives Equation
(EQ.
2-wire voltage determined loop equation given Equation
(EQ.
Equation rearranged solve 4-wire 2wire gain V2W/VIN shown Equation
(EQ.
Combining Equation Equation gives expression terms shown Equation
(EQ.
Given: f=100k, Ra4=200k, Ra1=267k, ZO=600, RS=100, RP=50. Note: making equal 4-wire 2-wire gain becomes
voltage therefore function Note: Contribution from VGSX (middle term Equation zero transhybrid circuit, reference section titled "Transhybrid Balance G(4-4)". This reduces Equation Equation
(EQ.
Transmit Gain across HC5503PRC (V2W VTX)
output voltage SLIC (VTX) defined Equation being equal 4RSIL. equal twice input voltage (2VRX) divided total loop resistance shown Figure load impedance 600, then gain across HC5503PRC input voltage VRX. Likewise, load impedance 811, (next example with complex load) then gain across HC5503PRC 400/811 times input voltage VRX.
Substituting 4RSIL (Equation Equation combining this with Equation results equation terms external resistors input voltage (Equation 19).
(EQ.
Transmit Gain (V2W VGSX)
2-wire 4-wire gain equal VGSX voltage divided 2-wire voltage V2W, reference Figure
VGSX -V2W (EQ.
0.47µ INTERSIL HC5503PRC VFRO
RZ02
LOOP EQUATION (2RP+2R S)IL
R*4RS RP+RS VFXI+ VFXI+
TEXAS INSTRUMENTS TP3057A
0.47µ 4RSIL
RZ01 VGSX
FIGURE RECEIVE GAIN G(4-2), TRANSMIT GAIN (2-4) TRANSHYBRID BALANCE (FEEDBACK CIRCUIT ONLY)
AN9872
A2-4 FEEDBACK 4RSIL 2VRX RTOTAL 2VRX RING
OpAmp CODEC configured differential amplifier with output defined Equation
(EQ.
values Ra2, Ra5, RZO1 RZO2 should scaled 1000 minimize effects parallel resistance gain adjustment resistor (Figure Resistors adjust gain input signal from TP3057A account +4dB gain receive path. Scaling complex load shown
Reactive sistive -100 (EQ.
4RSIL
FEEDBACK
FIGURE TRANSMIT GAIN ACROSS HC5503PRC (V2W VTX)
VGSX only function feedback resistors RZO1 Equation This because considered ground this analysis, thereby effectively grounding positive terminal OpAmp.
(EQ.
Note: When matching complex impedance some impedance models (900+2.15µF, K=100) will cause OpAmp feedback open currents, bringing OpAmp output rail. resistor with value about times reactance capacitor (21.6nF) frequency interest (200Hz example) placed parallel with capacitor order solve problem (368k 21.6nF capacitor).
Substituting Equation -V2W/ZO into Equation equals:
(EQ.
Reference Design HC5503PRC TP3057A with Load Impedance
design criteria follows: 4-wire 2-wire gain V2W) equal 2-wire 4-wire gain (V2W equal Wire Return Loss greater than -30dB (200Hz 4kHz) 100. Figure gives reference design using Intersil HC5503PRC SLIC Texas Instruments TP3057A combined CODEC filter. Also shown Figure voltage levels specific points circuit. These voltages will used adjust gains network.
equal (actual values were multiplied 1000 reduce loading effects opamps). Simplifying Equation assuming Ra2=4RS from Equation results Equation
(EQ.
transmit gain 2-wire 4-wire equal one.
Transhybrid Balance G(4-4)
Transhybrid balance measure well input signal canceled (that being received SLIC) from transmit signal (that being transmitted from SLIC CODEC). Without this function, voice communication would difficult because echo. signals (Figure phase. summed together with correct magnitudes input Combo transmit OpAmp, they will cancel present VGSX output. circuit Figure been that SLIC matches load impedance that both G(4-2) G(2-4) adjusted flat over frequency.
Impedance Matching
impedance matching 2-wire side input voltage equal zero. This effectively grounds VFXI+ input amplifier. achieve 2-wire 4wire gain (V2W need increase gain amplifier overcome -4dB loss TP3057A. required gain found using Equation repeated here convenience Equation
(EQ.
AN9872
G4-2
0dBm0 (600) 0.7745VRMS INTERSIL HC5503PRC 100k 267k 316k 0.47µ 200k
0dBm0(600) 0.7745VRMS
+4dBm0(600) 1.22765VRMS
0dBm0 (600) 0.7745VRMS
VFRO 1.74k RZ02 600k
TEXAS INSTRUMENTS TP3057A
525k
VFXI+ VFXIRZ01 600k +4dBm0(600) 1.22765VRMS VGSX
0.47µ 0dBm0(600) 0.7745VRMS -3.52dBm0(600) (0.7745)(2/3)VRMS V2W(2/3) 255k
0dBm0(600) 0.7745VRMS
G2-4
FIGURE REFERENCE DESIGN HC5503PRC TP3057A WITH LOAD IMPEDANCE
Substituting required voltage levels (Figure VGSX (1.2276) (0.7745) rearranging solve results Equation Where: VGSX =1.585, Z0=RZ01
252.3 1.585 (EQ.
equals then equals 1.709k. closest standard value 1.74k.
Transhybrid Balance 600)
internal amplifier TP3057A used perform transhybrid balance function. discussion purpose, amplifier redrawn with external resistors Figure transfer function amplifier given Equation Equation
VOUT (EQ.
value needs scaled 1000 minimize effects parallel resistance RZ02 gain adjustment resistor nearest standard value 255k. needs increase (1.585) maintain same feedback impedance matching Equation
200k 1.585 317k (EQ.
600K VOUT 600K 255K (EQ.
closest standard value 316k. achieve 4-wire 2-wire gain equal need decrease input feedback circuit from VFRO account +4dB increase TP3057A. simple voltage divider will decrease 1.2276 volt input down required 0.7745 volts Equation
0.7745 1.2276 (EQ.
equal (0.7745VRMS)(2/3). equal 0.7745VRMS (0dBm0(600)). VOUT equal zero. results rearranging Equation solve substituting values shown Equation
941.17k 527.47k 3.352 1.568 (EQ.
Closest standard value 525k.
Rearranging solve results Equation
1.709 (EQ.
AN9872
RZ02 VFXI+ VFXIRa2
VOUT
Adjustment -3.5dBm0 Load Referenced
voltage equivalent 0dBm0 into (0dBm0(811)) calculated using Equation China complex load 1020Hz equal
0.90055V 0.001
RZ01
(EQ.
FIGURE TRANSHYBRID BALANCE CIRCUIT
Specific Implementation China
design criteria China specific solution follows: Desired line circuit impedance 680//0.1µF Receive gain (V2W/VDR) -3.5dB Transmit gain (VDX/V2W 0dBm0 defined into complex impedance 1020Hz 100. Figure gives reference design using Intersil HC5503PRC SLIC Texas Instruments TP3057A combined CODEC filter. Also shown Figure voltage levels specific points circuit. These voltages will used adjust gains network.
G4-2
gain referenced back 0dBm0(600) equal
0.90055VRMS 1.309dB 0.7745V (EQ.
adjustment -3.5dBm0 load referenced
Adjus 3.5dBm0 1.309dBm0 2.19 (EQ.
voltage load (referenced 600) given Equation
(EQ. 2.19 0.60196VRMS 0.001
-2.19dBm0(600) 0.60196VRMS 0.1µF INTERSIL HC5503PRC 200k 680k
-2.19dBm0(600) +4dBm0(600) 0.60196VRMS 100pF VFRO 1.22765VRMS
0dBm0(600) 0.7745VRMS
0.47µ
267k
274k 464k
200k
100k
RZ02
TEXAS INSTRUMENTS TP3057A
VFXI+ VFXIRa2
0.47µ 294k
RZ01 680k 200k 100pF VGSX
-2.19dBm0(600) 0.60196VRMS
-8.32dBm0(600) (0.60196)(400/ZL)VRMS
V2W(400/ZL)
+0.5dBm0(600) 0.82049VRMS
-3.5dBm0(600) 0.51769VRMS
G2-4
FIGURE REFERENCE DESIGN HC5503PRC TP3057A WITH CHINA COMPLEX LOAD IMPEDANCE
AN9872 Impedance Matching
impedance matching 2-wire side input voltage equal zero. This effectively grounds VFXI+ input amplifier. achieve 2-wire 4wire gain need increase gain amplifier overcome -4dB loss TP3057A. required gain found using Equation repeated here convenience Equation
VGSX (EQ.
equals then equals 962.1.
RZ02 VFXI+ VFXI+ VOUT
RZ01
FIGURE TRANSHYBRID BALANCE CIRCUIT
closest standard value 976.
Substituting required voltage levels (Figure VGSX (0.82049) (0.60196) rearranging solve results Equation Where: VGSX =1.363, Z0=RZ01:
293.47 1.363 (EQ.
Transhybrid Balance 680//0.1µF)
internal amplifier TP3057A used perform transhybrid balance function. discussion purpose, amplifier redrawn with external resistors Figure transfer function amplifier given Equation
VOUT (EQ.
value needs scaled 1000 minimize effects parallel resistance gain adjustment resistor nearest standard value 294k. needs increase (1.363) maintain same feedback impedance matching Equation
200k 1.363 272.6k (EQ.
impedance series parallel complex China load equal (multiplied 1000):
771k j249k (EQ.
closest standard value 274k. achieve 4-wire 2-wire gain equal need decrease input feedback circuit from VFRO account +4dB increase TP3057A. simple voltage divider will decrease 1.2276 volt input down required 0.60196 volts Equation
0.60196 1.2276 (EQ.
Setting VOUT equal zero, best transhybrid balance, rearranging equation Equation
771k j249k 771k j249k 294k -294k 771k j249 (EQ.
equal (0.60196VRMS)(400/811) equal 0.60196VRMS. results rearranging Equation solve substituting values shown Equation
273k j114k j199k 465k 25.3 0.636 j0.0302 (EQ.
Rearranging solve results Equation
0.9621 (EQ.
Closest standard value 464k.
AN9872 Specific Implementation Australia
design criteria Australia specific solution follows: Desired line circuit impedance 820//120nF Receive gain (V2W/VDR) -3.5dB Transmit gain (VDX/V2W 0dBm0 defined into complex impedance 1020Hz 100. Figure gives reference design using Intersil HC5503PRC SLIC Texas Instruments TP3057A combined CODEC filter. Also shown Figure voltage levels specific points circuit. These voltages will used adjust gains network.
Adjustment -3.5dBm0 Load Referenced
voltage equivalent 0dBm0 into (0dBm0(887)) calculated using Equation Australia complex load 1020Hz equal
0.936483V 0.001
(EQ.
gain referenced back 0dBm0(600) equal
0.936483V 1.64957dB 0.7745VRMS (EQ.
adjustment -3.5dBm0 load referenced
Adjus 3.5dBm0 1.649dBm0 1.85 (EQ.
voltage load (referenced 600) given Equation
(EQ. 1.85 0.625971V 0.001
G4-2
-1.85dBm0(600) 0.625971VRMS 120nF INTERSIL HC5503PRC 200k 820k
-1.85dBm0(600) +4dBm0(600) 0.625971VRMS 120pF VFRO 1.05k 1.22765VRMS
0dBm0(600) 0.7745VRMS
0.47µ
267k
261k 464k
220k
100k
RZ02
TEXAS INSTRUMENTS TP3057A
VFXI+ VFXIRa2
0.47µ 301k
RZ01 820k 220k 120pF VGSX
-1.85dBm0(600) 0.625971VRMS
V2W(400/ZL)
+0.5dBm0(600) 0.82049VRMS
-3.5dBm0(600) 0.51769VRMS
G2-4
FIGURE REFERENCE DESIGN HC5503PRC TP3057A WITH Australia COMPLEX LOAD IMPEDANCE
AN9872 Impedance Matching
impedance matching 2-wire side input voltage equal zero. This effectively grounds VFXI+ input amplifier. achieve 2-wire 4wire gain need increase gain amplifier overcome -4dB loss TP3057A. required gain found using Equation repeated here convenience Equation
VGSX (EQ.
equals then equals 1.04.
RZ02 VFXI+ VFXI+ VOUT
RZ01
FIGURE TRANSHYBRID BALANCE CIRCUIT
closest standard value 1.05k.
Substituting required voltage levels (Figure VGSX (0.82049) (0.625971) rearranging solve results Equation Where: VGSX =1.311, Z0=RZ01:
305.17 1.311 (EQ.
Transhybrid Balance 820//120nF)
internal amplifier TP3057A used perform transhybrid balance function. discussion purpose, amplifier redrawn with external resistors Figure transfer function amplifier given Equation
VOUT (EQ.
value needs scaled 1000 minimize effects parallel resistance gain adjustment resistor nearest standard value 301k. needs increase (1.311) maintain same feedback impedance matching Equation
200k 1.311 262.2k (EQ.
impedance series parallel complex Australia load equal (multiplied 1000):
807k j370k (EQ.
closest standard value 261k. achieve 4-wire 2-wire gain equal need decrease input feedback circuit from VFRO account +4dB increase TP3057A. simple voltage divider will decrease 1.2276 volt input down required 0.625971 volts Equation
0.625971 1.2276 (EQ.
Setting VOUT equal zero, best transhybrid balance, rearranging equation Equation
807k j370k 807k j370k 301k 301k 807k j370 (EQ.
Rearranging solve results Equation
1.04037 (EQ.
equal (0.625971VRMS)(400/887) equal 0.625971VRMS. results rearranging Equation solve substituting values shown Equation
261k j156k j258k 461k 0.659 j0.0368 (EQ.
Closest standard value 464k.
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