AN98007 TEA1114A transmission circuit with dialler interface regu
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Application TEA1114A voltage telephone transmission circuit with dialler interface regulated strong supply
AN98007
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Abstract
TEA1114A bipolar transmission circuit telephone sets. part TEA111x family. detailed description circuit blocks TEA1114A advices adjustments contained this report.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Application TEA1114A voltage telephone transmission circuit with dialler interface regulated strong supply
AN98007
Authors: Arion, Coenders, Malaurie
Keywords Telecom Demoboard TEA1114A Microphone DTMF Receive
Date: March 5th, 1998
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Summary
detailed description blocks TEA1114A given. possible settings adjust transmission characteristics explained. TEA1114A incorporates microphone amplifier, DTMF amplifier, receive amplifier earpiece amplifier. provides supplies peripherals including regulated. evaluation board TEA1114A available.
Note: information presented this document does form part quotation contract, believed accurate reliable changed without notice. liability will accepted publisher consequence use. Publication thereof does convey imply licence under patent other industrial property rights.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
CONTENTS
INTRODUCTION BLOCK DIAGRAMS PINNINGS DESCRIPTION TEA1114A.10 characteristics supply block 3.1.1 characteristics 3.1.2 Supplies peripherals.15 impedance.19 Microphone amplifier.20 Receive amplifier block Automatic gain control.27 DTMF amplifier "MUTE" function.31 Anti-sidetone network.32 3.8.1 TEA111x family bridge 3.8.2 Wheatstone bridge APPLICATION COOKBOOK EXAMPLE APPLICATION ELECTROMAGNETIC COMPATIBILITY REFERENCES
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
LIST FIGURES Fig. TEA1114A block diagram.8 Fig. TEA1114A pinning Fig. Basic application measurements Fig. characteristics configuration Fig. versus Fig. Main voltages versus line current Fig. voltage behavior line powered condition Fig. Influence resistor between SLPE between Fig. Influence Rslpe characteristics Fig. Configuration supplies Fig. versus line current.18 Fig. Current consumption VDD.19 Fig. Equivalent impedance Fig. Microphone channel Fig. Microphone gain versus frequency: influence temperature.22 Fig. Distortion line versus line signal (left) versus microphone signal TEA1114A Fig. Microphone noise versus line current Fig. Common mode rejection ratio microphone.23 Fig. Receive channel.24 Fig. Receive gain versus frequency: influence temperature Fig. Distortion versus input signal Fig. Distortion versus level loads Fig. Noise Fig. microphone gain versus line current Ragc Fig. DTMF channel TEA1114A.29 Fig. DTMF gain versus frequency: influence temperature.30 Fig. Distortion DTMF signal line versus input signal Fig. Microphone gain MUTE/ input current versus MUTE/ input voltage.31 Fig. Microphone receive gain reduction "mute" condition.32 Fig. Wheatstone bridge (left) TEA111x family anti-sidetone bridge (right) Fig. Equivalent average line impedance Fig. Basic application TEA1114A.38 Fig. Circuit diagram demoboard.39 Fig. Component placement diagram demoboard
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
INTRODUCTION
TEA1114A offers microphone, receive line interface functions required telephone sets. performs interface between line transducers handset. TEA1114A includes also DTMF amplifier dialling. selection between microphone amplifier DTMF amplifier made with "MUTE" function. MUTE/ input switches-off both microphone receive amplifiers switches-on DTMF amplifier. Furthermore, regulated supply provided dialler microcontroller. report divided into parts: first part, chapter gives detailed description different circuit blocks TEA1114A including operating principles, settings transmission characteristics performances different functions; second part describes consecutive steps design adjust applications using TEA1114A introduces demoboard.
Note: values parameters given this application note accurate possible, please, refer last product specification final ones.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
BLOCK DIAGRAMS PINNINGS
Fig. shows block diagram TEA1114A, pinning shown fig.
current voltage reference
MUTE/
DTMF
regulator MIC+ MICV
circuit
voltage circuit SLPE
Fig. TEA1114A block diagram
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
SLPE DTMF MUTE/
TEA1114A
Fig. TEA1114A pinning
MICMIC+
TEA1114A
NAME SLPE DTMF MUTE/ MIC+ MICn.c.
DESCRIPTION Positive line terminal Slope adjustment Line voltage regulator decoupling Receive amplifier input Automatic gain control DTMF input Regulated supply peripherals MUTE/ input Receive amplifier output Negative line terminal Earpiece amplifier inverting input Receive amplifier output inverting microphone input Inverting microphone input connected Supply voltage internal circuit
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
DESCRIPTION TEA1114A
curves shown this section result from measurement typical samples using schematic shown fig.
Cvcc
Cvdd
Peripheral supply
MIC+ Rast1
Ctx2 Ctx1
MIC+
Cemc
MIC-
MIC-
TEA1114A
Cgars
Ragc
Cgar
Cear
MUTE Rast2
3.92
MUTE/
DTMF SLPE
DTMF
Rast3 Rbal1 Cbal
Rslpe
Creg
Rbal2
Fig. Basic application measurements
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
3.1.1
characteristics supply block characteristics
Principle operation TEA1114A generates stabilized voltage (called Vref) between pins SLPE. This reference voltage, typically 4.15 temperature compensated. voltage used internal regulator generate stabilized Vref voltage decoupled capacitor Creg connected VEE. effective operation apparatus, TEA1114A must have resistance current high impedance speech signals. Creg capacitor, converted into equivalent inductance (see "set impedance" section), realizes this impedance conversion from value (Rslpe) value (Rcc +Rz//Cz audio frequency range). voltage SLPE proportional line current with offset supply current. This general configuration shown fig.
Isup from preamp Rgasint
internal circuitry
Rline Iline Rexch
Cvcc
regulator
Vexch
SLPE Islpe Rslpe
Cvdd
Creg
Fig. characteristics configuration regulates line voltage between pins SLPE. voltage calculated Vref Rslpe Islpe Islpe Iline Isup Iline line current current consumption supply current peripherals connected
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Isup Current consumed between regulator line current Iline flowing into apparatus determined exchange supply voltage Vexch, feeding bridge resistance Rexch, resistance telephone line Rline voltage across telephone including diode bridge. Below threshold line current (typically equal internal reference voltage (generating Vref) automatically adjusted lower value (down absolute minimum voltage This means that more sets operate parallel that very voltage feeding bridge line current higher value. line currents below this threshold current, TEA1114A reduced sending receiving performances, moreover voltage current Isup reduced. This called voltage area. internal circuitry TEA1114A supplied from VCC. line powered application, this voltage derived from line voltage means resistor (Rcc) must decoupled capacitor (Cvcc). Fig. shows current consumption (Icc) function supply voltage. 1,40E-03 1,20E-03 1,00E-03 8,00E-04 6,00E-04 4,00E-04 2,00E-04
Fig. versus
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Fig. shows main voltages function line current. 8,00E+00 7,00E+00 6,00E+00 5,00E+00 4,00E+00 3,00E+00 2,00E+00 1,00E+00 0,00E+00 0,02 0,04 VREF 0,06 0,08 0,12 0,14 Iline
Fig. Main voltages versus line current Fig. shows behavior voltage area line powered condition. VREF 0,002 0,004 0,006 0,008 0,01 Iline
Fig. voltage behavior line powered condition
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Adjustments performances reference voltage, Vref, adjusted means external resistor Rva. increased connecting resistor between pins SLPE, decreased connecting resistor between pins (see fig. line powered application, using voltage reduction reduces peripheral supply capabilities: must least 0.25 higher than Vdd. ensure correct operation, advised adjust Vref value lower than higher than (the maximum operating voltage must guaranteed application well safe operating temperature). These adjustments will slightly affect parameters: there will small change temperature coefficient Vref slight increase spread this voltage reference matching between internal external resistors. Furthermore, resistor connected between will slightly affect apparatus impedance (see section "set impedance").
Vref 7,00E+00 6,00E+00 5,00E+00 4,00E+00 3,00E+00 2,00E+00 1,00E+00 LN/REG SLPE/REG 1000 10000 (kohms)
Fig. Influence resistor between SLPE between
slope voltage influenced Rslpe resistor shown fig. value Rslpe slightly modified even preferred changing this value will affect more than characteristics, also influences gains, characteristics, maximum output swing line voltage threshold Ith.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
0,02 Rslpe=20 Rslpe=33 0,04 Rslpe=10 Rslpe=27 0,06 0,08 Rslpe=15 Iline
Fig. Influence Rslpe characteristics
3.1.2
Supplies peripherals
Fig. shows architecture supply block.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Isup
SENSE
Switch
Cvdd
Cvcc
Fig. Configuration supplies
3.1.2.1 Supply
Principle operation supply voltage normally used supply internal circuitry TEA1114A. However, small current drawn supply peripheral circuits having ground reference. supply voltage depends current consumed peripheral circuits shown following formula: VCC0 Rccint (Irec VCC0 Irec internal current necessary supply receive output amplifier realize peak voltage across earpiece impedance Irec Rccint internal equivalent impedance between Rccint output impedance voltage supply point. seen from fig.5, internal supply current depends voltage VCC, means that impedance internal circuitry connected between infinite. While supplying peripheral circuit VCC, supply current flowing through resistor decreases value voltage then reduces consumption. impedance combination with Irec Rccint which includes parallel impedance internal circuitry connected between VEE. line current equal equal this Rccint impedance approximately
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
limited minimum value ensure correct operation, will limited maximum value. limit imposed requirement maintain minimum permitted voltage between SLPE which called Vmin. maximum current available depends settings Vref, Rcc(+Rz), Rslpe required signal level line receive outputs. simplify calculation, will worst case Rccint, which Rcc, gives: Irec Vref Rslpe Iline Irec Irec VCCmin Vmin Rslpe Iline Irec Ipmax VCCmin Ipmax Vref Vmin (Rcc Rslpe Irec Rslpe Vmin Rslpe Zline Adjustments performances impedance connected between also determines impedance, easiest increase current capability supply point increase reference voltage Vref connecting resistor between pins SLPE (see 3.1.1).
3.1.2.2 Supply
Principle operation regulated supply dialler microcontroller. speech mode, line powered while trickle mode ringer mode externally powered. When line powered, provide least when equals value typically correlated with value line voltage follow: 3.55 3.55 0.28
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Fig. shows versus line current.
0,002 0,004 0,006 0,008 0,01 Iline
Fig. versus line current correlation between line voltage done order voltage difference between least 0.25 block diagram, transistors drive line current either VEE: when voltage higher than current driven VDD, when voltage lower than line current driven VEE, when voltage between both transistors conducting order minimize distortion. When equals constant courant Isup typically) sunk from This constant current doesn't affect return loss value taken into account characteristic. this condition, current available output least When lower than both currents Isup reduced accordingly. trickle mode ringer mode, works shunt regulator trickle mode current consumption shunt regulator dramatically reduced order have typically when lower than ringer mode, shunt regulator able sink between VEE. Fig. shows current consumptions VDD.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
1,00E-05 1,00E-06 1,00E-07 1,00E-08 1,00E-09 1,00E-10
0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,11 0,12 0,13 0,14 0,15 Iringer Fig. Current consumption this supply structure, TEA1114A cannot used combination with TEA1083/A, TEA1085/A, TEA1093 OM5153. this configuration, stability possible.
impedance
Principle operation TEA1114A behaves like equivalent inductance that presents impedance (Rslpe) high impedance (Rp) speech signals. integrated resistance order 17.5 +/-15%. parallel with external realized Cvcc. Thus, audio frequency range, apparatus impedance
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
(called impedance) mainly determined resistor. Fig. shows equivalent schematic impedance.
Vref
Creg Rslpe internal resistor
SLPE
Rslpe
Creg
Cvcc
Fig. Equivalent impedance Adjustments performances When decreasing reference voltage Vref, resistor connected between parallel (see fig. slightly modifying impedance. complex impedance required, resistor replaced complex network (see fig. :Rcc Cz). resistance which influences value becomes
Microphone amplifier
Principle operation fig. block diagram microphone amplifier TEA1114A depicted.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
from DTMF
MIC+ MICV
circuit
Rgasint
Rexch
SLPE Rslpe
Creg
Cvcc
Cexch
Fig. Microphone channel microphone amplifier symmetrical high input impedances (typically times between pins MIC+ MIC- with maximum tolerances 15%). input this microphone amplifier able handle signals mVrms with less than total harmonic distortion. seen from fig. microphone amplifier itself built parts: preamplifier which realizes voltage current conversion, end-amplifier which realizes current voltage conversion. overall gain (Gvtx) microphone amplifier from inputs MIC+/MIC- output given following equation: Gvtx Avtx Avtx (Rgasint Rrefint) (Ri//Zline Rslpe) with: apparatus impedance, Rcc//Rp (typically 17.5 Rgasint internal resistor realizing current voltage conversion (typically 29.5 with spread +/-15%) Rrefint internal resistor determining current internal current stabilizer (typically 7.25 with spread correlated spread Rgasint) Zline load impedance line during measurement gain control factor varying from Iline Iline when function applied (see chapter details) Using these typical values equation assuming Zline find gain equal
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Gvtx Avtx
Iline
different gain controls (AGC; MUTE/) microphone preamplifier stage, modifying transconductance.
Adjustments performances shows typical frequency response gain microphone amplifier TEA1114A. |Gain| (dB) 44,8 44,6 44,4 44,2 43,8 43,6 43,4 43,2 |75°C| |50°C|
44,26
44,44 44,3 43,99
44,34
1000 |-25°C|
10000 Frequency (Hz)
Fig. Microphone gain versus frequency: influence temperature shows distortion signal line function line signal function microphone signal 15mA 70mA Output level (Vrms)
Fig. Distortion line versus line signal (left) versus microphone signal TEA1114A
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Fig. shows microphone noise (psophometrically weighted: curve) versus line current nominal gain when resistor connected between inputs MIC+ MIC-. Noise (dBmp)
0,015 0,035 0,055 0,075 0,095 Iline Fig. Microphone noise versus line current Fig. shows common mode rejection ratio curves present this fig. first spectrum signal when microphone signal applied MIC- while MIC+ shorted VEE, second spectrum signal when microphone signal applied pins MIC- MIC+ shorted together. Both signals kHz, difference between curves gives CMRR. (dBV) -100 -120 1000 common 2000 differential 3000 4000 5000 Frequency (Hz)
Fig. Common mode rejection ratio microphone
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Receive amplifier block
Principle operation fig. block diagram receive amplifier depicted.
MUTE/ Rgarint
DTMF
Re21 Re23 Re22
Vcc/2
Fig. Receive channel seen from fig. receive amplifier block built three parts: preamplifier which realizes voltage current conversion followed end-amplifier which realizes current voltage conversion earpiece amplifier itself with gain externally determined. preamplifier asymmetrical high input impedance between pins VEE. equal with maximum tolerance +/-15%. earpiece amplifier TEA1114A able drive loads down impedance while receive amplifier only drive loads down output capability suitable several kind earpieces drive either dynamic, magnetic piezo-electric earpieces. case magnetic dynamic earpieces, capacitor series required decoupling. overall gain Gvrx receive amplifier from input output given equation: Gvrx Avrx Avrx 2.41 Rgarint/Rrefint with: Rgarint internal resistor realizing current voltage conversion (typically with spread +/-15%) Rrefint internal resistor determining current internal current stabilizer (typically 7.25 with spread correlated spread Rgarint) gain control factor varying from Iline Iline when function applied (see chapter details) Using these typical values equation, find gain equal Gvrx Avrx Iline
different gain controls (AGC; MUTE/) receive preamplifier stage, modifying transconductance.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Adjustments performances gain earpiece amplifier externally determined, adjusted between this purpose, fig. shows ways setting this gain. gain between compensates approximately attenuation provided antisidetone network. external capacitors Cgar (connected between Cgars (connected between VEE) ensure stability earpiece amplifier when relationship Cgars Cgar fulfilled. capacitor Cgar provides first order pass filter, which cut-off frequency determined with Re2, furthermore, highpass filter required capacitor inserted series with Re1. Fig. shows frequency response typicall gain receive amplifier from different temperatures.
|Gain| (dB) 33,8 33,6 33,4 33,2 |75°C| |25°C| 1000 |0°C| |-25°C| 10000 Frequency (Hz)
Fig. Receive gain versus frequency: influence temperature maximum output swing depends line voltage, resistor, current consumption circuit, current consumption peripheral circuits load impedance receiving input handle signals mVrms with less than THD. Fig. shows distortion when limitation related input voltage line current equal with gain this amplifier. Fig. shows distortion signal function signal with loads line current gain.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
0,002 0,004 0,006 0,008 0,01 0,012 0,014 0,016 0,018 0,02 0,022 Input level (Vrms) Fig. Distortion versus input signal
450ohm 150ohm Output level (Vrms)
Fig. Distortion versus level loads Fig. shows noise loaded with (psophometrically weighted: curve) function line current with gain this amplifier. This curve been done with open input With antisidetone network connected input part microphone noise generated line will added but, thanks microphone noise value, effect almost negligible.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Noise (dBVp) ,015 ,020 ,025 ,030 ,035 ,040 ,045 ,050 ,055 ,060 ,065 ,070 Iline Fig. Noise
Automatic gain control
Principle operation TEA1114A performs automatic line loss compensation. automatic gain control varies gain microphone receive amplifiers accordance with line current. enable this function, must connected VEE. line currents below current threshold, Istart (typically mA), gain control factor equal giving maximum value gains Gvtx Gvrx. this threshold current exceeded, gain control factor reduced then gains controlled microphone receive amplifiers also reduced. When line current reaches other threshold current, Istop (typically mA), gain control factor limited minimum value equal 0.5, giving lower value microphone receive controlled gains. gain control range both amplifiers typically which corresponds approximately line length (0.5 twisted pair copper) with attenuation dB/km. attenuation correlated current Iagc sunk AGC: when this current lower than typically gains maximum, when this current higher than typically gains minimum. This current proportional voltage between pins SLPE VEE. There internal resistor which sets Istart Istop, adding externally series (between pins VEE) reduces Iagc increases values Istart Istop. Adjustments performances TEA1114A used with different exchange supply voltages different feeding bridge resistances. this purpose, resistor Ragc, inserted between pins VEE. This Ragc resistor increases both threshold currents Istart Istop proportionally. Fig. shows control microphone gain versus line current different values Ragc. When function required, must left open, then control factor equals both controlled gains their maximum values. When Ragc value Istart high, increasing value Rslpe reduces proportionally Istart shifts lower currents. this case, value Istop also reduced gains modified. value Rslpe increased lot, possible restore typical gains connecting parallel series network which makes total impedance
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
|Ragc=0| |Ragc=10k| 0,015 0,025 0,035 0,045 0,055 0,065 0,075 0,085 Iline |Ragc=15k| |Ragc=22k| |Ragc=27k|
Fig. microphone gain versus line current Ragc
DTMF amplifier
principle operation fig.25, block diagram DTMF channel TEA1114A depicted.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
MUTE/
from receive preamp
Rgarint
DTMF
Vcc/2
from microphone preamp Rgasint
Rexch
SLPE
Cvcc Rslpe
Cexch
Fig. DTMF channel TEA1114A DTMF amplifier a-symmetrical high input impedance between pins DTMF with maximum spread +/-15%. input biased VEE, when input DTMF signal polarized VEE, decoupling capacitor necessary. DTMF amplifier built parts: preamplifier which realizes voltage current conversion same end-amplifier microphone amplifier. applied DTMF channel. overall gain (Gvmf) DTMF amplifier from input DTMF output given following equation: Gvmf Avmf Avmf =0.246 (Rgasint Rrefint) (Ri//Zline Rslpe) with: apparatus impedance, Rcc//Rp (typically 17.5 Rgasint internal resistor realizing current voltage conversion (typically 29.5 with spread +/-15%) Rrefint internal resistor determining current internal current stabilizer (typically 7.25 with spread correlated spread Rgasint)
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Zline load impedance line during measurement Using these typical values equation assuming Zline find gain equal Gvmf Avmf Furthermore, DTMF signal attenuated sent confidence tone. Fig. shows frequency response DTMF amplifier different temperatures. |Gain| (dB) 26,8 26,6 26,4 26,2 25,8 25,6 25,4 25,2 |80°C| |25°C| |-25°C| Frequency (Hz)
Fig. DTMF gain versus frequency: influence temperature input DTMF amplifier handle signals mVrms with less than THD. Fig. shows distortion line versus input signal Iline
0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,11 Input level (Vrms)
Fig. Distortion DTMF signal line versus input signal
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
"MUTE" function
Principle operation "mute" realizes electronic switching between speech mode dialling mode. level applied MUTE/ input, both microphone receive channels disabled while DTMF channel enabled. applying high level leaving MUTE/ open microphone receive channels enabled while DTMF channel disabled. MUTE/ input pull-up structure VCC, directly driven open drain output. Nevertheless, case structure microcontroller side, push-pull output structure recommended polarize properly input microcontroller when varies current will flow from this pin). threshold voltage level 0.65 typically with temperature coefficient mV/°C. Fig. shows microphone gain reduction MUTE/ input current versus MUTE/ input voltage.
gain (dB) Vmute
Imute 1,00E-06 0,00E+00 -1,00E-06 -2,00E-06 -3,00E-06 -4,00E-06 -5,00E-06 -6,00E-06 Vmute
Fig. Microphone gain MUTE/ input current versus MUTE/ input voltage Adjustments performances Fig. shows microphone receive amplifier gain reduction Iline input signal kHz. curves present these graphics, first shows spectrum signal line when signal applied microphone inputs respectively when MUTE/ high level, second shows same signal when MUTE/ level. difference between curves this frequency gives gain reduction.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
level (dBm600 -100
MUTE channel
level (dBV) -100 -110
MUTE channel
1000 muted
2000
3000
4000
5000
1000 muted
2000
3000
4000
5000
Frequency (Hz) muted
muted
Frequency (Hz)
Fig. Microphone receive gain reduction "mute" condition "mute" function works down voltage equal about 1.65 below this threshold, microphone receive amplifiers remain always enabled independently MUTE/ input level. maximum voltage allowed MUTE/ input minimum GND-0.4
Anti-sidetone network
Principle operation avoid microphone signal come back with high level receive channel, anti-sidetone circuit uses microphone signal from SLPE (which opposite phase) cancel microphone signal input receive amplifier. anti-sidetone bridge already used TEA111x TEA106x) families conventional Wheatstone bridge shown fig. used design antisidetone network.
Zline
Zbal
Zline
Rast1
Rast2
Rslpe SLPE
Rast1
Rslpe Rast3 SLPE Zbal
Fig. Wheatstone bridge (left) TEA111x family anti-sidetone bridge (right) TEA111x TEA106x) family anti-sidetone bridge advantage relative flat transfer function audio frequency range between input output both with real complex impedances. Furthermore, attenuation bridge receive signal (between pins independent
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
value chosen Zbal after impedance been fixed condition shown equation fulfilled. Therefore, readjustment overall receive gain necessary many cases. Compare previous one, Wheatstone bridge advantages needing resistor less smaller capacitor Zbal. disadvantages include dependence attenuation bridge value chosen Zbal frequency dependence that attenuation moreover, input stage introduce some distortion high level signal. This requires some readjustment overall receive gain.
3.8.1
TEA111x family bridge
anti-sidetone circuit composed Rcc//Zline, Rast1, Rast2, Rast3, Rslpe Zbal. Maximum compensation obtained when following conditions fulfilled: Rslpe Rast1 Rast2 Rast3 [Rast2 Rast3 Rslpe Rast1 Rslpe Zbal Zline scale factor chosen meet compatibility with standard value capacitor Zbal. practice, Zline varies strongly with line length line type. Consequently, value Zbal chosen with average line length giving acceptable sidetone suppression with short long lines. suppression further depends accuracy with which Zbal equals this average line impedance. Example Let's optimize theorical equivalent average line impedance shown Fig. 1265
Fig. Equivalent average line impedance compatibility capacitor value Zbal with standard capacitor value from series (220 nF): 0.636 Rast2, value 3.92 been chosen. using previous equations, calculate Zbal, Rast1, Rast3. find Rast1 Rast3 Zbal series with attenuation receive line signal between derived from following equation: Rast2 Rast1 Rast2 Rast2 Rast3 Zbal With values used this example, gives kHz. receive amplifier input impedance, typically
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
3.8.2
Wheatstone bridge
conditions optimum suppression given Zbal Rast1 Rslpe Zline) Also, this bridge type, value Zbal chosen that corresponds with average line length. attenuation received line signal between given Rast1 Zbal Rast1 used adjust bridge attenuation; value influence balance bridge.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
APPLICATION COOKBOOK
this chapter, procedure making basic application given. Refering fig. design flow given number steps which should made. possible every step, components involved their influence every step given.
Step
setting
Adjustment
Adjust setting TEA1114A local requirements. Voltage LN-VEE This voltage adjusted changing Vref: increased with resistor between pins SLPE decreased down with resistor between LN).
slope
slope might modified changing value Rslpe (this advised: gains modified, characteristic modified).
Supply point
line powered applications, depends values Vref resistive part impedance network (Rcc Rz).
Artificial inductor
value adjusted changing value Creg: smaller value speeds-up current shape during transients decreases value inductance therefore affects frequencies.
Impedance sidetone After setting required impedance, sidetone optimized using sidetone network order minimize loop gain line conditions. adjusted that step. Application impedance adjusted with impedance network connected between (Rcc Rz//Cz).
Sidetone
Adjust Zbal (Rbal1, Rbal2, Cbal) according line characteristics.
Internally defined, characteristics (Istart Istop) shiftted higher line currents with external Ragc resistor connected between VEE. case necessary shift Istart Istop lower current values, value Rslpe must increased proportionally (see
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Step
Microphone gain
Adjustment
TEA1114A microphone receive gains microphone gain application adjusted before entering pins MIC+/MIC- TEA1114A. reduced using resistor Rtx3 which forms bridge attenuator with Rtx1 Rtx2. Ctx1, Ctx2 form high-pass filter with Rtx1, Rtx2 series with input impedance MIC+/MIC-. capacitor Cmic forms low-pass filter with impedance microphone resistors Rmicp/Rmicm.
Earpiece gain
earpiece gain application adjusted means resistors Re2. capacitor parallel with forms low-pass filter, stability ensured with capacitor Cgars Cgar between pins VEE. gain between fixed
TEA1114A DTMF gain DTMF DTMF selected with level MUTE/. level line must adjusted before entering DTMF. capacitor removed when input signal biased VEE.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
EXAMPLE APPLICATION
demo board (OM5838) available. TEA1114A used various applications, this demoboard includes only TEA1114A with basic environment. Fig. gives schematic basic application TEA1114A, fig. gives schematic demoboard while fig. gives component placement diagram. these schematics, capacitors connected with dotted lines resistors drawn with dotted lines indicated immunity purpose. According application, possible connect electret microphone instead VCC. this case, current capability would reduced electret consumption current capability would increased same value (which would allow slight increase earphone amplifier capability).
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Rfeed
Cvcc
Cfeed
Rprot
Cvdd
C101
Rmicp
Rast1
MIC+
Rtx2 Rtx3
Ctx2
Cmic
MICP MICM
MIC-
Rtx1
Ctx1
C102
Rmicm
Cgars
Cgar
Rear
Cear
EAR+
Ragc
TEA1114A
MUTE Rast2
3.92
EAR-
DTMF SLPE
MUTE_
Rast3 Rbal1
Rslpe
Creg
Cbal
Rbal2
Fig. Basic application TEA1114A
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
12.1
C106
C108
C103
MIC+
MIC+ MICR19
BAS11
C113
MIC-
C102
C105
C107
TEA1114A
22.1
C112
MUTE
MUTE_
DTMF SLPE
Fig. Circuit diagram demoboard
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Fig. Component placement diagram demoboard
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
ELECTROMAGNETIC COMPATIBILITY
common international specification exists immunity, different assembly methods lead different solutions, only some advices provided. advisable take care impedance GND, smallest always best. This means that Ground (VEE) trace must always large possible, best have second layer dedicated this purpose. MIC+/MIC- inputs also sensitive signals entering these pins would amplified). Care taken with lay-out microphone amplifier, which also helpful noise, providing good decoupling VEE. Capacitor hundred forming low-pass filters added input amplifier (C101, C102). impedance capacitors parallel with electrolythic between well parallel with Creg capacitor help. Usually impedance capacitor connected between (C12) helps conducted interferences, this capacitor parallel with impedance network apparatus, value must small enough. general when connections coming from external environment (e.g. MICP, MICM, demoboard), better filter signal before influences close environment TEA1114A (e.g. action C107, C108, C112, C113 demoboard).
very high frequencies parasitic inductance capacitors well length their connections about becomes major concern inhibit effect these capacitors.
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
REFERENCES
TEA1114A voltage transmission circuit with dialler interface regulated strong supply Device specification TEA1114A Line Interface Demonstration Board User Manual OM5838 TEA1114A Line Interface Demonstration Board (report ETT/UM97001.1) Philips Semiconductors Semiconductors Wired Telecom Systems Data Handbook -IC03a
Philips Semiconductors Semiconductors Wired Telecom Systems Application Handbook -IC03b
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
APPENDIX LIST ABBREVIATIONS DEFINITIONS
DTMF Gvmf Gvrx Gvtx Iline Irec Islpe Istart Istop Isup MUTE/ OM5838 Rast Rexch Line terminals application example Automatic Gain Control: line loss compensation Balance Return Loss: matching between apparatus impedance reference Dual Tone Multi Frequency ElectroMagnetic Compatibility Earpiece amplifier gain adjustment TEA1114A DTMF amplifier gain Receive gain Microphone gain Integrated circuit Current consumption TEA1114A Current supply Line current Current consumption peripherals Internal current consumption (from VCC) receive amplifier Receive amplifier input TEA1114A Part line current flowing through SLPE Start current function Stop current function Supply current voltage regulator Threshold current voltage part Scale factor anti-sidetone network Artificial inductor voltage stabilizer MUTE/ input TEA1114A Demoboard TEA1114A Earpiece amplifier output TEA1114A Resistor adjust sidetone bridge attenuation Antisidetone resistor Filter capacitor equivalent inductor connection TEA1114A Bridge resistance exchange Radio Frequency Interference
TEA1114A transmission circuit with dialler interface regulated strong supply Application Note
Rgarint Rgasint SLPE MIC+/MICVCC Vref Vslpe Zbal
Internal resistance (134 which sets receive gain Internal resistance (29.5 which sets microphone gain Internal resistance between Voltage adjustment resistor Receive output Slope input TEA1114A Total Harmonic Distortion Microphone amplifier input pins TEA1114A Positive supply TEA1114A Regulated supply Ground reference TEA1114A voltage between Stabilized reference voltage between SLPE voltage level between SLPE Input impedance receive amplifier TEA1114A Anti-sidetone network balance impedance Gain control factor
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