CN85102113B - Audio frequency transmission circuit formed by line-votage stabilizer type transmitting amplifier - Google Patents
Audio frequency transmission circuit formed by line-votage stabilizer type transmitting amplifier Download PDFInfo
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- CN85102113B CN85102113B CN85102113A CN85102113A CN85102113B CN 85102113 B CN85102113 B CN 85102113B CN 85102113 A CN85102113 A CN 85102113A CN 85102113 A CN85102113 A CN 85102113A CN 85102113 B CN85102113 B CN 85102113B
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- resistor
- voltage
- line
- amplifier
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Abstract
The present invention relates to a transfer magnifier in an audio frequency transmission loop of a telephone device, which can stabilize line direct current voltage. According to the present invention, the structure of a transfer magnifier can be properly selected and has the function of line voltage stabilizer. By dint of a resistor, the gain of the line voltage stabilizer can be changed, and other properties of the audio frequency transmission loop can not be influenced. High gain is possible. Reasons for causing the drift of the line direct current voltage are the detuning of the sound amplification pre-amplifier(in the front of the transfer magnifier) and the temperature fluctuation of reference voltage. According to the present invention, the drift can be greatly reduced by increasing reference voltage and additional temperature independent current sources.
Description
The present invention relates to an audio transmission circuit that the line direct voltage is provided for telephone device by subscribers feeder.It is made up of amplify preamplifier and the transmission amplifier of high output impedance.Transmission amplifier is a line voltage stabilizer, and it comprises the input stage that is made of feedback operational amplifier; With the output stage that forms by output transistor and corresponding emitter resistance device.Output stage and subscribers feeder are connected in parallel, and the output termination of the preamplifier that amplifies is to the signal input part of operational amplifier, and transmission amplifier will include reference voltage source, and it will be the stable generation reference voltage of line voltage.
Above-mentioned audio transmission circuit is described in article " is applicable to the sound circuit able to programme of phone converter " to some extent, and this article is published at periodical IEEE＜solid state circuit〉V01.SC-17, NO.6,1982.10, PP1149-1157.
During work, the telephone set that is connected on the public telephone network subscribers feeder can have DC voltage component by the telephone exchange reception through this subscribers feeder, circuit direct voltage, alternating voltage component, and the line voltage distribution of received signal composition.In addition, its circuit direct voltage is modulated into transmission signals through this telephone set with the signal that will transmit.
Management organization has stipulated to install the maximum direct voltage of two ends, and this maximum direct voltage further depends on line current again.The exemplary value of max line direct voltage is 5.7 volts when 10 milliamperes of line currents for example.In telephone device, the line direct voltage is regulated by the voltage stabilizer in the transmission amplifier.
Audio transmission circuit described in the above-mentioned IEEE article is made up of transmission amplifier.This amplifier can not only the stability line direct voltage, also includes a Yi Sideng electric bridge, producing anti-sidetone effect, and can realize desirable line terminal impedance voluntarily.Have the characteristic of the audio transmission circuit of above-mentioned functions, depend on passive component, it has also determined the gain of transmission amplifier.Obviously, increasing above-mentioned gain with straightforward procedure, is very difficult and other characteristics of audio transmission circuit are had no adverse effect.
Target for this reason, the present invention will provide the notion of a novelty for audio transmission circuit.Therein, the gain of transmission amplifier is decided by parts, and does not influence other characteristics of audio transmission circuit.
In order to finish above-mentioned target, according to the present invention, the feature of audio transmission circuit is:
-one voltage divider is attempted by on the subscribers feeder, and it is connected in series with first resistor after being connected in parallel by second resistor and capacitor again, and the emitter resistance device is the part of second resistor;
A signal input part of-operational amplifier connects emitter to output transistor by feedback circuit, and feedback circuit is made up of reference voltage source, a constant-current source and a feedback resistor;
Another input termination of-operational amplifier is to the tie point of first resistor and second resistor.
Because the parts of decision transmission amplifier and line voltage stabilizer characteristic, its structure choice must compare success, so the gain of transmission amplifier only depends on the numerical value of feedback resistor.After the audio transmission circuit realization is integrated, only need provide an outside regulating resistor now, promptly feedback resistor changes the purpose that gains with realization.
Because in transmission circuit of the present invention, line terminal impedance is not to realize voluntarily by transmission amplifier, so its additional advantage is to obtain an effective distributing point, and by it to other all circuit supplies of audio transmission circuit.Also in other words, a line terminal resistance might be connected with a feed capacitors in series now, and constitute independently whole road terminal impedance.Tie point between line terminal resistance and feed capacitor can be used as the DC feedback point now, in fact do not have alternating voltage now at the capacitor two ends.
The preamplifier that amplifies in the audio transmission circuit when not having input signal, produces an output DC stream through regular meeting, is commonly referred to offset current.The reason that causes above-mentioned offset current is for example fluctuation of the drift of circuit block performance or temperature.Preamplifier carefully designs its differential input stage though integrated-type amplifies, and the order of magnitude of its offset current amplitude still reaches 1 microampere.
In audio transmission circuit of the present invention, its preamplifier that amplifies will connect the high resistive input to transmission amplifier.Offset current will produce direct voltage, i.e. an offset voltage at the feedback resistor two ends.This offset voltage of feedback circuit will form the deviation of line voltage stabilizer apparently by reference voltage, produced the deviation of line direct voltage thus.
When utilizing forward biased diode as voltage reference circuit, its reference voltage for example is 0.6 volt.The possible numerical value of feedback resistor is 180 kilo-ohms, so when offset current is 1 microampere, its offset voltage will be 0.18 volt.Like this, in above-mentioned numeric example, when the constant and line current of other conditions hour, about 30% drift will take place in the line direct voltage.
Management organization's regulation, the line direct voltage can not surpass predetermined numerical value, for example 5.7 volts.When adopting habitual diode bridge, the voltage of its two end is 1.5 volts, so the voltage of audio transmission circuit two ends must be no more than 4.2 volts.Because when the miscellaneous part of design audio transmission circuit, wish that the line direct voltage is high as much as possible, so importantly make the drift of line direct voltage as much as possible little.
The concrete device of audio transmission circuit of the present invention can reduce the drift of line direct voltage.It is characterized in that having two forward biased diodes at least, be connected in series equidirectionally and become reference voltage source.
Above-mentioned measure will reduce the relative variation of feedback circuit direct voltage, because the effect of public addressor amplifier offset current will reduce, its multiple equals the number of diode in the feedback circuit.
The advantage of the concrete device of audio transmission circuit of the present invention is that any variations in temperature of reference voltage source can both be compensated with simple method.It is characterized in that at two ends of voltage divider (in transmission amplifier) electric capacity additionally and connect an independent current source, the symbol of its temperature coefficient is with the opposite in sign of the temperature coefficient of reference voltage source.
If it is suitable that the resistance of voltage divider resistance is selected, then when reference voltage for example reduced, the voltage drop at the first resistor two ends was because the corresponding increase of current source current will increase compensatoryly.
To with method for example the present invention be described in more detail with reference to the accompanying drawings now.In different figure, corresponding parts provide identical reference number, this:
Shown in Figure 1 is the audio transmission circuit of a band transmission amplifier consistent with the present invention.
Shown in Figure 2 is an audio transmission circuit with the corresponding to band transmission amplifier of the present invention, and its structure is particularly suitable for reducing source value of moving of line voltage.
Audio transmission circuit shown in Figure 1 is made up of following parts: transmission amplifier 1, and it also can be used as the line voltage stabilizer; Line terminal resistor 2, its numerical example is 600 Europe in this way; Feed capacitor 3, its numerical example is 10 microfarads in this way; The preamplifier 4 that amplifies, it is connected with the signal input part of transmission amplifier.The preamplifier that amplifies has high input impedance, so can symbolically be an amplifier that has independent current source.Line terminal resistor 2 has formed a cascaded structure with feed capacitor 3, and it will be connected on subscribers feeder end points 5-1 and the 5-2 by diode bridge (not drawing in Fig. 1) commonly used.The tie point 19 of line terminal resistor and feed capacitor 3 has formed a direct voltage distributing point with the high decay of alternating voltage component.
By the current input signal that the preamplifier 4 that amplifies provides, input transmission amplifier 1 makes it produce an output signal electric current that flows through transistor 10.Because the input impedance of operational amplifier 6 is very high, so in fact its input current will all flow in the feedback resistor 15.Since the numerical value of emitter resistance device 11 more than with its parallel resistor device 12, capacitor 14 sequential circuits be little, so in fact the output signal electric current of operational amplifier 6 will all flow into emitter resistance device 11.In order to determine the current gain of transmitting stage 1, necessary chosen in advance output signal electric current is to the ratio of current input signal.
Because capacitor 14 for signal code, does not in fact have impedance, so in fact do not have signal impedance at the positive input of operational amplifier 6 yet.Because the high-gain of operational amplifier 6 is also like this at its reverse input end.Because feedback resistor 15 must equate with the signal voltage at emitter resistance device 11 two ends, so current ratio, that is the current gain of transmitting stage 1 will equal the resistance value ratio of resistor 15 and resistor 11.By above-mentioned numeric example of lifting, its current gain is the 9000(79 decibel).
As the transmission amplifier 1 of voltage stabilizer, the line direct voltage that it is regulated will be decided by the numerical value of following different components.The voltage at capacitor 14 two ends, the voltage of operational amplifier 6 positive inputs and the voltage of reverse input end are mutual etc.Under zero the situation, there is not direct current to flow through feedback resistor 15, because be so the emitter voltage of transistor 10 will hang down a diode forward pressure drop Ud than described voltage at input dc power stream.The resistance R of resistor 12
12Expression, then the voltage at its two ends also equals diode forward pressure drop Ud apparently, and its resistance of resistor 13(R
13Expression) voltage at two ends will be its R
13/ R
12Doubly.
The line direct voltage is resistor 13,12 and its resistance of emitter resistance device 11(R
EExpression) summation of both end voltage, owing to flow through the electric current of resistor 2 only the line is busy the very fraction of direct current, so as many as its resistance of the direct voltage at resistor 11 two ends and line direct current I
1Product.Therefore, line direct voltage V
1To have
V
1=I
1R+(1+R
13/R
12)Ud(1）
Utilize aforesaid numerical example, when the line direct current is 15 milliamperes and diode forward pressure drop when being 0.6 volt, can get the line direct voltage by formula (1) calculating is 4.2 volts.
Output stage 7 as the transmission amplifier 1 of voltage stabilizer must have sufficiently high impedance to the ac voltage signal in the audiorange, so that prevent the influence to line terminal impedance as much as possible.This necessary high impedance can be realized, because see fashionable from end points 5-1 and 5-2, capacitor 14, resistor 13,11 can be looked at as with operational amplifier 6 be an inductor, and the numerical value of its apparent inductance equals the product of the capacitance of the numerical value of numerical value, resistor 13 of resistor 11 and capacitor 14.Use above-mentioned numeric example, the numerical value of this apparent inductance is about 4.4 henries.
The high current gain of transmitting stage 1 (79 decibels), but mat with the resistance of feedback resistor 15 select enough high the realization.When whole offset currents (for example 1 microampere) of the preamplifier 4 that amplifies flow into feedback resistor 15, will produce high offset voltage (for example 0.18 volt) at its two ends because of feedback resistor 15 numerical value are high.This is undesirable under certain conditions.
Line direct voltage (being regulated by voltage stabilizer) drift by offset voltage produces will force the designer to select low adjusting direct voltage rated value, so that the maximum requirement that makes the line direct voltage satisfy management organization all the time to be proposed; Or the gain that makes transmitting stage 1 is selected much lowerly.Low gain will limit the application of audio transmission circuit widely, so be that people are undesirable.When the line direct voltage is selected two low rated values, under opposite situation, the drift of voltage will make the line direct voltage may be lower than the selected rated value of designer, and this numerical value is very low.By above-mentioned numeric example, when the max line direct voltage was 4.2 volts, its specified line direct voltage must be chosen as 3.0 volts.Numerical value and direction at offset current are under the disadvantageous situation, and when the line direct current of supposition, the numerical value of line direct voltage will be 1.8 volts.Low like this numerical value, for example power supply is inappropriate to other electronic circuits of audio transmission circuit.
Shown in Figure 2 is that an audio transmission circuit consistent with the present invention specifically installs.Therein, the problem of above-mentioned relevant drift has solved; Equally, temperature fluctuation has reduced the influence of diode (being voltage reference diode 16) voltage.
Compared to Figure 1, in audio transmission circuit circuit diagram shown in Figure 2, voltage reference diode 16 is replaced by two voltage reference diode 16-1 and 16-2 that are connected in series; And additional independent current source 18 being arranged, it and capacitor 14 are in parallel.These changes will cause the modification of transmission amplifier 1 parameter.The numerical value that resistor 13 is present for example is 16 kilo-ohms; And the numerical value of resistor 12 for example is 21.5 kilo-ohms.
Diode 16-1 and 16-2 are because current source 17 and forward bias.The current temperature coefficient of current source 18 will compensate the influence of diode voltage and line direct voltage temperature coefficient.After having current source 18, can be expressed as the effect of line direct voltage and add an extraneous term in formula (1), its size equals resistance value R
13With the current value I that flows through current source 18
0Product.
Line direct voltage V
1Computing formula now change into
V
1=I
dR
E+2(1+R
13/R
12)Ud+I
0R
13（2）
In formula (2), R
12And R
13Must fill in the modification value now.Reference voltage 2U
dCoefficient, its numerical value now is about 1.75.
When the offset voltage at resistance two ends was constant, offset voltage reduced about 3.7 times to the influence of line direct voltage drift.Its reason is that the coefficient of 2Ud in the formula (2) will be than U in the formula (1)
dCoefficient reduce about 3.7 times.Obviously, this line direct voltage drift will be acceptable numerical value.
Flow through the electric current in the current source 18, will not rely on the load of current source.This current DC is proportional to temperature, and its temperature coefficient is for just.The power supply of this pattern, for example from article " integrated linear tandem circuit " " Philips's technology review " Vol.32,1971, its essence as can be known among the No.1.Mat is selected the numerical value of resistor 12 and 13 suitably, can realize that current source 18 positive temperature coefficients produce effect to the line direct voltage, just in time compensate the effect of diode 16-1 and 16-2 negative temperature coefficient.
Claims (6)
1, audio transmission circuit that the line direct voltage is provided for telephone device by subscribers feeder, it is made up of amplify preamplifier and the transmission amplifier of high output impedance, transmission amplifier is a line voltage stabilizer, and it comprises the input stage that is made of feedback operational amplifier; With the output stage that forms by output transistor and corresponding emitter resistance device, output stage and subscribers feeder are connected in parallel, amplify the output termination of preamplifier to the signal input part of operational amplifier, and transmission amplifier will include reference voltage source, it will be the stable generation reference voltage of line voltage, it is characterized in that:
-one voltage divider is attempted by on the subscribers feeder, and it is connected in series with first resistor after being connected in parallel by second resistor and capacitor again, and the emitter resistance device is the part of second resistor;
A signal input part of-operational amplifier connects emitter to output transistor by feedback circuit, and feedback circuit is made up of reference voltage source, a constant-current source and a feedback resistor;
Another input termination of-operational amplifier is to the tie point of first resistor and second resistor.
2, audio transmission circuit according to claim 1 is characterized in that, has the biasing of two diode forward, equidirectional being connected in series at least and forms reference voltage source.
3, the feature of audio transmission circuit according to claim 1 and 2 is, transmission amplifier includes an independent current source, the symbol of its temperature coefficient, with the opposite in sign of reference voltage source temperature coefficient, this current source will be attempted by two ends of capacitor in the voltage divider.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN85102113A CN85102113B (en) | 1985-04-01 | 1985-04-01 | Audio frequency transmission circuit formed by line-votage stabilizer type transmitting amplifier |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN85102113A CN85102113B (en) | 1985-04-01 | 1985-04-01 | Audio frequency transmission circuit formed by line-votage stabilizer type transmitting amplifier |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN85102113A CN85102113A (en) | 1987-01-31 |
| CN85102113B true CN85102113B (en) | 1988-12-28 |
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ID=4792269
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN85102113A Expired CN85102113B (en) | 1985-04-01 | 1985-04-01 | Audio frequency transmission circuit formed by line-votage stabilizer type transmitting amplifier |
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| Country | Link |
|---|---|
| CN (1) | CN85102113B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7952333B2 (en) | 2005-06-01 | 2011-05-31 | Nxp B.V. | Circuit and method for determining current in a load |
| CN106444948B (en) * | 2016-11-01 | 2017-12-12 | 无锡思泰迪半导体有限公司 | A kind of voice coil motor driving chip offset current and maximum output current bearing calibration |
-
1985
- 1985-04-01 CN CN85102113A patent/CN85102113B/en not_active Expired
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| Publication number | Publication date |
|---|---|
| CN85102113A (en) | 1987-01-31 |
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