CA1088631A - Adaptive audio compressor - Google Patents
Adaptive audio compressorInfo
- Publication number
- CA1088631A CA1088631A CA343,218A CA343218A CA1088631A CA 1088631 A CA1088631 A CA 1088631A CA 343218 A CA343218 A CA 343218A CA 1088631 A CA1088631 A CA 1088631A
- Authority
- CA
- Canada
- Prior art keywords
- amplifier
- level
- audio
- signal
- input
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
- H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/02—Transmitters
- H04B1/04—Circuits
- H04B2001/0408—Circuits with power amplifiers
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
- Amplifiers (AREA)
Abstract
ADAPTIVE AUDIO COMPRESSOR
ABSTRACT
An amplitude modulated transmitter includes an audio amplifier which, via a radio frequency (RF) power supply modulator, modulates an RF amplifier and carrier. Fluctua-tions in the direct current DC bias to the RF amp, such as are common in mobile applications, vary the modulation index of the transmitted signal.
To minimize DC bias affects on the modulation index, the invention contemplates an audio compressor which senses both audio signal level and DC bias level and, in response thereto, controls audio signal compression to maintain the desired percent modulation. Compression is effected by changing the bias on a semiconductor device which, in turn, attenuates audio signals at the input of a fixed gain audio amplifier. A feedback path around the audio amplifier senses both DC voltage and audio signal level and produces an appropriate control signal to bias the semiconductor device, thereby altering audio compression.
ABSTRACT
An amplitude modulated transmitter includes an audio amplifier which, via a radio frequency (RF) power supply modulator, modulates an RF amplifier and carrier. Fluctua-tions in the direct current DC bias to the RF amp, such as are common in mobile applications, vary the modulation index of the transmitted signal.
To minimize DC bias affects on the modulation index, the invention contemplates an audio compressor which senses both audio signal level and DC bias level and, in response thereto, controls audio signal compression to maintain the desired percent modulation. Compression is effected by changing the bias on a semiconductor device which, in turn, attenuates audio signals at the input of a fixed gain audio amplifier. A feedback path around the audio amplifier senses both DC voltage and audio signal level and produces an appropriate control signal to bias the semiconductor device, thereby altering audio compression.
Description
2 0 BACKGROUND OF THE INVENTION
This invention relates to electronic signal compressors and, more particularly, to an audio compressor for use in an-amplitude modulated transmitter.
Compression amplifiers are well known in the art. Such amplifiers are commonly used in audio signal applications wherein the dynamic range of an audio signal must be compressed to adapt the signal to a particular function. For example, audio compressors are used in the recording of music on tape and on phonograph disc. In particular, audio compressors . . , ,. , ' .-. .
,: .-- .
.
: ' ~CM-76699 lU88631 are utilized in radio frequency signal transmitters to maintain a given index of modulation in the RF signal.
Thus, amplitude modulated radio frequency transmitters are known to employ audio compressors as an attempt to maintain the percentage modulation within a given maximum.
A problem suffered with prior art amplitude modulated transmitters which employ audio compressors is that the modulation index is a function of ~C bias to the radio fre-guency amplification stage. Generally, as the DC bias to a class C RF amplifier decreases, a given audio signal will modulate the RF amplifier to a higher modulation index.
Conversely, as the DC bias voltage increases, percent modula-tion decreases. This problem is particularly acute in mobile operated transmitters wherein the DC bias voltage may undergo a substantial change in value.
.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide an improved audio compressor whose compression characteristic ;~;
is adaptive to a changing DC bias potential.
It is a particular object of this invention to provide an above described audio compressor for use in a mobile, amplitude modulated transmitter to provide a constant percent modulation.
Briefly, according to the invention, a signal processor which is responsive to a DC voltage includes an amplifier which accepts AC signals at its input and reproduces them with a fixed gain at its output. An attenuator is located !
at the input of the amplifier for controlling the level bf AC signals at the amplifier input responsive to a control signal. A first circuit senses the level of the DC voltage and produces a sense signal representative thereof. A
.' 108~3631 second circuit senses the level of the AC signals produced at the output of the amplifier and develops a corresponding representative signal. The signals from the first and second circuits are processed through a control signal means which develops a predetermined control signal in response thereto.
This control signal is coupled to the attenuator by coupling means whereby the level of AC signals at the amplifier input, and thereby output, are controlled responsive to both the AC
signal level and the DC bias potential.
More particularly, there is provided in an AM
transmitter wherein an audio signal modulates an RF carrier, and wherein the percent modulation of the RF carrier is a function of a DC supply voltage, the improvement comprising:
a means for sensing the level of the DC supply -voltage, and means for sensing the audio signal level and adjusting the audio level in response to both the sensed DC
supply voltage and sensed audio signal level to maintain a substantially constant percent modulation level and the percent modulation within a given maximum limit, wherein the ratio of the audio signal level to the DC supply voltage level is maintained at a substantially constant level despite variations in the DC supply voltage level.
In an AM transmitter described in the previous paragraph, there is further provided an audio amplifier, having an input and an output, for receiving an audio signal at its input, amplifying the received signal by a fixed gain factor and producing the amplified signal at the output;
a voltage divider having a pair of series connected resistors, the free end of one resistor connected to the DC
supply voltage, the free end of the remaining resistor connected to the amplifier output;
- 1088631.
a means for rectifying and filtering AC signals produced at the common connection of the resistors;
a feedback amplifier having an input, an output and a predetermined activation level, the feedback amplifier output remaining in a constant state for input signals below the acti-vation level, the feedback amplifier otherwise processing signals at its input to produce a predetermined output signal corresponding to the input signal;
a means for coupling the common connection of the resistors and the rectified and filtered AC signals to the input of the feedback amplifier such that the amplifier remains in its constant state over a given range of DC and rectified AC signals;
a signal controlled attenuator for controlling the magnitude of the input signals to the amplifier in response to :~
received control signals; and a means for coupling the output signal from the feedback amplifier to the attenuator for controlling the attenu-ation thereof, such that when the feedback amplifier is in its constant state the attenuator is at minimum attenuation, the attenuator increasing in attenuation for increasing feedback ~
amplifier input signals above the activation state. ~:
BRIEF DESCRIPTION OF THE DRAWING
The attached figure is a schematic diagram of an .
amplitude modulated transmitter which includes the adaptive compressor according to the invention. :
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
The figure illustrates an amplitude modulated trans-mitter, especially suited to mobile applications, wherein audio signals to be transmitted over an RF carrier are generated via a microphone 12. The audio signals are thereafter pre-', .
, . ' .
iO~8631amplified by amplifier 14, further ampli'ied by audio ampli-fier 16 and capacitively coupled through capacitor 18 to the primary wi.~ding 22 of.a power supply modulating.trans'ormer 20. The modulating transformer 20 secondary winding 24 couples between a direct current (DC) supply bias A+ and a DC bias input 28 of an RF power amplifier 26.
The RF power amplifier 26 normally produces at its output terminal an RF carrier which is generated by an oscillator 30 and amplified by an exciter 32 before being passed to the input of the RF power amplifier 26. Audio `CM-76699 ~ 088631 signals on the primary 22 of transformer 20 modulate the bias A+ to the RF power amplifier 26 whereby the output from the RF power amplifier is an amplitude modulated RF carrier.
The amplitude modulated carrier is filtered via a scrape filter 34 which is tuned to pass only those signals in the desired passband thereby rejecting out of band signals generated through nonlinearities in the system. The output of the filter drives an antenna 38.
Inherent within this amplitude modulating scheme is the fact that the value of DC bias A~ at the DC bias input 28 of RF amplifier 26 causes a variance in the modulation of the RF carrier. Thus, especially in mobile applications wherein the DC bias A+ tends to vary, the percent modulation is very DC bias dependent. This is undesireable in that there are prescribed limits for percent modulation, and that an improved signal can be recovered at the receiver if the percent modulation remains constant.
To compensate for DC bias supply variations, an improved compressor utilizing a feedback circuit 40 is employed. The input to the compressor is taken off of a voltage divider which is comprised of a pair of series connected resistors 42, 44.The free end of resistor 42 connects to the DC bias A+ whereas the free end of resistor 44 connects to the output of audio amplifier 16 and, therefore, to the primary 22 of transformer 20. The connection is made on the negative side of capacitor 18 and, therefore, since the primary 22 of transformer 20 connects to ground potential, the free end of resistor 44 is essentially connected to ground for DC analysis purposes. The common connection 46 of the resïstors produce a DC voltage which is representative of the DC bias potential A+ voltage, and an AC voltage which is representative of the .. ~ .
~, .
.
.
, 76699 ~ ~ ~31 AC.signal level at the output of amplifier 16. Thus, the vol-tage at connection 46 can be expressed as follows:
R44 A+ Vac 42 where Va is the level of AC voltage at the primary 22 of transformer 20. The AC signals are rectified by a rectifier 48 and filtered by a capacitor 50. This resultant DC voltage . is applied through diode 48 to the input of an amplifier 52.
Amplifier 52 is comprised of a pair of NPN transistors 54, 56, whereby transistor 54 is connected in a common emitter configuration, with transistor 56 acting as a voltage follower.
Both transistors include load resistors which couple to a common bias resistor which connects to a bias potential, and transistor 54 is provided with an emitter resistor col1pled to ground potential. The output from the amplifier 52 is taken at the emitter of transistor 56 and is filtered by a filter capacitor 58 and applied via a voltage divider, comprised of a series resistor 60 and a shunt resistor 62, to the base terminal of an attenuator transistor 64. Attenua-tor transistor 64 has its collector connected to the input terminal of the amplifier 16, and its emitter connected to ground potential. Control signals at the base of transistor 64 cause the attenuator to either increase or decrease in . .
impedance thereby increasing or decreasing, respectively, the AC input signals to amplifier 16. Thus, the level of AC
signals appearing at the output of amplifier 16, and the primary of transformer 20, is dependent on the control signal appearing at the base of *ransistor 64, which is in turn dependent on amplifier 52 and the sense voltages appear-ing at the common connection 46 of the voltage divlder 42, 44. A feedback resis-tor 66 is provided from the output of the amplifier 52 to its input p.~ovidlng a reference DC bias level to the base of transistor 54 which causes approximately 1.0 volt to appear at the emitter of transistor 56. Resistors 60 and 62 voltage divide the 1 volt to a level which in insuf-ficient to turn on attenuator 64.
For voltages at the base of transistor 59 which are ' about its reference bias level, thc amplifier produces this ' constant 1.0 volt level at its output. However, for applied control ~oltages at the base of transistor 54 which are less than the reference bias level, an increased voltage appears at the emitter of transistor 56 causing an increased conduction of transistor 64 and increased attenuation of the signals of .
the input at amplifier 16.
By approximating the threshold voltage at the common connection 46 at which transistor 54 will begin turning off ~ ' as zero volts, the above equation can be rearranged where:
- V = 44 . A+
ac Hence, the compressor process is directly dependent on the DC bias potential level~A+. By selecting the resistor ratio of R44 to R42 any desired AC voltage.Vac may be developed -to correspond to a given DC supply bias potential A+.
With the adaptive feedback loop 40, as the DC bias potential A+ increases thus tending to cause a, decrease of the modulation ---' index for the same level of audio input signal, the system reacts by increasing the voltage at the base of transistor 54 thus requiring a larger AC signal at the output of amplifier 16 to begin compression. The result is an increased audio ~
- signal at the output of amplifier 16 which exactly compensates for the increase in DC bias potential A+ thereby maintaining the modulation index. Conversely, as DC bias potential A+
decreases, the voltage at the base of transistor 54 is ~ ' biased closer to cutoff, whereby the control signal on transistor 64 reduces the collector impedance thereof, thereby decreasing the audio signal level at the output of amplifier 16.
It should be noted that the compressor circuit auto-matically varies the compression level dependent upon the power supply A+ level without changing the compression range. Further, the circuit is largely temperature insensi-tive since changes in the turn-on voltage of transistor 54 are compensated by a corresponding change in diode 48. ~:
In summary, an improved audio compressor has been described which responds to changes in the DC bias level to thereby alter the compression characteristic. In the pre-ferred embodiment of the invention, the improved compressoris shown to have superior performance in maintaining the modulatiol index of an amplitude modulated transmitter at a substantially constant level.
- - _ .
' ~ .
,.
: !' , .
This invention relates to electronic signal compressors and, more particularly, to an audio compressor for use in an-amplitude modulated transmitter.
Compression amplifiers are well known in the art. Such amplifiers are commonly used in audio signal applications wherein the dynamic range of an audio signal must be compressed to adapt the signal to a particular function. For example, audio compressors are used in the recording of music on tape and on phonograph disc. In particular, audio compressors . . , ,. , ' .-. .
,: .-- .
.
: ' ~CM-76699 lU88631 are utilized in radio frequency signal transmitters to maintain a given index of modulation in the RF signal.
Thus, amplitude modulated radio frequency transmitters are known to employ audio compressors as an attempt to maintain the percentage modulation within a given maximum.
A problem suffered with prior art amplitude modulated transmitters which employ audio compressors is that the modulation index is a function of ~C bias to the radio fre-guency amplification stage. Generally, as the DC bias to a class C RF amplifier decreases, a given audio signal will modulate the RF amplifier to a higher modulation index.
Conversely, as the DC bias voltage increases, percent modula-tion decreases. This problem is particularly acute in mobile operated transmitters wherein the DC bias voltage may undergo a substantial change in value.
.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide an improved audio compressor whose compression characteristic ;~;
is adaptive to a changing DC bias potential.
It is a particular object of this invention to provide an above described audio compressor for use in a mobile, amplitude modulated transmitter to provide a constant percent modulation.
Briefly, according to the invention, a signal processor which is responsive to a DC voltage includes an amplifier which accepts AC signals at its input and reproduces them with a fixed gain at its output. An attenuator is located !
at the input of the amplifier for controlling the level bf AC signals at the amplifier input responsive to a control signal. A first circuit senses the level of the DC voltage and produces a sense signal representative thereof. A
.' 108~3631 second circuit senses the level of the AC signals produced at the output of the amplifier and develops a corresponding representative signal. The signals from the first and second circuits are processed through a control signal means which develops a predetermined control signal in response thereto.
This control signal is coupled to the attenuator by coupling means whereby the level of AC signals at the amplifier input, and thereby output, are controlled responsive to both the AC
signal level and the DC bias potential.
More particularly, there is provided in an AM
transmitter wherein an audio signal modulates an RF carrier, and wherein the percent modulation of the RF carrier is a function of a DC supply voltage, the improvement comprising:
a means for sensing the level of the DC supply -voltage, and means for sensing the audio signal level and adjusting the audio level in response to both the sensed DC
supply voltage and sensed audio signal level to maintain a substantially constant percent modulation level and the percent modulation within a given maximum limit, wherein the ratio of the audio signal level to the DC supply voltage level is maintained at a substantially constant level despite variations in the DC supply voltage level.
In an AM transmitter described in the previous paragraph, there is further provided an audio amplifier, having an input and an output, for receiving an audio signal at its input, amplifying the received signal by a fixed gain factor and producing the amplified signal at the output;
a voltage divider having a pair of series connected resistors, the free end of one resistor connected to the DC
supply voltage, the free end of the remaining resistor connected to the amplifier output;
- 1088631.
a means for rectifying and filtering AC signals produced at the common connection of the resistors;
a feedback amplifier having an input, an output and a predetermined activation level, the feedback amplifier output remaining in a constant state for input signals below the acti-vation level, the feedback amplifier otherwise processing signals at its input to produce a predetermined output signal corresponding to the input signal;
a means for coupling the common connection of the resistors and the rectified and filtered AC signals to the input of the feedback amplifier such that the amplifier remains in its constant state over a given range of DC and rectified AC signals;
a signal controlled attenuator for controlling the magnitude of the input signals to the amplifier in response to :~
received control signals; and a means for coupling the output signal from the feedback amplifier to the attenuator for controlling the attenu-ation thereof, such that when the feedback amplifier is in its constant state the attenuator is at minimum attenuation, the attenuator increasing in attenuation for increasing feedback ~
amplifier input signals above the activation state. ~:
BRIEF DESCRIPTION OF THE DRAWING
The attached figure is a schematic diagram of an .
amplitude modulated transmitter which includes the adaptive compressor according to the invention. :
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT OF THE INVENTION
The figure illustrates an amplitude modulated trans-mitter, especially suited to mobile applications, wherein audio signals to be transmitted over an RF carrier are generated via a microphone 12. The audio signals are thereafter pre-', .
, . ' .
iO~8631amplified by amplifier 14, further ampli'ied by audio ampli-fier 16 and capacitively coupled through capacitor 18 to the primary wi.~ding 22 of.a power supply modulating.trans'ormer 20. The modulating transformer 20 secondary winding 24 couples between a direct current (DC) supply bias A+ and a DC bias input 28 of an RF power amplifier 26.
The RF power amplifier 26 normally produces at its output terminal an RF carrier which is generated by an oscillator 30 and amplified by an exciter 32 before being passed to the input of the RF power amplifier 26. Audio `CM-76699 ~ 088631 signals on the primary 22 of transformer 20 modulate the bias A+ to the RF power amplifier 26 whereby the output from the RF power amplifier is an amplitude modulated RF carrier.
The amplitude modulated carrier is filtered via a scrape filter 34 which is tuned to pass only those signals in the desired passband thereby rejecting out of band signals generated through nonlinearities in the system. The output of the filter drives an antenna 38.
Inherent within this amplitude modulating scheme is the fact that the value of DC bias A~ at the DC bias input 28 of RF amplifier 26 causes a variance in the modulation of the RF carrier. Thus, especially in mobile applications wherein the DC bias A+ tends to vary, the percent modulation is very DC bias dependent. This is undesireable in that there are prescribed limits for percent modulation, and that an improved signal can be recovered at the receiver if the percent modulation remains constant.
To compensate for DC bias supply variations, an improved compressor utilizing a feedback circuit 40 is employed. The input to the compressor is taken off of a voltage divider which is comprised of a pair of series connected resistors 42, 44.The free end of resistor 42 connects to the DC bias A+ whereas the free end of resistor 44 connects to the output of audio amplifier 16 and, therefore, to the primary 22 of transformer 20. The connection is made on the negative side of capacitor 18 and, therefore, since the primary 22 of transformer 20 connects to ground potential, the free end of resistor 44 is essentially connected to ground for DC analysis purposes. The common connection 46 of the resïstors produce a DC voltage which is representative of the DC bias potential A+ voltage, and an AC voltage which is representative of the .. ~ .
~, .
.
.
, 76699 ~ ~ ~31 AC.signal level at the output of amplifier 16. Thus, the vol-tage at connection 46 can be expressed as follows:
R44 A+ Vac 42 where Va is the level of AC voltage at the primary 22 of transformer 20. The AC signals are rectified by a rectifier 48 and filtered by a capacitor 50. This resultant DC voltage . is applied through diode 48 to the input of an amplifier 52.
Amplifier 52 is comprised of a pair of NPN transistors 54, 56, whereby transistor 54 is connected in a common emitter configuration, with transistor 56 acting as a voltage follower.
Both transistors include load resistors which couple to a common bias resistor which connects to a bias potential, and transistor 54 is provided with an emitter resistor col1pled to ground potential. The output from the amplifier 52 is taken at the emitter of transistor 56 and is filtered by a filter capacitor 58 and applied via a voltage divider, comprised of a series resistor 60 and a shunt resistor 62, to the base terminal of an attenuator transistor 64. Attenua-tor transistor 64 has its collector connected to the input terminal of the amplifier 16, and its emitter connected to ground potential. Control signals at the base of transistor 64 cause the attenuator to either increase or decrease in . .
impedance thereby increasing or decreasing, respectively, the AC input signals to amplifier 16. Thus, the level of AC
signals appearing at the output of amplifier 16, and the primary of transformer 20, is dependent on the control signal appearing at the base of *ransistor 64, which is in turn dependent on amplifier 52 and the sense voltages appear-ing at the common connection 46 of the voltage divlder 42, 44. A feedback resis-tor 66 is provided from the output of the amplifier 52 to its input p.~ovidlng a reference DC bias level to the base of transistor 54 which causes approximately 1.0 volt to appear at the emitter of transistor 56. Resistors 60 and 62 voltage divide the 1 volt to a level which in insuf-ficient to turn on attenuator 64.
For voltages at the base of transistor 59 which are ' about its reference bias level, thc amplifier produces this ' constant 1.0 volt level at its output. However, for applied control ~oltages at the base of transistor 54 which are less than the reference bias level, an increased voltage appears at the emitter of transistor 56 causing an increased conduction of transistor 64 and increased attenuation of the signals of .
the input at amplifier 16.
By approximating the threshold voltage at the common connection 46 at which transistor 54 will begin turning off ~ ' as zero volts, the above equation can be rearranged where:
- V = 44 . A+
ac Hence, the compressor process is directly dependent on the DC bias potential level~A+. By selecting the resistor ratio of R44 to R42 any desired AC voltage.Vac may be developed -to correspond to a given DC supply bias potential A+.
With the adaptive feedback loop 40, as the DC bias potential A+ increases thus tending to cause a, decrease of the modulation ---' index for the same level of audio input signal, the system reacts by increasing the voltage at the base of transistor 54 thus requiring a larger AC signal at the output of amplifier 16 to begin compression. The result is an increased audio ~
- signal at the output of amplifier 16 which exactly compensates for the increase in DC bias potential A+ thereby maintaining the modulation index. Conversely, as DC bias potential A+
decreases, the voltage at the base of transistor 54 is ~ ' biased closer to cutoff, whereby the control signal on transistor 64 reduces the collector impedance thereof, thereby decreasing the audio signal level at the output of amplifier 16.
It should be noted that the compressor circuit auto-matically varies the compression level dependent upon the power supply A+ level without changing the compression range. Further, the circuit is largely temperature insensi-tive since changes in the turn-on voltage of transistor 54 are compensated by a corresponding change in diode 48. ~:
In summary, an improved audio compressor has been described which responds to changes in the DC bias level to thereby alter the compression characteristic. In the pre-ferred embodiment of the invention, the improved compressoris shown to have superior performance in maintaining the modulatiol index of an amplitude modulated transmitter at a substantially constant level.
- - _ .
' ~ .
,.
: !' , .
Claims (5)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. In an AM transmitter wherein an audio signal modulates an RF carrier, and wherein the percent modulation of the RF carrier is a function of a DC supply voltage, the improvement comprising:
a means for sensing the level of the DC supply vol-tage, and means for sensing the audio signal level and adjusting the audio level in response to both the sensed DC supply voltage and sensed audio signal level to maintain a substantially con-stant percent modulation level and the percent modulation within a given maximum limit, wherein the ratio of the audio signal level to the DC supply voltage level is maintained at a substantially constant level despite variations in the DC supply voltage level.
a means for sensing the level of the DC supply vol-tage, and means for sensing the audio signal level and adjusting the audio level in response to both the sensed DC supply voltage and sensed audio signal level to maintain a substantially con-stant percent modulation level and the percent modulation within a given maximum limit, wherein the ratio of the audio signal level to the DC supply voltage level is maintained at a substantially constant level despite variations in the DC supply voltage level.
2. The improvement of claim 1 comprising:
an audio amplifier, having an input and an output, for receiving an audio signal at its input, amplifying the received signal by a fixed gain factor and producing the ampli-fied signal at the output;
a voltage divider having a pair of series connected resistors, the free end of one resistor connected to the DC
supply voltage, the free end of the remaining resistor connected to the amplifier output;
a means for rectifying and filtering AC signals pro-duced at the common connection of the resistors;
a feedback amplifier having an input, an output and a predetermined activation level, the feedback amplifier output remaining in a constant state for input signals below the acti-vation level, the feedback amplifier otherwise processing sig-nals at its input to produce a predetermined output signal cor-responding to the input signal;
a means for coupling the common connection of the resistors and the rectified and filtered AC signals to the input of the feedback amplifier such that the amplifier remains in its constant state over a given range of DC and rectified AC signals;
a signal controlled attenuator for controlling the magnitude of the input signals to the amplifier in response to received control signals; and a means for coupling the output signal from the feed-back amplifier to the attenuator for controlling the attenuation thereof, such that when the feedback amplifier is in its con-stant state the attenuator is at minimum attenuation, the attenuator increasing in attenuation for increasing feedback amplifier input signals above the activation state.
an audio amplifier, having an input and an output, for receiving an audio signal at its input, amplifying the received signal by a fixed gain factor and producing the ampli-fied signal at the output;
a voltage divider having a pair of series connected resistors, the free end of one resistor connected to the DC
supply voltage, the free end of the remaining resistor connected to the amplifier output;
a means for rectifying and filtering AC signals pro-duced at the common connection of the resistors;
a feedback amplifier having an input, an output and a predetermined activation level, the feedback amplifier output remaining in a constant state for input signals below the acti-vation level, the feedback amplifier otherwise processing sig-nals at its input to produce a predetermined output signal cor-responding to the input signal;
a means for coupling the common connection of the resistors and the rectified and filtered AC signals to the input of the feedback amplifier such that the amplifier remains in its constant state over a given range of DC and rectified AC signals;
a signal controlled attenuator for controlling the magnitude of the input signals to the amplifier in response to received control signals; and a means for coupling the output signal from the feed-back amplifier to the attenuator for controlling the attenuation thereof, such that when the feedback amplifier is in its con-stant state the attenuator is at minimum attenuation, the attenuator increasing in attenuation for increasing feedback amplifier input signals above the activation state.
3. The improvement of claim 2 further comprising:
a DC biased RF amplifier for carrying the RF carrier;
and a modulation transformer having a primary winding coupled between the output of the audio amplifier and a reference potential and a secondary winding coupled between the DC supply voltage and the RF amplifier for supplying DC
bias thereto, whereby audio signals on the transformer primary modulate the RF carrier.
a DC biased RF amplifier for carrying the RF carrier;
and a modulation transformer having a primary winding coupled between the output of the audio amplifier and a reference potential and a secondary winding coupled between the DC supply voltage and the RF amplifier for supplying DC
bias thereto, whereby audio signals on the transformer primary modulate the RF carrier.
4. The improvement of claim 1 further comprising temperature compensating means for maintaining a substantially constant percent modulation level over variations in temperature which result in changes in the turn-on voltage of switching means which initiate the adjusting of the level of the audio signal.
5. The improvement of claim 2 further comprising temperature compensating means for maintaining the ratio of the amplitude of the AC signal at the amplifier output to the DC
voltage level substantially constant over variations in tempera-ture which result in changes in the turn-on voltage (activation level) of the feedback amplifier.
voltage level substantially constant over variations in tempera-ture which result in changes in the turn-on voltage (activation level) of the feedback amplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA343,218A CA1088631A (en) | 1976-03-25 | 1980-01-08 | Adaptive audio compressor |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/670,505 US4110699A (en) | 1976-03-25 | 1976-03-25 | Adaptive audio compressor |
| CA269,933A CA1079362A (en) | 1976-03-25 | 1977-01-18 | Adaptive audio compressor |
| CA343,218A CA1088631A (en) | 1976-03-25 | 1980-01-08 | Adaptive audio compressor |
| US670,505 | 1984-11-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088631A true CA1088631A (en) | 1980-10-28 |
Family
ID=27164880
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA343,218A Expired CA1088631A (en) | 1976-03-25 | 1980-01-08 | Adaptive audio compressor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088631A (en) |
-
1980
- 1980-01-08 CA CA343,218A patent/CA1088631A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4602218A (en) | Automatic output control circuitry for RF power amplifiers with wide dynamic range | |
| CA2094133C (en) | Linear gain control amplifier | |
| US5530923A (en) | Dual mode transmission system with switched linear amplifier | |
| US5107225A (en) | High dynamic range closed loop automatic gain control circuit | |
| US5038112A (en) | Levelling control circuit | |
| US5283536A (en) | High dynamic range closed loop automatic gain control circuit | |
| US3967219A (en) | Signal compressors and expanders | |
| CA2154530A1 (en) | Mobile communication device having an output power sensor succeeding a transmission filter | |
| US4216427A (en) | Adaptive audio compressor | |
| US4110692A (en) | Audio signal processor | |
| US4617522A (en) | Temperature regulated feedforward amplifier | |
| US4060764A (en) | Transceiver audio system | |
| US4366450A (en) | Automatic gain control circuit | |
| US4110699A (en) | Adaptive audio compressor | |
| CA1186024A (en) | Automatic gain control of a single gate gaas fet amplifier | |
| CA1088631A (en) | Adaptive audio compressor | |
| US4085389A (en) | Amplitude modulation circuit | |
| US3769612A (en) | Compressing andor expanding circuit having non linear control circuitto reduce modulation noise | |
| US4041390A (en) | Transceiver squelch circuit | |
| US4375618A (en) | Linearized FM quadrature detector | |
| JPS6234168B2 (en) | ||
| US4247948A (en) | Automatic modulation control in transmitter | |
| US3740670A (en) | Integral rf modamp | |
| US4038603A (en) | Transmitter modulation limiter | |
| KR810000752B1 (en) | Adaptive audio compressor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |