1. An audio amplifier apparatus, suitable for driving a loudspeaker, the audio amplifier apparatus comprising:
a soft charge unit, coupled to the loudspeaker through an output terminal, and supplying a driving current according to a first control signal to soft charge the loudspeaker, so as to gradually increase a voltage level on the output terminal;
a first amplification module, coupled to the output terminal, receiving an audio signal according to the first control signal, and amplifying the audio signal to output a first amplified signal for driving the loudspeaker, wherein the first amplification module comprises:
a first amplifier, having an input terminal and an output terminal, wherein the input terminal of the first amplifier receives the audio signal, and the output terminal of the first amplifier outputs the first amplified signal; and
a first capacitor, having a first end and a second end, wherein the first end of the first capacitor is coupled to the input terminal of the first amplifier, and the second end of the first capacitor is coupled to the output terminal of the first amplifier;
a second amplification module, coupled to the output terminal, receiving the audio signal according to a second control signal, and amplifying the audio signal to output a second amplified signal for driving the loudspeaker,
wherein the soft charge unit generates the second control signal by comparing the voltage level on the output terminal with a predetermined voltage level,
wherein when the voltage level on the output terminal is smaller than the predetermined voltage level, only the first amplification module amplifies the audio signal in response to the first control signal to output the first amplified signal for driving the loudspeaker,
wherein when the voltage level on the output terminal reaches the predetermined voltage level, only the second amplification module amplifies the audio signal in response to the second control signal to output the second amplified signal for driving the loudspeaker;
a first resistor, having a first end and a second end, wherein the first end of the first resistor is coupled to the output terminal of the first amplifier;
a first switch, having a first terminal and a second terminal, and turned on or off according to the first control signal, wherein the first terminal of the first switch receives the audio signal, and the second terminal of the first switch is coupled to the input terminal of the first amplifier and the first end of the first capacitor; and
a second switch, having a first terminal and a second terminal, and turned on or off according to the first control signal, wherein the first terminal of the second switch is coupled to the second end of the first resistor, and the second terminal of the second switch is coupled to the output terminal of the first amplifier,
wherein when the voltage level on the output terminal is not equal to the predetermined voltage level, the first switch and the second switch are turned on according to the first control signal, and when the voltage level on the output terminal is equal to the predetermined voltage level, the first switch and the second switch are turned off according to the first control signal.
2. The audio amplifier apparatus according to claim 1, wherein a driving capability of the first amplification module is lower than a driving capability of the second amplification module.
3. The audio amplifier apparatus according to claim 1, wherein the predetermined voltage level is equal to 1N of a voltage level of a supply voltage received by the audio amplifier apparatus, wherein N is a positive real number not smaller than 1.
4. The audio amplifier apparatus according to claim 1, wherein when the soft charge unit determines that the voltage level on the output terminal is equal to the predetermined voltage level, the soft charge unit enables the second control signal to allow the second amplification module to receive the audio signal, so as to generate the second amplified signal.
5. The audio amplifier apparatus according to claim 4, wherein when the second control signal is enabled, the first control signal is disabled so that the soft charge unit stops soft charging the loudspeaker and the first amplification module stops receiving the audio signal.
6. The audio amplifier apparatus according to claim 1, wherein the second amplification module comprises:
a second amplifier, having an input terminal and an output terminal, wherein the input terminal of the second amplifier receives the audio signal, and the output terminal of the second amplifier outputs the second amplified signal; and
a second capacitor, having a first end and a second end, wherein the first end of the second capacitor is coupled to the input terminal of the second amplifier, and the second end of the second capacitor is coupled to the output terminal of the second amplifier.
7. The audio amplifier apparatus according to claim 6, wherein the second amplification module further comprises:
a third switch, having a first terminal and a second terminal, and turned on or off according to the second control signal, wherein the first terminal of the third switch receives the audio signal, and the second terminal of the third switch is coupled to the input terminal of the second amplifier and the first end of the second capacitor,
wherein when the voltage level on the output terminal is not equal to the predetermined voltage level, the third switch is turned off according to the second control signal, and when the voltage level on the output terminal is equal to the predetermined voltage level, the third switch is turned on according to the second control signal.
8. The audio amplifier apparatus according to claim 6 further comprising:
a first feedback resistor, having a first end and a second end, wherein the first end of the first feedback resistor receives the audio signal, and the second end of the first feedback resistor is coupled to the input terminals of the first amplifier and the second amplifier; and
a second feedback resistor, having a first end and a second end, wherein the first end of the second feedback resistor is coupled to the second end of the first feedback resistor and the input terminals of the first amplifier and the second amplifier, and the second end of the second feedback resistor is coupled to the soft charge unit and the output terminals of the first amplifier and the second amplifier.
9. The audio amplifier apparatus according to claim 6 further comprising:
a pre-amplifier, having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the pre-amplifier is coupled to the output terminal, the second input terminal of the pre-amplifier is coupled to a predetermined voltage, and the output terminal of the pre-amplifier is coupled to the first amplification module and the second amplification module.
10. The audio amplifier apparatus according to claim 1, wherein the soft charge unit comprises:
a current source, supplying the driving current according to a supply voltage;
a first soft charge switch, having a first terminal and a second terminal, and turned on or off according to the first control signal, wherein the first terminal of the first soft charge switch is coupled to the current source;
a delay capacitor, having a first end and a second end, wherein the first end of the delay capacitor is coupled to the second terminal of the first soft charge switch, and the second end of the delay capacitor is coupled to a ground voltage; and
a delay resistor, having a first end and a second end, wherein the first end of the delay resistor is coupled to the second terminal of the first soft charge switch and the first end of the delay capacitor, and the second end of the delay resistor is coupled to the first amplification module and the second amplification module,
wherein when the first soft charge switch is turned on according to the first control signal, the driving current gradually increases the voltage level on the output terminal by the delay capacitor and the delay resistor.
11. The audio amplifier apparatus according to claim 10, wherein the soft charge unit further comprises:
a second soft charge switch, having a first terminal and a second terminal, and turned on or off according to the first control signal, wherein the first terminal of the second soft charge switch is coupled to the second end of the delay resistor, and the second terminal of the second soft charge switch is coupled to the output terminal.
12. The audio amplifier apparatus according to claim 11, wherein when the soft charge unit determines that the voltage level on the output terminal is not equal to the predetermined voltage level, the first soft charge switch and the second soft charge switch are turned on according to the first control signal, and when the soft charge unit determines that the voltage level on the output terminal is equal to the predetermined voltage level, the first soft charge switch and the second soft charge switch are turned off according to the first control signal.
13. The audio amplifier apparatus according to claim 11, wherein the soft charge unit further comprises:
a comparator, having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the comparator is coupled to a predetermined voltage, the second input terminal of the comparator is coupled to the second terminal of the second soft charge switch and the output terminal, and the output terminal of the comparator outputs a comparison signal, wherein the comparator generates the comparison signal according to a comparison result between the voltage level on the output terminal and the predetermined voltage level; and
a latch, coupled to the output terminal of the comparator, and generating the second control signal by latching the comparison signal.
14. The audio amplifier apparatus according to claim 1, wherein the first control signal and the second control signal are inverse to each other.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An apparatus for measuring electrical isolation between a plurality of POE (Power-Over-Ethernet) conductors in a POE system and earth ground, the apparatus comprising:
an alternating current (AC) generator having a first terminal and a second terminal;
a capacitor having a first terminal coupled to at least one of the POE conductors which normally has high isolation from earth ground and having a second terminal coupled to the first terminal the AC generator;
a current-to-voltage converter having a first terminal coupled to the second terminal of the AC generator having a second terminal coupled to earth ground, and having a third terminal for providing an AC voltage representative of the AC current flowing in the series connected AC generator, capacitor, and current-to-voltage converter;
an AC detector having a first terminal coupled to the third terminal of the current-to-voltage converter and having a second terminal for providing a direct current (DC) voltage representative of the AC current flowing in the series connected AC generator, capacitor, and current-to-voltage converter; and
a comparator having a first terminal coupled to the second terminal of the AC detector, having a second terminal coupled to a reference voltage source, and having a third terminal, wherein the comparator is adapted to change a voltage state of the third terminal as the voltage at the first terminal of the comparator goes above and below the reference voltage at the second terminal of the comparator, and wherein, in a condition of high isolation between the POE conductors and earth ground, the AC current flow in the series connected AC generator, capacitor, and current-to-voltage converter is below the comparison threshold set by the reference voltage such that the comparator output is indicative of high isolation and wherein, in a condition of reduced isolation between the POE conductor and earth ground, the AC current flow in the series connected AC generator, capacitor, and current-to-voltage converter is above the comparison threshold set by the reference voltage such that the comparator output is indicative of isolation loss.
2. The apparatus of claim 1, wherein the current-to-voltage converter is a transformer.
3. The apparatus of claim 1, wherein the current-to-voltage converter is a resistor.
4. The apparatus of claim 1, wherein the apparatus further comprises a second comparator having a first terminal coupled to the second terminal of the AC detector, having a second terminal coupled to a second reference voltage, and having a third terminal, wherein the second comparator is adapted to change a voltage state of the third terminal as the voltage at the first terminal of the second comparator goes above and below a second reference voltage at the second terminal of the second comparator, wherein the amplitude of the detected AC voltage is compared to the threshold of the second comparator to monitor operational condition of the isolation loss detector circuitry.
5. The apparatus of claim 1, wherein the apparatus further comprises:
a low-pass filter having a first terminal coupled to the third terminal of the current-to-voltage converter and a second terminal; and
a synchronous rectifier having a first terminal coupled to a second terminal of the low-pass filter, wherein the AC voltage present at the output of the current-to-voltage converter is filtered to reduce interference, then converted to a DC voltage by synchronous rectification, and wherein the filtered and rectified signal is compared with a threshold voltage to determine if isolation loss has occurred.
6. The apparatus of claim 5, wherein the apparatus further comprises an integrator which averages the amplitude of the rectified voltage over many cycles of the AC generator, wherein interference from other AC signals at lower frequencies than the frequency of the AC generator is reduced.
7. An apparatus for measuring electrical isolation between a plurality of POE (Power-Over-Ethernet) conductors in a POE system and earth ground, the apparatus comprising:
an AC generator having a first terminal and a second terminal;
a first capacitor having a first terminal coupled to at least one of the POE conductors which normally has high isolation from earth ground and having a second terminal coupled to the first terminal of the AC generator;
a second capacitor having a first terminal coupled to the first terminal of the first capacitor and to the POE conductor;
an AC detector having a first terminal coupled to the second terminal of the second capacitor and having a second terminal for providing a DC voltage representative of the AC voltage present on the POE conductor; and
a comparator having a first terminal coupled to the second terminal of the AC detector, having a second terminal coupled to a reference voltage, and having a third terminal, wherein the comparator is adapted to change a voltage state of the third terminal as the voltage at the first terminal of the comparator goes above and below the reference voltage at the second terminal of the comparator, and wherein, in a condition of high isolation between the POE conductors and earth ground, the AC voltage present at the first terminal of the AC detector causes a DC voltage at the second terminal of the AC detector which is above the comparison threshold set by the reference voltage such that the comparator output is indicative of high isolation and wherein in a condition of reduced isolation between the POE conductor and earth ground, the AC voltage present at the first terminal of the AC detector causes a DC voltage at the second terminal of the AC detector which is below the comparison threshold set by the reference voltage such that the comparator output is indicative of isolation loss.
8. The apparatus of claim 7, wherein the apparatus further comprises:
a low-pass filter having a first terminal coupled to the second terminal of the second capacitor; and
a synchronous rectifier having a first terminal coupled to a second terminal of the low-pass filter, wherein the AC voltage present at the second terminal of the second capacitor is filtered to reduce interference, then converted to a DC voltage by synchronous rectification, and wherein the filtered and rectified signal is compared with a threshold voltage to determine if isolation loss has occurred.
9. The apparatus of claim 8, wherein the apparatus further comprises an integrator which averages the amplitude of the rectified voltage over many cycles of the AC generator, wherein interference from other AC signals at lower frequencies than the frequency of the AC generator is reduced.
10. A method for measuring electrical isolation between a plurality of conductors in a POE (Power-Over-Ethernet) system and earth ground, the method comprising:
injecting an alternating current into at least one of the conductors in the POE system, which current flows between earth ground and the at least one conductor in the POE system;
measuring the amplitude of the injected current;
comparing the amplitude of the injected current to a first reference threshold, wherein, under normal conditions of negligible isolation loss between the at least one conductor of the POE system and earth ground, the amplitude of the injected current is less than the first reference threshold, and in conditions of isolation loss, the injected current is greater than the first reference threshold, and wherein the state of the comparison is indicative of isolation loss.
11. The method of claim 10, wherein the method further comprises:
coupling bypass capacitance between the at least one conductor in the POE system and earth ground; and
comparing the amplitude of the injected current to another reference threshold which is lower than the first reference threshold, wherein, under normal conditions of negligible isolation loss but of increased flow of the injected alternating current caused by the bypass capacitance from the at least one conductor in the POE system to earth ground, the amplitude of the injected current is greater than a second reference threshold such that the state of the comparison to the second another reference threshold is indicative of proper operation of the isolation loss detection circuitry and wherein a decrease of the injected current below the second reference threshold is indicative of a failure of the isolation loss detection circuitry.
12. The method of claim 10, wherein the step of measuring the amplitude of the injected current further comprises:
converting a sample of the injected current to an AC voltage proportional to the injected current;
synchronously rectifying the AC voltage proportional to the injected current by commutating the AC voltage signal with a switching signal coupled from the generator of the injected current, the switching signal having the same frequency and a stable phase compared to the AC voltage proportional to the injected current; and
integrating over a time period the rectified output of the synchronously rectifying the AC voltage step, wherein a DC voltage responsive to the amplitude of the injected current is generated, and wherein noise on the injected current is rejected.
13. An apparatus for measuring electrical isolation between a plurality of POE (Power-Over-Ethernet) conductors in a POE system and earth ground, the apparatus comprising:
a transformer having primary and secondary windings, having a first primary terminal, having a second primary terminal coupled to earth ground, having a third secondary terminal, and having a fourth secondary terminal coupled to local system ground;
a capacitor having a first terminal coupled to at least one of the POE conductors which normally has high isolation from earth ground and having a second terminal coupled to the first primary terminal of the transformer;
an AC generator having a first terminal coupled to local system ground and having a second terminal coupled to a first terminal of a resistor;
a second terminal of the resistor coupled to the third secondary terminal of the transformer;
an AC detector having a first terminal coupled to the second terminal of the AC generator and the first terminal of the resistor, having a second terminal coupled to the second terminal of the resistor and the third secondary terminal of the transformer, and having a third output terminal upon which is present a DC voltage representative of the AC current flowing in the series connected AC generator, resistor and transformer secondary; and
a comparator having a first terminal coupled to the third output terminal of the AC detector, having a second terminal coupled to a reference voltage, and having a third terminal which changes voltage state as the voltage at the first terminal of the comparator goes above and below the reference voltage at the second terminal of the comparator, wherein, in a condition of high isolation between the POE conductors and earth ground, the impedance across the secondary winding of the transformer is relatively high, being responsive to the impedance across the primary winding of the transformer, causing a relatively low AC current to flow in the resistor and further causing the output of the AC detector to be below the comparison threshold set by the reference voltage such that the comparator output is indicative of high isolation, and wherein, in a condition of reduced isolation between the POE conductors and earth ground, the impedance across the secondary winding of the transformer is relatively low, being responsive to the impedance across the primary winding of the transformer, causing a relatively high AC current to flow in the resistor and further causing the output of the AC detector to be above the comparison threshold set by the reference voltage such that the comparator output is indicative of low isolation.
14. A method for measuring electrical isolation between a plurality of conductors in a POE (Power-Over-Ethernet) system and earth ground, comprising the steps:
coupling a first terminal of the primary of a transformer through a capacitor to conductors of the POE system,
coupling a second terminal of the primary of the transformer to earth ground, wherein the impedance of the secondary of the transformer is responsive to the impedance between at least one of the conductors of the POE system and earth ground;
coupling an AC signal through a series connection of the secondary of the transformer and a series resistor;
measuring the amplitude of the resulting AC voltage across the resistor;
comparing the amplitude of the AC voltage to a reference threshold, wherein, under normal conditions of negligible isolation loss between the at least one conductor of the POE system and the earth ground, the amplitude of the AC voltage is less than the reference threshold, and in conditions of isolation loss, the AC voltage is greater than the first reference threshold, and wherein the state of the comparison is indicative of isolation loss.