Current modulator with dynamic amplifier impedance compensation
First Claim
1. A current modulator to supply a modulated supply current to a power amplifier responsive to an amplitude modulation signal, the current modulator comprising:
- a modulation control circuit generating a modulation control signal responsive to the amplitude modulation signal;
an output circuit generating the modulated supply current responsive to the modulation control signal;
a reference circuit generating a reference current proportional to the modulated supply current, and including a reference control element responsive to an inferential sense signal to maintain the reference current at a known proportionality relative to the modulated supply current; and
a detection circuit generating the inferential sense signal as a function of an operating voltage of the power amplifier and the reference current such that the inferential sense signal varies in dependence on power amplifier (PA) AM modulation impedance.
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Accused Products
Abstract
An amplitude modulation circuit (modulator) provides modulated supply current, possibly in combination with modulated supply voltage, to a radio frequency (RF) power amplifier (PA), and includes a detection circuit responsive to changes in the ratio of that voltage to the modulated supply current, described herein as its AM modulation impedance. Such impedance (resistance) changes commonly arise from changing coupling characteristics at the RF antenna assembly driven by the PA. A gain control circuit may be associated with the detection circuit, and made responsive thereto, thus allowing adjustment of modulation gain control responsive to changes in PA AM modulation impedance. In one embodiment, this arrangement permits the modulator to hold a fixed modulation gain over changing PA AM modulation impedance, while in other embodiments, modulation gain varies in response to PA impedance changes to avoid signal clipping. Such clipping might otherwise occur where current modulation values in combination with increased PA resistance would result in PA voltages exceeding the supply voltage of the PA.
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Citations
68 Claims
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1. A current modulator to supply a modulated supply current to a power amplifier responsive to an amplitude modulation signal, the current modulator comprising:
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a modulation control circuit generating a modulation control signal responsive to the amplitude modulation signal;
an output circuit generating the modulated supply current responsive to the modulation control signal;
a reference circuit generating a reference current proportional to the modulated supply current, and including a reference control element responsive to an inferential sense signal to maintain the reference current at a known proportionality relative to the modulated supply current; and
a detection circuit generating the inferential sense signal as a function of an operating voltage of the power amplifier and the reference current such that the inferential sense signal varies in dependence on power amplifier (PA) AM modulation impedance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
a detection circuit to generate a sense signal proportional to quiescent supply current into the power amplifier;
a closed loop control circuit to adjust the bias voltage applied to the power amplifier such that the quiescent supply current equals the desired quiescent current value.
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24. The current modulator of claim 23, wherein the closed loop control circuit of the bias controller comprises:
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an error amplifier to generate an error signal based on a difference between the sense signal and a quiescent current reference voltage representing the desired quiescent current value; and
a track-and-hold circuit adjusting the bias voltage responsive to the error signal in a first state, and holding an adjusted level of the bias voltage in a second state irrespective of the error signal.
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25. The current modulator of claim 24, wherein the bias controller further comprises a timing function generating a bias calibration pulse, and wherein the track-and-hold circuit operates in one of the first and second states in dependence upon the bias calibration pulse.
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26. The current modulator of claim 25, wherein the bias controller further comprises an input control switch responsive to the bias calibration pulse to decouple the current modulation control circuit from the amplitude modulation signal during adjustment of the bias voltage.
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27. The current modulator of claim 25, wherein the bias controller further comprises a gain control circuit to selectively adapt the modulation control gain of the current modulator to facilitate bias voltage adjustment.
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28. The current modulator of claim 25, wherein the gain control circuit is responsive to the bias calibration pulse such that the modulation control gain of the current modulator is adapted during the bias calibration pulse.
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29. The current modulator of claim 25, wherein the current modulator includes a first feedback loop coupling a feedback control input of the modulation control circuit to an output of the current modulator, such that the first feedback loop provides supply voltage modulation feedback, and further includes a second feedback loop coupling the feedback control input of the modulation control circuit to a feedback voltage in the reference circuit responsive to the reference current, such that the second feedback loop provides supply current modulation feedback.
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30. The current modulator of claim 29, wherein the bias controller further includes a feedback switching circuit for selectively decoupling the second feedback loop from the current modulation control circuit during the bias calibration pulse.
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31. The current modulator of claim 24, wherein the bias controller includes switching circuits responsive to a transmit enable pulse, such that the modulation control circuit is de-coupled from the amplitude modulation signal during assertion of the transmit enable pulse.
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32. The current modulator of claim 31, wherein the switching circuits further enable the track-and-hold circuit during assertion of the transmit enable pulse to allow dynamic adjustment of the bias voltage responsive to differences between the quiescent current reference voltage and the detection signal during RF transmit operations.
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33. The current modulator of claim 32, further comprising a quiescent current reference voltage controller to dynamically control RF transmit power during the transmit operations by dynamically controlling a magnitude of the quiescent current reference voltage.
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34. In a current modulator supplying a modulated current to a power amplifier, a method of inferentially sensing power amplifier (PA) AM modulation impedance in a current modulator where a power amplifier is supplied with a modulated supply current, the method comprising:
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generating said modulated supply current in an output circuit responsive to an amplitude modulation signal;
generating a reference current in a reference circuit proportional to the modulated supply current; and
slaving an operating voltage of the reference circuit generated by the reference current to an operating voltage of power amplifier such that the reference current is maintained at a known proportionality relative to the modulated supply current irrespective of changes in the PA AM modulation impedance; and
generating an inferential sense signal as a function of the operating voltage of the power amplifier and the reference current. - View Dependent Claims (35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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47. A current modulator to supply a modulated supply current to a power amplifier responsive to an amplitude modulation signal, the current modulator comprising:
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an output circuit generating the modulated supply current responsive to the amplitude modulation signal;
a reference circuit generating a reference current proportional to the modulated supply current, said reference circuit including an operating voltage generated by the reference current and slaved to an operating voltage of the power amplifier such that the reference current is maintained at a known proportionality relative to the modulated supply current; and
a detection circuit generating an inferential sense signal as a function of an operating voltage of the power amplifier and the reference current such that the inferential sense signal varies in dependence on power amplifier (PA) impedance. - View Dependent Claims (48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68)
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Specification