System and method for current-mode amplitude modulation
First Claim
1. A method of compensating operation of a transmitter that includes av RF power amplifier being provided a modulated supply current, the method comprising:
- generating the modulated supply current as a scaled version of a modulated reference current by mirroring the modulated reference current via a current mirror circuit and configuring the current mirror circuit such that a reference voltage generated by the modulated reference current flowing into a reference load will substantially match an output voltage generated by the modulated supply current flowing into an effective DC resistance of the RF power amplifier for a nominal effective DC resistance of the RF power amplifier;
detecting a change in the effective DC resistance of the RF power amplifier away from the nominal effective DC resistance of the RF power amplifier by detecting a voltage imbalance in the current mirror circuit; and
compensating transmitter operation responsive to said detection.
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Accused Products
Abstract
An amplifier circuit includes a power amplifier biased for saturated mode operation, and a controllable current source to provide supply current to the power amplifier. The controllable current source effects desired amplitude modulation of the output signal from the power amplifier by modulating the supply current it provides responsive to an amplitude information signal. In one or more embodiments, the current source includes a circuit that is configured to adjust one or more transmitter operating parameters responsive to detecting changes in the effective DC resistance of the power amplifier. For example, the circuit may generate a compensation signal that reduces the effective DC resistance responsive to detecting that the effective DC resistance has undesirably increased. By way of non-limiting examples, such compensation may be effected by changing a current mirror, an amplifier-to-antenna impedance matching, an amplifier bias or device size, or imposing some form of transmit signal back-off.
72 Citations
24 Claims
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1. A method of compensating operation of a transmitter that includes av RF power amplifier being provided a modulated supply current, the method comprising:
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generating the modulated supply current as a scaled version of a modulated reference current by mirroring the modulated reference current via a current mirror circuit and configuring the current mirror circuit such that a reference voltage generated by the modulated reference current flowing into a reference load will substantially match an output voltage generated by the modulated supply current flowing into an effective DC resistance of the RF power amplifier for a nominal effective DC resistance of the RF power amplifier; detecting a change in the effective DC resistance of the RF power amplifier away from the nominal effective DC resistance of the RF power amplifier by detecting a voltage imbalance in the current mirror circuit; and compensating transmitter operation responsive to said detection. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A current modulation circuit for use with a RF power amplifier in a transmitter, the current modulation circuit comprising:
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a current mirror circuit configured to provide a modulated supply current to the RF power amplifier based on mirroring a modulated reference current that is modulated responsive to an amplitude information signal; a detection circuit configured to detect changes in an effective DC resistance of the RF power amplifier by detecting a voltage imbalance in the current mirror circuit and generating a detection signal responsive thereto; and a control circuit configured to compensate the transmitter responsive to the detection signal. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification