Power amplifier saturation detection
First Claim
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1. A power amplifier circuit for a radio frequency (RF) transmitter, the power amplifier circuit comprising:
- a power amplifier including a first output transistor and a second output transistor, the first output transistor including a first output transistor terminal coupled to a first supply voltage, and the second output transistor including a second output transistor terminal coupled to a second supply voltage;
a first duty cycle detector including;
a first input coupled to the first output transistor terminal;
a first limiter coupled to the first output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and
a first averaging filter coupled to an output of the first limiter;
a second duty cycle detector including;
a second input coupled to the second output transistor terminal;
a second limiter coupled to the second output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and
a second averaging filter coupled to an output of the second limiter; and
a comparator circuit configured to produce a saturation detection output signal, the comparator circuit including a first input and a second input, the first input configured to be coupled to one of the first duty cycle detector and the second duty cycle detector, and the second input coupled to a reference voltage circuit.
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Abstract
In a portable radio transceiver, a power amplifier system includes a saturation detector that detects power amplifier saturation in response to duty cycle of the amplifier transistor collector voltage waveform. The saturation detection output signal can be used by a power control circuit to back off or reduce the amplification level of the power amplifier to avoid power amplifier control loop saturation.
18 Citations
25 Claims
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1. A power amplifier circuit for a radio frequency (RF) transmitter, the power amplifier circuit comprising:
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a power amplifier including a first output transistor and a second output transistor, the first output transistor including a first output transistor terminal coupled to a first supply voltage, and the second output transistor including a second output transistor terminal coupled to a second supply voltage; a first duty cycle detector including;
a first input coupled to the first output transistor terminal;
a first limiter coupled to the first output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and
a first averaging filter coupled to an output of the first limiter;a second duty cycle detector including;
a second input coupled to the second output transistor terminal;
a second limiter coupled to the second output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and
a second averaging filter coupled to an output of the second limiter; anda comparator circuit configured to produce a saturation detection output signal, the comparator circuit including a first input and a second input, the first input configured to be coupled to one of the first duty cycle detector and the second duty cycle detector, and the second input coupled to a reference voltage circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for detecting power amplifier saturation in a radio frequency (RF) transmitter, the method comprising:
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amplifying an RF signal using a first output transistor of a power amplifier when the RF signal is within a first frequency band to obtain a first amplified RF signal and using a second output transistor of the power amplifier when the RF signal is within a second frequency band to obtain a second amplified RF signal, the first output transistor including a first output transistor terminal coupled to a first supply voltage, and the second output transistor including a second output transistor terminal coupled to a second supply voltage; detecting a duty cycle of the amplified RF signal by;
limiting positive voltage excursions of the first amplified RF signal while passing negative voltage excursions of the first amplified RF signal to produce a first limited signal;
limiting positive voltage excursions of the second amplified RF signal while passing negative voltage excursions of the second amplified RF signal to produce a second limited signal; and
averaging the first limited signal to produce a first averaged signal and averaging the second limited signal to produce a second averaged signal;providing a signal representing the duty cycle to a first input of a comparator circuit and a reference voltage to a second input of the comparator circuit; and producing a saturation detection output signal in response to a comparison of the signal representing the duty cycle with the reference voltage. - View Dependent Claims (10, 11, 12, 13)
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14. A mobile wireless telecommunication device, comprising:
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a user interface; an antenna; a baseband subsystem coupled to the user interface; and a radio frequency (RF) subsystem coupled to the baseband subsystem and the antenna, the RF subsystem including a transmitter and a receiver, the transmitter including a modulator, an up converter and a power amplifier system, the power amplifier system including;
a power amplifier having a first output transistor and a second output transistor, the first output transistor having a first output transistor terminal coupled to a first supply voltage, the second output transistor having a second output transistor terminal coupled to a second supply voltage;
a first limiter section coupled to the first output transistor terminal, the first limiter section blocking positive voltage excursions and limiting negative voltage excursions;
a first averaging filter section coupled to an output of the first limiter section;
a second limiter section coupled to the second output transistor terminal, the second limiter section blocking positive voltage excursions and passing negative voltage excursions;
a second averaging filter section coupled to an output of the second limiter section; and
a comparator circuit, the comparator circuit having first and second comparator inputs and producing a saturation detection output signal. - View Dependent Claims (15, 16, 17, 18, 19)
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20. A transmitter comprising:
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a modulator; an up converter; and a power amplifier system including;
a power amplifier including a first output transistor and a second output transistor, the first output transistor including a first output transistor terminal coupled to a first supply voltage, the second output transistor including a second output transistor terminal coupled to a second supply voltage;
a first limiter section coupled to the first output transistor terminal, the first limiter section blocking positive voltage excursions and limiting negative voltage excursions;
a first averaging filter section coupled to an output of the first limiter section;
a second limiter section coupled to the second output transistor terminal, the second limiter section blocking positive voltage excursions and passing negative voltage excursions;
a second averaging filter section coupled to an output of the second limiter section; and
a comparator circuit, the comparator circuit having first and second comparator inputs and producing a saturation detection output signal. - View Dependent Claims (21, 22, 23, 24, 25)
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Specification