Envelope limiting for polar modulators
View Patent ↗Envelope limiting for a polar modulator. A system is provided that intelligently compresses the amplitude modulation in a polar modulator so that it can be implemented with a single-stage variable gain amplifier. Limiting the amplitude modulation range on the low side prevents collapse of the transmit signal's time-varying envelope and eases circuit implementation. Limiting the amplitude modulation range on the high side reduces the peak-to-average ratio of the waveform and thereby improves the efficiency of the radio transmitter.
1. In a radio transmitter, a control circuit for improving the efficiency of the radio transmitter's polar modulator, the control circuit comprising:
logic to set a modulation signal to an upper threshold level when the modulation signal exceeds the upper threshold level, wherein the logic to set the modulation signal to the upper threshold level comprises logic to set the modulation signal to the upper threshold level based on a peak-to-average ratio of a transmit signal;
logic to set the modulation signal to a lower threshold level when the modulation signal falls below the lower threshold level; and
logic to modulate one or both of a power amplifier stage and a variable gain amplifier stage using the modulation signal.
2. In a radio transmitter, a control circuit for improving the efficiency of the radio transmitter's polar modulator, the control circuit comprising:
logic to set a modulation signal to an upper threshold level when the modulation signal exceeds the upper threshold level;
logic to set the modulation signal to a lower threshold level when the modulation signal falls below the lower threshold level, wherein the logic to set the modulation signal to the lower threshold level comprises logic to set the modulation signal to the lower threshold level based on a reference signal; and
logic to modulate one or both of a power amplifier stage and a variable gain amplifier stage using the modulation signal.
3. Apparatus for improving the efficiency of a polar modulator, the apparatus comprising:
logic to set amplitude modulation data to an upper threshold level when a modulation signal exceeds the upper threshold level, wherein the logic to set the amplitude modulation data to the upper threshold level comprises logic to set the amplitude modulation data to the upper threshold level based on a peak-to-average ratio of a transmit signal;
logic to set the amplitude modulation data to a lower threshold level when the modulation signal falls below the lower threshold level;
logic to set the amplitude modulation data to the modulation signal when the modulation signal is between the upper threshold level and the lower threshold level; and
logic to modulate one or both of a power amplifier and a variable gain amplifier based on the amplitude modulation data.
4. Apparatus for improving the efficiency of a polar modulator, the apparatus comprising:
logic to set amplitude modulation data to an upper threshold level when a modulation signal exceeds the upper threshold level;
logic to set the amplitude modulation data to a lower threshold level when the modulation signal falls below the lower threshold level, wherein the logic to set the amplitude modulation data to the lower threshold level comprises logic to set the amplitude modulation data to the lower threshold level based on a reference signal;
logic to set the amplitude modulation data to the modulation signal when the modulation signal is between the upper threshold level and the lower threshold level; and
logic to modulate one or both of a power amplifier and a variable gain amplifier based on the amplitude modulation data.
5. Apparatus for improving the efficiency of a polar modulator, the apparatus comprising:
means for setting a modulation signal to an upper threshold level when the modulation signal exceeds the upper threshold level, wherein the means for setting the modulation signal to the upper threshold level comprises means for setting the modulation signal to the upper threshold level based on a peak-to-average ratio of a transmit signal;
means for setting the modulation signal to a lower threshold level when the modulation signal falls below the lower threshold level; and
means for modulating one or both of a power amplifier and a variable gain amplifier based on the modulation signal.
6. Apparatus for improving the efficiency of a polar modulator, the apparatus comprising:
means for setting a modulation signal to an upper threshold level when the modulation signal exceeds the upper threshold level;
means for setting the modulation signal to a lower threshold level when the modulation signal falls below the lower threshold level, wherein the means for setting modulation signal to the lower threshold level comprises means for setting the modulation signal to the lower threshold level based on a reference signal; and
means for modulating one or both of a power amplifier and a variable gain amplifier based on the modulation signal.