Automatic frequency tuning system and method for an FM-band transmit power amplifier
First Claim
1. An automatic frequency tuning system for a transmit power amplifier having an antenna feed line coupled to an output of an output driver, comprising:
- a shunt capacitor array having a plurality of series capacitors selectably couplable to said antenna feed line to apply a programmable shunt capacitance thereto;
a peak detector circuit couplable to said antenna feed line associated with a first terminal node and a last terminal node of said series capacitors, said peak detector circuit further including;
a) a first switch and a second switch that are configured to couple a first capacitor of the peak detector circuit, which is also coupled to the first terminal node, either toi) a noninverting input of a sense amplifier of the peak detector circuit;
orii) ground; and
a processor configured to control said peak detector circuit to determine a ratio of voltage levels measured at said nodes at a given power level of said output driver.
1 Assignment
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Accused Products
Abstract
An automatic frequency tuning system and method for a transmit power amplifier. The transmit power amplifier has an antenna feed line including a series capacitor and is coupled to an output of an output driver. In one embodiment, the system includes: (1) a shunt capacitor array having a plurality of capacitors selectably couplable to the antenna feed line to apply a programmable shunt capacitance thereto, (2) a peak detector circuit couplable to nodes of the antenna feed line associated with both terminals of the series capacitor and (3) a processor configured to control the peak detector circuit to determine a ratio of voltage levels measured at the nodes at a given power level of the output driver.
21 Citations
22 Claims
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1. An automatic frequency tuning system for a transmit power amplifier having an antenna feed line coupled to an output of an output driver, comprising:
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a shunt capacitor array having a plurality of series capacitors selectably couplable to said antenna feed line to apply a programmable shunt capacitance thereto; a peak detector circuit couplable to said antenna feed line associated with a first terminal node and a last terminal node of said series capacitors, said peak detector circuit further including; a) a first switch and a second switch that are configured to couple a first capacitor of the peak detector circuit, which is also coupled to the first terminal node, either to i) a noninverting input of a sense amplifier of the peak detector circuit;
orii) ground; and a processor configured to control said peak detector circuit to determine a ratio of voltage levels measured at said nodes at a given power level of said output driver. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An automatic frequency tuning method for a transmit power amplifier having an antenna feed line including a series capacitor and coupled to an output of an output driver, comprising:
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setting a synthesizer frequency to a desired FM-band channel frequency; setting said output driver at a power level at which insubstantial leakage occurs in bands other than said FM band; finding a shunt capacitor setting that corresponds to a minimum voltage level at a first node between said output driver and said series capacitor; increasing said power level to a level at which said peak detector circuit is capable of sensing differences between measurement points close to a voltage gain peak; computing ratios of measured voltage levels at said first node and a second node across said series capacitor from said first node for a plurality of shunt capacitor settings; and programming said shunt capacitor array with a shunt capacitor setting associated with one of said ratios. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17)
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18. An automatic frequency tuning method for a transmit power amplifier having an antenna feed line including a series capacitor and coupled to an output of an output driver, comprising:
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shorting inputs of a peak detector circuit together; measuring a DC offset of a sense amplifier of said peak detector circuit; setting a synthesizer frequency to a desired FM channel frequency; setting a power level of an FM transmitter to a level at which insubstantial leakage occurs in bands other than the FM band; connecting an input of said peak detector circuit to a first node between an output driver and a series capacitor; adjusting an attenuation ratio of a capacitor divider at an input of said peak detector circuit; sweeping shunt capacitor settings across a range of settings; finding a minimum of voltage measurements; increasing said power level to a level at which said peak detector circuit can sense differences between the measurement points proximate a voltage gain peak; sweeping shunt capacitor settings about said voltage gain peak; and computing a voltage level ratio at each of said shunt capacitor settings. - View Dependent Claims (19, 20, 21, 22)
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Specification