LOW POWER FM TRANSMITTER
First Claim
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1. A frequency modulated (FM) transmitter, comprising:
- a baseband processor operable to produce a complex modulated digital signal;
a Digital-to-Analog Converter (DAC) coupled to receive the complex modulated digital signal and operable to convert the complex modulated digital signal to a complex modulated analog signal;
a low pass filter coupled to receive the complex modulated analog signal and operable to produce a filtered complex modulated analog signal;
a mixer coupled to receive the filtered complex modulated analog signal and operable to up-convert the filtered complex modulated analog signal to a modulated RF signal;
a power amplifier coupled to receive the modulated RF signal and operable to produce an amplified modulated RF signal; and
a transmit signal strength indicator (TSSI) coupled to receive the modulated RF signal and operable to measure the output power of the modulated RF signal, the TSSI being further operable to generate a power control signal indicative of the output power of the modulated RF signal and to provide the power control signal to the baseband processor;
wherein the baseband processor is further operable to generate a gain control signal based on the power control signal to control a respective gain of the DAC, low pass filter and power amplifier to maintain a substantially constant transmit voltage over an FM frequency band.
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Abstract
An FM transmitter operates at low power by maintaining a substantially constant transmit voltage over the FM frequency band. A transmit signal strength indicator (TSSI) is provided at the output of the FM transmitter to measure the power at the output of the power amplifier. The TSSI generates a power control signal indicative of the output power and inputs the power control signal to the baseband processor. The baseband processor generates gain control signals to control the gain of various analog stages of the FM transmitter based on the power control signal.
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Citations
20 Claims
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1. A frequency modulated (FM) transmitter, comprising:
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a baseband processor operable to produce a complex modulated digital signal; a Digital-to-Analog Converter (DAC) coupled to receive the complex modulated digital signal and operable to convert the complex modulated digital signal to a complex modulated analog signal; a low pass filter coupled to receive the complex modulated analog signal and operable to produce a filtered complex modulated analog signal; a mixer coupled to receive the filtered complex modulated analog signal and operable to up-convert the filtered complex modulated analog signal to a modulated RF signal; a power amplifier coupled to receive the modulated RF signal and operable to produce an amplified modulated RF signal; and a transmit signal strength indicator (TSSI) coupled to receive the modulated RF signal and operable to measure the output power of the modulated RF signal, the TSSI being further operable to generate a power control signal indicative of the output power of the modulated RF signal and to provide the power control signal to the baseband processor; wherein the baseband processor is further operable to generate a gain control signal based on the power control signal to control a respective gain of the DAC, low pass filter and power amplifier to maintain a substantially constant transmit voltage over an FM frequency band. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14)
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- 11. The FM transmitter of claim 11, wherein the tune control signal tunes the power amplifier to produce an amplitude voltage of over 1 volt and a peak-to-peak voltage of over 2 volts.
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15. A method for operating an FM transmitter, comprising:
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producing a complex modulated digital signal; converting the complex modulated digital signal to a complex modulated analog signal by a Digital-to-Analog converter (DAC); filtering the complex modulated analog signal to produce a filtered complex modulated analog signal by a low pass filter; up-converting the filtered complex modulated analog signal to a modulated RF signal; amplifying the modulated RF signal and operable to produce an amplified modulated RF signal by a power amplifier; measuring the output power of the modulated RF signal; generating a power control signal indicative of the output power of the modulated RF signal; and generating a gain control signal based on the power control signal to control a respective gain of the DAC, low pass filter and power amplifier to maintain a substantially constant transmit voltage over an FM frequency band. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification