Directional coupler for communication system
An improved directional coupler that significantly reduces the signal degradation problems associated with distortion caused by circuit elements used to measure the transmitted power. In a selected embodiment, the directional coupler of the present invention comprises a plurality of active elements, such as capacitors, that have values selected to ensure that the distortion created by circuit elements used to measure forward transmitted power. In an embodiment of the invention, capacitors have values selected to minimize in-band distortion signals at the fundamental carrier frequency of the transmitted signal and also at the second and third harmonics of the fundamental carrier frequency.
1. A communication system comprising:
a radio module operable to generate an RE signal at a predetermined frequency; and
a directional coupler operably coupled to said radio module to measure the power of said RF signal, said directional coupler further comprising:
an envelope detector comprising a detector diode and a capacitor; and
distortion minimization circuitry operable to minimize distortion generated by said envelope detector at frequencies corresponding to said predetermined frequency and harmonics thereof, said distortion minimization circuitry comprising a first capacitor coupled to said diode, said first capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the fundamental frequency of said RE signal, and a second capacitor coupled to said diode, said second capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the second harmonic of said fundamental frequency of said RF signal.
2. The communication system of claim 1 , wherein said distortion minimization circuitry further comprises a third capacitor coupled to said diode, said third capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the third harmonic of said fundamental frequency of said RF signal.
3. The communication system of claim 2 , wherein said first RF signal has a fundamental frequency in the 2.4 GHz band.
4. A method of measuring the transmitted power of an RF signal, comprising:
generating an RF signal at a predetermined frequency;
measuring the transmitted power of said RF signal using a directional coupler having an envelope detector comprising a detector diode and a capacitor; and
minimizing distortion generated by said envelope detector at frequencies corresponding to said predetermined frequency and harmonics thereof by coupling first and second capacitors to said diode, said first capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the fundamental frequency of said RF signal, said second capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the second harmonic of said fundamental frequency of said RF signal.
5. The method of claim 4 , wherein said distortion is minimized by coupling a third capacitor to said diode, said third capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the third harmonic of said fundamental frequency of said RF signal.
6. The method of claim 5 , wherein said first RF signal has a fundamental frequency in the 2.4 GHz band.
7. An integrated circuit for enabling data communication between a host device and at least one wirelessly enabled external device, comprising:
a host interface;
a radio module operably coupled to said host interface, wherein said radio module is operable to generate an RF signal at a predetermined frequency; and
a directional coupler operably coupled to said radio module to measure the power of said RF signal, said directional coupler further comprising:
an envelope detector comprising a detector diode and a capacitor; and
distortion minimization circuitry operable to minimize distortion generated by said envelope detector at frequencies corresponding to said predetermined frequency and harmonics thereof, said distortion minimization circuitry comprising a first capacitor coupled to said diode, said first capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the fundamental frequency of said RF signal, and a second capacitor coupled to said diode, said second capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the second harmonic of said fundamental frequency of said RF signal.
8. The communication system of claim 7 , wherein said distortion minimization circuitry further comprises a third capacitor coupled to said diode, said third capacitor having a capacitance value for minimizing distortion in the frequency band corresponding to the third harmonic of said fundamental frequency of said RF signal.
9. The communication system of claim 8 , wherein said first RF signal has a fundamental frequency in the 2.4 GHz band.