Active Harmonic Filters for Integrated Radio Frequency Amplifiers

Abstract

A radio frequency front end circuit includes an output signal transmission line, an amplifier circuit with an input connected to a radio frequency signal source and an output connected to the output signal transmission line. A harmonic suppression circuit is connected to the amplifier circuit, and includes an active circuit element having a frequency-dependent impedance and is tuned as a reflective trap with a negative capacitance for one or more rejection frequency ranges each corresponding to a multiple of a fundamental frequency of a signal generated by the radio frequency signal source.

1 . An active filter connectible to a transmission line from an output of an amplifier for reducing harmonics of a signal being amplified thereby, the active filter comprising:
 an operational amplifier with an inverting input, a non-inverting input, and a single-ended output;   a resistor network connected to the non-inverting input and to the single-ended output;   a first inductive-capacitive element connected to the inverting input and to the single-ended output and defining a first rejection frequency notch corresponding to an inductance and a capacitance of the first inductive-capacitive element; and   a filter circuit interface node defined at a junction of the first inductive-capacitive element to which the transmission line is connectible and having a frequency-dependent negative capacitance corresponding to a low frequency gain of the operational amplifier, half power point bandwidth of the operational amplifier, and output impedance as defined by the resistor network and the first inductive-capacitive element connected thereto.   
     
     
         2 . The active filter of  claim 1  further comprising a second inductive-capacitive element connected to the inverting input and defining a second rejection frequency notch corresponding to an inductance and capacitance of the second inductive-capacitive element. 
     
     
         3 . The active filter of  claim 2  wherein the first inductive-capacitive element and the second inductive-capacitive element are tuned for the first rejection frequency notch and the second rejection frequency to overlap. 
     
     
         4 . The active filter of  claim 1  further comprising a direct current decoupling element connecting the filter circuit interface node to the transmission line, and including a first capacitor and a second capacitor. 
     
     
         5 . The active filter of  claim 4  wherein the first capacitor and the second capacitor are connected in series. 
     
     
         6 . The active filter of  claim 4  wherein the first capacitor and the second capacitor are connected in parallel.  7 - 37 . (canceled) 
     
     
         38 . A radio frequency front end circuit comprising:
 an output signal transmission line;   an amplifier circuit with an input connected to a radio frequency signal source and an output connected to the output signal transmission line;   an operational amplifier with an inverting input, a non-inverting input, and a single-ended output;   a resistor network connected to the non-inverting input and to the single-ended output;   a first inductive-capacitive element connected to the inverting input and to the single-ended output and defining a first rejection frequency notch corresponding to an inductance and a capacitance of the first inductive-capacitive element; and   a filter circuit interface node defined at a junction of the first inductive-capacitive element to which the output signal transmission line is connectible and having a frequency-dependent negative capacitance corresponding to a low frequency gain of the operational amplifier, half power point bandwidth of the operational amplifier, and output impedance as defined by the resistor network and the first inductive-capacitive element connected thereto.   
     
     
         39 . The radio frequency front end circuit of  claim 38  further comprising a second inductive-capacitive element connected to the inverting input and defining a second rejection frequency notch corresponding to an inductance and capacitance of the second inductive-capacitive element. 
     
     
         40 . The radio frequency front end circuit of  claim 39  wherein the first inductive-capacitive element and the second inductive-capacitive element are tuned for the first rejection frequency notch and the second rejection frequency to overlap. 
     
     
         41 . The radio frequency front end circuit of  claim 38  further comprising a direct current decoupling element connecting the filter circuit interface node to the output signal transmission line, and including a first capacitor and a second capacitor. 
     
     
         42 . The radio frequency front end circuit of  claim 41  wherein the first capacitor and the second capacitor are connected in series. 
     
     
         43 . The radio frequency front end circuit of  claim 41  wherein the first capacitor and the second capacitor are connected in parallel. 
     
     
         44 . The radio frequency front end circuit of  claim 38  further comprising a first tank circuit having a first port connectible to the amplifier circuit and a second port connected to the filter circuit interface node, the first tank circuit at least partly defining a first harmonic trap. 
     
     
         45 . The radio frequency front end circuit of  claim 44  further comprising a second tank circuit having a first port connectible to the amplifier circuit and a second port connected to the first port of the first tank circuit, the first tank circuit and the second tank circuit at least partly defining the first harmonic trap. 
     
     
         46 . A radio frequency communications module comprising:
 a packaging substrate on which a plurality of components are mounted;   an output signal transmission line disposed on the packaging substrate;   an amplifier circuit implemented on the packaging substrate, the amplifier circuit including an input connected to a radio frequency signal source and an output connected to the output signal transmission line;   an operational amplifier implemented on the packaging substrate, the operational amplifier including an inverting input, a non-inverting input, and a single-ended output;   a resistor network implemented on the packaging substrate and connected to the non-inverting input and to the single-ended output;   a first inductive-capacitive element implemented on the packaging substrate and connected to the inverting input and to the single-ended output and defining a first rejection frequency notch corresponding to an inductance and a capacitance of the first inductive-capacitive element; and   a filter circuit interface node defined at a junction of the first inductive-capacitive element on the packaging substrate to which the output signal transmission line is connectible and having a frequency-dependent negative capacitance corresponding to a low frequency gain of the operational amplifier, half power point bandwidth of the operational amplifier, and output impedance as defined by the resistor network and the first inductive-capacitive element connected thereto.   
     
     
         47 . The radio frequency communications module of  claim 46  further comprising a second inductive-capacitive element implemented on the packaging substrate and connected to the inverting input and defining a second rejection frequency notch corresponding to an inductance and capacitance of the second inductive-capacitive element. 
     
     
         48 . The radio frequency communications module of  claim 47  wherein the first inductive-capacitive element and the second inductive-capacitive element are tuned for the first rejection frequency notch and the second rejection frequency to overlap. 
     
     
         49 . The radio frequency communications module of  claim 46  further comprising a direct current decoupling element implemented on the packaging substrate and connecting the filter circuit interface node to the output signal transmission line, the direct current coupling element including a first capacitor and a second capacitor. 
     
     
         50 . The radio frequency communications module of  claim 49  wherein the first capacitor and the second capacitor are connected in series. 
     
     
         51 . The radio frequency communications module of  claim 49  wherein the first capacitor and the second capacitor are connected in parallel. 
     
     
         52 . The radio frequency communications module of  claim 46  further comprising a first tank circuit implemented on the packaging substrate and having a first port connectible to the amplifier circuit and a second port connected to the filter circuit interface node, the first tank circuit at least partly defining a first harmonic trap. 
     
     
         53 . The radio frequency communications module of  claim 46  further comprising a second tank circuit implemented on the packaging substrate and having a first port connectible to the amplifier circuit and a second port connected to the first port of the first tank circuit, the first tank circuit and the second tank circuit at least partly defining the first harmonic trap.