Active Harmonic Filters for Integrated Radio Frequency Amplifiers
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.