Wideband high frequency chokes
View Patent ↗An n-stage RF choke comprises a series connection of two or more inductors connected in series between a source and a load. The inductor closest to the source has the largest inductance and the inductance closest to the load has the smallest inductance. The inductances of any inductors between the inductor closest to the supply and the inductor closest to the load decrease as a function of distance from the supply. The junctions between the inductors in the series connection are shunted to ground by capacitors connected in series with resistors that provide a matched termination for increasing bandwidth by lowering circuit Q factors and eliminating resonant frequencies. The capacitor closest to the supply has the largest capacitance and the capacitor closest to the load has the smallest capacitance. Any intermediate capacitors decrease in capacitance as a function of distance from the supply. Such an arrangement provides a high impedance that isolates the load from the supply at a wide range of frequencies.
1. An amplifier, comprising:
a transistor;
a power supply that provides bias current for the transistor;
a choke connected between the power supply and the transistor, comprising first and second inductors connected in series between an output terminal of the power supply and a bias terminal of the transistor, one of the first and second inductors being closer to the power supply than the other of the first and second inductors, the inductor closer to the power supply having an inductance that is greater than that of the other inductor; and
a capacitive impedance connecting a junction between the first and second inductors to ground.
2. The amplifier of claim 1 , in which the capacitive impedance comprises:
a capacitor; and
a resistor in series with the capacitor.
3. The amplifier of claim 1 , in which the first and second inductors comprise conductive spirals formed on a dielectric substrate.
4. A method of increasing the frequency range at which a choke provides a high impedance, comprising the step of:
connecting a plurality of inductors in series, the sizes of the inductors in the series decreasing from one end of the series connection to the other end of the series connection; and
connecting one or more capacitive impedances from one or more junctions between the inductors to ground.
5. An electrical circuit, comprising:
a source;
a load;
an n-stage wideband choke, where “n” is greater than one, connecting the source and the load, comprising “n” inductors each having a respective inductance connected in series between the source and the load, the inductances of the inductors in the series connection decreasing as a function of distance from the source; and
one or more capacitive impedances connecting junctions between the “n” inductors to ground.
6. The circuit of claim 5 , in which the one or more capacitive impedances each comprise a resistor in series with a capacitor.
7. The circuit of claim 6 , in which the capacitors each have a respective capacitance, the capacitances decreasing as a function of distance from the source.