Multimode operation for differential power amplifiers
An RF circuit for wireless devices comprises a single differential power amplifier and an impedance balancing circuit for each frequency band. The impedance balancing circuit serves both to provide an appropriate impedance at the output of the amplifier as the operating mode of the device changes, and also transforms the differential output of the amplifier to a single-ended output. The impedance balancing circuit optionally comprises a BALUN circuit and a variable capacitor that is varied as the operating mode changes in order to vary the impedance at the output of the amplifier.
1. A circuit comprising:
a differential power amplifier configured to produce a differential output signal;
an impedance balancing circuit electrically coupled to the differential amplifier and configured to receive the differential output signal therefrom, the impedance balancing circuit including
a first transmission line and a second transmission line, each of the two transmission lines having a first end and a second end,
each transmission line comprising an electrically conductive strip, a ground plane adjacent to the electrically conductive strip, and a dielectric layer disposed between the electrically conductive strip and the ground plane, the ground plane being characterized by a width that is greater than a width of the electrically conductive strip, wherein the differential output signal is applied across the ground planes of the two transmission lines at the respective first ends thereof,
a first electrical connection joining the electrically conductive strips of the two transmission lines at the first ends thereof,
a second electrical connection joining the ground planes of the two transmission lines at the second ends thereof,
the impedance balancing circuit configured to produce a single-ended output signal from the electrically conductive strip of the first transmission line at the second end thereof; and
a variable capacitor electrically coupled to the electrically conductive strip of the second transmission line at the second end thereof.
2. The circuit of claim 1 wherein each transmission line comprises a microstrip.
3. The circuit of claim 1 further comprising a mode switch electrically coupled to receive the single-ended output signal from the impedance balancing circuit and configured to switch the single-ended output signal between a plurality of output ports.
4. The circuit of claim 3 further comprising a number of duplexers, one duplexer of the number of duplexers electrically coupled to each output port of the plurality of output ports.
5. The circuit of claim 1 wherein the second electrical connection joining the ground planes of the two transmission lines at the second ends thereof is additionally coupled to ground.
6. The circuit of claim 1 wherein the second electrical connection joining the ground planes of the two transmission lines at the second ends thereof is additionally coupled to a DC bias voltage.
7. A device operable in at least one frequency band and being switchable between a number of operating modes in each of the frequency bands, the device comprising:
an antenna;
a plurality of receiver amplifiers, each receiver amplifier of the plurality dedicated to a different operating mode of the number of operating modes;
a first differential power amplifier, having an input and an output, and configured to operate within a first frequency band of the at least one frequency band and further configured to produce an amplified differential output signal at the output from a differential input signal received at the input, the first differential power amplifier being solely dedicated to the first frequency band;
a first impedance balancing circuit in electrical communication with the first differential power amplifier and configured to receive the differential output signal from the output of the first differential power amplifier and further configured to produce a single-ended output signal from the differential output signal, the first impedance balancing circuit being tunable to change an impedance applied to the output of the first differential power amplifier as the operating mode is switched;
an antenna switch configured to alternatingly couple the antenna to either the first impedance balancing circuit or to couple the antenna to the plurality of receiver amplifiers.
8. The device of claim 7 further comprising a mode switch and a number of duplexers equal to the plurality of receiver amplifiers, wherein the mode switch is in electrical communication with the first impedance balancing circuit and configured to receive the single-ended output signal therefrom, each duplexer of the number of duplexers being configured to alternatingly couple the antenna switch to either the mode switch or to couple the antenna switch to one receiver amplifier of the plurality of receiver amplifiers.
9. The device of claim 7 wherein the first impedance balancing circuit comprises
a first transmission line and a second transmission line, each of the two transmission lines having a first end and a second end,
each transmission line being comprised of an electrically conductive strip, a ground plane adjacent to the electrically conductive strip, and a dielectric layer disposed between the electrically conductive strip and the ground plane, the ground plane being characterized by a width that is greater than a width of the electrically conductive strip, wherein the differential output signal is applied across the ground planes of the two transmission lines at the respective first ends thereof,
a first electrical connection joining the electrically conductive strips of the two transmission lines at the first ends thereof,
a second electrical connection joining the ground planes of the two transmission lines at the second ends thereof,
the first impedance balancing circuit being configured to produce the single-ended output signal from the electrically conductive strip of the first transmission line at the second end thereof; and
a variable capacitor electrically coupled to the electrically conductive strip of the second transmission line at the second end thereof.
10. The device of claim 9 wherein each transmission line comprises a microstrip.
11. The device of claim 9 wherein the second electrical connection joining the ground planes of the two transmission lines at the second ends thereof is additionally coupled to ground.
12. The device of claim 9 wherein the second electrical connection joining the ground planes of the two transmission lines at the second ends thereof is additionally coupled to a DC bias voltage.
13. The device of claim 7 further comprising
a second differential power amplifier, having an input and an output, and configured to operate within a second frequency band and further configured to produce an amplified differential output signal at the output from a differential input signal received at the input, the second differential power amplifier being solely dedicated to the second frequency band; and
a second impedance balancing circuit in electrical communication with the second differential power amplifier and configured to receive the differential output signal from the output of the second differential power amplifier and further configured to produce a single-ended output signal from the differential output signal, the second impedance balancing circuit being tunable to change an impedance applied to the output of the second differential power amplifier as the operating mode is switched.