Broadband sliding-mode outphasing power amplifier with high efficiency
A dual-input microwave power amplifier (PA) with high-efficiency. The PA exploits the continuum of modes between the Doherty and Chireix PA mode of operation to achieve 40% fractional bandwidth while relying on the physical linear dispersion of the transmission lines of the lossless output combiner. A constant output is achieved at peak power over the entire bandwidth. The output backoff varies from 6 dB in the Doherty mode to 8 dB in the Chireix mode. The PA operates over a wider range of frequencies from 1 to 8 GHz. The dual-input PA operates in mixed-mode and thus requires variable input power drives and outphasing angle.
1 . A dual transistor power amplifier (PA), comprising:
a main branch transmission line (TL 1 ) having a main transistor and having a characteristic impedance R opt ;
an auxiliary branch transmission line (TL 2 ) having an auxiliary transistor and having the characteristic impedance R opt ;
a common load (R L ) to which the main branch transmission line and the auxiliary branch transmission line are connected,
wherein the main branch transmission line (TL 1 ) and the auxiliary branch transmission line (TL 2 ) are matching networks established at a current-source reference plane (CSRP), and
wherein the dual transistor PA provides a sliding mode on a Chireix-Doherty continuum by mapping an electrical length of the main branch transmission TL 1 and an electrical length the auxiliary branch transmission TL 2 across a targeted frequency band of operation with an outphasing angle.
2 . The dual transistor power amplifier of claim 1 , wherein the electrical length is determined with the following relationship:
Θ
1
/
2
=
Θ
O
{
1
,
2
}
ω
ω
O
,
and
wherein
Θ
O
1
=
π
2
,
Θ o 2 =π , ω=2πf, where f is a frequency of operation, wherein ω o =2πf H , where f H is a maximum frequency in a desired operating frequency range.
3 . The dual transistor power amplifier of claim 2 , wherein the dual transistor power amplifier operates in a Doherty mode of operation with 6 dB of output back-off (OBO) power at the maximum frequency when the outphasing angle between two inputs is equal to 90° which occurs when ω=ω o .
4 . The dual transistor power amplifier of claim 3 , wherein, as the frequency of operation deviates from ω o , the mode operation gradually changes from the Doherty mode of operation to a Chireix mode of operation with 8 dB of OBO power at a minimum frequency.
5 . The dual transistor power amplifier of claim 1 , wherein the dual transistor power amplifier provides 40% fractional bandwidth while relying on a physical linear dispersion of transmission lines of a lossless output combiner.
6 . The dual transistor power amplifier of claim 1 , wherein the dual transistor power amplifier provides a constant output at peak power over an entire bandwidth.
7 . The dual transistor power amplifier of claim 1 , wherein the common load maintains a predetermined impedance for the main transistor and the auxiliary transistor while an output power of the dual transistor power amplifier varies from a peak output power to a back-off output (OBO) power.
8 . The dual transistor power amplifier of claim 7 , wherein the common load provides a DC drain biasing for the dual transistor power amplifier.
9 . A method providing a sliding mode on a Chireix-Doherty continuum in a dual transistor power amplifier (PA) having a main branch transmission line (TL 1 ) having a main transistor and having a characteristic impedance R opt , an auxiliary branch transmission line (TL 2 ) having an auxiliary transistor and having the characteristic impedance R opt , and a common load (R L ) to which the mail branch transmission line and the auxiliary branch transmission line are connected, comprising:
establishing, at a current-source reference plane (CSRP), the main branch transmission line (TL 1 ) and the auxiliary branch transmission line (TL 2 ) as matching networks; and
mapping an electrical length of the main branch transmission TL 1 and an electrical length the auxiliary branch transmission TL 2 across a targeted frequency band of operation with an outphasing angle.
10 . The method of claim 9 , further comprising:
determining the electrical length of transmission lines according to:
Θ
1
/
2
=
Θ
O
{
1
,
2
}
ω
ω
O
,
and
wherein
Θ
O
1
=
π
2
,
Θ O 2 =π , and ω=2πf, where f is a frequency of operation, ω o =2πf H , where f H is a maximum frequency in a desired operating frequency range.
11 . The method of claim 10 , further comprising operating the dual transistor power amplifier operates in a Doherty mode of operation with 6 dB of output back-off (OBO) power at a maximum frequency when the outphasing angle between two inputs is equal to 90° which occurs when ω=ω o .
12 . The method of claim 11 , further comprising:
varying a frequency of operation from ω o ; and
changing the mode operation from the Doherty mode of operation to a Chireix mode of operation with 8 dB of OBO power at the minimum frequency.
13 . The method of claim 9 , further comprising providing 40% fractional bandwidth while relying on a physical linear dispersion of transmission lines of a lossless output combiner.
14 . The method of claim 9 , further comprising providing a constant output at peak power over an entire bandwidth.
15 . The method of claim 9 , further comprising:
maintaining a predetermined impedance at the common load for the main transistor and the auxiliary transistor as an output power of the dual transistor power amplifier varies from a peak output power to a back-off output (OBO) power.
16 . The method of claim 15 , further comprising providing, by the common load, a DC drain bias for dual transistor the power amplifier.