Doherty amplifier
View Patent ↗A Doherty amplifier has at least one peaking amplifier which has first and second drain connections, wherein the first drain connection is connected to the output network, and the other second drain connection is connection to the load. By providing two drain connections, separate package leads to the peaking amplifier can be taken into account when designing the impedance inverter and an output impedance. In this way, the circuit operation can be optimized both for the impedance inversion function and for driving the output load.
1. A Doherty amplifier for driving a load comprising:
a main amplifier package, comprising a main amplifier and a drain connection connecting a drain of the main amplifier to an output lead of the main amplifier package;
a peaking amplifier package, comprising a peaking amplifier, a first drain connection connecting a drain of the peaking amplifier to a first output lead of the peaking amplifier package, and a second drain connection connecting the drain of the peaking amplifier to a second output lead of the peaking amplifier package different from the first output lead;
an input network connecting an input of the Doherty amplifier to an input lead of the main amplifier package and to an input lead of the peaking amplifier package; and
an output network connecting the output lead of the main amplifier package and the first output lead of the peaking amplifier package;
wherein the output network, the drain capacitance of the main amplifier and the peaking amplifier, parasitics associated with the drain connection and output lead of the main amplifier package, and parasitics associated with the first drain connection and first output lead of the peaking amplifier package form an impedance inverter; and
wherein, during operation, the second output lead is connected to the load.
2. The amplifier as claimed in claim 1 , wherein the drain connection of the main amplifier package comprises bondwires extending between the output lead of the main amplifier package and a drain bar of the main amplifier, and wherein the parasitics associated with the drain connection and output lead of the main amplifier package comprise an inductance associated with the bondwires that extend between the output lead of the main amplifier package and the drain bar of the main amplifier and a capacitance associated with the output lead of the main amplifier package.
3. The amplifier as claimed in claim 2 , wherein the first drain connection of the peaking amplifier package comprises bondwires extending between the first output lead of the peaking amplifier package and a drain bar of the peaking amplifier, and wherein the parasitics associated with the first drain connection and the first output lead of the peaking amplifier package comprise an inductance associated with the bondwires that extend between the first output lead of the peaking amplifier package and the drain bar of the peaking amplifier and a capacitance associated with the first output lead of the peaking amplifier package.
4. The amplifier as claimed in claim 3 , wherein the output network comprises a transmission line with an impedance and electrical length such that it forms a quarter wave transmission line along with the inductances associated with the drain connection of the main amplifier package and the first drain connection of the peaking amplifier package, with the capacitances associated with the first output lead of the peaking amplifier package and with the output lead of the main amplifier package, and with the drain capacitances of the main amplifier and the peaking amplifier.
5. The amplifier as claimed in claim 1 , wherein the first and second output leads of the peaking amplifier package are arranged on opposite sides of the package.
6. The amplifier as claimed in claim 1 , comprising an impedance transformation network between the second drain connection and the load.
7. The amplifier as claimed in claim 6 , wherein the impedance transformation network comprises a wideband impedance matching circuit.
8. A radio frequency transmitter comprising a Doherty amplifier as claimed in claim 1 .
9. An integrated circuit comprising a Doherty amplifier as claimed in claim 1 .