High efficiency amplifier

A distributed amplifier, comprising:

• a first amplifier stage having an input;
• a transmission line;
• a second amplifier stage having an input, the second amplifier stage being coupled to the first amplifier stage through the transmission line, the transmission line providing an impedance load to the first amplifier stage;
• a drive circuit that receives an input signal to be amplified and produces a first drive signal and a second drive signal coupled respectively to the first and second inputs;
• and
• wherein the drive circuit generates the first and second drive signals to produce an approximately constant voltage at the junction of the first amplifier stage and the transmission line throughout a range of values of the second drive signal that produce output power ranging from a maximum output power to an output power less than the maximum output power.

A method of driving a plurality of N inputs to a distributed amplifier circuit, comprising:

• providing an N stage amplifier having N transistors, the amplifier having N−1 transmission line sections coupling N current nodes of the N transistors;
• receiving an input signal Pin(t) and producing therefrom N drive signals S1(t) . . . SN(t) such that over a first range of operation:
• SN(t) produces an output current from transistor N ranging from a maximum current to zero;
• SN−1(t) produces an output current from transistor N−1 that preserves the voltage at node N−1 constant over the range of output current from transistor N;
• and
• S1(t) through SN−2(t) produce maximum output current from transistors 1 through N−2.

A high efficiency distributed amplifier circuit, comprising:

• N stage amplifier having N transistors;
• N−1 transmission line sections coupling N current nodes of the N transistors;
• a drive signal generating circuit that receives an input signal Pin(t) and produces N drive signals S1(t) . . . SN(t), wherein the amplifier circuit produces an output in the form Pout(t)=GPin(t), with G representing the amplifier circuit's power gain;
• wherein the drive signal generating circuit produces the N drive signals such that over a first range of operation:
• SN(t) produces an output current from transistor N ranging from a maximum current to zero;
• SN−1(t) produces an output current from transistor N−1 that preserves the voltage at node N−1 constant over the range of output current from transistor N;
• and
• S1(t) through SN−2(t) produce maximum output current from transistors 1 through N−2.

A method of driving a distributed amplifier, comprising:

• providing a distributed amplifier having a first stage connected to a second stage through a transmission line, the second stage providing a portion of a virtual impedance load to the first stage;
• receiving an input signal m(t) to be amplified by the distributed amplifier;
• generating a first drive signal that varies as a function of m(t) to drive the first stage;
• generating a second drive signal that varies as a function of m(t) to drive the second stage;
• wherein the first drive signal varies as a function of m(t) from a maximum to zero as m(t) varies from a maximum value to m1;
• and
• wherein the second drive signal varies as a function of m(t) from a maximum value to zero as m(t) varies from a maximum value to a value m2, where m1 is less than m2.