Power amplifier with biasing scheme enabling high power operation
A disclosed structure includes a power amplifier and circuitry for implementing a biasing scheme that enables high power operation. The power amplifier includes parallel transistor chains connected to input and output transformers. Each chain includes series-connected first, second, and third n-type field effect transistors (NFETs) having front and back gates. The output transformer receives a variable positive power supply voltage generated using average power tracking. Front and back gates of each third NFET receive a positive bias voltage greater than or equal to the variable positive power supply voltage and a negative bias voltage, respectively. By negative back biasing the third NFETs, threshold voltages thereof are raised so a high positive bias voltage can be applied to the front gates to increase power output without violating reliability specifications. Optionally, by making the negative bias voltage temperature dependent, voltages at source regions of the third NFETs are held constant.
1 . A structure including:
an output transformer connected to receive a positive power supply voltage and having input terminals; and
transistor chains connected to the input terminals, respectively, of the output transformer,
wherein each transistor chain includes an N-type field effect transistor (NFET) having a front gate connected to receive a positive bias voltage and a back gate connected to receive a negative bias voltage, and
wherein the negative bias voltage is variable and temperature-dependent.
2 . The structure of claim 1 , wherein the negative bias voltage becomes more negative when temperature increases and becomes less negative when temperature decreases causing a threshold voltage of the N-type field effect transistor to remain constant.
3 . The structure of claim 1 , wherein the positive power supply voltage is power output dependent.
4 . The structure of claim 1 , wherein the positive bias voltage is higher than the positive power supply voltage.
5 . The structure of claim 1 ,
wherein each transistor chain includes at least a first NFET, a second NFET, and a third NFET connected in series between ground and an input terminal of the output transformer, and
wherein the third NFET has the front gate connected to receive the positive bias voltage and the back gate connected to receive the negative bias voltage.
6 . The structure of claim 5 ,
wherein the first NFET has a first back gate connected to ground and a first front gate connected to an output terminal of an input transformer, and
wherein the second NFET has second back gate connected to ground and a second front gate connected to receive a different positive bias voltage that is lower than the positive bias voltage and the positive power supply voltage.
7 . The structure of claim 5 , wherein the first NFET and the second NFET have lower threshold voltages than the third NFET.
8 . A structure including:
voltage generators outputting a positive power supply voltage, a negative bias voltage, a first positive bias voltage, and a second positive bias voltage, wherein the positive power supply voltage is higher than the first positive bias voltage and lower than the second positive bias voltage; and
an amplifier including:
an input transformer having output terminals;
an output transformer connected to receive the positive power supply voltage and having input terminals; and
transistor chains connected between the input transformer and the output transformer,
wherein each transistor chain includes a first N-type field effect transistor (NFET), a second NFET, and a third NFET connected in series between ground and an input terminal of the output transformer,
wherein the first NFET has a first back gate connected to ground and a first front gate connected to an output terminal of the input transformer,
wherein the second NFET has a second back gate connected to ground and a second front gate connected to receive the first positive bias voltage,
wherein the third NFET has a third back gate connected to receive the negative bias voltage and a third front gate connected to receive the second positive bias voltage, and
wherein the negative bias voltage is variable and temperature-dependent.
9 . The structure of claim 8 , wherein the positive power supply voltage, the negative bias voltage, the first positive bias voltage, and the second positive bias voltage are mode dependent.
10 . The structure of claim 8 , wherein the voltage generators include a negative bias voltage generator generating and outputting a temperature dependent negative bias voltage to the third back gate of the third NFET in each of the transistor chains.
11 . The structure of claim 10 , wherein the temperature dependent negative bias voltage becomes more negative when temperature increases and becomes less negative when temperature decreases causing a threshold voltage of the third NFET in each transistor chain to remain constant and ensuring that voltages at junctions between the second NFET and the third NFET in each transistor chain remain essentially constant at varying temperatures.
12 . The structure of claim 8 , wherein the voltage generators further include an average power tracking voltage generator monitoring a power output of the amplifier and generating and outputting a power output dependent positive supply voltage to the output transformer.
13 . The structure of claim 8 , wherein the voltage generators further include a voltage regulator generating and outputting the second positive bias voltage at a voltage level higher than the positive power supply voltage to avoid a gate-to-drain voltage that violates a time dependent dielectric breakdown off-state reliability rating for the third NFET.
14 . The structure of claim 8 , wherein the first NFET and the second NFET have lower threshold voltages than the third NFET.
15 . A structure including:
voltage generators outputting a positive power supply voltage, a negative bias voltage, a first positive bias voltage, and a second positive bias voltage, wherein the positive power supply voltage is higher than the first positive bias voltage and lower than the second positive bias voltage; and
an amplifier including:
an input transformer having output terminals;
an output transformer connected to receive the positive power supply voltage and having input terminals; and
transistor chains connected between the input transformer and the output transformer,
wherein each transistor chain includes a first N-type field effect transistor (NFET), a second NFET, and a third NFET connected in series between ground and an input terminal of the output transformer,
wherein the first NFET and the second NFET have lower threshold voltages than the third NFET,
wherein the first NFET has a first back gate connected to ground and a first front gate connected to an output terminal of the input transformer,
wherein the second NFET has a second back gate connected to ground and a second front gate connected to receive the first positive bias voltage,
wherein the third NFET has a third back gate connected to receive the negative bias voltage and a third front gate connected to receive the second positive bias voltage, and
wherein the negative bias voltage is variable and temperature-dependent.
16 . The structure of claim 15 , further comprising:
a semiconductor substrate including:
a Pwell and an Nwell laterally surrounding the Pwell; and
an additional Nwell below the Pwell and the Nwell; and
an insulator layer the semiconductor substrate over the Pwell and the Nwell,
wherein the third NFET of each transistor chain is on the insulator layer above the Pwell and the first NFET and the second NFET of each transistor chain are on the insulator layer above the Nwell.
17 . The structure of claim 15 , wherein the positive power supply voltage, the negative bias voltage, the first positive bias voltage, and the second positive bias voltage are mode dependent.
18 . The structure of claim 15 ,
wherein the voltage generators include a negative bias voltage generator generating and outputting a temperature dependent negative bias voltage to the third back gate of the third NFET in each of the transistor chains, and
wherein the temperature dependent negative bias voltage becomes more negative when temperature increases and becomes less negative when the temperature decreases causing a threshold voltage of the third NFET in each transistor chain to remain constant and ensuring that voltages at junctions between the second NFET and the third NFET in each transistor chain remain essentially constant at varying temperatures.
19 . The structure of claim 15 , wherein the voltage generators further include an average power tracking voltage generator monitoring a power output of the amplifier and generating and outputting a power output dependent positive supply voltage to the output transformer.
20 . The structure of claim 15 , wherein the voltage generators further include a voltage regulator generating and outputting the second positive bias voltage at a voltage level higher than the positive power supply voltage to avoid a gate-to-drain voltage that violates a time dependent dielectric breakdown off-state reliability rating for the third NFET.