Dynamically configurable bias circuit for controlling gain expansion of multi-mode single chain linear power amplifiers
View Patent ↗In a preferred embodiment, the gain expansion in low power mode of a single chain PA is minimized by dynamically adjusting the output impedance of the bias circuit of each gain stage for each mode of operation. Instead of switching in a series attenuator or switching in additional feedback in the first gain stage of a single-chain PA to limit the gain at the increased quiescent current level, this embodiment achieves linear performance by adjusting the quiescent current in each stage to the minimum level that meets the target gain and then increasing the output resistance of the bias circuit of each gain stage in low power mode (LPM) to provide the appropriate level of negative feedback at the base of each amplifying HBT to linearize the gain versus power response.
1. A bipolar radio-frequency amplifier having at least first and second modes of operation, at least one stage of the amplifier comprising:
a first semiconductor die including a bipolar transistor having an emitter, a base and a collector, a signal input and a signal output coupled to the bipolar transistor, a first bias circuit configured to generate a first bias current when the bipolar radio-frequency amplifier operates in the first mode of operation, a second bias circuit configured to generate a second bias current when the bipolar radio-frequency amplifier operates in the second mode of operation, the first bias circuit and the second bias circuit including a plurality of current mirrors, a current mirror ratio and a bias current mirror level selected to configure the amplifier at a particular quiescent bias current level based on a desired gain mode; and
a second semiconductor die including a voltage generator and complementary metal-oxide-semiconductor circuitry for selectively applying a voltage from the voltage generator to the first bias circuit or the second bias circuit.
2. The amplifier of claim 1 wherein the first bias circuit and the second bias circuit are parallel circuits associated with different current levels and different output resistances, where one of the first bias circuit or the second bias circuit is active for each mode of operation of the bipolar radio-frequency amplifier.
3. The amplifier of claim 1 wherein the first bias circuit and the second bias circuit include current mirrors, each having an output impedance that is selected to optimize gain expansion and linearity.
4. The amplifier of claim 1 wherein the quiescent bias current level is optimized for lower power levels of operation in a single amplifier chain.
5. The amplifier of claim 1 wherein the first semiconductor die is implemented in heterojunction bipolar transistor technology and the second semiconductor die is a complementary metal-oxide-semiconductor die.
6. The amplifier of claim 1 wherein the first bias circuit and the second bias circuit include a plurality of parallel circuits with output impedances optimized for different power modes and controlled by an external complementary metal-oxide-semiconductor die controller.
7. The amplifier of claim 1 wherein the first bias circuit and the second bias circuit include an array of at least two switched resistors positioned at an output of the first bias circuit and the second bias circuit, the resistors selected to produce a particular output resistance.
8. The amplifier of claim 1 wherein the first and second modes of operation correspond to different output powers.
9. A bipolar radio-frequency amplifier having at least first and second modes of operation, at least one stage of the amplifier comprising:
a first gallium arsenide semiconductor die including a bipolar transistor having an emitter, a base and a collector, a signal input and a signal output coupled to the bipolar transistor, a first bias circuit configured to generate a first bias current when the bipolar radio-frequency amplifier operates in the first mode of operation a second bias circuit configured to generate a second bias current when the bipolar radio-frequency amplifier operates in the second mode of operation, the first bias circuit and the second bias circuit including a plurality of current mirrors, and a current mirror ratio and a bias current mirror level selected to configure the amplifier at a particular quiescent bias current level based on a desired gain mode;
a second semiconductor die including a voltage generator and complementary metal-oxide-semiconductor circuitry for selectively applying a voltage from the voltage generator to the first bias circuit or the second bias circuit; and
a substrate on which the first gallium arsenide semiconductor die and the second semiconductor die are mounted.
10. The amplifier of claim 9 wherein the first bias circuit and the second bias circuit are parallel circuits associated with different current levels and different output resistances, where one of the first bias circuit or the second bias circuit is active for each mode of operation of the bipolar radio-frequency amplifier.
11. The amplifier of claim 9 wherein the first bias circuit and the second bias circuit include current mirrors, each having an output impedance that is selected to optimize gain expansion and linearity.
12. The amplifier of claim 9 wherein the quiescent bias current level is optimized for lower power levels of operation in a single amplifier chain.
13. The amplifier of claim 9 wherein the first bias circuit and the second bias circuit include a plurality of parallel circuits with output impedances optimized for different power modes and controlled by an external complementary metal-oxide-semiconductor controller.
14. The amplifier of claim 9 wherein the first bias circuit and the second bias circuit include an array of at least two switched resistors positioned at an output of the first bias circuit and the second bias circuit, the resistors selected to produce a particular output resistance.
15. The amplifier of claim 9 wherein the first and second modes of operation correspond to different output powers.