Amplifying system
View Patent ↗An amplifying system with increased linearity is disclosed. The amplifying system includes a first gain stage with a first gain characteristic, a second gain stage with a second gain characteristic, and bias circuitry configured to substantially maintain alignment of distortion inflection points between the first gain characteristic and the second gain characteristic during operation. The bias circuitry is configured to further maintain alignment of the distortion inflection points between the first gain characteristic and the second gain characteristic over design corners by providing substantially constant headroom between quiescent bias voltage and turnoff of the first gain stage and the second gain stage. In some embodiments the first gain characteristic is expansive and the second gain characteristic is compressive. In other embodiments the first gain characteristic is compressive and the second gain characteristic is expansive. In some embodiments the first gain stage is configured to provide RF degeneration control of gain.
1. An amplifying system comprising:
a first gain stage with a first gain characteristic;
a second gain stage with a second gain characteristic; and
bias circuitry that includes a reference headroom voltage generator and is configured to provide bias responsive to a reference voltage generated by the reference headroom voltage generator such that a voltage difference between a bias point and a threshold voltage of at least one of the first gain stage and the second gain stage is maintained at a constant level to substantially maintain alignment of distortion inflection points between the first gain characteristic and the second gain characteristic to limit total gain variations to less than 0.1 dB per dB of output stage power during operation for an input power to the first gain stage that ranges from −50 dB to 0 dB.
2. The amplifying system of claim 1 wherein the first gain characteristic is expansive and the second gain characteristic is compressive.
3. The amplifying system of claim 1 wherein the first gain characteristic is compressive and the second gain characteristic is expansive.
4. The amplifying system of claim 1 wherein the bias circuitry is configured to further substantially maintain alignment of the distortion inflection points between the first gain characteristic and the second gain characteristic over design corners by providing substantially constant headroom between quiescent bias voltage and turnoff of the first gain stage and the second gain stage.
5. The amplifying system of claim 1 wherein the first gain stage is configured to provide RF degeneration control of gain.
6. The amplifying system of claim 1 wherein the second gain stage comprises a plurality of gain segments with a segmentation control.
7. The amplifying system of claim 1 wherein the bias circuitry is further configured to substantially maintain alignment of distortion inflection points between the first gain characteristic and the second gain characteristic during operation by setting a substantially constant saturation voltage for each of the first gain stage and the second gain stage over design corners.
8. The amplifying system of claim 1 wherein the first gain stage is a driver stage that drives the second gain stage.
9. The amplifying system of claim 8 wherein the second gain stage is an output stage.
10. The amplifying system of claim 1 wherein the bias circuitry is further configured to provide a constant distortion bias with degeneration for at least one of the first gain stage and the second gain stage.
11. The amplifying system of claim 1 wherein the first gain stage and the second gain stage are both variable gain amplifiers.
12. The amplifying system of claim 1 further including a gain control loop wherein at least one of the first gain stage and the second gain stage is a variable gain stage that is configured to adjust gain in response to a feedback signal generated by the gain control loop.
13. The amplifying system of claim 12 wherein the gain control loop includes a gain sensor coupled in series with automatic constant distortion bias circuitry that is configured to receive a gain measurement signal from the gain sensor and generate the feedback signal.
14. The amplifying system of claim 1 further including a bias control loop wherein at least one of the first gain stage and the second gain stage is configured to adjust gain in response to the feedback signal generated by the bias control loop.
15. The amplifying system of claim 14 wherein the bias control loop includes a gain sensor coupled in series with automatic constant distortion bias circuitry that is configured to receive a gain measurement signal from the gain sensor and drive adjustable constant distortion bias circuitry to generate the feedback signal.
16. The amplifying system of claim 1 wherein the first gain stage is a driver stage that is configured to drive the second stage that is an output stage made up of a segmented amplifier controlled by a segmentation control driven by a feedback signal generated by a constant gain loop.
17. The amplifying system of claim 16 wherein the constant gain loop comprises a gain sensor and a flash analog-to-digital converter (ADC) that drives the segmentation control in response to a gain measurement signal generated by the gain sensor.
18. A method for an amplifying system comprising:
providing a first gain stage with a first gain characteristic;
providing a second gain stage with a second gain characteristic;
providing a reference headroom voltage generator;
biasing the first gain stage and the second gain stage in response to a reference voltage generated by the reference headroom voltage generator to provide a bias such that a voltage difference between a bias point and a threshold voltage of at least one of the first gain stage and the second gain stage is maintained at a constant level to substantially maintain alignment of distortion inflection points between the first gain characteristic and the second gain characteristic to limit total gain variations to less than 0.1 dB per dB of output stage power during operation for an input power to the first gain stage that ranges from −50 dB to 0 dB.
19. The method for the amplifying system of claim 18 wherein the first gain characteristic is expansive and the second gain characteristic is compressive.
20. The method for the amplifying system of claim 18 wherein the first gain characteristic is compressive and the second gain characteristic is expansive.
21. The method for the amplifying system of claim 18 further comprising biasing the first gain stage and the second gain stage to maintain alignment of the distortion inflection points between the first gain characteristic and the second gain characteristic over design corners.
22. The method for the amplifying system of claim 21 further comprising biasing the first gain stage and the second gain stage to maintain substantially constant headroom between quiescent bias voltage and turnoff of the first gain stage and the second gain stage.
23. The method for the amplifying system of claim 18 further comprising controlling gain of the first gain stage with RF degeneration.
24. The method of the amplifying system of claim 18 further comprising driving the second gain stage with the first gain stage.
25. The method of the amplifying system of claim 24 wherein the second gain stage comprises a plurality of gain segments with a segmentation control.
26. The method of the amplifying system of claim 18 further comprising setting a substantially constant saturation voltage for each of the first gain stage and the second gain stage to substantially maintain alignment of distortion inflection points between the first gain characteristic and the second gain characteristic over design corners during operation.
27. The method of the amplifying system of claim 18 further comprising biasing at least one of the first gain stage and the second gain stage to provide a constant distortion bias with degeneration for at the least one of the first gain stage and the second gain stage.