Amplifiers with boosted or deboosted source degeneration inductance

1. An apparatus comprising:

an amplifier circuit configurable to receive an input signal and provide an output signal for a first band group or a second output signal for a second band group, the amplifier circuit comprising a source degeneration inductor; and

a feedback circuit coupled between a node of the amplifier circuit and the source degeneration inductor, the feedback circuit configured to provide feedback to vary an input impedance of an amplifier comprising the amplifier circuit and the feedback circuit, the feedback circuit being enabled when the amplifier circuit provides the output signal for the first band group and disabled when the amplifier circuit provides the second output signal for the second band group.

2. The apparatus of claim 1 , the amplifier circuit comprising:

a gain transistor coupled to the source degeneration inductor and configurable to receive and amplify the input signal; and

a cascode transistor coupled to the gain transistor and configurable to provide the output signal.

3. The apparatus of claim 2 , the amplifier circuit further comprising:

a second cascode transistor coupled to the gain transistor and configurable to provide a second output signal.

4. The apparatus of claim 3 , the amplifier circuit further comprising:

a second gain transistor coupled to a second source degeneration inductor and configurable to receive and amplify a second input signal;

a third cascode transistor coupled to the second gain transistor and the cascode transistor; and

a fourth cascode transistor coupled to the second gain transistor and the second cascode transistor.

5. The apparatus of claim 2 , the feedback circuit comprising:

a second gain transistor coupled to the cascode transistor and configurable to receive and amplify the output signal; and

a second cascode transistor coupled between the second gain transistor and the source degeneration inductor.

6. The apparatus of claim 1 , further comprising:

a second feedback circuit coupled between a second node of the amplifier circuit and the source degeneration inductor or a second source degeneration inductor within the amplifier circuit.

7. The apparatus of claim 2 , the amplifier circuit further comprising:

an adjustable capacitor coupled between a gate and a source of the gain transistor.

8. The apparatus of claim 5 , the gain transistor and the cascode transistor comprising N-channel metal oxide semiconductor (NMOS) transistors, and the second gain transistor and the second cascode transistor comprising P-channel metal oxide semiconductor (PMOS) transistors.

9. The apparatus of claim 1 , the amplifier circuit configurable to provide either the output signal or a second output signal in a single-output mode and to provide both the output signal and the second output signal in a multi-output mode.

10. The apparatus of claim 9 , the feedback circuit being enabled in the single-output mode and disabled in the multi-output mode.

11. The apparatus of claim 1 , the feedback circuit being programmable to provide feedback or no feedback.

12. The apparatus of claim 1 , the feedback circuit being always enabled to provide feedback.

13. The apparatus of claim 1 , the feedback circuit having a variable gain to provide a variable input impedance for the amplifier.

14. A method comprising:

amplifying an input signal with an amplifier circuit comprising a source degeneration inductor to obtain an output signal for a first band group or a second output signal for a second band group;

providing feedback with a feedback circuit coupled between a node of the amplifier circuit and the source degeneration inductor to vary an input impedance of an amplifier comprising the amplifier circuit and the feedback circuit;

enabling the feedback circuit when the output signal for the first band group is provided; and

disabling the feedback circuit when the second output signal for the second band group is provided.

15. The method of claim 14 , further comprising:

providing either the output signal or a second output signal in a single-output mode;

providing both the output signal and the second output signal in a multi-output mode;

enabling the feedback circuit in the single-output mode; and

disabling the feedback circuit in the multi-output mode.

16. An apparatus comprising:

means for amplifying an input signal to obtain an output signal for a first band group or a second output signal for a second band group, the means for amplifying comprising means for degenerating; and

means for providing feedback coupled between a node of the means for amplifying and the means for degenerating, the means for providing feedback configured to vary an input impedance of an amplifier means comprising the means for amplifying and the means for providing feedback, the means for providing feedback being enabled when the means for amplifying provides the output signal for the first band group and being disabled when the means for amplifying provides the second output signal for the second band group.

17. The apparatus of claim 16 , the means for amplifying configured to provide either the output signal or a second output signal in a single-output mode and to provide both the output signal and the second output signal in a multi-output mode, and the means for providing feedback being enabled in the single-output mode and disabled in the multi-output mode.