Low-noise amplifier (LNA) input impedance adjustment circuit
Aspects of the present disclosure provide a circuit configured to adjust an input impedance of an amplifier such as a low-noise amplifier. In certain aspects, the circuit is coupled to a node, wherein the node is between a first transistor and a second transistor of the amplifier. The circuit may include an inductor and a capacitor coupled in series, wherein the inductor is coupled with one or more load inductors of the amplifier through negative magnetic coupling.
1. An apparatus, comprising:
an amplifier, comprising:
a first transistor having a gate, a source, and a drain, wherein the gate of the first transistor is coupled to an input of the amplifier, and the source of the first transistor is coupled to a ground;
a second transistor having a gate, a source, and a drain, wherein the gate of the second transistor is configured to receive a bias voltage, and the source of the second transistor is coupled to the drain of the first transistor;
a first inductor coupled between the drain of the second transistor and a supply rail; and
a circuit coupled to a node, wherein the node is between the first transistor and the second transistor, and the circuit comprises:
a second inductor, wherein the second inductor is coupled with the first inductor through negative magnetic coupling; and
a capacitor coupled in series with the second inductor.
2. The apparatus of claim 1 , wherein the circuit is coupled between the node and the supply rail.
3. The apparatus of claim 1 , wherein the circuit is coupled between the node and the ground.
4. The apparatus of claim 1 , further comprising a filter coupled to the input of the amplifier.
5. The apparatus of claim 4 , wherein the filter comprises a bandpass filter.
6. The apparatus of claim 1 , wherein the amplifier further comprises a third inductor magnetically coupled with the first inductor.
7. The apparatus of claim 6 , wherein the third inductor is coupled to an output of the amplifier.
8. The apparatus of claim 7 , further comprising a mixer coupled to the output of the amplifier.
9. The apparatus of claim 1 , wherein the amplifier further comprises a source inductor coupled between the source of the first transistor and the ground.
10. The apparatus of claim 1 , wherein the amplifier further comprises a gate inductor coupled between the gate of the first transistor and the input of the amplifier.
11. The apparatus of claim 1 , wherein the capacitor comprises a variable capacitor.
12. The apparatus of claim 11 , wherein the variable capacitor comprises multiple switching-capacitor circuits coupled in parallel, each of the switching-capacitor circuits comprising a respective capacitor and a respective switch coupled in series.
13. The apparatus of claim 1 , wherein the first inductor is coupled to an output of the amplifier.
14. The apparatus of claim 13 , further comprising a mixer coupled to the output of the amplifier.
15. The apparatus of claim 1 , further comprising a radio frequency (RF) front-end module, wherein the RF front-end module includes:
the amplifier; and
a filter coupled to the input of the filter.
16. The apparatus of claim 15 , wherein the filter comprises a bandpass filter.
17. The apparatus of claim 15 , wherein the RF front-end module is coupled between an antenna and a receive circuit.
18. The apparatus of claim 17 , wherein the receive circuit is integrated on a chip coupled to the RF front-end module.
19. The apparatus of claim 1 , further comprising:
a second capacitor coupled to the first inductor; and
a resistor coupled to the first inductor.
20. The apparatus of claim 19 , wherein the second capacitor is coupled in parallel with the first inductor.
21. The apparatus of claim 19 , wherein the resistor is coupled in parallel with the first inductor.