Low noise amplifier for wideband tunable matching

1. A low noise amplifier having a common source and source degeneration structure, the low noise amplifier comprising:

a first inductor having one terminal connected to an input terminal receiving a signal; a second inductor having one terminal connected to a ground;

a MOS transistor having a gate connected to the first inductor, a source connected to the other terminal of the second inductor, and a drain transmitting a signal;

a variable capacitor connected between the source and gate of the MOS transistor and varying an input matching frequency at the input terminal, wherein a tunable range of the variable capacitor is equal to or greater than a sum of a parasitic capacitance generated at a pad of an integrated circuit connected to the input terminal and a parasitic capacitance generated at a package; and

a shunt inductor connected between the gate of the MOS transistor and the ground.

2. The low noise amplifier as recited in claim 1 , wherein the variable capacitance is continuously varied in response to a control signal.

3. The low noise amplifier as recited in claim 1 , wherein the variable capacitor includes:

a plurality of switches connected in parallel and switched in response to a control signal; and

a plurality of unit capacitors connected to the corresponding switches.

4. The low noise amplifier as recited in claim 1 , wherein the shunt inductor being resonated with a parasitic capacitor capacitance generated at the gate of the MOS transistor in association with a parasitic inductance generated at the gate of the MOS transistor.

5. The low noise amplifier as recited in claim 4 , further comprising a capacitor connected between the shunt inductor and the ground.

6. The low noise amplifier as recited in claim 5 , further comprising:

a third inductor having one terminal connected to a negative input terminal receiving a signal;

a fourth inductor having one terminal connected to the ground;

a differential-input MOS transistor having a gate connected to the third inductor, a source connected to the other terminal of the fourth inductor, and a drain transmitting a signal; and

a differential-input variable capacitor connected between the source and gate of the differential-input MOS transistor so as to vary the input matching frequency at the input terminal,

wherein the shunt inductor is connected between the gate of the differential-input MOS transistor and the ground.

7. The low noise amplifier as recited in claim 1 , further comprising a shunt capacitor connected to the input terminal, the shunt capacitor being resonated with a parasitic inductance component applied to the gate of the MOS transistor in association with a parasitic capacitance generated at a gate of the MOS transistor.

8. The low noise amplifier as recited in claim 7 , wherein the shunt capacitor is connected between the input terminal and the ground.

9. The low noise amplifier as recited in claim 7 , further comprising:

a third inductor having one terminal connected to a negative input terminal receiving a signal;

a fourth inductor having one terminal connected to the ground;

a differential-input MOS transistor having a gate connected to the third inductor, a source connected to the other terminal of the fourth inductor, and a drain transmitting a signal; and

a differential-input variable capacitor connected between the source and gate of the MOS transistor so as to vary the input matching frequency at the input terminal,

wherein the shunt capacitor is connected between the input terminal and the ground.