Low noise amplifier circuit
An amplifier for converting a single-ended input signal to a differential output signal. The amplifier comprises a first transistor, a second transistor, a third transistor and a fourth transistor. The first transistor, configured in common-source or common-emitter mode, receives the single-ended input signal and generates a first part of the differential output signal. The second transistor, also configured in common-source or common-emitter mode, generates a second part of the differential output signal. The third and fourth transistors are capacitively cross-coupled. The amplifier further comprises inductive degeneration such that a source or emitter of the first transistor is connected to a first inductor and a source or emitter of the second transistor is connected to a second inductor.
1. An amplifier comprising a pair of inductively degenerated transistors that are configured to perform single-ended-to-differential conversion to convert a single-ended input signal to a differential output signal, wherein the single-ended-to-differential conversion is performed in such a way that noise and nonlinearity due to a second or auxiliary branch of the amplifier are cancelled in the differential output signal, wherein a source of each inductively degenerated transistor of the pair of inductively degenerated transistors is connected to a respective inductor, wherein the amplifier further comprises a third transistor and a fourth transistor, and wherein the third transistor and fourth transistor are cross-coupled to each other and connected to a first transistor and a second transistor of the pair of inductively degenerated transistors.
2. The amplifier of claim 1 , wherein an input impedance of the amplifier is configured to match an output impedance of a radio frequency filter at a respective operating frequency.
3. The amplifier of claim 1 , wherein the amplifier is a Low Noise Amplifier (LNA) of a receiver of a wireless communication device.
4. The amplifier of claim 1 , wherein the first transistor is configured in common-source or common-emitter mode, to receive the single-ended input signal and generate a first part of the differential output signal, a source or emitter of the first transistor being connected to a first end of a first inductor, and a gate or base of the first transistor being coupled to the single-ended input signal.
5. The amplifier of claim 4 , wherein the second transistor is configured in common-source or common-emitter mode, to generate a second part of the differential output signal, a source or emitter of the second transistor being connected to a first end of a second inductor.
6. The amplifier of claim 5 , wherein:
a drain or collector of the first transistor is coupled to a gate or base of the fourth transistor via a first capacitor;
a drain or collector of the second transistor is coupled to a gate or base of the third transistor via a second capacitor;
the drain or collector of the first transistor is connected to a source or emitter of the third transistor, the drain or collector of the second transistor is connected to a source or emitter of the fourth transistor; and
the drain or collector of the first transistor is coupled to a gate or base of the second transistor directly or via a third capacitor.
7. A method in a receiver for operating at multiple frequency bands, the method comprising: receiving in one or more radio-frequency filters, a single-ended input signal; generating in the one or more radio-frequency filters, a single-ended output signal based on the single-ended input signal; receiving the generated single-ended output signal in one or more amplifiers; and converting, by a pair of inductively degenerated transistors in the one or more amplifiers, the single-ended output signal to a differential output signal in the one or more amplifiers, wherein input impedances of the one or more amplifiers are configured to match output impedances of the one or more radio frequency filters at respective operating frequencies, wherein a source of each inductively degenerated transistor of the pair of inductively degenerated transistors is connected to a respective inductor, wherein an amplifier of the one or more amplifiers further comprises a third transistor and a fourth transistor, and wherein the third transistor and fourth transistor are cross-coupled to each other and connected to a first transistor and a second transistor of the pair of inductively degenerated transistors.
8. The method of claim 7 , wherein noise and nonlinearity due to a second branch of the one or more amplifiers are cancelled in the differential output signal.
9. The method of claim 7 , further comprising:
controlling an input impedance of the one or more amplifiers to match an output impedance of the one or more radio-frequency filters at respective operating frequencies.
10. A wireless communication device comprising a receiver, the receiver comprising an amplifier comprising a pair of inductively degenerated transistors that are configured to perform single-ended-to-differential conversion to convert a single-ended input signal to a differential output signal, wherein the single-ended-to-differential conversion is performed in such a way that noise and nonlinearity due to a second or auxiliary branch of the amplifier are cancelled in the differential output signal, wherein a source of each inductively degenerated transistor of the pair of inductively degenerated transistors is connected to a respective inductor, wherein the amplifier further comprises a third transistor and a fourth transistor, and wherein the third transistor and fourth transistor are cross-coupled to each other and connected to a first transistor and a second transistor of the pair of inductively degenerated transistors.
11. The wireless communication device of claim 10 , wherein the receiver is a multiband receiver.