Two-stage LNA with mutual coupling
Compact low noise amplifiers that have wide-band coverage while meeting necessary input matching and output matching characteristics. Embodiments include a wide-band, two-stage LNA with minimum degradation in performance compared to multiple narrow-band, single-stage LNAs. A generalized embodiment includes a first amplifier stage having a terminal coupled to a mutually coupled inductor circuit and to a second amplifier stage. The second amplifier stage includes a terminal coupled to the mutually coupled inductor circuit. The mutually coupled inductor circuit comprises electromagnetically coupled inductors L 1 , L 2 . Second terminals of the first and second amplifier stages are coupled to respective degeneration inductors. The electromagnetically coupled inductors L 1 , L 2 of the inductor circuit substantially increase the output bandwidth of the LNA with minimum degradation in performance.
1. A low noise amplifier, including:
(a) a first amplifier stage comprising:
(1) at least one input field effect transistor (FET) each having a gate configured to receive an associated radio frequency (RF) input signal, a source configured to be coupled to an associated degeneration inductor, and a drain; and
(2) a second FET having a gate configured to receive a first bias voltage, a source coupled to the drain of the at least one input FET, and a drain coupled to a first output node;
(b) a second amplifier stage comprising:
(1) a third FET having a gate coupled to the first output node, a source configured to be coupled to an associated degeneration inductor, and a drain; and
(2) a fourth FET having a gate configured to receive a second bias voltage, a source coupled to the drain of the third FET, and a drain coupled to a second output node;
(c) an inductor circuit including:
(1) a first inductor coupled to the output of the first output node and configured to be coupled to a first supply voltage; and
(2) a second inductor coupled to the second output node and configured to be coupled to a second supply voltage;
wherein the first inductor and the second inductor are electromagnetically coupled such that a mutual coupling factor K exists between the first inductor and the second inductor of the inductor circuit.
2. The invention of claim 1 , wherein the mutual coupling factor K is equal to or greater than about −0.5 and less than or equal to about +0.5.
3. The invention of claim 1 , wherein the mutual coupling factor K is equal to or greater than about −0.3 and less than or equal to about +0.3.
4. The invention of claim 1 , wherein the absolute value of the mutual coupling factor K is in a range from and including about 0.3 to and including about 0.5.
5. The invention of claim 1 , further including, for each input FET, a matching network coupled to the gate of such input FET and configured to receive the associated RF input signal.
6. The invention of claim 1 , further including a tuning capacitor coupled between the first output node and the gate of the third FET.
7. The invention of claim 1 , further including a selectable-value capacitor coupled in parallel with a corresponding one of the first inductor and/or the second inductor.
8. The invention of claim 1 , further including a selectable-value resistor coupled in parallel with a corresponding one of the first inductor and/or the second inductor.
9. The invention of claim 1 , wherein the FETs are MOSFETs.
10. The invention of claim 1 , wherein the FETs are MOSFETs made by a silicon-on-insulator process.
11. A low noise amplifier, including:
(a) a first amplifier stage comprising:
(1) at least one input field effect transistor (FET) each having a gate configured to receive an associated radio frequency (RF) input signal, a source configured to be coupled to an associated degeneration inductor, and a drain; and
(2) a second FET having a gate configured to receive a first bias voltage, a source coupled to the drain of the at least one input FET, and a drain coupled to a first output node;
(b) a second amplifier stage comprising a third FET having a gate coupled to the first output node, a source configured to be coupled to an associated degeneration inductor, and a drain coupled to a second output node; and
(c) an inductor circuit including:
(1) a first inductor coupled to the output of the first output node and configured to be coupled to a first supply voltage; and
(2) a second inductor coupled to the second output node and configured to be coupled to a second supply voltage;
wherein the first inductor and the second inductor are electromagnetically coupled such that a mutual coupling factor K exists between the first inductor and the second inductor of the inductor circuit.
12. The invention of claim 11 , wherein the mutual coupling factor K is equal to or greater than about −0.5 and less than or equal to about +0.5.
13. The invention of claim 11 , wherein the mutual coupling factor K is equal to or greater than about −0.3 and less than or equal to about +0.3.
14. The invention of claim 11 , wherein the absolute value of the mutual coupling factor K is in a range from and including about 0.3 to and including about 0.5.
15. The invention of claim 11 , further including, for each input FET, a matching network coupled to the gate of such input FET and configured to receive the associated RF input signal.
16. The invention of claim 11 , further including a tuning capacitor coupled between the first output node and the gate of the third FET.
17. The invention of claim 11 , further including a selectable-value capacitor coupled in parallel with a corresponding one of the first inductor and/or the second inductor.
18. The invention of claim 11 , further including a selectable-value resistor coupled in parallel with a corresponding one of the first inductor and/or the second inductor.
19. The invention of claim 11 , wherein the FETs are MOSFETs.
20. The invention of claim 11 , wherein the FETs are MOSFETs made by a silicon-on-insulator process.