Constant-phase attenuator techniques in radio frequency front end (RFFE) amplifiers
Aspects of the disclosure relate to devices, wireless communication apparatuses, methods, and circuitry implementing a low noise amplifier (LNA) with phase-shifting circuitry to achieve a continuous phase at the output of the LNA. One aspect is an amplifier including a high gain active path comprising active circuitry, and a low gain path comprising passive circuitry and phase-shifting circuitry. In one or more aspects, the phase-shifting circuitry is configured to shift a phase of an input signal within the low gain path such that the phase of an output signal outputted from the low gain path approximately matches a phase of an output signal outputted from the high gain active path. In at least one aspect, a gain of the high gain active path is higher than a gain of the low gain passive path.
1. An amplifier having an input and an output and comprising:
a high gain path coupled between the input and the output and comprising active circuitry; and
a low gain path coupled between the input and the output and comprising phase-shifting circuitry,
wherein the phase-shifting circuitry is configured to shift a phase of an input signal within the low gain path such that the phase of an output signal at the output of the amplifier from the low gain path approximately matches a phase of the output signal at the output of the amplifier from the high gain path, and wherein a gain of the high gain path is higher than a gain of the low gain path, wherein the phase shifting circuitry comprises an inductor coupled in series between the input and the output of the amplifier, the phase-shifting circuitry further comprising a first shunt capacitor and a second shunt capacitor, the inductor coupled between the first shunt capacitor and the second shunt capacitor, wherein the inductor is tapped by a third shunt capacitor.
2. The amplifier of claim 1 , wherein at least one of the first shunt capacitor, the second shunt capacitor, and the third shunt capacitor is a tunable capacitor that is configured to tune an amount of shift of the phase of the input signal within the low gain path.
3. The amplifier of claim 1 , wherein at least one of the first shunt capacitor and the second shunt capacitor is configured to be disabled to disable the phase-shifting circuitry such that the phase of the input signal within the low gain path is not shifted.
4. The amplifier of claim 1 , wherein the inductor is center-tapped by the third shunt capacitor.
5. The amplifier of claim 1 , further comprising a capacitor in series with the phase shifting circuitry.
6. The amplifier of claim 1 , wherein the first shunt capacitor and the second shunt capacitor are variable capacitors.
7. The amplifier of claim 1 , wherein the third shunt capacitor is coupled in parallel to a switch.
8. The amplifier of claim 1 , further comprising a capacitor coupled in series with the inductor, the first shunt capacitor coupled between the capacitor and the inductor.
9. The amplifier of claim 1 , wherein the inductor forms a portion of an impedance matching network of the low gain path.
10. The amplifier of claim 1 , further comprising a switch coupled between the input and the inductor.
11. The amplifier of claim 1 , wherein the phase-shifting circuitry provides for at least one of a positive 180 degrees phase shift or a negative 180 degrees phase shift.
12. The amplifier of claim 1 , wherein the active circuitry comprises at least one transistor having a gate coupled to an input of the amplifier, a source coupled to ground, and a load coupled between a power supply and a drain of the at least one transistor.
13. The amplifier of claim 1 , wherein the amplifier is a low noise amplifier (LNA), and wherein the gain of the low gain path is approximately zero such that the low gain path is a bypass path bypassing the active circuitry of the high gain path.
14. A method of operation for an amplifier, the method comprising:
outputting, by a high gain active path comprising active circuitry, a first signal comprising a first phase;
receiving, by a low gain passive path comprising passive circuitry, a second signal comprising a second phase,
wherein a gain of the high gain active path is higher than a gain of the low gain passive path;
shifting, by a phase-shifting circuitry within the low gain passive path, the second phase of the second signal to a third phase to generate a third signal comprising the third phase; and
outputting, by the low gain passive path, the third signal comprising the third phase, wherein the third phase approximately matches the first phase.
15. The method of claim 14 , wherein the phase-shifting circuitry comprises at least one inductor and at least one capacitor, and wherein at least one of the at least one capacitor is a tunable capacitor that is configured to tune an amount of shift of the second phase of the second signal within the low gain passive path.
16. The method of claim 15 , further comprising disabling the phase-shifting circuitry such that the second phase of the second signal within the low gain passive path is not shifted.
17. The method of claim 15 , wherein at least one of the at least one inductor provides for phase-shifting and impedance matching.
18. The method of claim 15 , wherein one of the at least one capacitor is a series capacitor that provides for an improved quality factor (Q) for the amplifier, which corrects for any phase slope differences between the third phase of the third signal outputted from the low gain passive path and the first phase of the first signal outputted from the high gain active path.
19. An amplifier having an input and an output and comprising:
a high gain path coupled between the input and the output and comprising active circuitry; and
a low gain path coupled between the input and the output and comprising phase-shifting circuitry,
wherein the phase-shifting circuitry is configured to shift a phase of an input signal within the low gain path such that the phase of an output signal at the output of the amplifier from the low gain path approximately matches a phase of the output signal at the output of the amplifier from the high gain path, and wherein a gain of the high gain path is higher than a gain of the low gain path, wherein the phase-shifting circuitry comprises a first inductor coupled to a first end of a capacitor, and a second inductor coupled to a second end of the capacitor.
20. An amplifier having an input and an output and comprising:
a high gain path coupled between the input and the output and comprising active circuitry; and
a low gain path coupled between the input and the output and comprising phase-shifting circuitry,
wherein the phase-shifting circuitry is configured to shift a phase of an input signal within the low gain path such that the phase of an output signal at the output of the amplifier from the low gain path approximately matches a phase of the output signal at the output of the amplifier from the high gain path, and wherein a gain of the high gain path is higher than a gain of the low gain path, wherein the phase-shifting circuitry comprises two inductors coupled together in series, and a shunt capacitor having a first end coupled between the two inductors and a second end coupled to ground.