US-20260128713-A1 - OSCILLATOR CIRCUITS WITH FLICKER NOISE SUPPRESSION BY PHASE-SHIFTED SELF-INJECTION

Abstract

An oscillator circuit includes a first cross coupled pair, a second cross coupled pair, a resonant circuit coupled between the first cross coupled pair and the second cross coupled pair and a first injection circuit. The resonant circuit includes a first node outputting a first voltage signal and a second node outputting a second voltage signal. The first injection circuit is coupled to the first cross coupled pair and injects a first compensating current with a first predetermined phase to a predetermined node of the first cross coupled pair.

Inventors

• Jiun-Yan Chen
• Chao-Ching Hung
• Yu-Li Hsueh

Assignees

• MEDIATEK INC.

Dates

Publication Date

20260507

Application Date

20250523

Claims (20)

1. 1 . An oscillator circuit, comprising: a first cross coupled pair; a second cross coupled pair; a resonant circuit, coupled between the first cross coupled pair and the second cross coupled pair and comprising a first node outputting a first voltage signal and a second node outputting a second voltage signal; and a first injection circuit, coupled to the first cross coupled pair and injecting a first compensating current with a first predetermined phase to a predetermined node of the first cross coupled pair.
2. 2 . The oscillator circuit of claim 1 , wherein the first cross coupled pair comprises: a first transistor, comprising a first electrode, a second electrode and a third electrode; and a second transistor, comprising a first electrode, a second electrode and a third electrode, wherein the first electrode of the first transistor is coupled to the second electrode of the second transistor, and the first electrode of the second transistor is coupled to the second electrode of the first transistor, and wherein the predetermined node is a node connecting to the third electrode of the first transistor.
3. 3 . The oscillator circuit of claim 2 , wherein the first electrode of the first transistor is coupled to the first node of the resonant circuit and the first electrode of the second transistor is coupled to the second node of the resonant circuit, and wherein the first voltage signal is provided to the first injection circuit.
4. 4 . The oscillator circuit of claim 2 , wherein the first injection circuit comprises: a filter circuit, coupled to the third electrode of the first transistor and receiving the first voltage signal; and a feedthrough circuit, coupled to the filter circuit and providing a current path between the third electrode of the first transistor and a power supply node.
5. 5 . The oscillator circuit of claim 2 , wherein the first injection circuit injects the first compensating current in response to the first voltage signal, and the first predetermined phase is a 90-degree phase.
6. 6 . The oscillator circuit of claim 2 , further comprising: a second injection circuit, coupled to the third electrode of the second transistor and injecting a second compensating current with a second predetermined phase to the third electrode of the second transistor.
7. 7 . The oscillator circuit of claim 6 , wherein the second voltage signal is provided to the second injection circuit and the second injection circuit injects the second compensating current in response to the second voltage signal.
8. 8 . The oscillator circuit of claim 1 , wherein the second cross coupled pair comprises: a third transistor, comprising a first electrode, a second electrode and a third electrode; and a fourth transistor, comprising a first electrode, a second electrode and a third electrode, wherein the first electrode of the third transistor is coupled to the second electrode of the fourth transistor, and the first electrode of the fourth transistor is coupled to the second electrode of the third transistor.
9. 9 . The oscillator circuit of claim 8 , further comprising: a third injection circuit, coupled to the third electrode of the third transistor and injecting a third compensating current with a third predetermined phase to the third electrode of the third transistor.
10. 10 . The oscillator circuit of claim 9 , wherein the first voltage signal is provided to the third injection circuit and the third injection circuit injects the third compensating current in response to the first voltage signal.
11. 11 . The oscillator circuit of claim 8 , further comprising: a fourth injection circuit, coupled to the third electrode of the fourth transistor and injecting a fourth compensating current with a fourth predetermined phase to the third electrode of the fourth transistor.
12. 12 . The oscillator circuit of claim 11 , wherein the second voltage signal is provided to the fourth injection circuit and the fourth injection circuit injects the fourth compensating current in response to the second voltage signal.
13. 13 . An oscillator circuit, comprising: a first cross coupled pair; a second cross coupled pair; a resonant circuit, coupled between the first cross coupled pair and the second cross coupled pair and comprising a first node outputting a first voltage signal and a second node outputting a second voltage signal; and a plurality of injection circuits, each being coupled to one of the first cross coupled pair and the second cross coupled pair and injecting a compensating current with a predetermined phase to a predetermined node of the one of the first cross coupled pair and the second cross coupled pair, wherein one of the injection circuits comprises: a filter circuit, coupled to the predetermined node of the one of the first cross coupled pair and the second cross coupled pair and receiving one of the first voltage signal and the second voltage signal; and a feedthrough circuit, coupled to the filter circuit and providing a current path between the predetermined node and a power supply node.
14. 14 . The oscillator circuit of claim 13 , wherein the injection circuits comprise: a first injection circuit, coupled to the first cross coupled pair; a second injection circuit, coupled to the first cross coupled pair; a third injection circuit, coupled to the second cross coupled pair; and a fourth injection circuit, coupled to the second cross coupled pair.
15. 15 . The oscillator circuit of claim 14 , wherein the first cross coupled pair comprises: a first transistor, comprising a first electrode, a second electrode and a third electrode; and a second transistor, comprising a first electrode, a second electrode and a third electrode, wherein the first electrode of the first transistor is coupled to the second electrode of the second transistor, and the first electrode of the second transistor is coupled to the second electrode of the first transistor, and wherein the first injection circuit is coupled to the third electrode of the first transistor and the second injection circuit is coupled to the third electrode of the second transistor.
16. 16 . The oscillator circuit of claim 14 , wherein the second cross coupled pair comprises: a third transistor, comprising a first electrode, a second electrode and a third electrode; and a fourth transistor, comprising a first electrode, a second electrode and a third electrode, wherein the first electrode of the third transistor is coupled to the second electrode of the fourth transistor, and the first electrode of the fourth transistor is coupled to the second electrode of the third transistor, and wherein the third injection circuit is coupled to the third electrode of the third transistor and the fourth injection circuit is coupled to the third electrode of the fourth transistor.
17. 17 . The oscillator circuit of claim 14 , wherein the first voltage signal is provided to the first injection circuit and the third injection circuit, and the second voltage signal is provided to the second injection circuit and the fourth injection circuit.
18. 18 . The oscillator circuit of claim 14 , wherein the first injection circuit injects a first compensating current in response to the first voltage signal, the second injection circuit injects a second compensating current in response to the second voltage signal, the third injection circuit injects a third compensating current in response to the first voltage signal, and the fourth injection circuit injects a fourth compensating current in response to the second voltage signal.
19. 19 . The oscillator circuit of claim 13 , wherein the predetermined phase is a 90-degree phase.
20. 20 . The oscillator circuit of claim 13 , wherein there is a 180-degree phase shift between the first voltage signal and the second voltage signal.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/715,681, filed on Nov. 4, 2024. The content of the application is incorporated herein by reference. BACKGROUND Current noise significantly impacts the performance of oscillator circuits, primarily reflected in the degradation of phase noise. When current noise is injected into the oscillator's resonant circuit, the noise signal propagates through the resonant circuit and the oscillator's gain path, affecting the output signal. The injected current noise influences the oscillator's instantaneous phase, leading to phase deviations. The phase deviation of the oscillator is sensitive to the timing of the current noise injection. For the injected current noise with the same magnitude, different phase deviations are generated as the time of injection into the oscillator is different. Impulse Sensitivity Function (ISF) is a mathematical model used to describe the sensitivity of oscillators to external perturbations, particularly in the analysis of phase noise. ISF is represented as Γ(x), which characterizes the oscillator's response to unit impulses at different points within its cycle. The more symmetric the curve of ISF is, the better flicker noise suppression capability the oscillator circuit has. However, due to the nonlinear characteristics of oscillator circuits, ISF curves are often asymmetrical. Therefore, improving the symmetry of the ISF curve to enhance noise suppression capability is an important issue in oscillator circuit design. SUMMARY According to an embodiment of the invention, an oscillator circuit comprises a first cross coupled pair, a second cross coupled pair, a resonant circuit coupled between the first cross coupled pair and the second cross coupled pair and a first injection circuit. The resonant circuit comprises a first node outputting a first voltage signal and a second node outputting a second voltage signal. The first injection circuit is coupled to the first cross coupled pair and injects a first compensating current with a first predetermined phase to a predetermined node of the first cross coupled pair. According to another embodiment of the invention, an oscillator circuit comprises a first cross coupled pair, a second cross coupled pair, a resonant circuit coupled between the first cross coupled pair and the second cross coupled pair and a plurality of injection circuits. The resonant circuit comprises a first node outputting a first voltage signal and a second node outputting a second voltage signal. Each injection circuit is coupled to one of the first cross coupled pair and the second cross coupled pair and injects a compensating current with a predetermined phase to a predetermined node of the one of the first cross coupled pair and the second cross coupled pair. One of the injection circuits comprises a filter circuit and a feedthrough circuit. The filter circuit is coupled to the predetermined node of the one of the first cross coupled pair and the second cross coupled pair and receives one of the first voltage signal and the second voltage signal. The feedthrough circuit is coupled to the filter circuit and provides a current path between the predetermined node and a power supply node. These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic diagram of an oscillator circuit according to an embodiment of the invention. FIG. 2 shows an exemplary circuit diagram of an injection circuit according to an embodiment of the invention. FIG. 3 shows an exemplary circuit diagram of an oscillator circuit according to a first embodiment of the invention. FIG. 4 shows an exemplary circuit diagram of an oscillator circuit according to a second embodiment of the invention. FIG. 5 depicts an exemplary circuit diagram of an injection circuit to illustrate the relationship between the drain current and the gate voltage according to an embodiment of the invention. FIG. 6 is a schematic diagram showing the generation of symmetric effective ISF which is achieved by injecting the compensating current with a predetermined phase according to an embodiment of the invention. FIG. 7 is a schematic diagram showing the phase of the load when looking into the resonant circuit according to an embodiment of the invention. DETAILED DESCRIPTION FIG. 1 shows a schematic diagram of an oscillator circuit according to an embodiment of the invention. The oscillator circuit 100 may comprise cross coupled pairs 110 and 120, a resonant circuit 130 and one or more injection circuits, such as the injection circuits 140-1, 140-2, 140-3 and 140-4. The resonant circuit 130 is coupled between the cross coupled pairs 110 and 120 and comprises a first node ou