Injection-locked frequency divider

This application claims the priority benefit of Taiwan application serial no. 95135751, filed on Sep. 27, 2006. All disclosure of the Taiwan application is incorporated herein by reference.

1. Field of the Invention

The present invention relates to an injection-locked frequency divider. More particularly, the present invention relates to an injection-locked frequency divider with an increased locking range by the use of a feedback action of transformers.

2. Description of Related Art

Frequency dividers have been widely applied in mixed signal integrated circuits, for example, crucial elements of multiplexers, phase locked loops, and frequency synthesizers. In recent years, in response to the requirements of consumers and the changes of systems technologies, an injection-locked frequency divider from among various kinds of frequency dividers attracts more attention due to its applicability in the operation of a high-speed system.

FIG. 1 is a schematic structural view of a conventional injection-locked frequency divider. Referring to FIG. 1 , the conventional injection-locked frequency divider 100 is constructed by an LC-tank oscillator 110 and a signal injection unit 120 . The signal injection unit 120 receives an injection signal S IN1 . The LC-tank oscillator 110 adjusts its oscillation frequency through a reactance control signal S IP1 . When the oscillation frequency of the LC-tank oscillator 110 approaches one half of the frequency of the injection signal S IN1 , the conventional injection-locked frequency divider 100 is in a locked state and a frequency division signal S DI1 is generated. Since the LC-tank oscillator 110 has a high oscillation frequency, the conventional injection-locked frequency divider 100 is applicable in a high-speed system. However, since the LC-tank oscillator 110 cannot provide a wide oscillation frequency range, the locking range of the conventional injection-locked frequency divider 100 is limited, thereby affecting the application range of the conventional injection-locked frequency divider 100 in practice.

FIG. 2 is a schematic structural view of another conventional injection-locked frequency divider. Referring to FIG. 2 , the conventional injection-locked frequency divider 200 is constructed by an LC-tank oscillator 210 and a signal injection unit 220 . Similarly, the signal injection unit 220 also receives an injection signal S IN2 . The LC-tank oscillator 210 adjusts its oscillation frequency through a reactance control signal S IP2 . When the oscillation frequency of the LC-tank oscillator 210 approaches one half of the frequency of the injection signal S IN2 , the conventional injection-locked frequency divider 200 is in the locked state and a frequency division signal S DI2 is generated. However, in high-frequency operation, an injection current I 2 is diminished by the parasitic capacitance in the signal injection unit 220 . Therefore, in practical application, the signal injection unit 220 must provide a larger injection current I 2 to maintain the primary characteristics of the conventional injection-locked frequency divider 200 .

FIG. 3 is a schematic structural view of still another conventional injection-locked frequency divider. Referring to FIG. 3 , the conventional injection-locked frequency divider 300 comprises an LC-tank oscillator 310 , a signal injection unit 320 , and a current-limiting unit 330 . Similarly, in a locked state, the injection-locked frequency divider 300 generates a frequency division signal S DI3 through the LC-tank oscillator 310 . In order to solve the defects of the conventional injection-locked frequency divider 200 , the conventional injection-locked frequency divider 300 receives an injection signal S IN3 through the signal injection unit 320 . In another aspect, under the circumstance that an injection current I 3 is controlled by the current-limiting unit 330 , the power consumption of the conventional injection-locked frequency divider 300 is efficiently limited. The LC-tank oscillator 310 adjusts its oscillation frequency through a reactance control signal S IP3 and the current-limiting unit 330 adjusts and controls the injection current I 3 according to a bias current control signal S BI3 . However, the conventional injection-locked frequency divider 300 still has the problem of a narrow locking range.

In view of the above, in the practical application, the conventional injection-locked frequency divider has the problems of narrow locking range and high power consumption. In other words, the conventional injection-locked frequency divider cannot be widely used in various mixed signal integrated circuits due to such problems.

Accordingly, the present invention is directed to an injection-locked frequency divider with an increased locking range of its circuit by the use of the feedback action of transformers.

The present invention provides an injection-locked frequency divider, which is used to perform a frequency division action on an injection signal to generate a frequency division signal. The injection-locked frequency divider comprises a variable reactance unit, a signal injection unit, a first switch, a second switch, a first transformer, and a second transformer. In the aspect of overall operation, the variable reactance unit, the first switch, the second switch, the first transformer, and the second transformer construct a transformer-based LC-tank oscillator. The signal injection unit receives the injection signal. When the injection-locked frequency divider is in a locked state, the transformer-based LC-tank oscillator outputs the frequency division signal through a first connecting terminal and a second connecting terminal.

It should be noted that the first switch and the second switch are cross-coupled. The primary-side coil of the first transformer is coupled between the first connecting terminal and a ground terminal, and the secondary-side coil of the first transformer is coupled between the second terminal of the first switch and an operating voltage. The primary-side coil of the second transformer is coupled between the second connecting terminal and the ground terminal, and the secondary-side coil of the second transformer is coupled between the second terminal of the second switch and the operating voltage.

Furthermore, the present invention further provides an injection-locked frequency divider, which is used to perform a frequency division action on an injection signal to generate a frequency division signal. The injection-locked frequency divider comprises a variable reactance unit, a signal injection unit, a first switch, a second switch, a first transformer, and a second transformer. In the aspect of overall operation, the variable reactance unit, the first switch, the second switch, the first transformer, and the second transformer construct a transformer-based LC-tank oscillator. The signal injection unit receives the injection signal. When the injection-locked frequency divider is in a locked state, the transformer-based LC-tank oscillator outputs the frequency division signal through a first connecting terminal and a second connecting terminal.

It should be noted that the first switch and the second switch are cross-coupled. The primary-side coil of the first transformer is coupled between the first connecting terminal and a ground terminal, and the secondary-side coil of the first transformer is coupled between the control terminal of the first switch and the second connecting terminal. The primary-side coil of the second transformer is coupled between the second connecting terminal and the ground terminal, and the secondary-side coil of the second transformer is coupled between the control terminal of the second switch and the first connecting terminal.

Furthermore, the present invention provides an injection-locked frequency divider, which is used to perform a frequency division action on an injection signal to generate a frequency division signal. The injection-locked frequency divider comprises a variable reactance unit, a signal injection unit, a first P-type transistor, a second P-type transistor, a first transformer, and a second transformer. In the aspect of overall operation, the variable reactance unit, the first P-type transistor, the second P-type transistor, the first transformer, and the second transformer construct a transformer-based LC-tank oscillator. The signal injection unit receives the injection signal. When the injection-locked frequency divider is in a locked state, the transformer-based LC-tank oscillator outputs the frequency division signal through a first connecting terminal and a second connecting terminal.

It should be noted that in the overall architecture, the first P-type transistor and the second P-type transistor are cross-coupled. The primary-side coil of the first transformer is coupled between the first connecting terminal and a ground terminal, and the secondary-side coil of the first transformer is coupled between the base of the first P-type transistor and an operational voltage. The primary-side coil of the second transformer is coupled between the second connecting terminal and the ground terminal, and the secondary-side coil of the second transformer is coupled between the base of the second P-type transistor and the operational voltage.

According to another aspect of the present invention, an injection-locked frequency divider is provided, which is used to perform a frequency division action on an injection signal to generate a frequency division signal. The injection-locked frequency divider comprises a variable reactance unit, a signal injection unit, a first switch, a second switch, a first transformer, and a second transformer. In the aspect of overall operation, the variable reactance unit, the first switch, the second switch, the first transformer, and the second transformer construct a transformer-based LC-tank oscillator. The signal injection unit receives the injection signal. When the injection-locked frequency divider is in a locked state, the transformer-based LC-tank oscillator outputs the frequency division signal.

It should be noted that the transformer-based LC-tank oscillator is derived from two single ended Armstrong oscillators. Therefore, in the overall architecture, the primary-side coil of the first transformer is coupled between the first terminal of the first switch and a ground terminal, and the secondary-side coil of the first transformer is coupled between the control terminal of the first switch and the ground terminal. The primary-side coil of the second transformer is coupled between the first terminal of the second switch and the ground terminal, and the secondary-side coil of the second transformer is coupled between the control terminal of the second switch and the ground terminal.

In view of the above, the injection-locked frequency divider of the present invention employs transformers coupled in various manners. Therefore, by employing the feedback action of the transformers, the injection-locked frequency divider of the present invention not only has a wide locking range but also promotes the application in various mixed signal integrated circuits.

In order to the make aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.

FIG. 1 is a schematic structural view of a conventional injection-locked frequency divider.

FIG. 2 is a schematic structural view of another conventional injection-locked frequency divider.

FIG. 3 is a schematic structural view of still another conventional injection-locked frequency divider.

FIG. 4 is a schematic structural view of an injection-locked frequency divider according to an embodiment of the present invention.

FIG. 5 is a schematic structural view of an injection-locked frequency divider derived from the embodiment of FIG. 4 .

FIG. 6 is a schematic structural view of another injection-locked frequency divider derived from the embodiment of FIG. 4 .

FIG. 7 is a schematic structural view of an injection-locked frequency divider according to yet another embodiment of the present invention.

FIG. 8 is a schematic structural view of an injection-locked frequency divider according to another embodiment of the present invention.

FIG. 9 is a schematic structural view of an injection-locked frequency divider according to still another embodiment of the present invention.

FIG. 10 is a schematic structural view of an injection-locked frequency divider derived from the embodiment of FIG. 9 .

FIG. 11 is a schematic structural view of another injection-locked frequency divider derived from the embodiment of FIG. 9 .

The main technical features of the present invention involve using transformers coupled in various manners to increase the locking range of an injection-locked frequency divider. The injection-locked frequency divider of the present invention will be described in the following embodiments. However, it is known that these embodiments are not intended to limit the present invention. Those skilled in the art can make some modifications to the following embodiments without departing from the spirit and scope of the present invention, and the modifications still fall within the scope of the present invention.

FIG. 4 is a schematic structural view of an injection-locked frequency divider according to an embodiment of the present invention. Referring to FIG. 4 , the injection-locked frequency divider 400 includes a variable reactance unit 410 , a signal injection unit 420 , switches SW 41 and SW 42 , and transformers 430 and 440 . The variable reactance unit 410 has connecting terminals N 41 and N 42 . The signal injection unit 420 is coupled to the connecting terminals N 41 and N 42 . A first terminal of the switch SW 41 is coupled to the connecting terminal N 41 and a control terminal of the switch SW 41 is coupled to the connecting terminal N 42 . A first terminal of the switch SW 42 is coupled to the connecting terminal N 42 and a control terminal of the switch SW 42 is coupled to the connecting terminal N 41 . A primary-side coil 430 a of the transformer 430 is coupled between the connecting terminal N 41 and a ground terminal, and a secondary-side coil 430 b of the transformer 430 is coupled between a second terminal of the switch SW 41 and an operating voltage V DD . A primary-side coil 440 a of the transformer 440 is coupled between the connecting terminal N 42 and the ground terminal, and a secondary-side coil 440 b of the transformer 440 is coupled between a second terminal of the switch SW 42 and the operating voltage V DD .

Furthermore, the variable reactance unit 410 includes variable capacitors C 41 and C 42 , and the signal injection unit 420 includes a switch SW 43 . A first terminal of the variable capacitor C 41 is coupled to the connecting terminal N 41 , a first terminal of the variable capacitor C 42 is coupled to the connecting terminal N 42 , and a second terminal of the variable capacitor C 41 and a second terminal of the variable capacitor C 42 are coupled with each other. Additionally, a first terminal of the switch SW 43 is coupled to the connecting terminal N 41 and a second terminal is coupled to the connecting terminal N 42 .

It should be noted that the switches SW 41 and SW 42 respectively includes a P-type transistor, and the switch SW 43 includes an N-type transistor. However, the architecture of the switches SW 41 -SW 43 is not limited there-to and those skilled in the art can replace the switches SW 41 -SW 43 with other equivalent elements as required to achieve the purpose of the present invention, which shall also construed to be within the scope of the present invention.

Referring to FIG. 4 , in the aspect of the overall operation mechanism, the variable reactance unit 410 , the switches SW 41 and SW 42 , and the transformers 430 and 440 construct a transformer-based LC-tank oscillator. A resonator of the transformer-based LC-tank oscillator is constructed by the variable reactance unit 410 and the transformers 430 and 440 . The switches SW 41 and SW 42 are cross-coupled to provide a negative resistance. Here, the negative resistance provided by the switches SW 41 and SW 42 compensates the parasitic resistance in the resonator, such that the transformer-based LC-tank oscillator maintains oscillation. In another aspect, a second terminal of the variable capacitor C 41 receives a reactance control signal S IP4 . Thus, the variable reactance unit 410 adjusts its reactance value according to the reactance control signal S IP4 , such that the oscillation frequency of the transformer-based LC-tank oscillator changes accordingly.

During the generation of a frequency division signal S DI4 , the injection-locked frequency divider 400 receives an injection signal S IN4 through the signal injection unit 420 , wherein the frequency of the injection signal S IN4 is denoted by f 4 . When the oscillation frequency of the transformer-based LC-tank oscillator approaches one half of the frequency f 4 , the injection-locked frequency divider 400 is in a locked state and the frequency division signal S DI4 is output through the connecting terminals N 41 and N 42 , wherein the frequency of the frequency division signal S DI4 is one half of the frequency f 4 .

It should be noted that the injection-locked frequency divider 400 can increase the locking range of its circuit by using the feedback action formed by the transformers 430 and 440 . Furthermore, under the feedback action of the transformers 430 and 440 , a node voltage V 41 and a node voltage V 42 are of the same phase, and a node voltage V 43 and a node voltage V 44 are of the same phase. In other words, when a node voltage V 45 decreases, the node voltages V 41 and V 42 rise accordingly. Similarly, when a node voltage V 46 decreases, the node voltages V 43 and V 44 rise accordingly. In this manner, the feedback action of the transformers 430 and 440 will efficiently improve the amplitude of the frequency division signal S DI4 , thus promoting the injection-locked frequency divider 400 operating at a lower operating voltage V DD .

According to the embodiment described in FIG. 4 , different types of injection-locked frequency dividers are derived from the injection-locked frequency divider 400 , and the details will be described one by one as follows.

FIG. 5 is a schematic structural view of an injection-locked frequency divider derived from the embodiment of FIG. 4 . Referring to FIG. 5 , the injection-locked frequency divider 500 includes a variable reactance unit 510 , a signal injection unit 520 , switches SW 51 and SW 52 , and transformers 530 and 540 . The variable reactance unit 510 has connecting terminals N 51 and N 52 . The signal injection unit 520 is coupled to the connecting terminals N 51 and N 52 . A first terminal of the switch SW 51 is coupled to the connecting terminal N 51 and a control is coupled to the connecting terminal N 52 . A first terminal of the switch SW 52 is coupled to the connecting terminal N 52 and a control terminal of the switch SW 52 is coupled to the connecting terminal N 51 .

Furthermore, a primary-side coil 530 a of the transformer 530 is coupled between the connecting terminal N 51 and a ground terminal, a secondary-side coil 530 b of the transformer 530 is coupled between a second terminal of the switch SW 51 and an operating voltage V DD . A primary-side coil 540 a of the transformer 540 is coupled between the connecting terminal N 52 and the ground terminal, and a secondary-side coil 540 b of the transformer 540 is coupled between a second terminal of the switch SW 52 and the operating voltage V DD . The details of the architecture and couple relationships of other means are similar to those in the embodiment of FIG. 4 and will not be described herein again.

Referring to FIGS. 4 and 5 , the injection-locked frequency dividers 500 and 400 have substantially the same operating principle. The variable reactance unit 510 , the switches SW 51 and SW 52 , and the transformers 530 and 540 construct a transformer-based LC-tank oscillator. The oscillation frequency of the transformer-based LC-tank oscillator changes along with a reactance control signal S IP5 . When the injection-locked frequency divider 500 is in the locked state, the connecting terminals N 51 and N 52 output a frequency division signal S DI5 , and at this time, the frequency of the frequency division signal S DI5 is one half of the frequency of an injection signal S IN5 .

However, the main difference between the injection-locked frequency dividers 500 and 400 lies in that the secondary-side coil 430 b of the transformer 430 and the secondary-side coil 530 b of the transformer 530 have opposite voltage polarities and the secondary-side coil 440 b of the transformer 440 and the secondary-side coil 540 b of the transformer 540 have opposite voltage polarities. Under this state, the injection-locked frequency divider 500 can increase the locking range of its circuit still by using the feedback action of the transformers 530 and 540 . However, different from the injection-locked frequency divider 400 , the feedback action of the transformers 530 and 540 is a negative feedback mechanism. Therefore, under the feedback action of the transformers 530 and 540 , the amplitude of the frequency division signal S DI5 decreases accordingly, so as to promote alleviating the distortion of its waveform. Other details of the embodiment in FIG. 5 have been illustrated in the embodiment in FIG. 4 , and will not be described herein again.

FIG. 6 is a schematic structural view of another injection-locked frequency divider derived from the embodiment of FIG. 4 . Referring to FIG. 6 , the injection-locked frequency divider 600 includes a variable reactance unit 610 , a signal injection unit 620 , switches SW 61 and SW 62 , transformers 630 and 640 , and a current-limiting unit 650 . The variable reactance unit 610 has connecting terminals N 61 and N 62 . The signal injection unit 620 is coupled to the connecting terminals N 61 and N 62 . A first terminal of the switch SW 61 is coupled to the connecting terminal N 61 and a control terminal of the switch SW 61 is coupled to the connecting terminal N 62 . A first terminal of the switch SW 62 is coupled to the connecting terminal N 62 , and a control terminal of the switch SW 62 is coupled to the connecting terminal N 61 .

Furthermore, a primary-side coil 630 a of the transformer 630 is coupled between the connecting terminal N 61 and a ground terminal, and a secondary-side coil 630 b of the transformer 630 is coupled between a second terminal of the switch SW 61 and the current-limiting unit 650 . A primary-side coil 640 a of the transformer 640 is coupled between the connecting terminal N 62 and the ground terminal, and a secondary-side coil 640 b of the transformer 640 is coupled between a second terminal of the switch SW 62 and the current-limiting unit 650 . The current-limiting unit 650 is coupled to the operating voltage V DD , the secondary-side coil 630 b of the transformer 630 , and the secondary-side coil 640 b of the transformer 640 .

Furthermore, the current-limiting unit 650 includes a switch SW 63 . A first terminal of the switch SW 63 is coupled to the secondary-side coils 630 b and 640 b , the second terminal of the switch SW 63 is coupled to the operating voltage V DD , and the control terminal of the switch SW 63 is used to receive a bias current control signal S BI6 . It should be noted that the switch SW 61 includes a P-type transistor, and the architecture of the switch SW 61 will not be limited to this. Those skilled in the art can replace the switch SW 61 with other elements in accordance with the design requirements. The details of the architecture and coupling relationship of other means are similar to those in the embodiment of FIG. 4 and will not be repeated.

Referring to FIGS. 4 and 6 , the injection-locked frequency dividers 600 and 400 have substantially the same operating principles. The variable reactance unit 610 , the switches SW 61 and SW 62 , and the transformers 630 and 640 construct a transformer-based LC-tank oscillator. The oscillation frequency of the transformer-based LC-tank oscillator changes along with a reactance control signal S IP6 . When the injection-locked frequency divider 600 is in the locked state, the connecting terminals N 61 and N 62 output a frequency division signal S DI6 , and at this time, the frequency of the frequency division signal S DI6 is one half of the frequency of an injection signal S IN6 .

The main difference between the injection-locked frequency dividers 600 and 400 lies in that the injection-locked frequency divider 600 further has the current-limiting unit 650 . Here, the current-limiting unit 650 adjusts and controls a current flowing through the injection-locked frequency divider 600 according to the bias current control signal S BI6 . In this manner, the power consumption of the injection-locked frequency divider 600 can be efficiently reduced. Other details of the embodiment in FIG. 6 have been illustrated in the embodiment in FIG. 4 , and will not be described repeated.

From another point of view, FIG. 7 is a schematic structural view of an injection-locked frequency divider according to yet another embodiment of the present invention. Referring to FIG. 7 , the injection-locked frequency divider 700 includes a variable reactance unit 710 , a signal injection unit 720 , switches SW 71 and SW 72 , and transformers 730 and 740 . The variable reactance unit 710 has connecting terminals N 71 and N 72 . The signal injection unit 720 is coupled to the connecting terminals N 71 and N 72 . The switch SW 71 is coupled between the connecting terminal N 71 and an operating voltage V DD . The switch SW 72 is coupled between the connecting terminal N 72 and the operating voltage V DD . A primary-side coil 730 a of the transformer 730 is coupled between the connecting terminal N 71 and a ground terminal, and a secondary-side coil 730 b of the transformer 730 is coupled between a control terminal of the switch SW 71 and the connecting terminal N 72 . A primary-side coil 740 a of the transformer 740 is coupled between the connecting terminal N 72 and the ground terminal, and a secondary-side coil 740 b of the transformer 740 is coupled between a control terminal of the switch SW 72 and the connecting terminal N 71 .

Furthermore, the variable reactance unit 710 includes variable capacitors C 71 and C 72 , and the signal injection unit 720 includes a switch SW 73 . A first terminal of the variable capacitor C 71 is coupled to the connecting terminal N 71 , a first terminal of the variable capacitor C 72 is coupled to the connecting terminal N 72 , and a second terminal of the variable capacitor C 71 and a second terminal of the variable capacitor C 72 are coupled with each other. In addition, a first terminal of the switch SW 73 is coupled to the connecting terminal N 71 and a second terminal of the switch SW 73 is coupled to the connecting terminal N 72 .

It should be noted that the switches SW 71 and SW 72 respectively include a P-type transistor, and the switch SW 73 includes an N-type transistor. However, the architecture of the switches SW 71 -SW 72 is not limited to this and those skilled in the art can replace the switches SW 71 -SW 72 with other elements.

Referring to FIG. 7 , the variable reactance unit 710 , the switches SW 71 and SW 72 , and the transformers 730 and 740 construct a transformer-based LC-tank oscillator. A resonator of the transformer-based LC-tank oscillator is constructed by the variable reactance unit 710 and the transformers 730 and 740 . The switches SW 71 and SW 72 are cross-coupled to provide a negative resistance. Here, the negative resistance provided by the switches SW 71 and SW 72 compensates the parasitic resistance in the resonator, such that the transformer-based LC-tank oscillator maintains oscillation. In another aspect, a second terminal of the variable capacitor C 71 receives a reactance control signal S IP7 . The variable reactance unit 710 adjusts its reactance value according to the reactance control signal S IP7 , such that the oscillation frequency of the transformer-based LC-tank oscillator changes accordingly.

During the generation of a frequency division signal S DI7 , the injection-locked frequency divider 700 receives an injection signal S IN7 through the signal injection unit 720 , wherein the frequency of the injection signal S IN7 is denoted by f 7 . When the oscillation frequency of the transformer-based LC-tank oscillator approaches one half of the frequency f 7 , the injection-locked frequency divider 700 is in the locked state, and the frequency division signal S DI7 is output through the connecting terminals N 71 and N 72 . At this time, the frequency of the frequency division signal S DI7 is one half of the frequency f 7 .

It should be noted that, when a node voltage V 71 decreases, a node voltage V 72 not only rises with the on/off of the switch SW 71 , but also further rises with the feedback action of the transformer 730 . Similarly, when a node voltage V 73 decreases, a node voltage V 74 not only rises with the on/off of the switch SW 72 , but also further rises with the feedback action of the transformer 740 . In this manner, the injection-locked frequency divider 700 increases the locking range of its circuit by using the feedback action of the transformers 730 and 740 . Under the feedback action formed of the transformers 730 and 740 , the amplitude of the frequency division signal S DI7 is efficiently enlarged, thus promoting the injection-locked frequency divider 700 operating at a low operating voltage.

FIG. 8 is a schematic structural view of an injection-locked frequency divider according to another embodiment of the present invention. Referring to FIG. 8 , the injection-locked frequency divider 800 includes a variable reactance unit 810 , a signal injection unit 820 , P-type transistors MP 81 and MP 82 , and transformers 830 and 840 . The variable reactance unit 810 has connecting terminals N 81 and N 82 . The signal injection unit 820 is coupled to the connecting terminals N 81 and N 82 . A drain of the P-type transistor MP 81 is coupled to the connecting terminal N 81 , a gate of the P-type transistor MP 81 is coupled to the connecting terminal N 82 , and a source of the P-type transistor MP 81 is coupled to an operating voltage V DD . A drain of the P-type transistor MP 82 is coupled to the connecting terminal N 82 , a gate of the P-type transistor MP 82 is coupled to the connecting terminal N 81 , and a source of the P-type transistor MP 82 is coupled to the operating voltage V DD .

Furthermore, a primary-side coil 830 a of the transformer 830 is coupled between the connecting terminal N 81 and a ground terminal, and a secondary-side coil 830 b of the transformer 830 is coupled between a base of the P-type transistor MP 81 and the operating voltage V DD . A primary-side coil 840 b of the transformer 840 is coupled between the connecting terminal N 82 and the ground terminal, and a secondary-side coil 840 b of the transformer 840 is coupled between a base of the P-type transistor MP 82 and the operating voltage V DD .

Furthermore, the variable reactance unit 810 includes variable capacitors C 81 and C 82 , and the signal injection unit 820 includes a switch SW 81 . A first terminal of the variable capacitor C 81 is coupled to the connecting terminal N 81 , a first terminal of the variable capacitor C 82 is coupled to the connecting terminal N 82 , and a second terminal of the variable capacitor C 81 and a second terminal of the variable capacitor C 82 are coupled with each other. A first terminal of the switch SW 81 is coupled to the connecting terminal N 81 and a second terminal of the switch SW 81 is coupled to the connecting terminal N 82 . It should be noted that the switch SW 81 includes an N-type transistor. However, the architecture of the switch SW 81 is not limited to this, and those skilled in the art can replace the switch SW 81 with other elements in accordance with the design requirements.

Referring to FIG. 8 , the variable reactance unit 810 , the P-type transistors MP 81 and MP 82 , and the transformers 830 and 840 construct a transformer-based LC-tank oscillator. The resonator of the transformer-based LC-tank oscillator is constructed by the variable reactance unit 810 and the transformers 830 and 840 . The P-type transistors MP 81 and MP 82 are cross-coupled to provide a negative resistance. The negative resistance provided by the P-type transistors MP 81 and MP 82 compensates the parasitic resistance in the resonator, such that the transformer-based LC-tank oscillator maintains oscillation. In another aspect, a second terminal of the variable capacitor C 81 receives a reactance control signal S IP8 . The variable reactance unit 810 adjusts its reactance value according to the reactance control signal S IP8 , such that the oscillation frequency of the transformer-based LC-tank oscillator changes accordingly.

In another aspect, the signal injection unit 820 is used to receive an injection signal S IN8 , wherein the frequency of the injection signal S IN8 is denoted by f 8 . When the injection-locked frequency divider 800 is in the locked state, the connecting terminals N 81 and N 82 output a frequency division signal S DI8 , and at this time, the frequency of the frequency division signal S DI8 is one half of the frequency f 8 . In addition, as those described in the aforementioned embodiments, the feedback action of the transformers 830 and 840 promotes the increase of the locking range of the injection-locked frequency divider 800 and the realization of the low operating voltage.

FIG. 9 is a schematic structural view of an injection-locked frequency divider according to still another embodiment of the present invention. Referring to FIG. 9 , the injection-locked frequency divider 900 includes a variable reactance unit 910 , a signal injection unit 920 , switches SW 91 and SW 92 , and transformers 930 and 940 . A first terminal of the switch SW 91 is used to output a frequency division signal S DI9 , and a second terminal of the switch SW 91 is coupled to an operating voltage V DD . A first terminal of the switch SW 92 is used to output a frequency division signal S DI9 , and a second terminal of the switch SW 92 is coupled to the operating voltage V DD . A primary-side coil 930 a of the transformer 930 is coupled between a first terminal of the switch SW 91 and a ground terminal, and a secondary-side coil 930 b of the transformer 930 is coupled between a control terminal of the switch SW 91 and the ground terminal.

Furthermore, a primary-side coil 940 a of the transformer 940 is coupled between a first terminal of the switch SW 92 and the ground terminal, and a secondary-side coil 940 b of the transformer 940 is coupled between a control terminal of the switch SW 92 and the ground terminal. The variable reactance unit 910 has connecting terminals N 91 and N 92 , wherein the connecting terminal N 91 is coupled to the secondary-side coil 930 b of the transformer 930 and the connecting terminal N 92 is coupled to the secondary-side coil 940 b of the transformer 940 . The signal injection unit 920 is coupled to the connecting terminals N 91 and N 92 .

Furthermore, the variable reactance unit 910 includes variable capacitors C 91 and C 92 , and the signal injection unit 920 includes a switch SW 93 . A first terminal of the variable capacitor C 91 is coupled to the connecting terminal N 91 , a first terminal of the variable capacitor C 92 is coupled to the connecting terminal N 92 , and a second terminal of the variable capacitor C 91 and a second terminal of the variable capacitor C 92 are coupled with each other. A first terminal of the switch SW 93 is coupled to the connecting terminal N 91 and a second terminal of the switch SW 93 is coupled to the connecting terminal N 92 .

It should be noted that the switches SW 91 and SW 92 respectively include a P-type transistor, and the switch SW 93 includes an N-type transistor. However, the architecture of the switches SW 91 -SW 93 is not limited to this, and those skilled in the art can replace the switches SW 91 -SW 93 with other equivalent elements in order to achieve the purpose of the present invention, which shall be also construed to be within the scope of the present invention.

Referring to FIG. 9 , in the overall operating mechanism, the variable reactance unit 910 , the switches SW 91 and SW 92 , and the transformers 930 and 940 construct a transformer-based LC-tank oscillator. The transformer-based LC-tank oscillator is also referred to as the Armstrong oscillator. The switch SW 91 and the transformer 930 form a single ended Armstrong oscillator. Similarly, the switch SW 92 and the transformer 940 form another single ended Armstrong oscillator. Here, the two single ended Armstrong oscillators and the variable reactance unit 910 construct a differential output Armstrong oscillators, i.e., the transform-based LC-tank oscillator.

It should be noted that a second terminal of the variable capacitor C 91 receives a reactance control signal S IP9 . Thus, the variable reactance unit 910 adjusts its reactance value according to a reactance control signal S IP9 , such that the oscillation frequency of the transformer-based LC-tank oscillator changes accordingly.

In another aspect, the signal injection unit 920 is used to receive an injection signal S IN9 , wherein the frequency of the injection signal S IN9 is f 9 . Through a transmission path provided by the signal injection unit 920 , the injection signal S IN9 is outputted to the control terminals of the switches SW 91 and SW 92 . At this time, when the switches SW 91 and SW 92 are turned on/off, the transformer-based LC-tank oscillator starts to oscillate. After that, when the injection-locked frequency divider 900 enters the locked state, the connecting terminals N 91 and N 92 output the frequency division signal S DI9 , wherein the frequency of the frequency division signal S DI9 is one half of the frequency f 9 .

It should be noted that when a node voltage V 91 decreases, a node voltage V 92 not only rises with the on/off of the switch SW 91 , but also further rises with the feedback action of the transformer 930 . Similarly, when a node voltage V 93 decreases, a node voltage V 94 not only rises with the on/off of the switch SW 92 , but also further rises with the feedback action of the transformer 940 . In this manner, the injection-locked frequency divider 900 increases the locking range of its circuit by using the feedback action of the transformers 930 and 940 . Under the feedback action of the transformers 930 and 940 , the amplitude of the frequency division signal S DI9 is efficiently enlarged, thus promoting the injection-locked frequency divider 900 operating at a low operating voltage.

According to the embodiment described in FIG. 9 , different types of injection-locked frequency dividers are derived from the injection-locked frequency divider 900 and the details will be described one by one as follows.

FIG. 10 is a schematic structural view of an injection-locked frequency divider derived from the embodiment of FIG. 9 . Referring to FIG. 10 , the injection-locked frequency divider 1100 includes a variable reactance unit 1010 , a signal injection unit 1020 , switches SW 101 and SW 102 , and transformers 1030 and 1040 . A first terminal of the switch SW 101 is used to output a frequency division signal S DI10 , and a second terminal of the switch SW 101 is coupled to an operating voltage V DD . A first terminal of the switch SW 102 is used to output the frequency division signal S DI10 , and a second terminal of the switch SW 102 is coupled to the operating voltage V DD . A primary-side coil 1030 b of the transformer 1030 is coupled between the first terminal of the switch SW 101 and a ground terminal, and a secondary-side coil 1030 b of the transformer 1030 is coupled between a control terminal of the switch SW 101 and the ground terminal.

Furthermore, a primary-side coil 1040 a of the transformer 1040 is coupled between a first terminal of the switch SW 102 and the ground terminal, and a secondary-side coil 1040 b of the transformer 1040 is coupled between a control terminal of the switch SW 102 and the ground terminal. The variable reactance unit 1010 has connecting terminals N 101 and N 102 , wherein the connecting terminal N 101 is coupled to the primary-side coil 1030 a of the transformer 1030 and the connecting terminal N 102 is coupled to the primary-side coil 1040 b of the transformer 1040 . The signal injection unit 1020 is coupled between the connecting terminals N 101 and N 102 . The details of the architecture and coupling relationship of other means are similar to those in the embodiment of FIG. 9 and will not be described herein again.

Referring to FIGS. 9 and 10 together, the injection-locked frequency dividers 1100 and 900 have substantially the same operating principles. The variable reactance unit 1010 , the switches SW 101 and SW 102 , and the transformers 1030 and 1040 construct a transformer-based LC-tank oscillator. The oscillation frequency of the transformer-based LC-tank oscillator changes with a reactance control signal S IP10 . When the injection-locked frequency divider 1100 is in the locked state, the connecting terminals N 101 and N 102 output a frequency division signal S DI10 , and at this time, the frequency of the frequency division signal S DI10 is one half of the frequency of an injection signal S IN10 .

However, the main difference between the injection-locked frequency dividers 1100 and 900 lies in that the connecting terminals N 101 and N 102 of the injection-locked frequency divider 1100 are coupled to the primary-side coils of the transformers 1030 and 1040 respectively, and the connecting terminals N 91 and N 92 of the injection-locked frequency divider 900 are coupled to the secondary-side coils of the transformers 930 and 940 respectively. However, in the embodiment of FIG. 10 , the injection-locked frequency divider 1100 increases the locking range and realizes a low operating voltage still by using the feedback action of the transformers 1030 and 1040 . Other details of the embodiment of FIG. 10 have been illustrated in the embodiment of FIG. 9 , and will not be described herein again.

FIG. 11 is a schematic structural view of another injection-locked frequency divider derived from the embodiment of FIG. 9 . Referring to FIG. 11 , an injection-locked frequency divider 1200 includes a variable reactance unit 1110 , a signal injection unit 1120 , switches SW 111 and SW 112 , transformers 1130 and 1140 , and a current-limiting unit 1150 . A first terminal of the switch SW 111 is used to output a frequency division signal S DI11 , and a second terminal of the switch SW 111 is coupled to the current-limiting unit 1150 . A first terminal of the switch SW 112 is used to output the frequency signal S DI11 , and a second terminal of the switch SW 112 is coupled to the current-limiting unit 1150 . A primary-side coil 1130 a of the transformer 1130 is coupled between the first terminal of the switch SW 111 and a ground terminal, and a secondary-side coil 1130 b of the transformer 1130 is coupled between a control terminal of the switch SW 111 and the ground terminal.

Furthermore, a primary-side coil 1140 a of the transformer 1140 is coupled between the first terminal of the switch SW 112 and the ground terminal, and a secondary-side coil 1140 b is coupled between a control terminal of the switch SW 112 and the ground terminal. The variable reactance unit 1110 has connecting terminals N 111 and N 112 , wherein the connecting terminal N 111 is coupled to the secondary-side coil 1130 b of the transformer 1130 and the connecting terminal N 112 is coupled to the secondary-side coil 1140 b of the transformer 1140 . The signal injection unit 1120 is coupled to the connecting terminals N 111 and N 112 . The current-limiting unit 1150 is coupled to an operating voltage V DD , a second terminal of the switch SW 111 , and a second terminal of the switch SW 112 .

Furthermore, the current-limiting unit 1150 includes a switch SW 113 . A first terminal of the switch SW 113 is coupled to the second terminals of the switches SW 111 and SW 112 , the second terminal of the switch SW 113 is coupled to the operating voltage V DD , and the control terminal of the switch SW 113 is used to receive a bias current control signal S BI11 . It should be noted that the switch SW 113 includes a P-type transistor, but the architecture of the switch SW 113 is not limited to this. Those skilled in the art can replace the switch SW 113 with other elements in accordance with the design requirements. The details of the architecture and coupling relationship of other means are similar to those of the embodiment of FIG. 9 and will not be described herein again.

Referring to FIGS. 9 and 11 together, the injection-locked frequency dividers 1200 and 900 have substantially the same operating principles. The variable reactance unit 1110 , the switches SW 111 and SW 112 , and the transformers 1130 and 1140 construct a transformer-based LC-tank oscillator. The oscillation frequency of the transformer-based LC-tank oscillator changes with a reactance control signal S IP11 . When the injection-locked frequency divider 1200 is in the locked state, the connecting terminals N 111 and N 112 output a frequency division signal S DI11 , and at this times, the frequency of the frequency division signal S DI11 is one half of the frequency of an injection signal S IN11 .

The main difference between the injection-locked frequency dividers 1200 and 900 lies in that the current-limiting unit 1150 is further added in the injection-locked frequency divider 1200 . At this time, the current-limiting unit 1150 adjusts and controls a current flowing through the injection-locked frequency divider 1200 according to the bias current control signal S BI11 . In this manner, the power consumption of the injection-locked frequency divider 1200 can be efficiently reduced. Other details of the embodiment of FIG. 11 have been illustrated in the embodiment of FIG. 9 , and will not be described herein again.

In view of the above, by employing transformers coupled in various manners, the present invention can increase the locking range of the injection-locked frequency divider. Furthermore, due to the feedback action of the transformers, the injection-locked frequency divider of the present invention has a low operating voltage, and is suitable to be applied in various mixed signal integrated circuits.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.