JP2003188688A - Ring oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an oscillation frequency high while keeping an amplitude. <P>SOLUTION: A ring oscillator is formed by circularly connecting two unit amplifiers 1a, 2a. Each of the amplifiers comprises a pair of emitter follower circuits 51a, 52a and a differential amplifier 53a. Inverse output of each of the circuits 51a, 52a is connected to an intermediate node between load resistors 26a, 27a and an intermediate node between load resistors 28a, 29a. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator widely used in clock circuits, and more particularly to a ring oscillator suitable for integration and capable of oscillating at high frequency.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram of a configuration example of a conventional ring oscillator (reference document: S. Finocchiaro et al.
ign of bipolar RF ring oscillators '' Proceedings of
1999International Conference on Electronics, Circ
uits and Systems, p. 35l-358). This circuit is composed of a unit amplifier 1d, a unit amplifier 2d, and an output buffer 3d. The number of unit amplifiers, that is, the number of stages of the ring oscillator is two, and the unit amplifiers 1d and 2 are shown.
d illustrates a differential signal input / differential signal output type. The oscillation frequency control terminal 4d is used for each unit amplifier 1d, 2d.
It is possible to control the oscillation frequency of the ring oscillator by controlling the current value of the current source. 5d and 6d are CLK output terminals.

FIG. 14 is a circuit diagram of a conventional unit amplifier which constitutes the ring oscillator shown in FIG. In FIG. 14, the transistor 11d and the current source 13d form an emitter follower circuit, and the transistor 12d and the current source 14d form another emitter follower circuit. On the other hand, the transistor 15d, the transistor 16d,
The resistor 18d, the resistor 19d and the variable current source 17d form a differential amplifier. The emitter outputs of both emitter follower circuits are both transistors 15d and 16 of the differential amplifier.
It is entered in the base of d. Reference numerals 20d and 21d are input terminals, 22d and 23d are output terminals, 24d is an oscillation frequency control terminal, and 25d is a power supply terminal.

FIG. 15 is a schematic diagram modeling the circuit function of the conventional unit amplifier shown in FIG. In FIG. 15, input signals from the input terminals 20d and 21d are input to the emitter follower circuits 5ld and 52d and sent to the differential amplifier 53d. In addition, the emitter follower circuit 5
The inverted outputs of Id and 52d mean the collector terminals of the transistors 11d and 12d in FIG. In the conventional example, the collector terminals of the transistors 11d and 12d are grounded, and the inverted outputs of the emitter follower circuits 5ld and 52d have no influence on the operation of the differential amplifier 53d. In FIG. 15, resistors 18d and 19 are provided for the sake of explanation.
Although d is described independently, the resistors 18d and 19d are also components of the differential amplifier 53d as described with reference to FIG.

FIG. 16 is a time chart showing the operation of each part of the conventional unit amplifier shown in FIG. In the two-stage ring oscillator using the differential signal input / differential signal output type unit amplifier shown in FIG.
After passing from d to the unit amplifier 2d, it is input to the inverting input side of the unit amplifier 1d, passes through the unit amplifier 2d, and is again input to the non-inverting input side of the unit amplifier 1d to make one round. Therefore, observing the phase of each part (nodes A to C) at a certain time, the unit amplifier rotates the phase by π / 2 (90 degrees). When the delay time of the emitter follower circuits 5ld and 52d is t1 and the delay time of the differential amplifier 53d is t2, the oscillation frequency f of the conventional ring oscillator is f = 0.25 / (t1 + t2). When it is desired to increase the oscillation frequency, t1 or t2 (or both) may be shortened.

[0006]

As described above, in order to increase the oscillation frequency of the conventional ring oscillator, it is sufficient to shorten t1 or t2 (or both). t1, t2
In order to shorten the voltage, it is generally known that the current flowing through each device is increased or the amplitude is decreased. However, the value of the current passed through each device is limited in order to ensure the reliability of the device, so there is an upper limit. Further, it is possible to increase the frequency by reducing the amplitude by reducing the load resistance. However, if the amplitude is reduced, it is necessary to increase the amplification factor of the output buffer and the phase noise deteriorates.

An object of the present invention is to provide a ring oscillator capable of relaxing the limitation when increasing the oscillation frequency of such a conventional ring oscillator and increasing the frequency while keeping the amplitude large. .

[0008]

The invention according to claim 1 is
A ring oscillator comprising a plurality of unit amplifiers connected in a loop in multiple stages, wherein the unit amplifiers are composed of a pair of transistors inputting the output from the previous stage to the base, and a current source is connected to the emitter of each transistor. A pair of emitter follower circuits, a pair of transistors whose emitter outputs of the pair of emitter follower circuits are input to a base and a current source is connected to a common emitter, and a load resistor having an intermediate node connected to the collectors of the respective transistors. And a collector of the emitter follower circuit of the pair is connected to an intermediate node of each of the load resistors of the differential amplifier.

According to a second aspect of the present invention, there is provided a ring oscillator in which a plurality of unit amplifiers are connected in multiple stages in a ring shape, wherein the unit amplifier comprises a pair of transistors for inputting an output from the preceding stage to a base. A pair of emitter follower circuits in which a current source is connected to the emitter of each transistor,
A differential amplifier having a pair of transistors each having a common emitter connected to a current source and a load resistor connected to a collector of each of the transistors, the emitter outputs of the pair of emitter follower circuits being input to a base; The collectors of the pair of emitter follower circuits,
The ring oscillator is characterized in that the collectors of the respective transistors of the differential amplifier are connected to the common connection points of the respective load resistors.

According to a third aspect of the invention, in the invention according to the first or second aspect, the current source of the differential amplifier is a variable current source whose current value can be controlled from the outside. And

A fourth aspect of the present invention is the variable current source according to the first or second aspect, wherein the current source of the differential amplifier and the current source of each of the emitter follower circuits can control the current value from the outside. A ring oscillator characterized in that.

The invention according to claim 5 relates to claims 1, 2, and 3.
Alternatively, in the invention according to 4, the ring oscillator is characterized in that each transistor of the unit amplifier is replaced with a field effect transistor in which the base is a gate, the collector is a drain, and the emitter is a source.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] FIG. 1 is a block diagram of a first embodiment of a ring oscillator. This circuit is composed of a unit amplifier 1a, a unit amplifier 2a, and an output buffer 3a. The number of unit amplifiers, that is, the number of stages of the ring oscillator is 2, and the unit amplifiers 1a and 2a are
Is a differential signal input / differential signal output type. The oscillation frequency control terminal 4a is connected to the current source of each unit amplifier 1a, 2a, and the oscillation frequency of the ring oscillator can be controlled by controlling the current value. 5
Reference characters a and 6a are CLK output terminals. Up to this point, it is the same as the conventional ring oscillator.

FIG. 2 is a circuit diagram of a unit amplifier constituting the ring oscillator shown in FIG. In FIG. 2, the transistor 11a and the current source 13a constitute an emitter follower circuit, and the transistor 12a and the current source 14a.
Constitutes another emitter follower circuit. On the other hand, the transistor 15a, the transistor 16a, and the resistor 26
a, 27a, 28a, 29a and the variable current source 17a form a differential amplifier. 20a and 21a are input terminals,
22a and 23a are output terminals, 24a is an oscillation frequency control terminal, and 25a is a power supply terminal. Unlike the conventional ring oscillator, the load resistance of the differential amplifier of the first embodiment is the series connection of the resistors 26a and 27a and the resistors 28a and 29a.
In series connection, and the collector terminals of the transistors 11a and 12a of the emitter follower circuit in the preceding stage are connected to the intermediate node of each load resistance in the series connection.

FIG. 3 is a schematic diagram modeling the circuit function of the unit amplifier of FIG. In FIG. 3, the input terminal 20
The input signals from a and 21a are the emitter follower circuit 5
la, 52a, and is sent to the differential amplifier 53a. The inverted output of the emitter follower circuits 5la and 52a means the collector terminals of the transistors 11a and 12a in FIG. In the conventional example, the transistor 1
The collector terminals of 1d and 12d are grounded, and the inverted outputs of the emitter follower circuits 5ld and 52d have no influence on the operation of the differential amplifier 53d. On the other hand, in the first embodiment, the transistors 11a and 12a are
Of the differential amplifier 53a has load resistors (resistors 26a and 27a) and load resistors (resistors 28a and 29a).
, The inverted outputs of the emitter follower circuits 5la and 52a affect the operation of the differential amplifier 53a. This will be explained next.

FIG. 4 is a time chart showing the operation of each unit of the unit amplifier of FIG. In the two-stage ring oscillator using the differential signal input / differential signal output type unit amplifiers shown in FIG. 1, signals are transmitted from the unit amplifier 1a to the unit amplifier 2
After passing to a, it is input to the inverting input side of the unit amplifier 1a, passes through the unit amplifier 2a, and is again input to the non-inverting input side of the unit amplifier 1a to make one round. Therefore, observing the phase of each part (nodes A to C) at a certain time, the unit amplifier rotates the phase by π / 2 (90 degrees). When the delay time of the emitter follower circuits 51a and 52a is t3 and the delay time of the differential amplifier 53a is t4, the oscillation frequency f of the first embodiment is f = 0.25 / (t3 + t4).

Here, the emitter follower circuits 51a, 5a
The delay time t3 of 2a is almost equal to the delay time t1 in the conventional ring oscillator (t1 = t3). On the other hand, the output of the differential amplifier 53a includes the emitter follower circuit 51
A part of the inverted outputs of a and 52a is added via the resistance division of the load resistance. For example, paying attention to the phase relationship at the node C (output of the differential amplifier 53a), a part of the signal of the node B (output of the emitter follower circuit 5la = inverted output of the emitter follower circuit 52a) having a preceding phase is added to the node C. Therefore, the delay time of the original differential amplifier 53a is t2, which is the same as the conventional example, whereas the delay time of the differential amplifier 53a in the first embodiment is shortened to t4 (t2> t4). . As a result, the oscillation frequency of the first embodiment becomes higher than that of the conventional ring oscillator under the same current condition. In the conventional ring oscillator, when the load resistance of the differential amplifier 53d is reduced to increase the frequency, there arises a problem that the amplitude decreases in proportion to this, but in the first embodiment, the load resistance is reduced. Since it is possible to increase the frequency without doing so, it is possible to suppress the decrease in amplitude due to the increase in frequency.

FIG. 5 is a diagram showing the relationship between the amplitude and the oscillation frequency of the first embodiment of the ring oscillator. The parameters of the actual device were used for the calculation, and the current values of the emitter follower circuits 51a and 52a and the differential amplifier 53a were constant. The resistance value of the resistors 26a and 28a is R1, the resistance value of the resistors 27a and 28a is R2, and the resistance division ratio (FF
FF rate = (R1 / (R1 + R2)) × 100. In the conventional ring oscillator, the FF ratio is 0%, and when R1 = R2 is selected in the first embodiment, the FF ratio is FF.
The rate is 50%. FIG. 5 plots the amplitude and the oscillation frequency when the load resistance is changed for each FF rate. As shown in FIG. 5, there is a trade-off relationship in which the amplitude decreases as the oscillation frequency increases, but in the first embodiment (FF ratio 50%), the conventional example (FF ratio 0
%), This trade-off relationship is relaxed, and it is understood that the amplitude can be kept large even if the oscillation frequency is designed to be high. Further, in the first embodiment, by designing the FF ratio, it is possible to design the oscillation frequency and the amplitude so as to match the application.

[Second Embodiment] FIG. 6 is a block diagram showing a second embodiment of the ring oscillator. This circuit includes a unit amplifier 1b, a unit amplifier 2b, an output buffer 3
b. The number of unit amplifiers, that is, the number of stages of the ring oscillator is 2, and the unit amplifiers 1b and 2b are of a differential signal input / differential signal output type. The oscillation frequency control terminal 4b is connected to the current source of each unit amplifier 1b, 2b, and the oscillation frequency of the ring oscillator can be controlled by controlling the current value. 5b,
6b is a CLK output terminal. The process up to this point is the same as in the first embodiment.

FIG. 7 is a circuit diagram of a unit amplifier constituting the ring oscillator shown in FIG. In FIG. 7, the transistor 11b and the current source 13b form an emitter follower circuit, and the transistor 12b and the current source 14b.
Constitutes another emitter follower circuit. On the other hand, the transistor 15b, the transistor 16b, and the resistor 26
b, 28b and the variable current source 17b constitute a differential amplifier. Reference numerals 20b and 21b are input terminals, 22b and 23b are output terminals, 24b is an oscillation frequency control terminal, and 25b is a power supply terminal. Unlike the above-described first embodiment, in the second embodiment, the load resistance of the differential amplifier (resistor 26b,
28b) and the collectors of the transistors 15b and 16b are connected to the collector terminals of the transistors 11b and 12b of the preceding emitter follower circuit. In other words, the second embodiment is the first
This corresponds to the case where the resistance division ratio (FF rate) in the above embodiment is set to 100%.

FIG. 8 is a schematic diagram modeling the circuit function of the unit amplifier shown in FIG. In FIG. 8, input signals from the input terminals 20b and 21b are input to the emitter follower circuits 51b and 52b and sent to the differential amplifier 53b. In addition, the emitter follower circuits 51b and 52b
Is the inverted output of the transistors 11b and 12b in FIG.
Means the collector terminal of. In the first embodiment,
The inverted outputs of the emitter follower circuits 51b and 52b were connected to the intermediate node of the load resistor, but in the second embodiment, the inverted outputs of the emitter follower circuits 51b and 52b are the outputs of the load resistors (resistors 26b and 28b). Terminal (22
b, 23b) side. As a result, the inverted outputs of the emitter follower circuits 51b and 52b are changed to the differential amplifier 5
The influence that affects the operation of 3b can be maximized.

FIG. 9 is a time chart showing the operation of each part of the unit amplifier shown in FIG. In the two-stage ring oscillator using the differential signal input / differential signal output type unit amplifiers shown in FIG. 6, the signal passes from the unit amplifier 1b to the unit amplifier 2b, and then to the inverting input side of the unit amplifier 1b. The input signal passes through the unit amplifier 2b, and again the unit amplifier 1b.
It is input to the non-inverting input side of and goes around. Therefore, observing the phase of each part (nodes A to C) at a certain time, the unit amplifier rotates the phase by π / 2 (90 degrees). When the delay time of the emitter follower circuits 51b and 52b is t5 and the delay time of the differential amplifier 53b is t6, the oscillation frequency f of the second embodiment is t = 0.25 / (t5 + t6).

Here, the emitter follower circuits 51b, 5
The delay time t5 of 2b is the delay time t3 in the first embodiment.
Is approximately equal to (t3 = t5). On the other hand, the output of the differential amplifier 53b includes the emitter follower circuits 51b and 5b.
The inverted output of 2b is directly added. For example, focusing on the phase relationship at the node C (output of the differential amplifier 53b),
Node B (emitter follower circuit 51b) that precedes in phase
The signal of (output = emitter follower circuit 52b inverted output) is current added to C. Therefore, the original differential amplifier 53
While the delay time of b is t2, which is the same as that of the conventional example, the delay time of the differential amplifier 53b of the second embodiment is shortened to t6 (t2> t6). As a result, the oscillation frequency of the second embodiment is higher than that of the conventional ring oscillator under the same current condition.

In the conventional ring oscillator, when the load resistance of the differential amplifier 53d is reduced to increase the frequency, there arises a problem that the amplitude decreases in proportion to this, but in the second embodiment, the load resistance is reduced. Since it is possible to increase the frequency without decreasing the value, it is possible to suppress the decrease in amplitude due to the increase in frequency.

FIG. 10 is a diagram showing the relationship between the amplitude and the oscillation frequency of the second embodiment of the ring oscillator. The parameters of the actual device were used for the calculation, and the current values of the emitter follower circuits 5lb and 52b and the differential amplifier 53b were constant. The second embodiment corresponds to the plot showing that the FF rate is 100%. For comparison, the conventional ring oscillator (FF rate = 0%) and the case where R1 = R2 is selected in the first embodiment (FF rate = 50%) are also shown. As shown in FIG. 10, there is a trade-off relationship in which the amplitude decreases as the oscillation frequency increases, but the second embodiment (FF ratio 10
0%), this trade-off relationship is relaxed compared to the conventional example (FF ratio 0%) and the first embodiment (FF ratio 50%), and the amplitude is large even if the oscillation frequency is designed to be high. It turns out that it is possible to keep. However, the first embodiment may be suitable for applications in which obtaining a large amplitude is a priority.

[Third Embodiment] FIG. 11 is a block diagram of a ring oscillator according to a third embodiment. This circuit
It is composed of a unit amplifier 1c, a unit amplifier 2c, and an output buffer 3c. The number of unit amplifiers, that is, the number of stages of the ring oscillator is 2, and the unit amplifiers 1c and 2c are of a differential signal input / differential signal output type. The oscillation frequency control terminal 4c is connected to the current source of each unit amplifier 1c, 2c, and the oscillation frequency of the ring oscillator can be controlled by controlling the current value. 5c, 6c
Is a CLK output terminal. The process up to this point is the same as in the first and second embodiments.

FIG. 12 is a circuit diagram of a unit amplifier constituting the ring oscillator shown in FIG. The third embodiment has a configuration in which the current sources 13a and 14a of the emitter follower circuit in the first embodiment are replaced with variable current sources 41c and 42c. In the first embodiment, the oscillation frequency of the ring oscillator is controlled by the variable current source 17a, while in the second embodiment, the variable current sources 17c, 41c, 4 are used.
2c controlled. In the first embodiment, the delay time t3 of the emitter follower circuit is equal to the delay time t1 of the conventional example, but in the third embodiment, the delay time of the emitter follower circuit is changed by adjusting the variable current sources 41c and 42c. be able to. As a result, in the third embodiment, the variable range of the oscillation frequency can be expanded as compared with the first embodiment.

[Other Embodiments] The above first to first embodiments
Although the bipolar transistor is used as the transistor in the third embodiment, a field effect transistor can also be used. In this case, the gate, source and drain of the field effect transistor may be connected to the connection points of the base, emitter and collector of the bipolar transistor, respectively.

[0029]

As described above, the ring oscillator of the present invention has an advantage that the oscillation frequency can be increased while maintaining the amplitude.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of a ring oscillator.

FIG. 2 is a circuit diagram of a unit amplifier included in the ring oscillator of FIG.

FIG. 3 is a schematic diagram modeling the circuit function of the unit amplifier of FIG.

FIG. 4 is a time chart showing the operation of each unit of the unit amplifier of FIG.

5 is a diagram showing the relationship between the amplitude and the oscillation frequency of the ring oscillator of FIG.

FIG. 6 is a block diagram of a second embodiment of a ring oscillator.

FIG. 7 is a circuit diagram of a unit amplifier included in the ring oscillator of FIG.

8 is a schematic diagram modeling the circuit function of the unit amplifier of FIG. 7. FIG.

9 is a time chart showing the operation of each unit of the unit amplifier of FIG.

10 is a diagram showing the relationship between the amplitude and the oscillation frequency of the ring oscillator shown in FIG.

FIG. 11 is a block diagram of a third embodiment of a ring oscillator.

12 is a circuit diagram of a unit amplifier forming the ring oscillator of FIG.

FIG. 13 is a block diagram of a conventional ring oscillator.

FIG. 14 is a circuit diagram of a unit amplifier included in the ring oscillator of FIG.

FIG. 15 is a schematic diagram modeling the circuit function of the unit amplifier of FIG.

16 is a time chart showing the operation of each unit of the unit amplifier of FIG.

[Explanation of symbols]

1a, 1b, 1c, 1d: unit amplifiers 2a, 2b, 2c, 2d: unit amplifiers 3a, 3b, 3c, 3d: output buffers 4a, 4b, 4c, 4d: oscillation frequency control terminals 5a, 5b, 5c, 5d: CLK output terminals 6a, 6b, 6c, 6d: CLK output terminals 11a, 11b, 11c, 11d: transistors 12a, 12b, 12c, 12d: transistors 13a, 13b, 13d: current sources 14a, 14b, 14d: current source 15a, 15b, 15c, 15d: Transistors 16a, 16b, 16c, 16d: Transistors 17a, 17b, 17c, 17d: Variable current source 18d: Resistor 19d: Resistors 20a, 20b, 20c, 20d: Input terminals 21a, 21b, 21c , 21d: input terminals 22a, 22b, 22c, 22d: output terminals 23a, 23b, 2 c, 23d: output terminals 24a, 24b, 24c, 24d: oscillation frequency control terminals 25a, 25b, 25c, 25d: power supply terminals 26a, 26b, 26c: resistors 27a, 27c: resistors 28a, 28b, 28c: resistors 29a, 29c: Resistor 41c: Variable current source 42c: Variable current sources 51a, 51b, 51c, 51d: Emitter follower circuits 52a, 52b, 52c, 52d: Emitter follower circuits 53a, 53b, 53c, 53d: Differential amplifier

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shibata             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F term (reference) 5J043 AA04 FF03 GG02 GG08

Claims (5)

[Claims] 1. A ring oscillator comprising a plurality of unit amplifiers connected in a loop in multiple stages, wherein the unit amplifier comprises a pair of transistors for inputting an output from the previous stage to a base, and a current is supplied to an emitter of each of the transistors. A pair of emitter follower circuits to which a source is connected, a pair of transistors to which the emitter outputs of the pair of emitter follower circuits are input at their bases and a current source is connected to a common emitter, and an intermediate node connected to the collectors of the respective transistors. A differential amplifier including a load resistor having a ring, wherein each collector of the pair of emitter follower circuits is connected to an intermediate node of each load resistor of the differential amplifier. Oscillator. 2. A ring oscillator in which a plurality of unit amplifiers are connected in a loop in multiple stages, wherein the unit amplifier comprises a pair of transistors for inputting the output from the previous stage to a base, and a current is supplied to an emitter of each of the transistors. A pair of emitter follower circuits to which a source is connected, a pair of transistors to which the emitter outputs of the pair of emitter follower circuits are input to the base and a current source is connected to the common emitter, and loads connected to the collectors of the respective transistors. A differential amplifier including a resistor, wherein each collector of the pair of emitter follower circuits is connected to a common connection point of the collector of each transistor of the differential amplifier and each load resistor. And ring oscillator. 3. The ring oscillator according to claim 1, wherein the current source of the differential amplifier is a variable current source whose current value can be controlled from the outside. 4. The ring oscillator according to claim 1, wherein the current source of the differential amplifier and the current source of each of the emitter follower circuits are variable current sources whose current values can be controlled externally. Characteristic ring oscillator. 5. The ring oscillator according to claim 1, 2, 3, or 4, wherein each transistor of the unit amplifier is a field effect transistor in which the base is a gate, the collector is a drain, and the emitter is a source. A ring oscillator characterized by being replaced.