JPH11112231A - Small amplitude oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise occurred in a power source and ground by connecting a resistance element for adjusting amplitude which a small amplitude oscillation circuit oscillates and oscillating the small amplitude oscillation circuit with amplitude in a range narrower than voltage between first power source and ground. SOLUTION: A resistance element 26 that is connected between the power source Vtt having potential lower than the potential of the power source VDD, which is supplied to the small amplitude oscillation circuit 10, and higher than the potential of ground GND, which is supplied to the small amplitude oscillation circuit 10, and the output node B of the small amplitude oscillation circuit 10 and that adjusts amplitude which the small amplitude oscillation circuit 10 oscillates is provided. The resistance element 26 is adjusted to oscillate at amplitude in the range narrower than voltage between the power source VDD and ground GND. Namely, amplitude which the small amplitude oscillation circuit 10 oscillates is regulated to small one in the range of the minimum potential of an oscillation pulse to maximum potential by appropriately controlling the potential of the power source Vtt and the resistance value of the resistance element 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-amplitude oscillating circuit that oscillates with an amplitude smaller than a voltage between a power supply and a ground.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing an example of a conventional oscillation circuit. The illustrated oscillation circuit 42 is a Colpitts-type oscillation circuit that oscillates at a predetermined frequency, and includes a crystal oscillator 12, an oscillation buffer 14, a feedback resistor 16, and capacitors 18 and 20. The crystal oscillator 12, the oscillation buffer 14, and the feedback resistor 16 are connected in parallel with each other, and the capacitance elements 18 and 20 are connected between both ends of the crystal oscillator 12 and the ground, respectively.

In the illustrated example, an oscillation buffer 14 is an inverter, and is a P-type MOS transistor (hereinafter referred to as a PMO transistor).
S) 22 and an N-type MOS transistor (hereinafter, referred to as S)
NMOS 24). PMOS 22 and N
The sources of the MOS 24 are a power supply VDD and a ground G, respectively.
ND, its gate is connected to the node A which is the input of the oscillation buffer 14, and its drain is short-circuited to the node B which is the output of the oscillation buffer 14.
It is connected to the.

In the oscillation circuit 42, the quartz oscillator 1
2 outputs a sine wave of a predetermined frequency. The feedback resistor 16 is a bias resistor connecting both ends of the crystal unit 12, and includes the oscillation buffer 14 and the capacitance elements 18 and 2.
Together with 0, the sine wave output from the crystal oscillator 12 is amplified to a predetermined amplitude. The sine wave amplified to a predetermined amplitude is shaped into a square wave by an output buffer (not shown),
For example, it is supplied to the internal circuit of the semiconductor device as a clock signal or the like.

In the oscillation circuit 42, during the oscillation operation, the PMOS 22 and the N
Since one of the MOSs 24 is almost completely turned on or off and the other is almost completely turned off or on correspondingly, the node B which is the output of the oscillation buffer 14
Makes a full swing between power and ground. For example, when the potential of the power supply VDD is 3.3 V and the potential of the ground GND is 0 V, the node B performs a full swing between 3.3 V and 0 V.

As described above, in the conventional oscillation circuit 42, the node B, which is the output of the oscillation buffer 14, makes a full swing between the power supply and the ground. A large current flows through the power supply and the ground inside the semiconductor chip according to the oscillation frequency of the oscillation circuit 42 due to the charging / discharging current, the through current, and the like, and noise occurs at the power supply and the ground due to the influence of an inductance component parasitic to the power supply and the ground. There was a problem of doing.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art,
An object of the present invention is to provide a small-amplitude oscillation circuit capable of reducing noise generated in a power supply and a ground in a semiconductor chip.

[0008]

In order to achieve the above object, the present invention provides a small-amplitude oscillation circuit which oscillates with an amplitude in a range narrower than a voltage between a first power supply and a ground,
The small-amplitude oscillation circuit is connected between a second power supply having a potential lower than the potential of the first power supply and higher than the potential of the ground and an output node of the small-amplitude oscillation circuit. It is intended to provide a small-amplitude oscillation circuit having a resistance element for adjusting the amplitude of the oscillation signal.

Here, it is preferable that the second power supply use a power supply used in a small-amplitude interface, having a potential lower than the potential of the first power supply and higher than the potential of the ground. preferable.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a small-amplitude oscillation circuit according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 is a circuit diagram of a small-amplitude oscillation circuit according to an embodiment of the present invention. The illustrated small-amplitude oscillation device 10
5 is lower than the potential of the power supply VDD supplied to the small-amplitude oscillation circuit 10 and is lower than the potential of the ground GND supplied to the small-amplitude oscillation circuit 10 in the conventional oscillation circuit shown in FIG. It has a resistance element 26 connected between the power supply Vtt having a high potential and the output node B of the small amplitude oscillation circuit 10 for adjusting the amplitude at which the small amplitude oscillation circuit 10 oscillates.

That is, in the small-amplitude oscillation circuit 10,
The basic oscillation circuit is a Colpitts-type crystal oscillation circuit, which is the same as the conventional oscillation circuit 42 shown in FIG. 5, and includes a crystal oscillator 12, an oscillation buffer 14, and a feedback resistor 1.
6 and capacitance elements 18 and 20. Here, the crystal oscillator 12, the oscillation buffer 14, and the feedback resistor 16 are connected in parallel with each other, and the capacitance elements 18, 20 are
Each is connected between both ends of the crystal unit 12 and the ground.

The oscillation buffer 14 in the illustrated example is an inverter, and is a P-type MOS transistor (hereinafter referred to as a PMO transistor).
S) 22 and an N-type MOS transistor (hereinafter, referred to as S)
NMOS 24). PMOS 22 and N
The source of the MOS 24 is connected to the power supply and the ground, the gate is connected to the node A serving as the input of the oscillation buffer 14, and the drain is short-circuited and connected to the node B serving as the output of the oscillation buffer 14. I have.

In the small-amplitude oscillation circuit 10, the crystal oscillator 12 outputs a sine wave of a predetermined frequency. The feedback resistor 16 is a bias resistor connecting both ends of the crystal unit 12, and includes the oscillation buffer 14 and the capacitive element 1.
Along with 8, 20, the sine wave output from the crystal unit 12 is amplified to a predetermined amplitude. The resistance element 26 adjusts the small-amplitude oscillation circuit 10 to oscillate with an amplitude in a range narrower than the voltage between the power supply VDD and the ground GND.

The amplitude oscillated by the small-amplitude oscillation circuit 10 of the present invention can be adjusted by the potential of the power supply Vtt and the resistance value of the resistance element 26. That is, the potential of the power supply Vtt is lower than the potential of the power supply VDD, and
Since it is higher than the potential of ND, the minimum potential of the oscillation pulse is
The potential difference between the power supply Vtt and the ground GND is determined by resistance division by the ON resistance of the NMOS 24 and the resistance value of the resistance element 26 of the inverter constituting the oscillation buffer 14.

The maximum potential of the oscillation pulse is determined by the power supply VD
The potential difference between D and the power supply Vtt is determined by resistance division by the ON resistance of the PMOS 22 and the resistance of the resistance element 26 of the inverter constituting the oscillation buffer 14. Therefore, the oscillation amplitude of the small-amplitude oscillation circuit 10 of the present invention can be adjusted to a small amplitude in the range from the minimum potential to the maximum potential of the oscillation pulse by appropriately adjusting the potential of the power supply Vtt and the resistance value of the resistance element 26. Can be restricted to

FIG. 2 is a circuit diagram showing an embodiment of a small-amplitude oscillation circuit according to the present invention. This small-amplitude oscillation circuit 28 uses a NOR gate having one input terminal connected to the ground as the oscillation buffer 14 in the small-amplitude oscillation circuit 10 of the present invention shown in FIG.
Furthermore, a limiting resistor 30 is provided between the feedback resistor 16 on the output node B side and the crystal unit 12 for reliably oscillating the small-amplitude oscillation circuit 28.

In the small-amplitude oscillation circuit 28, the potential of the power supply VDD supplied is 3.32V. On the other hand, the potential of the power supply Vtt supplied to one end of the resistance element 26 is 1.55 V as shown in FIG. The frequency of the crystal unit 12 is 2 MHz, and the feedback resistance 1
6, the resistance value of each of the limiting resistor 30 and the resistance element 26 is 1
MΩ, 1.1 KΩ and 1.3 KΩ, and the capacitance element 1
The capacitances of 8, 20 are both 30 pF.

In the small-amplitude oscillation circuit 28 shown in FIG. 2, the resistance value of the resistance element 26 is set to 1.3 KΩ.
The resistance value of the resistance element 26 is supplied to the resistance element 26, the size of the PMOS and NMOS transistors constituting the logic gate serving as the oscillation buffer 14, the oscillation frequency and the amplitude during the oscillation operation of the small-amplitude oscillation circuit of the present invention. Power supply V
Although it is appropriately determined depending on the potential of tt or the like, the resistance value is usually about 50 to 1 KΩ.

FIG. 3 is a timing chart showing an operation of the small-amplitude oscillation circuit according to the embodiment of the present invention. In this timing chart, the waveform W1 is an example in which the configuration obtained by removing the resistance element 26 from the small-amplitude oscillation circuit 28 of the present invention shown in FIG. 2 is a specific configuration of the conventional oscillation circuit shown in FIG. In this case, an example of the operation of the conventional oscillation circuit is shown, and a waveform W2 shows an example of the operation of the small-amplitude oscillation circuit 28 of the present invention shown in FIG.

As shown in this timing chart, the conventional oscillation circuit performs full swing at an amplitude in a voltage range between the power supply VDD and the ground GND, whereas the small oscillation of the present invention shown in FIG. The oscillation circuit 28 has a power supply V
It oscillates with a small amplitude in a range narrower than the voltage between DD and ground GND. Therefore, the small-amplitude oscillation circuit 2 of the present invention
8 can reduce the current consumption as compared with the conventional oscillation circuit, and as a result, the power supply VDD and the ground GND
Can be reduced.

The small-amplitude oscillation circuit of the present invention is basically as described above. In the illustrated example, an example in which the present invention is applied to a Colpitts-type crystal oscillation circuit is shown. However, the present invention is not limited to this. As an oscillation circuit to which the present invention is applied, for example, a crystal oscillator The present invention can be applied to all types of conventionally known oscillation circuits, such as other oscillation circuits that use a resonator, an oscillation circuit that uses a resonator such as a ceramic oscillator, and a CR oscillation circuit.

As shown in FIG. 1, when the small-amplitude oscillation circuit of the present invention is applied to a semiconductor device, basically, an oscillation buffer 14 is formed on a semiconductor chip,
2. It is preferable that the feedback resistor 16, the capacitance elements 18, 20 and the resistance element 26 are formed outside the semiconductor device so that the resistance value and the capacitance value can be appropriately adjusted.
By determining an appropriate resistance value or capacitance value in advance by experiment, a device other than the crystal resonator 12 may be built in the semiconductor device.

Further, for example, when a small-amplitude interface is used on a board on which the small-amplitude oscillation circuit of the present invention is mounted, the power supply Vtt is lower than the potential of the power supply VDD used in the small-amplitude interface. In addition, a power supply having a potential higher than the potential of the ground GND can be used. This eliminates the need to generate the power supply Vtt exclusively for the small-amplitude oscillation circuit of the present invention,
There is an advantage that the circuit configuration of the small-amplitude oscillation circuit of the present invention can be simplified.

FIG. 4 shows a conceptual diagram of an example of the small-amplitude interface. The illustrated small-amplitude interface 30 includes a driver 32, a receiver 34, and a driver 32.
Series resistor 3 connected in series between the
6, and a connection between the transmission line 40 and a power supply having a potential lower than the potential of the power supplied to the driver 32 and the receiver 34 and higher than the potential of the ground supplied to the driver 32 and the receiver 34 Terminating resistor 38.

In the small-amplitude interface 30, for example, when the potential of the power supplied to the driver 32 and the receiver 34 is 3.3 V and the potential of the power supplied to one end of the terminating resistor 38 is 1.5 V, the series resistor 36 Is adjusted to about 25 to 50Ω, and the resistance value of the terminating resistor 38 is adjusted to about 50Ω. In general, the small-amplitude interface has already been standardized for the purpose of reducing power consumption and electromagnetic radiation with a signal having a small amplitude transmitted through a transmission line.

Therefore, when a small-amplitude interface is used on a board, it is preferable to use the power supplied to the terminating resistor of the small-amplitude interface as the power supply Vtt of the small-amplitude oscillation circuit of the present invention. As described above, the small-amplitude oscillation circuit of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

[0028]

As described above in detail, the small-amplitude oscillation circuit of the present invention is lower than the potential of the first power supply supplied to the small-amplitude oscillation circuit and supplied to the small-amplitude oscillation circuit. A resistance element for adjusting the amplitude at which the small-amplitude oscillation circuit oscillates is connected between a second power supply having a potential higher than the potential of the ground and the output node of the small-amplitude oscillation circuit. The small-amplitude oscillation circuit oscillates with an amplitude in a range narrower than the voltage between the first power supply and the ground. Thus, according to the small-amplitude oscillation circuit of the present invention, the current consumption can be reduced as compared with the conventional oscillation circuit, so that the power supplied to the small-amplitude oscillation circuit is smaller than that of the conventional oscillation circuit. In addition, noise generated in the ground can be reduced. According to the small-amplitude oscillation circuit of the present invention, as the second power supply, a power supply used in the small-amplitude interface and having a potential lower than the potential of the first power supply and higher than the ground potential is used. By using this, it is not necessary to generate the second power supply exclusively for the small-amplitude oscillation circuit of the present invention, and the circuit configuration of the small-amplitude oscillation circuit of the present invention can be simplified.

[Brief description of the drawings]

FIG. 1 is a configuration circuit diagram of an embodiment of a small-amplitude oscillation circuit according to the present invention.

FIG. 2 is a configuration circuit diagram of an example showing a specific configuration of a small-amplitude oscillation circuit of the present invention.

FIG. 3 is a timing chart of one embodiment showing the operation of the small-amplitude oscillation circuit of the present invention.

FIG. 4 is a conceptual diagram of an example of a small amplitude interface.

FIG. 5 is a configuration circuit diagram of an example of a conventional oscillation circuit.

[Explanation of symbols]

 10, 28, 42 Small-amplitude oscillator 12 Crystal oscillator 14 Oscillation buffer 16 Feedback resistor 18, 20 Capacitance element 22 P-type MOS transistor 24 N-type MOS transistor 26 Resistance element 30 Small-amplitude interface 32 Driver 34 Receiver 36 Series resistor 38 Termination Resistance 40 Transmission line

Claims (2)

[Claims] 1. A small-amplitude oscillation circuit that oscillates with an amplitude in a range narrower than a voltage between a first power supply and a ground, wherein the oscillation circuit is lower than the potential of the first power supply and the potential of the ground. A small-amplitude oscillation circuit connected between a second power supply having a higher potential and an output node of the small-amplitude oscillation circuit, the resistor having a resistance element for adjusting the oscillation amplitude of the small-amplitude oscillation circuit. Amplitude oscillation circuit. 2. The power supply according to claim 1, wherein the second power supply is a power supply used in a small-amplitude interface and having a potential lower than the potential of the first power supply and higher than the potential of the ground. 2. The small-amplitude oscillation circuit according to claim 1, wherein