JPH0823230A - Crystal oscillator circuit - Google Patents

Abstract

PURPOSE:To provide a crystal oscillator circuit which can generate a sine wave of reduced distortions without constructing a filter and also can shorten the development period together with reduction of the number of parts by huffing the input oscillation of a CMOS inverter by an FET via a resistor. CONSTITUTION:The frequency that is selected by a crystal vibrator 6 and the capacitors 5 and 4 oscillates at the output of an inverter 1, and this oscillation produces the distortions by the power voltage of the inverter 1 and the Q of the vibrator 6. These distortions are improved through a frequency discriminator used for the vibrator 6 and both capacitors 5 and 4 and inputted to the inverter 1. An amplifier circuit which has a high input impedance to prevent reduction of the oscillation tolerance is required to take out the oscillation of reduced distortions that is inputted to the inverter 1. Thus a buffer circuit is used to input the oscillation to the gate of an FET 8 via a resistator 7 and to secure a high input impedance as a source follower. In such a constitution, a sine wave including reduced distortions can be outputted from the input of the inverter 1 via a buffer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillating circuit for identifying signals of radio equipment and the like.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional crystal oscillator circuit. The configuration of this conventional example will be described below with reference to FIG.

In FIG. 4, reference numeral 1 is a CMOS inverter, which is formed as a semiconductor integrated circuit. 2 is a resistance CM
Connected to the output and input of the OS inverter 1 and 3 is a resistor, one end of which is connected to the output of the CMOS inverter 1. 4 and 5 are capacitors, and 6 is a crystal oscillator. Of these, the capacitor 4 has one end connected to the resistor 3 and the crystal unit 6, and the other end grounded. The capacitor 5 has a crystal oscillator 6, a resistor 2 and a C at one end thereof.
It is connected to the input of the MOS inverter 1 and the other end is grounded. The CMOS inverter 1, the resistor 2, the resistor 3, the capacitor 4, the capacitor 5, and the crystal unit 6 form an oscillation circuit. 21 is a filter and its input side is CMO
It is connected to the S inverter 1 and the output side is connected to the output terminal of this circuit.

The operation of the crystal oscillator circuit configured as described above will be described below. When this circuit is viewed from an alternating current, a slight noise vibration occurs at the input of the CMOS inverter 1. This noise is amplified by the gain of the CMOS inverter 1, and the phase becomes opposite to C
It is transmitted from the output of the MOS inverter 1. Further, the amplified noise passes through the resistor 3 and the frequency discriminator including the capacitors 4, 5, and the crystal unit 6.
Here, as for noise, only a signal in the frequency range shown by the following equation determined by the crystal oscillator 6 enters the input of the CMOS inverter 1 in phase.

Fs = 1 / (2π√ (LC)) fp = 1 / (2π√ (LCC0 / (C + C0))) The oscillation frequency f is fs ≦ f ≦ fp L: Equivalent series inductance C of the crystal oscillator: Equivalent series capacitance of crystal unit C0: Equivalent parallel capacitance of crystal unit fs: Series resonance frequency of crystal unit fp: Parallel resonance frequency of crystal unit After that, oscillation becomes maximum value of Q of crystal unit 6. By the way it stabilizes. The resistor 2 is a feedback resistor for providing the operating point of the CMOS inverter 1 near the threshold.
The resistor 3 is a protective resistor that determines the bias voltage applied to the crystal unit 6 and defines the drive level. Filter 21
Is a filter for shaping the signal output from the CMOS inverter 1 into a sine wave. Therefore, a sine wave is output in the above configuration.

[0006]

However, in order to obtain a sine wave with the conventional crystal oscillator, the CMOS inverter 1 is used.
Since the gain is high, the waveform is clipped and distorted by the power supply voltage, and even if the gain is lowered, it is not possible to adjust the gain because of the semiconductor integrated circuit. There is also a method of lowering it, but in this case, rather than the distortion of the oscillation, the oscillation margin is deteriorated this time, which may cause the oscillation to stop.
I had no choice but to format it with 1. Therefore, the development period of the filter 21 becomes long, and the increase of the number of parts and the cost increase due to the addition of the filter 21 are problems.

The present invention solves the above-mentioned conventional problems, and an expensive filter 2 requiring such a long development period is used.
It is an object of the present invention to provide a crystal oscillator that does not require 1.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention oscillates an oscillation from the input of a CMOS inverter.
It is a configuration in which the buffer is performed at T.

[0009]

With this configuration, the crystal oscillator plays a role of a filter for shaping the output of the CMOS inverter into a sine wave and buffers it with the FET, so that the filter can be omitted without deteriorating the oscillation margin.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of one embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a crystal oscillation circuit of the present invention. In FIG. 1, reference numeral 1 is a CMOS inverter, which is formed as a semiconductor integrated circuit. 2 is a CMOS
The resistor 3 is connected to the output and input of the inverter 1, and one end thereof is connected to the output of the CMOS inverter 1. 4 and 5 are capacitors, and 6 is a crystal oscillator. Of these, the capacitor 4 has one end connected to the resistor 3 and the crystal unit 6, and the other end grounded. The capacitor 5 has a crystal oscillator 6, a resistor 2 and a CMOS at one end thereof.
It is connected to the input of the inverter 1 and the other end is grounded. The CMOS inverter 1, the resistor 2, the resistor 3, the capacitor 4, the capacitor 5, and the crystal unit 6 form an oscillation circuit. Reference numeral 8 is a FET, 7 is a resistor, and the input of the CMOS inverter 1 is connected to the gate of the FET 8 via the resistor 7. A load 9 is connected to the source of the FET 8.

The operation of the crystal oscillator circuit configured as described above will be described. First, the output of the inverter 1 oscillates at a frequency selected by the crystal unit 6, the capacitor 5, and the capacitor 4. The oscillation is distorted by the influence of the power supply voltage of the CMOS inverter 1 and the Q of the crystal unit 6. The distortion is improved by passing through the crystal oscillator 6, the capacitor 5, and the frequency discriminator of the capacitor 4, and enters the input of the CMOS inverter 1. In order to take out the low-distortion oscillation that enters the input of the CMOS inverter 1, an amplifier circuit with a high input impedance is required so as not to reduce the oscillation allowance. Therefore, through the resistor 7, the FET
Oscillation is input to the gate of 8 to serve as a source follower to form a buffer circuit with high input impedance. Therefore CM
A sine wave with less distortion can be output from the input of the OS inverter 1 via a buffer.

The output voltage from the FET 8 is shown in FIG. 2, and C is shown in FIG.
The output voltage waveform from the MOS inverter 1 is shown. It can be seen from FIGS. 2 and 3 that the distortion is improved.

[0014]

The present invention has the above-mentioned structure, and CM
A crystal that can generate a sinusoidal wave with little distortion without forming a filter by passing a buffer circuit formed of an FET from the input of the OS inverter, and can shorten the development period and the number of parts because a filter is not formed. An oscillator circuit can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining an operation in an embodiment of a crystal oscillation circuit of the present invention.

FIG. 2 is an FE in one embodiment of the crystal oscillation circuit of the present invention.
Output waveform diagram from T8

FIG. 3 is a CM in one embodiment of the crystal oscillation circuit of the present invention.
Output waveform diagram from the output of OS inverter 1

FIG. 4 is a circuit diagram for explaining the operation of a conventional crystal oscillation circuit.

[Explanation of symbols]

 1 CMOS inverter 2, 3, 7 resistance 4, 5 capacitor 6 crystal oscillator 8 FET 9 load

Claims (1)

[Claims] 1. The output of the CMOS inverter is connected to the input of the CMOS inverter via a first resistor,
The output of the CMOS inverter is connected to the input of the CMOS inverter via the second resistor and the crystal oscillator, the crystal oscillator is connected to the second resistor and the first capacitor, and the first capacitor is Grounded, the crystal oscillator, the input of the CMOS inverter, the first resistor, the third resistor, and the second capacitor are connected, the second capacitor is grounded, and the input of the CMOS inverter is Connected to the gate of the FET through the resistor 3
A crystal oscillation circuit, characterized in that the source of the FET is grounded via a load, and the oscillation of the input of the CMOS inverter is buffered by the FET via the third resistor.