JPS6291006A - Digital control temperature compensation voltage oscillator - Google Patents

Abstract

PURPOSE:To reduce switching noise by adding a circuit cutting off harmonics of an audible frequency band of a digital control signal fed to a transistor (TR) for switching capacitor. CONSTITUTION:A compensation data outputted from a PROM 3 is inputted to a data load capacity control signal conversion circuit 4 to decide TRs turned on/off and its control signal is outputted. A load capacity control signal outputted from the conversion circuit 4 has a waveform where harmonics causing slow leading/trailing are attenuated from a rectangular wave by integration circuits 5, 6. The waveform switches a capacity changeover TR 7. Since the change is slow in the switching operation of the TRs and the harmonics are attenuated, the change is slow similarly in the capacitance increase/decrease of a series capacitor and in the oscillating frequency change attended with the load capacity change, the harmonics are attenuated and the noise is reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a digitally controlled temperature compensation system that controls load capacitance by switching capacitors based on frequency-temperature characteristic information of a piezoelectric vibrator and obtains high frequency accuracy with respect to temperature. Regarding piezoelectric oscillators.

[Summary of the invention]

In a frequency control system using capacitor switching for a digitally controlled temperature compensated piezoelectric oscillator, the present invention adds a circuit to remove harmonic components in the audible frequency band of the digital control signal sent to the transistor for capacitor switching, thereby changing the load capacitance. By making it gentler, the switching noise that occurs when switching capacitors is reduced.

[Conventional technology]

Conventionally, as shown in FIG. 4, a method for controlling the load capacitance of a piezoelectric vibrator is to turn on or off nine switching transistors connected in series with a capacitor using a digital signal (rectangular wave). The capacitance of the capacitor in series with the transistor that is turned on is added to the load capacitance, and by controlling the number of capacitors that turn on and the number of capacitors that turn off so that the frequency remains constant with respect to temperature, a highly accurate frequency can be achieved. can get.

[Problems and Objectives to be Solved by the Invention] However, in the prior art described above, as shown in FIG. The infinite harmonic components of the capacitor are generated as noise when switching capacitors. In particular, since capacitor switching noise also occurs in the audible frequency band,
This temperature-compensated piezoelectric oscillator using the capacitor switching method is a communication W! When used as a base signal source for a device, there are problems such as noise when switching capacitors during a call, and incorrect data when switching capacitors during a data call. .

Therefore, the present invention aims to solve these problems.
The object is to provide a digitally controlled temperature compensated piezoelectric oscillator that does not generate noise when switching capacitors.

[Means for resolving gaps]

The digitally controlled temperature-compensated piezoelectric oscillator of the present invention controls the load capacitance using a capacitor switching method, and has a circuit that removes harmonic components in the audible frequency band of a digital waveform load capacitance control signal that controls the capacitor switching transistor. It is characterized by the fact that it is attached.

[Operation] According to the above configuration of the present invention, when the aE'FA wave component in the audio frequency band of the depantal signal for load capacitance control is removed, the switching of the transistor and the accompanying change in load capacitance can also be performed in the audio frequency band. There are no harmonic components, so frequency changes are also similar, reducing noise when switching capacitors.

〔Example〕

An example using an integrating circuit using a resistor capacitor will be described below as an embodiment of a circuit for removing harmonic components in the audio frequency band of the digitally controlled temperature-compensated piezoelectric oscillator of the present invention, with reference to FIG.

1 is a temperature sensor, 2 is a temperature-address conversion circuit, 3 is a removable read-only memory IJ (F ROM),
4 is a data load capacitance control signal conversion circuit, 51 to 5n are integrating circuit resistors, 61 to 6n are integrating circuit capacitors, and 5.6 constitutes an integrating circuit. 71 to 7n are transistors for capacitance switching, 81 to 8n are capacitors for one load (load capacity/volume control), 9 is a piezoelectric vibrator, and 10 is an oscillation circuit. n (n is a natural number) are used, and the same number of capacitance switching transistors 7 and integration circuits 5.6 are used.Q.The capacitance and number of capacitors 8 are based on the temperature characteristics of piezoelectric vibrator 9, the accuracy of compensation, It is determined comprehensively from the compensation temperature range.

Temperature information detected by the temperature sensor 1 is converted into an address of the FROM 3 by a temperature-address conversion circuit 2. The FROM 3 stores compensation data obtained by calculating the load capacity 1 necessary to obtain a stable circumferential mantissa for iM degrees from the frequency temperature characteristic information of the piezoelectric vibrator 9. ==-<
. The compensation data output from PR○M6 is input to the data load capacitance control signal conversion circuit 41, which determines which transistors to turn on and which transistors to turn off, and
] Outputs the balance signal. The load capacitance control signal outputted from 4 has a waveform in which harmonic components with gradual rises and falls are attenuated from a rectangular wave by an integrator circuit composed of 5.6 and 5.6 waveforms. By switching the capacitance switching transistor 7 in this d-type, the switching operation also produces a waveform in which harmonic components with slow rises and falls are attenuated. On the other hand, the capacitance switching transistors 71 to 7
n and the load capacitance control capacitors 81 to 8n connected in series thereto adjust the load capacitance 1 of the piezoelectric vibrator.

In operation, the presence of a capacitor connected in series with the turned-on capacitance switching transistor is added as a load capacitance. For example, if all capacitors have the same capacity and are set to C, then mxc (m
is a natural number and m≦n, and the switching transistors 71 to 7m are turned on. Therefore, since the switching operation of the capacitance switching transistor changes slowly and the harmonic components are attenuated, the change in oscillation frequency due to the capacitance reduction of the series capacitor and the change in load capacitance also changes slowly. harmonic components are attenuated. The time constant of the extra circuit is selected so that it is used as a reference source vibration for communication equipment and noise is reduced when switching capacitors.

Next, the second part of the digitally controlled temperature compensated piezoelectric loss generator of the present invention will be described.
An example in which a 1□C filter is used as a circuit for removing harmonic components will be described with reference to FIG. 2. 11 is a coil, 12 is a capacitor, and is a constant-shaped filter composed of the above components, which is a low-pass type. This filter replaces the integration circuit portion of the first embodiment. In other words, the 11 coils are replaced with 5 resistors, and the 12 capacitors are replaced with 6 capacitors. As a result, the harmonic components of the rectangular wave signal output from the data load capacity control signal conversion circuit 4 are attenuated, and the same effect as in the first embodiment can be obtained.

Next, the third part of the digitally controlled temperature compensated piezoelectric oscillator of the present invention
An example in which an active RO filter is used as a circuit for removing harmonic components will be described with reference to FIG. 1
3 is an operational amplifier, and by combining resistors and capacitors as shown in FIG. 3, it becomes a positive feedback low-pass filter. By replacing this filter with the integrating circuit portion of the first embodiment, the same effects as in the first embodiment can be obtained.

In the embodiment described above, as shown in FIG. 6, the rise and fall of the load capacitance control signal is made gentle by the integrating circuit, and frequency components in the audible band are attenuated. The noise in the audible band that occurs when the frequency changes slowly is reduced.

Note that the piezoelectric vibrator of the present invention is made of crystal, ceramic LiTa, etc.
The vibrator is made of materials such as 0a, Lint+Ox, and has vibration shapes such as thickness shear vibration, torsional vibration, and bending vibration.

〔Effect of the invention〕

As explained above, the present invention has a simple configuration in which a rectangular wave load capacitance control signal is passed through a high-resolution component removal circuit and sent to a load capacitance switching transistor, thereby reducing the noise generated when switching the load capacitance, and reducing the frequency. Short-term stability is improved, and even capacitor-switching temperature-compensated piezoelectric oscillators can be used as reference sources for communication equipment. Furthermore, all circuits except the piezoelectric vibrator and coil are one-chip Cj-MOB IC! Because it can be mounted on a computer, it is possible to provide a compact, low power consumption, high precision oscillator, which has the effect of making it possible to make various communication devices smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a digitally controlled temperature compensated piezoelectric oscillator according to the present invention. FIG. 2 is a harmonic component removal circuit diagram using an LOO filter, FIG. 3 is a harmonic component removal circuit diagram using an active RO filter, and FIG. 4 is a configuration diagram of a conventional digitally controlled temperature-compensated piezoelectric oscillator. FIG. 5 is a diagram of the operation of each part according to the conventional digital control system, and FIG. 6 is a diagram of the operation of each part of the digitally controlled temperature-compensated piezoelectric oscillator according to the present invention. 1...Temperature sensor 2...Temperature-address conversion circuit 3...
, -PROM 4... Data load capacitance control signal conversion circuit 51-5n... Resistor for integration circuit 61-6
n...Capacitors 71 to 7n for music/integration circuits...
...Capacity switching transistors 81 to 8n...
......Load capacity control capacitor 9...
...Piezoelectric vibrator 10...Oscillation circuit 11...Lo filter cocoil 12.
......-LC filter capacitor 13...
...more than an operational amplifier

Claims (1)

[Claims] A digitally controlled temperature compensated piezoelectric oscillator that performs load capacitance control by switching capacitors, the digitally controlled temperature compensated piezoelectric oscillator being equipped with a circuit that removes harmonic components in the audible frequency band of a digital control signal for capacitor switching. .