JPH09284048A - Electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the temperature compensation characteristic of a digital temperature compensation type crystal oscillator, to reduce the manufacture cost and to decrease the power consumption. SOLUTION: A digital temperature signal is obtained by applying A/D conversion to a signal being the sum of an analog signal of a temperature sensor 5 and an AC random signal. The digital temperature signal is given to a programmable memory 3, from which a digital temperature compensation signal is obtained. The digital temperature compensation signal is converted into an analog temperature compensation signal by a D/A converter 2. The analog temperature compensation signal fluctuated digitally timewise is integrated timewise by an integration circuit 7 and used as a voltage to control the frequency of a crystal oscillator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used in mobile phones, car phones and the like. The present invention relates to a digital temperature-compensated crystal oscillator and an electronic circuit (including a semiconductor integrated circuit) used for the oscillator.

[0002]

2. Description of the Related Art For a conventional digital temperature-compensated crystal oscillator, see "Ultrasonic TECHNO September 1995".
Is described in detail. That is, a digital temperature-compensated crystal oscillator (hereinafter, abbreviated as digital TCXO) uses a digital control to generate a frequency so that a constant oscillation frequency can be always obtained based on temperature information from a temperature sensor. It is a controlled oscillator. The output of the temperature sensor is converted into digital information by an A / O converter. Input to the digital programmable memory,
The temperature correction digital information corresponding to the temperature digital information is output. Further, the digital information for temperature correction is input to the D / A converter and converted into analog information for temperature correction and output. The frequency compensation analog information controls the frequency of the voltage-controlled crystal oscillator.

[0003]

However, the conventional digital TCXO has the following problems. (1) Since the digital signal is used for temperature compensation, the frequency change becomes discontinuous with respect to the temperature change. As a result, a communication error occurs due to the discontinuous change.

(2) A / D to enable frequency stability ± 1.0 × 10 ^-6 required for mobile phones and car phones
The resolution of the conversion needs to be increased, and the capacity of the programmable memory is increased accordingly, resulting in a high cost of the compensation system. (3) When a thermistor is used as the temperature sensor, the current consumption of the thermistor increases, and as a result,
The battery life of the mobile phone is short.

Therefore, the object of the present invention was made to solve the above problems. That is, the frequency is continuously compensated for the temperature change, and the low bit A / D converter and the low bit programmable memory can compensate the temperature at a low cost.
Another object of the present invention is to obtain a digital TCXO having a long battery life and a semiconductor integrated circuit used therein.

[0006]

According to the present invention, the following means are used to solve the above-mentioned problems. Addition means for adding the output from the AC signal generator to the analog output of the temperature sensor, A / D converter for inputting the analog signal from the addition means and converting and outputting to the temperature digital signal, and inputting the temperature digital signal Then, a programmable memory for outputting a digital signal for temperature compensation, an A / D converter for inputting the digital signal for temperature compensation and converting it to a first analog signal for temperature compensation, and a first temperature compensation The electronic device is composed of an integrating circuit which inputs an analog signal and outputs a second temperature compensating analog signal, and a voltage control transmitting circuit whose frequency is controlled by the second temperature compensating analog signal.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system block diagram showing an embodiment of a digital TCXO of the present invention. A temperature sensor 5 that outputs an analog voltage output of a linear function with respect to a temperature change, an addition unit 8 that adds the output of the temperature sensor 5 and an output from the AC signal generator 6, and a temperature analog signal from the addition unit 8 are input. A / D converter 4 for converting and outputting to a temperature digital signal and data for compensating the temperature characteristic of the oscillation frequency of the voltage controlled oscillator (hereinafter abbreviated as VCXO) 1, sandpaper,
A programmable memory 3 storing the relationship between the temperature digital signal and the temperature compensation digital signal, a D / A converter 2 for converting and outputting the temperature compensation digital signal from the memory 3 into a first temperature compensation analog signal, and a D / A The first temperature-compensated analog signal from the converter 2 is temporally averaged to obtain the second
Of the temperature-compensated analog signal, and the voltage-controlled oscillator 1 whose oscillation frequency is controlled by the second temperature-compensated analog signal output from the integrator circuit 7. With the configuration shown in FIG. 1, the temperature dependence of the temperature deviation (Δf / f) of the oscillation frequency has a smoothed characteristic that does not change discontinuously with respect to temperature, as shown in FIG.

The output signal from the AC signal generator used in the present invention may be any signal that changes AC-wise. A clean triangle or a white noise signal is preferable. In order to include the DC component in the AC signal generator 6, the addition unit 8 needs to remove the DC component. If the adding means 8 does not have a function of removing the DC component, a DC component removing filter may be provided between the adding means 8 and the AC signal generating means 6.

FIG. 4 is an electronic circuit diagram of the temperature sensor used in the present invention. The temperature sensor 5 includes diodes D1 and D2.
Is connected in series, and the voltage drop across the diode when a constant current is applied to the diode by the constant current source Ic is taken as the output voltage. In the case of FIG. 4, two diodes are connected in series. Since the temperature is 2.3 mv / ° C. per stage, the temperature sensitivity can be further increased by connecting a plurality of stages in series. Output terminal A of temperature sensor 5
A capacitor CA is connected to. Capacitor CA
Removes the DC component from the AC signal generator 6, and
It is provided to add only the AC component to the terminal A.
AC component is added to the sensor output, and A / D from terminal A
The added signal enters the converter 4. In the constant current operation type temperature sensor shown in FIG. 4, the constant current value is 10 μm.
Since it can be made smaller than A, the battery life can be extended. Further, since the temperature output is stable even when the battery voltage fluctuates, high temperature accuracy can be obtained.

The temperature sensor as shown in FIG. 4 can be formed by a semiconductor integrated circuit. Therefore, the digital T of the present invention
The CXO can be formed by a one-chip semiconductor integrated circuit except for crystal. In particular, by configuring all circuits with CMOS circuits, lower power consumption operation becomes possible.

In the case of the digital TCXO shown in FIG.
The integrating circuit smoothes the signal to the VCXO. Therefore, it is possible to obtain a stable frequency characteristic as shown in FIG. 3 even if the temperature of the programmable memory is not so much increased as in the conventional case. That is, if the temperature compensation level is the same as the conventional one, it can be achieved even if the capacity of the programmable memory is small. Therefore, when the temperature compensation system according to the present invention is configured on one chip, the cost can be reduced more than ever.

[0012]

As described above, the present invention has the following drop in the digital TCXO. (1) The temperature compensation of the voltage controlled oscillator can be controlled with respect to temperature changes without discontinuity.

(2) Since the highly accurate TCXO can be constructed with a low bit programmable memory, the manufacturing cost can be reduced. (3) Since the diode type sensor that operates with low power consumption is used as the temperature sensor, the life of the battery drive system can be extended.

[Brief description of drawings]

FIG. 1 is a system block diagram of a digital TCXO of the present invention.

FIG. 2 is a system block diagram of a conventional digital TCXO.

FIG. 3 is a temperature characteristic diagram of the digital TCXO of the present invention.

FIG. 4 is an electronic circuit diagram of the temperature sensor of the digital TCXO of the present invention.

[Explanation of symbols]

 1 VCXO 2 D / A converter 3 Programmable memory 4 A / D converter 5 Temperature sensor

Claims (1)

[Claims] 1. An adding means for adding an output from an AC signal generator to an analog output of a temperature sensor, an A / D converter for inputting an analog signal from the adding means and converting and outputting to a temperature digital signal, A programmable memory for inputting a temperature digital signal and outputting a temperature compensating digital signal; a D / A converter for inputting the temperature compensating digital signal and converting it to a first temperature compensating analog signal; It is composed of an integrating circuit which inputs a first temperature compensating analog signal and outputs a second temperature compensating analog signal, and a voltage control type oscillation circuit whose frequency is controlled by the second temperature compensating analog signal. Electronic device.