JPH03201808A - Temperature compensation oscillator - Google Patents

Abstract

PURPOSE:To enable the fine control of an oscillation frequency corresponding to a bias voltage value by providing a high input impedance amplifier, which applies an output to a voltage capacity converting element, and a pull-up circuit to pull-up a potential to an almost midpoint potential in the variable range of a bias voltage. CONSTITUTION:At an oscillator to execute temperature compensation by impressing a temperature compensating voltage Vt to a voltage capacity converting element 14 which controls the oscillation frequency, a bias circuit to execute the fine control of the oscillation frequency is formed by a high input impedance amplifier 17, which connects the input to a bias input terminal 18 and applies the output to the voltage capacity converting element 14, and the pull-up circuit to pull up the input of this high input impedance amplifier 17 to the almost midpoint potential in the various range of the bias voltage. Thus, the fine control of the oscillation frequency can be executed by the bias voltage and the oscillation frequency can be automatically tuned to an objective frequency without exerting the influence of a bias source characteristic upon a temperature compensating characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a temperature compensated oscillator that compensates for changes in oscillation frequency due to temperature changes, and in particular to improvements in a bias circuit that finely adjusts the oscillation frequency according to a bias voltage value. Regarding.

(Technical background of the invention and its problems) Recently, crystal oscillators have been widely used as standards for frequency, time, etc. Incidentally, a crystal resonator used in a crystal oscillator generally has a temperature coefficient, and its frequency changes with changes in temperature. For example, a typical AT-cut crystal oscillator used at a frequency of several MHz to several dozen MHz is
As shown in Figure 3, the temperature coefficient has a substantially cubic curve shape, its characteristics change minutely depending on the cutting angle, and the inflection point is 25.
It will be around ℃.

On the other hand, as electronic devices become more precise, even crystal oscillators tend to be required to have more stable oscillation frequencies.

A crystal oscillator that satisfies these requirements includes one in which an oscillation circuit is housed in a thermostatic oven. However, devices using a constant temperature oven are larger in size, consume more power, take longer to stabilize the frequency when the power is turned on, and are unreliable because the components are exposed to a relatively high temperature of about 70°C. There are also problems with sexuality.

For this purpose, a voltage capacitance conversion element such as a varicap is connected to the crystal resonator, a compensation voltage is generated by a compensation voltage generation circuit according to the temperature detected by a temperature detection element such as a thermistor, and this compensation voltage is There are some that perform temperature compensation by applying voltage to a varicap.

FIG. 2 is a block diagram showing an example of a conventional temperature-compensated oscillator of this type, in which a voltage-capacitance variable element 3, for example a varicap, is connected in series to a crystal resonator 2 of a so-called Colpitts-type crystal oscillator 1. .

Then, a temperature signal detected by a temperature sensor 4 such as a thermistor is applied to a compensation voltage generation circuit 5 to obtain a temperature compensation voltage, which is applied to the varicap 3. However, in such a temperature-compensated oscillator, if the frequency changes slightly due to changes in the crystal resonator over time, etc., it is necessary to be able to make fine adjustments in order to make the oscillation frequency accurately match the target frequency. For this reason, a bias voltage vb is applied to the varicap 3 from a bias input terminal 7 via a high resistance 6.

For boat fishing, as shown in the graph shown in Figure 3, in order to use the variable width of the bias voltage vb most efficiently, the target frequency fO should be set at approximately the midpoint potential of the variable width of the bias voltage vb. Designed to.

In this way, the oscillation frequency can be finely adjusted in accordance with the voltage applied to the bias input terminal 7, and it becomes possible to accurately match it to a predetermined target frequency.

However, in such a device, strictly speaking, if the internal resistance of the voltage source connected to the bias input terminal 7 changes, the temperature compensation characteristic due to the compensation voltage of the compensation voltage generating circuit 5 changes, making it impossible to obtain the desired compensation characteristic. Therefore, it is necessary to connect a variable constant voltage source with predetermined characteristics to the bias input terminal 7, which is extremely troublesome to handle in practice.

Further, if the bias input terminal 7 is set to an oven, the oscillation frequency will be approximately at the lower end of the frequency variable range by the bias voltage vb, and furthermore, the predetermined temperature compensation characteristic will not be obtained.

Furthermore, a temperature compensated oscillator with relatively high-end specifications that has such a bias input terminal and an oscillator with relatively simple specifications that do not have a bias input terminal may have different temperature compensation circuit configurations even if they have the same oscillation frequency. It is necessary to For this reason, there is a problem in that even if the oscillator is the same, separate temperature compensation circuits are required depending on the presence or absence of a bias input terminal.

For this reason, some devices are provided with separate voltage-capacitance conversion elements for temperature compensation and voltage-capacity conversion elements for bias.

However, this type of device has the problem that the electrical configuration becomes complicated and the number of elements that affect the oscillation frequency increases, making it difficult to perform highly accurate temperature compensation.

(Object of the Invention) The present invention has been made in view of the above circumstances, and the DC characteristics of the bias source do not impair the temperature compensation characteristics, and when a bias voltage is applied, the frequency is adjusted according to the value. If the oscillation frequency does not need to be finely adjusted, by opening the terminal, the frequency can be automatically set to approximately the center of the variable range due to the bias voltage. Temperature compensation allows you to obtain the desired temperature compensation characteristics. The purpose is to provide an oscillator.

(Summary of the Invention) The present invention provides an oscillator that performs temperature compensation by applying a temperature compensation voltage to a voltage-capacitance conversion element that controls the oscillation frequency.
The bias circuit that finely adjusts the oscillation frequency includes a high input impedance amplifier whose input is connected to the bias input terminal and whose output is given to the voltage capacitance conversion element, and the input of this high input impedance amplifier is connected to the bias voltage within the variable range of the bias voltage. It is characterized by comprising a pull-up circuit that pulls up the voltage to a point potential.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the block diagram shown in FIG.

In the figure, 11 is a temperature sensor, for example, a thermistor whose resistance value changes according to temperature changes. Reference numeral 12 denotes a compensation voltage generation circuit which receives a temperature signal corresponding to the detected temperature from the temperature sensor 11 and generates a temperature compensation voltage Vt.

The temperature compensation voltage Vt outputted from the compensation voltage generation circuit 12 is applied to the voltage capacitance conversion element 14 via the resistor 13 to control its capacitance.

This voltage-capacitance conversion element 14 is connected in series to a crystal resonator 16 of a Colpitts-type crystal oscillation circuit 15, for example, and finely varies its oscillation frequency to compensate for changes in the oscillation frequency due to temperature changes.

A high input impedance amplifier 17 is, for example, a voltage follower circuit with an amplification factor of 1, in which the inverting input of an operational amplifier is connected to the output. The input of this high input impedance amplifier 17 is connected to a bias input terminal 18 that provides an external control voltage, and is pulled up via a resistor 20 to a voltage n that is approximately at the midpoint of the variable range of the control voltage. There is. And the output of the high input impedance amplifier 17, that is, the bias voltage vb
is applied to the voltage capacitance conversion element 14 via the resistor 19.

With such a configuration, the compensation voltage Vt corresponding to the temperature detected by the temperature sensor 11 can be obtained by the compensation voltage generation circuit 12 and applied to the voltage capacitance conversion element 14 to perform temperature compensation. When the bias input terminal 18 is in an oven and no control voltage is applied, the input of the high input impedance amplifier 170 becomes the above-mentioned midpoint potential, and the control voltage t is automatically applied.
This becomes approximately the center frequency of the frequency variable width. Further, by applying a control voltage to the bias input terminal 18, the oscillation frequency can be finely adjusted according to the value of the control voltage.

Therefore, the compensation voltage generation circuit 12 and the bias input terminal 18
Since the high input impedance amplifier 17 disconnects the bias input terminal 18 from the bias input terminal 18 in terms of direct current, the internal impedance of the circuit connected to the bias input terminal 18 will not impair the temperature compensation characteristics.

Furthermore, a temperature-compensated oscillator with a relatively high-grade specification that has a bias input terminal and an oscillator with a relatively simple specification that does not have a bias input terminal can be manufactured with the same configuration and use a common crystal oscillator, so they can be made into a common model. There are some advantages to doing so.

Note that the present invention is not limited to the above embodiments,
For example, the high input impedance amplifier may be configured using not only an operational amplifier but also a field effect transistor or the like.

It goes without saying that the compensation voltage generating circuit may be one that generates a compensation voltage in an analog manner, or one that digitally reads compensation data from a storage element and performs compensation.

(Effects of the Invention) As detailed above, according to the present invention, the oscillation frequency can be finely adjusted by the bias voltage, and the oscillation frequency can be adjusted without the characteristics of the bias source affecting the temperature compensation characteristics. If it is not necessary to do so, by opening the bias input terminal, it is possible to provide a temperature compensated oscillator that can automatically adjust to the target frequency without impairing the temperature compensation characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a conventional temperature compensated oscillator, and FIG. 3 is a graph explaining frequency adjustment by bias voltage. 11 ・ l 2 ・ 14 φ l 5 ・ 16 ・ 17 ◆ l 8 ・ Temperature sensor compensation voltage generation circuit Voltage capacitance conversion element Oscillation circuit Crystal resonator High input impedance amplifier Bias input terminal

Claims (1)

[Scope of Claims] A temperature sensor that detects temperature, a compensation voltage generation circuit that outputs a temperature compensation voltage according to the detection output of this temperature sensor, and a capacitance that is controlled according to the output of this compensation voltage generation circuit. a piezoelectric vibrator whose frequency is controlled by the voltage-capacitance conversion element; an oscillation circuit that constitutes an oscillator together with the piezoelectric vibrator; a bias circuit that applies a bias voltage set to a predetermined frequency; the bias circuit includes a high input impedance amplifier whose input is connected to the bias input terminal and whose output is provided to the voltage capacitance conversion element; A temperature compensated oscillator comprising a pull-up circuit that pulls up the input of the impedance amplifier to approximately the midpoint potential of the variable range of the bias voltage.