KR100851314B1 - Apparatus for calibrating frequency of Voltage Controlled Temperatue Compensated Crystal Oscilator - Google Patents

Abstract

The present invention relates to a frequency calibration apparatus and method of VCTCXO. The frequency correction device of the VCTCXO is set from a voltage controlled temperature compensated crystal oscillator (VCTCXO), a phase locked loop (PLL) to which an output signal of the VCTCXO is fed back, and a reference frequency signal is input from the outside, a microcomputer, and the microcomputer. A value is input, and selectively switches the output terminal of the D / A converter, the phase locked loop and the D / A converter to convert the input setting value into an analog signal and output the converted signal, and the switched signal is input to the VCTCXO. And an A / D converter for capturing an analog signal input to the VCTCXO via the switching unit, converting the analog signal into a digital signal, and outputting the digital signal to the microcomputer. 'fixed voltage value' of the digital signal input from the A / D converter at the moment of phase lock Stored in the internal memory and to, by using the "constant voltage value, thereby correcting the frequency of the VCTCXO.

According to the present invention, the frequency of the VCTCXO can be corrected by inputting only the reference frequency signal from the outside.

VCTCXO, Reference Frequency, Frequency Calibration, PLL

Description

교정 ＣＴＣＸＯ frequency calibration device {Apparatus for calibrating frequency of Voltage Controlled Temperatue Compensated Crystal Oscilator}

1 is a circuit diagram illustrating a frequency calibration method of a VCTCXO according to the related art.

2 is a circuit diagram showing an overall frequency correction apparatus of the VCTCXO according to an embodiment of the present invention.

3 is a flowchart sequentially illustrating a frequency calibration method of the VCTCXO according to the preferred embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

20: frequency calibration device

200: VCTCXO

210: PLL

220: switching unit

230: microcomputer

240: A / D converter

250: D / A converter

The present invention relates to an apparatus and method for calibrating a frequency of VCTCXO. More specifically, an apparatus and method for calibrating the frequency of VCTCXO simply by inputting a reference frequency signal from the outside by using a phase locked loop and a microcomputer. It is about.

Voltage Controlled Temperature Compensated Crystal Oscillator (hereinafter referred to as 'VCTCXO') is a crystal oscillator that can adjust frequency and even temperature compensation by varying the voltage. It is applied to almost all electronic products related to frequency ranging from home appliances and mobile communication terminal products such as mobile phones, and it is a core component that generates a specific fixed frequency. In particular, the VCTCXO has the ability to control voltage as well as temperature compensation to oscillate at a constant frequency regardless of temperature.

On the other hand, measurement equipment such as signal generators use a phase locked loop (PLL) frequency synthesizer to obtain accurate and stable frequency stability. The stability of this frequency synthesizer is determined by the VCTCXO used as the reference frequency source. However, the accuracy of VCTCXO also decreases with time. As a result, as the accuracy of the signal of the VCTCXO used as the reference frequency source decreases, the accuracy of the measurement equipment using it also decreases with time. In order to solve this problem, the signal of VCTCXO must be calibrated periodically, which is called 'frequency calibration work'.

1 is a circuit diagram illustrating a circuit for a frequency calibration operation for a VCTCXO according to the prior art. Referring to FIG. 1, since the reference frequency output is changed according to the applied voltage, the conventional technique adjusts the reference frequency signal by adjusting the variable resistor 110 connected to the VCTCXO 100.

In order to adjust the reference frequency signal according to the conventional frequency calibration method, such as the need to open the case of the equipment to change the internal resistance occurs. Accordingly, the present applicant intends to propose a method that can automatically perform the frequency calibration work without opening the case of the equipment.

An object of the present invention for solving the above problems is to provide a frequency correction device of the VCTCXO that can output the correct frequency by performing a frequency correction operation by inputting only a reference frequency signal from the outside.

Another object of the present invention is to provide a frequency calibration method in which the VCTCXO can output an accurate frequency signal.

In order to achieve the above technical problem, the VCTCXO frequency correction apparatus according to the characteristics of the present invention,

Voltage controlled temperature compensated crystal oscillator (VCTCXO),

A phase locked loop (PLL) to which an output signal of the VCTCXO is fed back, and a reference frequency signal is input from the outside;

Micro computer,

A D / A converter which inputs a setting value from the microcomputer, converts the input setting value into an analog signal, and outputs the analog signal;

A switching unit for selectively switching the phase locked loop and an output terminal of the D / A converter and allowing the switched signal to be input to the VCTCXO;

An A / D converter for capturing an analog signal input to the VCTCXO via the switching unit, converting the analog signal into a digital signal, and outputting the digital signal to the microcomputer;

The switching unit is switched to the output terminal of the phase locked loop at the same time as the reference frequency signal is input to the phase locked loop, and is output to the output terminal of the D / A converter when the phase locked loop is phase locked. Characterized in that the switching,

The microcomputer stores the digital signal input from the A / D converter at the moment when the phase lock loop is phase locked in the internal memory as a 'fixed voltage value', and outputs the value to the D / A converter. Is set to '0',

After the switching unit is switched to the output terminal of the D / A converter, the microcomputer reads the value input to the A / D converter, and goes to the D / A converter until the readout value matches the 'fixed voltage value'. The output value of is incremented by '1', and finally the frequency calibration is terminated when the readout value matches the 'fixed voltage value'.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the frequency correction device 20 of the VCTCXO according to an embodiment of the present invention.

2 is a block diagram showing the overall configuration of the frequency correction device 20 of the VCTCXO according to an embodiment of the present invention. Referring to FIG. 2, the frequency calibrating apparatus 20 includes a VCTCXO 200, a PLL 210, a switching unit 220, a microcomputer 230, an A / D converter 240, and a D / A converter 250. It is provided. Hereinafter, each component described above will be described in detail.

The VCTCXO 200 is a device capable of adjusting the frequency of an output signal by varying a voltage input from the outside.

The PLL 210 is a phase locked loop, in which a reference frequency signal is input from the outside, connected to the input terminal of the VCTCXO 200 through the switching unit 220, and the signal output from the VCTCXO 220 is again. Feedback to the PLL. In general, the PLL 210 includes a phase comparator, a low pass filter, a voltage controlled oscillator (VCO), and the like, and detects a phase difference between an input signal and an output signal by a phase comparator, and the detected phase difference is used to detect the low pass filter. After converting into DC voltage and input to VCO, VCO has an oscillator circuit including a varactor. When the DC voltage corresponding to the phase difference is inputted, the VCO changes the capacitance of the varactor's capacitor, The oscillation frequency changes, resulting in an output frequency fixed to the phase of the input reference frequency.

The switching unit 220 is disposed to selectively switch with the PLL 210 and the D / A converter 250.

The A / D converter 240 receives an analog signal input to the VCTCXO 200, converts it into a digital signal, and transmits the analog signal to the microcomputer 230.

The D / A converter 250 converts the digital signal output from the microcomputer 230 into an analog signal and transmits the analog signal to the VCTCXO 200.

The microcomputer 230 receives and stores a reference voltage through the A / D converter 240, and then outputs the reference voltage to the VCTCXO through the D / A converter 9250.

Hereinafter, with reference to FIG. 3, the operation | movement of the frequency correction apparatus which has the above-mentioned structure is demonstrated sequentially. Referring to FIG. 3, first, a reference frequency is input to an input terminal of a PLL from outside (step 300), and then a switching unit is connected to an output terminal 'a' of a PLL (step 302).

Next, wait until the PLL is locked (step 310). After the PLL is fixed, the microcomputer reads the fixed voltage value input from the A / D converter and stores it in the internal memory (step 320).

Next, the switching unit is connected to the output terminal 'b' of the D / A converter connected to the microcomputer (step 330).

Next, the microcomputer sets and outputs an input value to the D / A converter as '0' (step 340). Then, the voltage value input to the microcomputer through the A / D converter is read (step 350).

If the microcomputer determines whether the voltage value input from the A / D converter matches the fixed voltage value stored in the memory (step 360), the microcomputer determines whether the input voltage value matches the fixed voltage value. The set value output to the / A converter is repeatedly increased by '1' (step 370).

The microcomputer terminates the frequency calibration operation when the voltage value input from the A / D converter matches the fixed voltage value stored in the memory.

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention defined in the appended claims.

According to the present invention, even without opening the case of the equipment of the VCTCXO, if only the reference frequency signal is input to the VCTCXO from the outside, it is possible to accurately perform the frequency calibration operation.

Claims (5)

Voltage controlled temperature compensated crystal oscillator (VCTCXO); A phase locked loop (PLL) to which an output signal of the VCTCXO is fed back and a reference frequency signal is input from the outside; Microcomputer; A D / A converter which inputs a setting value from the microcomputer, converts the input setting value into an analog signal, and outputs the analog signal; A switching unit for selectively switching the phase locked loop and an output terminal of the D / A converter and allowing the switched signal to be input to the VCTCXO; An A / D converter for capturing an analog signal input to the VCTCXO via the switching unit, converting the analog signal into a digital signal, and outputting the digital signal to the microcomputer. And storing the digital signal input from the A / D converter in the internal memory as a 'fixed voltage value', and then calibrating the frequency of the VCTCXO using the 'fixed voltage value'. VCTCXO's frequency calibration device. The switching circuit of claim 1, wherein the switching unit is switched to an output terminal of the phase locked loop while a reference frequency signal is input to the phase locked loop. And the switching unit switches to the output terminal of the D / A converter when the phase locked loop is locked. The output signal of the phase locked loop at the moment when the reference frequency signal input to the phase locked loop is phase locked is converted into a digital signal by the A / D converter. And a voltage value input to the microcomputer. According to claim 1, After the switching unit is switched to the output terminal of the D / A converter, the microcomputer sets the set value to '0' to output to the D / A converter, the value input to the A / D converter Read, and increase the set value by '1' until the read value matches the 'fixed voltage value'. Finally, when the read value matches the 'fixed voltage value', the frequency calibration is terminated. Frequency correction device of VCTCXO, characterized in that. Voltage controlled temperature compensated crystal oscillator (VCTCXO); A phase locked loop (PLL) to which an output signal of the VCTCXO is fed back and a reference frequency signal is input from the outside; Microcomputer; A D / A converter which inputs a setting value from the microcomputer, converts the input setting value into an analog signal, and outputs the analog signal; A switching unit for selectively switching the phase locked loop and an output terminal of the D / A converter and allowing the switched signal to be input to the VCTCXO; An A / D converter for capturing an analog signal input to the VCTCXO via the switching unit, converting the analog signal into a digital signal, and outputting the digital signal to the microcomputer; The switching unit is switched to the output terminal of the phase locked loop at the same time as the reference frequency signal is input to the phase locked loop, and is output to the output terminal of the D / A converter when the phase locked loop is phase locked. Characterized in that the switching, The microcomputer stores the digital signal input from the A / D converter at the moment when the phase lock loop is phase locked in the internal memory as a 'fixed voltage value', and outputs the value to the D / A converter. Is set to '0', After the switching unit is switched to the output terminal of the D / A converter, the microcomputer reads the value input to the A / D converter, and goes to the D / A converter until the readout value matches the 'fixed voltage value'. The output value of VCTCXO frequency correction device characterized in that the increment of the '1', and finally the frequency calibration is terminated when the read value matches the 'fixed voltage value'.

Images