KR20070071671A - Mobile communication terminal having rtc frequency compensation circuit - Google Patents

Abstract

A mobile communication terminal having an RTC(Real Time Clock) frequency compensation circuit is provided to automatically compensate and output an error of a frequency though the error is generated from the frequency outputted from an RTC circuit, therefore reliability and accuracy of time information can be continuously maintained. A crystal oscillator(X1) generates a low frequency clock signal. A frequency counter(110) counts the low-frequency clock signal by setting an inputted VCTCXO(Voltage Controlled Temperature Compensation Crystal Oscillator) to a reference frequency, and outputs an error value if an error is generated. A frequency controller(120) calculates the error value to output a frequency compensation control signal for compensating the error value. A capacitor array(140) selects and outputs a variable combination value of a capacitor for compensating an error frequency according to the frequency compensation control signal. An RTC circuit(130) compensates and outputs a count value of the low-frequency clock signal according to the variable value of the capacitor.

Description

Mobile communication terminal with RTC frequency compensation circuit {MOBILE COMMUNICATION TERMINAL HAVING RTC FREQUENCY COMPENSATION CIRCUIT}

1 is a block diagram of a RTC frequency compensation circuit of a GSM mobile communication terminal according to the present invention.

** Description of symbols for the main parts of the drawing **

X1: Crystal Oscillator 100: GSM Processor

110: frequency counter 120: frequency control unit

130: RTC circuit 140: capacitor array unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication terminal having an RTC frequency compensation circuit. In particular, the present invention compensates an error of a frequency output from an RTC circuit provided in a GSM mobile communication terminal due to a change in the surrounding environment such as ambient temperature or humidity. It is a technique to do.

In general, the GSM (Global System for Mobile Communications) system is a time division multiple access (TDMA) digital system that is commercially available mainly in European countries. And a synchronous data communication G3 fax communication. In GSM, it is essential to use a smart card as a SIM card, thereby identifying a subscriber terminal.

Since the mobile communication terminal adopting the GSM method uses the time information by using the RTC (Real Time Clock) circuit provided in the base station rather than using the time information transmitted from the base station, when an error occurs in the time information, Since the mobile terminal does not automatically recognize the error of the time information, the user must check the error and correct the time information directly.

The RTC circuit provided in the GSM-type mobile communication terminal counts a low frequency clock signal of 32.768 KHz to generate time information (seconds, minutes, hours). The RTC circuit controls the GSM processor provided in the mobile communication terminal to use time information generated by the RTC circuit in synchronization with a high frequency clock signal (VCTCXO).

In this case, the low frequency clock signal provided to the RTC circuit of the mobile communication terminal is generated by a crystal oscillator, and a high frequency clock signal VCTCXO is also provided externally.

The conventional RTC circuit counts 32.768KHz low frequency clock signals output from the crystal oscillator to generate inter-hour information (seconds, minutes, hours). At this time, one load capacitor is provided at the output of the RTC circuit. Compensate the frequency of the RTC circuit by providing a, and a feedback resistor to ensure that the RTC circuit operates stably.

However, due to the minute differences on each substrate that occur in the manufacturing process of the PCB substrate of the RTC circuit, each PCB substrate may have a frequency error. In other words, the static load capacitor value is slightly different for each PCB substrate of each manufactured RTC circuit, but the fixed load capacitor is actually used.

In addition, an error may occur due to a change in ambient temperature, such as a change in ambient temperature or humidity in the output frequency of the RTC circuit.

Accordingly, the above-described errors are continuously accumulated, and thus, an error occurs in time information of a GSM mobile communication terminal, or an error occurs in an additional function such as a notification function using time information.

The present invention has been made in view of the above-described conventional technology, and an object of the present invention is an error of a frequency output from an RTC circuit provided in a GSM mobile communication terminal due to a change in surrounding environment such as ambient temperature or humidity. To provide a mobile communication terminal having an RTC frequency compensation circuit capable of compensating for and outputting.

Another object of the present invention is to provide an additional function using the time information, such as a notification function, while correcting the output frequency when the error occurs in the output frequency due to the abnormality of the RTC circuit provided in the GSM-type mobile communication terminal It is to provide a mobile communication terminal having an RTC frequency compensation circuit for controlling to execute normally.

In order to achieve the above object, a mobile communication terminal having an RTC frequency compensation circuit according to the present invention includes a crystal oscillator for generating a low frequency clock signal; A frequency counter unit for counting the low frequency clock signal output from the crystal oscillator using the input high frequency clock signal VCTCXO as a reference frequency and outputting an error value when an error occurs; A frequency controller which calculates an error value output from the frequency counter unit and outputs a frequency compensation control signal for compensating the error value; A capacitor array unit which selects and outputs a variable combination value of a capacitor for compensating an error frequency according to a frequency compensation control signal output from the frequency controller; And an RTC circuit for compensating and outputting a count value of a low frequency clock signal according to a variable value of a capacitor output from the capacitor array unit.

Here, the capacitor array unit preferably has an array structure in which a plurality of capacitors having different values are connected in parallel.

According to the features of the present invention described above, even if an error occurs in the frequency output from the RTC circuit provided in the GSM-type mobile communication terminal due to the change in the surrounding environment such as temperature or humidity of the GSM-type mobile communication terminal. This has the advantage of automatically compensating for this and outputting it. Therefore, since the accuracy and reliability of the time information provided by the GSM-type mobile communication terminal can be maintained, it is controlled to execute additional functions using time information such as a notification function normally.

Hereinafter, an embodiment of an RTC frequency compensation circuit in a GSM mobile communication terminal of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an RTC frequency compensation circuit of a GSM mobile communication terminal according to the present invention.

Referring to FIG. 1, the RTC frequency compensation circuit of a GSM mobile communication terminal according to the present invention includes: a GSM processor 100 for displaying time information on a display window and controlling a compensation operation of an RTC frequency of the mobile communication terminal; A crystal oscillator (X1) for generating a low frequency clock signal; The low frequency clock signal output from the crystal oscillator (X1) is counted using the input high frequency clock signal (VCTCXO: Voltage Controlled Temperature Compensation Crystal Oscillator) as a reference frequency, and an error value is output when an error occurs. A frequency counter unit 110; A frequency controller 120 for calculating an error value output from the frequency counter unit 110 and outputting a frequency compensation control signal for compensating the error value; A capacitor array unit 140 for selecting and outputting a variable combination value of a capacitor for compensating an error frequency according to a frequency compensation control signal output from the frequency controller 120; The RTC circuit 130 compensates the count value of the low frequency clock signal according to the variable value of the capacitor output from the capacitor array unit 140.

Here, the capacitor array unit 140 has an array structure in which a plurality of capacitors having different values are connected in parallel, and the combined capacitor values are selected by the frequency compensation control signal output from the frequency controller 120. Do.

Hereinafter, the operation of the RTC frequency compensation circuit in the GSM mobile communication terminal according to the present invention will be described with reference to the accompanying drawings.

In general, a system clock signal for driving a main chipset, that is, a high frequency clock signal of 10 MHz or 13 MHz, exists in a GSM mobile communication terminal. The high frequency clock signal is a clock signal generated by a VCTCXO (Voltage Temperature Compensated Oscillator) and has a small variation due to normal temperature and has an accuracy of 0.15 ppm or less.

When power is applied to the GSM type mobile communication terminal, a low frequency clock signal of 32.768 KHz is generated from the crystal oscillator X1 and is applied to the frequency counter 110.

The frequency counter 110 receives the low frequency clock signal output from the crystal oscillator X1 and counts the frequency by using the 13 MHz high frequency clock signal VCTCXO as a reference frequency. That is, the reference frequency 13MHz is divided by the input low frequency clock signal, and if the quotient is 396, the output frequency of the crystal oscillator X1 is determined to be normal. It is determined that an error occurred in the frequency. At this time, the magnitude of the error value is summarized as +/- based on 396. For example, if +, the frequency of the crystal oscillator (X1) is greater than 32.768KHz, and if-, the frequency of the crystal oscillator (X1) is less than 32.768KHz.

The frequency controller 120 calculates an error value output from the frequency counter 110 and transfers a combination value of the appropriate capacitors to the capacitor array unit 140.

The capacitor array unit 140 selects a variable capacitance value of the capacitor as a combination value of the capacitors transmitted from the frequency controller 120, and applies the output signal to the crystal oscillator X1.

Since the operation of the RTC frequency compensation circuit of the GSM mobile communication terminal described above is performed every time an event occurs, it is able to actively cope with changes in the surrounding environment.

As described above, according to the RTC frequency compensation circuit in the GSM-type mobile communication terminal according to the present invention, the GSM-type mobile communication terminal is provided in the GSM-type mobile communication terminal by the change of the surrounding environment such as the temperature or humidity of the surroundings. Even if an error occurs in the frequency output from the RTC circuit, it provides an effect of automatically compensating for this and outputting the error.

Therefore, the accuracy and reliability of the time information provided by the GSM-type mobile communication terminal can be continuously maintained, and the overall product reliability can be maintained by controlling the additional function using the time information such as the notification function to be executed normally. have.

On the other hand, the present invention is not limited to the above-described embodiment, but can be modified and modified within the scope not departing from the gist of the present invention, such modifications and changes should be regarded as belonging to the following claims. will be.

Claims (2)

A crystal oscillator for generating a low frequency clock signal; A frequency counter unit for counting the low frequency clock signal output from the crystal oscillator using the input high frequency clock signal VCTCXO as a reference frequency and outputting an error value when an error occurs; A frequency controller which calculates an error value output from the frequency counter unit and outputs a frequency compensation control signal for compensating the error value; A capacitor array unit which selects and outputs a variable combination value of a capacitor for compensating an error frequency according to a frequency compensation control signal output from the frequency controller; And an RTC circuit for compensating and outputting a count value of a low frequency clock signal according to a variable value of a capacitor output from the capacitor array unit. The mobile communication terminal of claim 1, wherein the capacitor array unit has an array structure in which a plurality of capacitors having different values are connected in parallel.

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