JP2001077670A - Frequency-correcting circuit and traveling object communications equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency-correcting circuit and a traveling object communications equipment for improving the accuracy of oscillation frequency by absorbing changes in time passage and the variations in part characteristic. SOLUTION: A voltage-controlled oscillator 11 generates a reference frequency signal to be the reference of a local oscillation signal with an analog value, outputted from a DAC(digital/analog converter) 10 as the controlled voltage. A DSP 17 sets a parameter stored in a memory 20 to a DAC 10 at supplying of power, controls parameters with respect to the D/A converter, so that the transmitting frequency of a base station and the receiving frequency of this equipment matches with each other and updates the parameter of the memory 20 with the parameter when they match.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency correction circuit for correcting an oscillation frequency of a voltage controlled oscillator that generates a reference frequency signal serving as a reference of a local oscillation signal, and a mobile communication device.

[0002]

2. Description of the Related Art In a mobile communication device such as a cellular phone, a voltage control-temperature compensation type crystal oscillator (Voltage Controll) is used as an oscillator for generating a reference frequency serving as a reference of a local oscillation signal.
ed Temperature Compensated Crystal Oscillator: below
Called VC-TCXO. ) Is used to perform feedback control on the VC-TCXO in order to correct the error between the frequency of the transmission signal from the base station and the reception frequency of the mobile communication device.

FIG. 4 is a block diagram showing a configuration of a main part of a conventional mobile communication device. In FIG.
Performs the process of capturing the control channel of the base station and the feedback control of the reference frequency as follows. That is, (1) immediately after the power is turned on, the DSP 57 reads the initial control voltage value stored as a fixed value in the memory 60 and sends the initial control voltage to the VC-TCXO 51 through a digital-analog converter (hereinafter abbreviated as DAC) 50. Supply. This causes the VC-TCXO 51 to oscillate a reference frequency signal corresponding to the initial control voltage. Here, the initial control voltage value stored in the memory 60 is set to an optimal value at the time of factory shipment. (2) The synthesizer unit 54 generates a local oscillation signal of a frequency designated by the DSP 57 based on the reference frequency signal. At this time, the DSP 57 sequentially designates the frequency of the local oscillation signal so as to correspond to the plurality of transmission frequencies assigned for the control channel of the base station. (3) The receiving unit 55 sequentially receives the control channels of the transmission frequencies corresponding to the sequentially specified local oscillation signals. The control unit 56 measures the sensitivity (reception signal level and the like) of each received control channel, selects the control channel having the highest sensitivity, and specifies the frequency of the local oscillation signal corresponding to the transmission frequency to the synthesizer unit 54. . (4) The processing of the above (2) and (3) is completed, and the control channel with the highest sensitivity is selected.
5 using the error information obtained from step 5 so that the reception frequency in the receiver 55 matches the transmission frequency of the base station.
-Perform feedback control (or follow-up control) on the control voltage of the TCXO 51. Here, the error information is information indicating a difference between the reception frequency and the local oscillation frequency, and indicates a frequency of a so-called intermediate frequency signal (actually, the second intermediate frequency in the second stage by two-stage down-conversion). Signal frequency). By the feedback control, the DSP 57
Calibrates the control voltage (and thus the reference frequency) to follow the transmission frequency of the selected control channel, thereby improving the frequency stability of the base station with respect to the transmission frequency.

As described above, the conventional mobile communication device captures a plurality of control channels, selects the control channel having the highest sensitivity, and causes the selected control channel to follow the frequency by the above-described feedback control. If acquisition or selection of a control channel fails, the control channel is acquired again and the same processing is repeated.

[0005]

[Problems to be solved by the invention] However, VC-TCX
When the frequency error due to the aging of O51 or the variation in component characteristics increases, there is a problem that the receiving sensitivity at the time of capturing the control channel deteriorates. Generally, the accuracy of VC-TCXO is deteriorated by about one to several PPM / year due to aging (particularly, the change of the first year is large), and the sensitivity at the time of capturing is deteriorated. As a result, control channel acquisition and control channel selection cannot be performed correctly, or acquisition and selection are repeated.

In view of the above problems, an object of the present invention is to provide a frequency correction circuit and a mobile communication device that improve the accuracy of the oscillation frequency by absorbing aging of oscillators and variations in component characteristics.

A frequency correction circuit or a mobile communication device according to the present invention sets an initial value of a control voltage in a voltage controlled oscillator for generating a reference frequency signal serving as a reference of a local oscillation signal, and transmits the signal. A frequency correction circuit that controls the control voltage so that a reception frequency of a reception circuit determined based on a reference frequency signal follows a frequency of an incoming signal, wherein a storage unit that stores the initial value; A determination unit is provided for determining whether or not the control has converged, and an updating unit for updating an initial value of the storage unit with a value of the control voltage when it is determined that the control has converged.

[0007]

FIG. 1 is a block diagram showing a configuration of a mobile communication device according to an embodiment of the present invention. This mobile communication device is a digital-to-analog converter (hereinafter referred to as D-analog converter).
Abbreviated as AC. 10, a voltage control-temperature compensated crystal oscillator (hereinafter abbreviated as VC-TCXO) 11, a synthesizer unit 1
4, a receiving unit 15, a control unit 16, a temperature sensor 21, a transmitting unit 22, an antenna switch 23, antennas 24 and 25, and an initial value of a control voltage supplied to the VC-TCXO 11 through the DAC 10 is set to the VC-TCXO 11 It is configured to update to an optimal value with respect to fluctuation due to aging.

A circuit including the DAC 10, the VC-TCXO 11, and the synthesizer 14 generates a local oscillation signal. That is, the DAC 10 converts a parameter (digital value) set by the DSP 17 into an analog voltage and supplies the converted analog voltage to the VC-TCXO 11 as a control voltage. The VC-TCXO 11 generates an oscillation signal having a frequency according to the control voltage. The synthesizer section 14 includes a PLL circuit 13 and a voltage controlled oscillator (VCO) circuit.
-Generate a local oscillation signal of a frequency designated by the DSP 17 based on the oscillation signal of the TCXO 11. Below, VC-TCXO
The 11 oscillation signals are referred to as reference frequency signals.

The receiving unit 15 receives a transmission signal of a base station from the antennas 24 and 25 through the antenna switch 23 and down-converts the signal into a reception intermediate frequency signal. The reception frequency in the reception unit 15 is uniquely determined by the sum or difference between the frequency of the local oscillation signal and the reception intermediate frequency. The switching of the reception frequency is based on the switching of the frequency of the local oscillation signal. Note that the receiving unit 15 performs two-stage down-conversion and outputs error information indicating the frequency of the second intermediate frequency signal in the second stage to the DSP 17.

[0010] The temperature sensor 21 measures the temperature of the VC-TCXO 11 or the temperature around the VC-TCXO 11. The transmission unit 22
The digital signal input from the DSP 17 is modulated into a high-frequency signal and passed through the antenna switch 23 to the antenna 24,
Send from 25. This transmission frequency is determined according to the frequency of the local oscillation signal.

The antennas 24 and 25 are a whip antenna and a built-in plate antenna, and one of them is selected by the antenna switch 23 under the control of the control unit 16. The control unit 16 includes a DSP 17, a CPU 19, and a memory 20, and controls the entire mobile telephone (capture of a control channel of a base station and control of incoming and outgoing calls). The CPU 19 controls an operation unit (not shown) and a display unit (not shown). Memory 20
Stores an initial parameter table that stores initial parameters indicating the initial value of the control voltage of the VC-TCXO 11 in association with the temperature. The DSP 17 performs (A) initial parameter setting processing, (B) feedback control (or tracking control) to a reference frequency signal based on error information, (C) initial parameter updating processing, and (D) audio signal It performs audio signal processing such as encoding and decoding. (B)
Is a known technique already described in the section of the prior art, and therefore detailed description is omitted in this embodiment. For example, model number D5133F18 manufactured by Japan DSP Communication Co., Ltd.
-128EBBI ASIC (Application Slecified Integ
(Rated circuit) and can be used. Also, (D) is a well-known technology that has been standardized, and thus description thereof is omitted. <Initial Parameter Table> FIG. 2 shows an example of the initial parameter table stored in the memory 20. As shown in the figure, the initial parameter table stores the initial parameters corresponding to the temperatures. For example, at a temperature in the range of 21 to 30 degrees Celsius, the initial parameter is 80 in hexadecimal.
In the same figure, one initial parameter is made to correspond to a temperature zone of about 10 degrees. However, the temperature zone may be divided more finely, or only a frequently used temperature zone may be divided into small temperatures. You may. Temperature zones that are largely affected by aging may be finely divided.

The control voltage output to the VC-TCXO 11 when the initial parameter is set in the DAC 10 is shown outside the table column in FIG. Here, the control voltage of the VC-TCXO 11 is in the range of 1.5V +/- 1V. VC-TCXO11 in this case is, for example, KT1 of Kyocera Corporation.
Four series of voltage controlled-temperature compensated crystal oscillators can be used. <Initial Parameter Setting Process and Update Process> FIG. 3 is a flowchart showing the initial parameter setting process and the initial parameter updating process performed after the power is turned on.

Immediately after power-on or reset, the DSP 17
Acquires the temperature at that time from the temperature sensor 21 via the CPU 19 (step 31), reads an initial parameter corresponding to the temperature from the initial parameter table stored in the memory 20 (step 32), and stores the read initial parameter It is set in the DAC 10 (step 33).
The processing up to this point is the initial parameter setting processing.

After setting the initial parameters, the control unit 16 performs a process of capturing the control channel of the base station as follows.
A local oscillation signal of the frequency designated in P17 is generated.
The frequency is specified by setting a frequency division ratio from the DSP 17 to the PLL circuit 13. The DSP 17 sequentially designates the frequency of the local oscillation signal to the PLL circuit 13 so as to correspond to the plurality of transmission frequencies assigned for the control channel of the base station. The receiving unit 15 sequentially receives the control channels of the transmission frequencies corresponding to the sequentially specified local oscillation signals. The control unit 16 measures the sensitivity (received signal level, bit error rate, etc.) of each received control channel for each received control channel. Further, the control unit 16 selects the control channel having the highest sensitivity from all the measured control channels, and specifies the frequency of the local oscillation signal corresponding to the transmission frequency to the synthesizer unit 54. This ends the capture process.

During and after the acquisition process, the DSP
Reference numeral 17 performs feedback control of the reference frequency described above. With this feedback control, the parameters set in the DAC 10 are appropriately changed. Further, in parallel with the feedback control, the DSP 17 updates the initial parameters as follows. First, the DSP 17 checks the reception state, that is, calculates the bit error rate (step 3).
5) It is determined whether or not a bit error rate (BER) is “0”. It is desirable to make this determination continuously for a certain period of time. The fact that the bit error rate is 0 means that the feedback control converges, that is, the tracking is performed by the tracking control, and a good parameter such that the transmission frequency and the reception frequency of the base station coincide with each other is determined by the DAC 10
Means that it is set to

If the bit error rate is "0", the DSP 17 obtains time alignment information transmitted from the base station on the control channel (step 36). here,
The time alignment information is information indicating how much (how many symbols) the transmission timing of the mobile communication device should be shifted, and is determined according to the received electric field strength measured by the base station and the like. The received electric field strength is approximately proportional to the distance between the base station and the mobile communication device, and when the distance is short and communication is good, the time alignment information uses “0” symbols (that is, shift “0” symbols). Show.

If the time alignment information transmitted from the base station is "0", the DSP 17
(Step 38), read initial parameters corresponding to the temperature from the initial parameter table (step 39), check the current parameters set in the DAC 10 (step 40), and obtain the obtained initial parameters. If the absolute value of the difference between the parameter and the current parameter is equal to or smaller than the threshold value (step 41), the parameter is updated by overwriting the initial parameter in the initial parameter table with the current parameter (step 42).

In this case, the threshold value is determined such that the value of the parameter is accidentally changed for both the bit error rate and the time alignment information.
This is performed in order to prevent the initial parameter table from being updated when the value is “0” or an abnormal value that cannot occur due to aging. 1 for parameter table
The value may be about 0 (hexadecimal).

As described above, according to the mobile communication device of the present invention, even if the frequency of the reference frequency signal of the VC-TCXO 11 is shifted due to aging, the parameter at the time of convergence by the feedback control, that is, Since the parameter corresponding to the reference frequency signal following the transmission frequency of the base station is updated by overwriting the initial parameter table, the initial oscillation period at the next start-up (that is, required for the feedback control to converge) Also during the period, a reference frequency signal that follows the transmission frequency from the beginning can be obtained. In other words, VC-TCXO11
The change of the oscillation frequency due to the aging of other components and other components can be corrected over a long period of time, and the absolute accuracy of the reference frequency signal during the initial oscillation can be improved.

Further, the variation of the VC-TCXO11 and the DAC1
Variations in related components such as 0, and errors in the oscillation frequency of the VC-TCXO 11 due to variations in characteristics due to mounting these components on the board are absorbed, so that the absolute accuracy of the reference frequency signal can be improved. For example, 800MHZ
In the z-band mobile phone system, the base station tracking accuracy of the mobile communication device is 1.5 PPM.
Although it is required by the standard to be less than or equal to PPM, a general VC-TCXO has an aging of the frequency of 1 to several PPM, and in the mobile communication device of the present invention, by updating the initial parameters, Even during the period of the initial oscillation, the secular change can be absorbed and the level can be substantially improved to about 0.35 PPM.

Further, since the initial parameter table stores a plurality of initial parameters corresponding to the temperatures,
More reliable temperature compensation for the temperature deviation of the VC-TCXO 11 can be performed. Moreover, it is not necessary to use a high-precision expensive component as the VC-TCXO 11, and a cheaper component can be used. Therefore, when the mobile communication device is powered on or reset, it is possible to capture the control channels of a plurality of base stations with high sensitivity without being affected by aging or component variations even if the feedback control is not converged. Can do it. <Other Modifications> In the above embodiment, since the temperature compensation type voltage controlled oscillator is used, the temperature compensation is doubled in addition to the temperature compensation by the initial parameter table. Although depending on the temperature compensation characteristics of the temperature-compensated voltage-controlled oscillator itself, the initial parameter table is configured to store one initial parameter common to all temperatures instead of a plurality of initial parameters corresponding to temperatures. May be. In this case, the temperature sensor 21 is unnecessary.

Conversely, instead of the VC-TCXO 11 in the above embodiment, a voltage-controlled oscillator (VC-CXO) which is not a temperature-compensated type
May be used. Further, in the flow shown in FIG. 3, the initial parameter table is updated on the condition that the time alignment information is “0”. However, for example, the initial parameter table may be set on the condition that the value is +/− 2 or less.

In the flow shown in FIG. 3, the initial parameter table is updated on the condition that the bit error rate is "0". However, the initial parameter table may be updated on condition that the bit error rate is not more than +/- 2.

[0024]

The frequency correction circuit (or mobile communication device) of the present invention sets an initial value of a control voltage in a voltage-controlled oscillator that generates a reference frequency signal serving as a reference of a local oscillation signal,
A frequency correction circuit that performs tracking control of the control voltage so that a reception frequency of a reception circuit determined based on a reference frequency signal follows a frequency of a transmitted signal, and a storage unit that stores the initial value. A determination means for determining whether or not the tracking control has converged, and an updating means for updating an initial value of the storage means with the value of the control voltage when the convergence control is determined.

According to this configuration, when the frequency accuracy of the reference frequency signal is deviated due to aging of the oscillator or variation in component characteristics, the value of the control voltage after the follow-up control is initialized. Since the storage means is updated as a value, even during the period from the start of the next initial oscillation to the time of following control, the frequency accuracy can be maintained and improved without being affected by aging due to variations in components.

In addition, since it is not necessary to use an expensive voltage-controlled oscillator with high absolute accuracy, the cost can be reduced. Here, the storage unit stores a plurality of initial values corresponding to the temperature, and the frequency correction circuit (or the mobile communication device) further includes a temperature measurement unit that measures the temperature of the voltage-controlled oscillator or a temperature around the voltage-controlled oscillator. Means, and control means for reading an initial value corresponding to the temperature measured at the time of power-on from the storage means, and supplying a control voltage indicated by the initial value to the voltage-controlled oscillator, wherein the updating means has converged. The initial value corresponding to the temperature measured when the determination is made may be updated.

According to this configuration, since the initial value is stored in correspondence with the temperature, it is possible to further perform temperature compensation for absorbing a temperature deviation of the voltage controlled oscillator. Since there is no need to use an expensive temperature-compensated voltage-controlled oscillator, the cost can be further reduced. Here, the determination means may determine that the convergence has occurred if the bit error rate of the received signal is equal to or less than a threshold value.

According to this configuration, the state in which the bit error rate of the received signal is equal to or less than the threshold value, that is, the state in which the tracking control has converged, is easily determined, and the storage means is updated with the control voltage appropriate as the initial value. can do. In addition, the mobile communication device of the present invention generates a DA converter that converts a parameter to be set into an analog value and a reference frequency signal that is a reference of a local oscillation signal by using the analog value output from the DA converter as a control voltage. A voltage-controlled oscillator, a storage unit for storing a parameter indicating an initial value of the control voltage, and a parameter stored in the storage unit, which is set in the DA converter when the power is turned on. An arithmetic processing unit that controls the parameters of the DA converter so that the parameters match, and updates the parameters of the storage unit with the parameters when the parameters match.

According to this configuration, when the frequency accuracy of the reference frequency signal deviates due to aging of the oscillator or variation in component characteristics, the storage means is updated with the value of the control voltage as an initial value. Therefore, even during the period from the start of the next initial oscillation to the time when the follow-up control is performed, the frequency accuracy can be maintained and improved without the secular change being affected by the variation of the components.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a main part of a mobile communication device according to an embodiment of the present invention.

FIG. 2 shows an example of an initial parameter table stored in a memory 20.

FIG. 3 is a flowchart illustrating an initial parameter setting process and an initial parameter updating process.

FIG. 4 is a block diagram showing a configuration of a main part of a conventional mobile communication device.

[Explanation of symbols]

 Reference Signs List 10 DAC 13 PLL circuit 14 Synthesizer unit 15 Receiving unit 16 Control unit 17 DSP 19 CPU 20 Memory 21 Temperature sensor 22 Transmitting unit 23 Antenna switch 24 Antenna

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J103 AA00 AA07 DA00 DA21 DA27 DA34 DA44 GA12 HC00 JA04 JA19 5K004 AA05 FJ15 FJ17 5K020 DD00 DD22 EE00 GG04 JJ02 LL00 NN00 NN10 5K027 AA11 BB04 CC08

Claims (7)

[Claims] An initial value of a control voltage is set in a voltage-controlled oscillator that generates a reference frequency signal serving as a reference of a local oscillation signal, and a frequency of a signal transmitted is determined based on the reference frequency signal. A frequency correction circuit that performs tracking control of the control voltage so that a reception frequency tracks, a storage unit that stores the initial value, and a determination unit that determines whether the tracking control has converged. Updating means for updating the initial value of the storage means with the value of the control voltage at the time of the determination. 2. The storage means stores a plurality of initial values corresponding to temperature, the frequency correction circuit further includes a temperature measurement means for measuring a temperature of the voltage controlled oscillator or a temperature around the temperature, and a power supply. Control means for reading an initial value corresponding to the temperature measured at a time from the storage means, and supplying a control voltage indicated by the initial value to the voltage-controlled oscillator, wherein the updating means measures when it is determined that the temperature has converged. 2. The frequency correction circuit according to claim 1, wherein an initial value corresponding to the set temperature is updated. 3. The frequency correction circuit according to claim 1, wherein the determination unit determines that the tracking control has converged if the bit error rate of the received signal is equal to or less than a threshold value. 4. An initial value of a control voltage is set in a voltage-controlled oscillator that generates a reference frequency signal serving as a reference of a local oscillation signal, and a reception frequency determined based on the reference frequency signal follows the transmission frequency of the base station. A mobile communication device that performs tracking control of the control voltage as described above, wherein a storage unit that stores the initial value, a determination unit that determines whether the tracking control has converged, and when it is determined that the tracking control has converged. Updating means for updating the initial value of the storage means with the control voltage value of the mobile communication device. 5. The storage means stores a plurality of initial values corresponding to temperature, the mobile communication device further comprises a temperature measurement means for measuring a temperature of the voltage controlled oscillator or a temperature around the voltage controlled oscillator, and a power supply. Control means for reading from a storage means an initial value corresponding to the temperature measured at the time of turning on, and supplying a control voltage indicated by the initial value to a voltage-controlled oscillator, wherein the updating means, when it is determined that convergence is determined, 5. The mobile communication device according to claim 4, wherein an initial value corresponding to the measured temperature is updated. 6. The mobile communication device according to claim 4, wherein the determination unit determines that the tracking control has converged if the bit error rate of the received signal is equal to or less than a threshold value. 7. A DA converter for converting a set parameter into an analog value, a voltage controlled oscillator for generating a reference frequency signal as a reference of a local oscillation signal using an analog value output from the DA converter as a control voltage, A storage unit for storing a parameter indicating an initial value of the control voltage; and a parameter stored in the storage means, which is set in the DA converter when the power is turned on, so that the frequency of the transmitted signal matches the reception frequency. A mobile communication device, comprising: a processing unit that controls a parameter of the storage unit and updates a parameter of the storage unit with a parameter when the state is matched.