JP2002158562A - AFC circuit - Google Patents

Abstract

(57) [Problem] To remove a delay in frequency offset average value calculation processing in an AFC circuit. SOLUTION: By adding a frequency correction value obtained from characteristics of the digital / analog converter 16 to an estimated frequency offset value before a control value of the digital / analog converter 16 converges, a digital / analog converter 16 is obtained.
The delay of the averaging process due to the switching of the control value is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication system suitable for use in a mobile communication system such as a mobile station or a base station.
Related to FC circuit.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a configuration of a conventional AFC circuit. In FIG. 1, a conventional AFC circuit includes a demodulation unit 11 that performs demodulation using a received signal S _IN and a local oscillation signal S _LO as inputs, and a reception signal S _IN included in a demodulated signal S _IF demodulated by the demodulation unit 11. A measuring unit 12 for measuring and averaging an error between the frequency f _IN and the frequency f _LO of the local oscillation signal S _LO , and an error average value Δf calculated by the measuring unit 12
The conversion unit 15 for converting the control value D ₁ of the digital-to-analog converter 16, a control value D ₁ of the digital-to-analog converter 16 and digital-to-analog converter, the control voltage V
A digital-to-analog converter 16 for outputting _CONT, a voltage controlled oscillator 17 for generating a local oscillation signal S _LO having a frequency corresponding to the control voltage V _CONT, digital measurement section 12
And a control unit 13 for controlling the analog converter 16.

In this conventional AFC circuit, a reception signal S _IN
The average value Δf of the error between the frequency f _IN of the local oscillation signal S _{LO and} the frequency f _LO of the local oscillation signal S _LO is calculated, and the control value D ₁ of the digital-to-analog converter 16 is obtained using the average value Δf of the error. change the frequency f _LO of the oscillation signal S _{L O,}
So that it cancels the error between the frequency f _LO of the frequency f _IN and the local oscillation signal S _LO of the received signal S _IN.

[0004]

However [0005] In the conventional AFC circuit, when the average value of the error between the frequency f _LO of the frequency f _IN and the local oscillation signal S _LO of the received signal S _IN, FIG. 7 as shown in, for using the value from the time t ₀ when the frequency is somewhat stable control value D ₁ of the local oscillation signal S _LO affected by the update of a digital-to-analog converter 16 in the averaging process, the local oscillation signal time Δt until the frequency of the S _LO is stabilized can not be used in the averaging process,
Therefore, there is a problem that it takes time to calculate the average value.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an AFC circuit capable of shortening the processing time for averaging the error between the frequency of the received signal and the frequency of the local oscillation signal. .

[0006]

The AFC circuit of the present invention comprises:
Demodulation means for demodulating a received signal and a local oscillation signal as inputs, and measurement for measuring and averaging an error between a frequency of the reception signal and a frequency of the local oscillation signal included in the demodulated signal demodulated by the demodulation means. Means, a correction value calculating means for calculating a correction value corresponding to an error between the frequency of the received signal and the frequency of the local oscillation signal included in the demodulated signal demodulated by the demodulating means, and digitally calculating the error average value. Converting means for converting the control value into a control value for analog conversion, digital-to-analog converting means for converting the control value from digital to analog, and outputting a control voltage; and generating a local oscillation signal having a frequency corresponding to the control voltage. A voltage-controlled oscillating unit, wherein the measuring unit adds the correction value calculated by the correction value calculating unit in the error measurement averaging, A configuration to determine the value.

According to this configuration, the time until the frequency of the local oscillation signal, which has not been used in the past, becomes stable can be used for averaging the correction value calculated by the measuring section. The averaging process time for the difference between the frequency of the local oscillation signal and the frequency of the local oscillation signal can be reduced.

Further, the AFC circuit of the present invention comprises the above-mentioned AFC circuit.
In the circuit, the correction value calculation means employs a configuration in which the correction value is calculated by using a mathematical expression of the characteristic of the digital / analog conversion means.

According to this configuration, when calculating the correction value,
Since the mathematical expression of the characteristic of the digital-to-analog conversion means is used, the data required for the calculation is reduced accordingly, so that the correction value can be calculated with a small memory amount.

Further, the AFC circuit of the present invention comprises the above AFC circuit.
The circuit includes a conversion table created based on the characteristics of the digital / analog conversion means, and the correction value calculation means employs a configuration using the conversion table in calculating the correction value.

According to this configuration, in the correction value calculation,
Since the conversion table created based on the characteristics of the digital / analog conversion means is used, the correction value can be calculated with a small amount of calculation.

Further, the AFC circuit of the present invention comprises the above AFC circuit.
The circuit includes a conversion table created based on the characteristics of the digital-to-analog conversion means, and the correction value calculation means uses a formula of the characteristics of the digital-to-analog conversion means and the conversion table in calculating the correction value. take.

According to this configuration, the amount of memory and the amount of calculation can be adjusted as needed.

The mobile station of the present invention employs a configuration including the above-mentioned AFC circuit.

A base station according to the present invention employs a configuration including the above AFC circuit.

The mobile communication system according to the present invention is described in claim 5.
A configuration including the mobile station described above and the base station according to claim 6 is adopted.

According to the mobile station and the base station, since the mobile station and the base station are provided with the AFC circuit of the present invention, the frequency stability can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention is to reduce the averaging processing time by interpolating the time Δt until stabilization, which has not been used in the conventional method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of an AFC circuit according to Embodiment 1 of the present invention. Note that, in this figure, the same parts as those in FIG. 6 described above are denoted by the same reference numerals.

In this figure, a received signal S _IN input to a demodulation unit 11 is demodulated based on a local oscillation signal S _LO output from a voltage controlled oscillator 17 and output as a demodulated signal S _IF . Measuring unit 12 measures the error between the frequency f _LO of the frequency f _IN and the local oscillation signal S _LO of the received signal S _IN that is included in the demodulated signal S _IF. After the measurement of the frequency error by the measurement unit 12, the control unit 13 instructs the correction value calculation unit 14 to output the correction value α at the measurement time to the measurement unit 12, and at the same time, instructs the measurement unit 12 to output the correction value calculation unit 14 Is instructed to add the correction value α calculated in. After repeating this operation for a preset time, the digital / analog converter 16 is instructed to update the voltage control value V _CONT .

The correction value calculating section 14 converts the correction value α at the time t into a digital value in accordance with an instruction from the control section 13.
It calculates based on the characteristics of the analog converter 16 and outputs the result to the measuring unit 12. The measurement unit 12 receives the correction value α calculated by the correction value calculation unit 14 according to an instruction from the control unit 13 and adds the correction value α to the frequency error between the frequency f _IN and the frequency f _LO . After a preset time, a time averaging process of the frequency error is performed, and the average value Δ of the frequency error is obtained.
f is output to the converter 15.

The converter 15 converts the digital-to-analog converter 16 based on the average value Δf of the input frequency errors.
And outputs the control value D _1. The digital-to-analog converter 16 receives the control value D ₁ from the conversion unit 15 according to an instruction from the control unit 13 and updates and outputs the voltage control value V _CONT based on its own characteristics.

The voltage controlled oscillator 17 outputs a local oscillation signal S _LO based on the updated voltage control value V _CONT. Thereafter, the process is repeated until the frequency f _{LO of} the local oscillation signal S _LO changed by the update of the voltage control value V _CONT from the demodulation unit 11 converges.

Next, a specific example of the averaging process will be described with reference to FIG.
This will be described with reference to FIG. FIG. 2 shows the measuring unit 12 in FIG.
FIG. 6 is a diagram showing a time change of a frequency error between a frequency f _IN of a received signal and a frequency f _LO of a local oscillation signal included in a demodulated signal measured by the method shown in FIG.

[0026] First, at time t _0, measuring unit 12 measures the frequency error of the frequency f _LO of the frequency f _IN and the local oscillation signal S _LO of the received signal S _IN that is included in the demodulated signal S _IF. When the measurement is completed, the result is notified to the control unit 13.
Upon receiving the result, the control unit 13 instructs the correction value calculation unit 14 to calculate the correction value at time t ₀ and output the correction value to the measurement unit 12, and at the same time, instructs the measurement unit 12 to calculate the correction value.
Instructs adding the correction value to be output to the frequency error of the time t ₀ by. At this time, the control unit 13 instructs the digital / analog converter 16 to update the voltage control value V _CONT at a preset time t _T.

The correction value calculation unit 14 calculates a correction value α ₀ at time t ₀ based on the characteristics of the digital-to-analog converter 16 in accordance with an instruction from the control unit 13, and
Output to Measurement unit 12, in accordance with an instruction from the control unit 13 adds the frequency error at time t ₀ the correction value alpha ₀ at time t ₀ which is calculated by the correction value calculation unit 14.
The added frequency error is converted into a control value D ₁ by the converter 15 and input to the digital-to-analog converter 16.

At this time, if there is no instruction from the control unit 13,
The voltage control value V _CONT is not updated. For even after time t _1, adds the correction value alpha ₁ to the frequency error at time t ₁ as well. This operation is repeated until the preset time t _T, at time t _T, calculated outputs the time average of the frequency error is added to the correction value by the measurement unit 12. At this time t _T
Then, the control unit 13 instructs to switch the control value D ₁ input to the digital / analog converter 16.

The average value Δf of the frequency error calculated by the measuring unit 12 is input to the converter 15, converted into a control value D ₁ of the digital / analog converter 16 and output. The digital / analog converter 16 receives the control value D ₁ as an input,
As instructed by the control unit 13, the control unit 13 updates and outputs the voltage control value V _CONT according to the control value D ₁ .

When the voltage control value V _CONT is input to the voltage controlled oscillator 17, a local oscillation signal S _LO having a local oscillation frequency f _LO corresponding to the voltage is output. The output local oscillation signal is input to the demodulator 11, is demodulated along with the input signal S _IN is output as a demodulated signal S _IF. By repeating this operation, the frequency of the local oscillation signal approaches the frequency of the input signal.

As described above, in the AFC circuit of the present embodiment, the time until the frequency of the local oscillation signal, which has not been conventionally used, stabilizes is also used for the averaging process. It is possible to shorten the processing time for averaging the frequency and the error.

(Embodiment 2) FIG. 3 is a block diagram showing a configuration of an AFC circuit according to Embodiment 2 of the present invention. In this figure, the same parts as those in FIG. 1 described above are denoted by the same reference numerals. Hereinafter, the AFC circuit according to the present embodiment will be described with reference to FIG. Equation (1) is a correction value calculation equation in the correction value calculation unit 18.

Β = f (x, t) (1) In this embodiment, the received signal S _IN included in the demodulated signal S _IF
In calculating the correction value β for interpolating the error between the frequency f _IN of the local oscillation signal S _{LO and} the frequency f _LO of the local oscillation signal S _LO , a mathematical expression of the characteristic of the digital / analog converter 16 is used.

Next, the calculation of the correction value will be described with reference to equation (1). When the control unit 13 instructs the correction value calculation unit 18 to calculate the correction value β at the time t, the correction value calculation unit 18 converts the correction value β at the time t into Expression (1) showing the characteristic of the digital-to-analog converter 16. Calculate using
In Expression (1), x represents the amount of change in the correction value, and t represents time.

The correction value calculating section 18 first measures the change amount x of the correction value at time t ₀ according to the instruction from the control section 13. Next, the correction value β ₀ is calculated by substituting the time t ₀ and the change amount x of the correction value into the equation (1), and outputs the correction value β ₀ to the measuring unit 12.
Similarly, for the correction value after time t _1, the correction value at the time corresponding to the amount of change is calculated and output to the measurement unit 12. This operation is repeated for a preset time t _T , and the calculated correction value is used for the averaging process.

As described above, in the AFC circuit of the present embodiment, since the correction value is calculated using the mathematical expression of the characteristic of the digital / analog converter 16, it is possible to calculate the correction value with a small memory amount.

(Embodiment 3) FIG. 4 is a block diagram showing a configuration of an AFC circuit according to Embodiment 3 of the present invention. FIG. 5 is an example of a conversion table for calculating a correction value in the correction value calculation unit 14 of the AFC circuit shown in FIG. This embodiment, when calculating the correction value γ for interpolating an error between the frequency f _LO of the frequency f _IN and the local oscillation signal S _LO of the received signal S _IN that is included in the demodulated signal S _IF, digital-to-analog converter A conversion table in which the characteristics of the device 16 are tabulated is used. In the conversion table shown in FIG. 5, x represents the amount of change in the correction value, and t represents time.

Next, the correction value calculation will be described with reference to FIG. When the correction value calculation unit 14 is instructed by the control unit 13 to calculate the correction value γ at time t,
The correction value γ at the time t is calculated with reference to a conversion table 19 indicating the characteristics of the digital / analog converter 16.

The correction value calculating section 14 first measures the change amount x of the correction value at time t ₀ according to an instruction from the control section 13. Then calculates a correction value gamma ₀ which corresponds to a change amount x of the correction value at time t ₀ is output to the measuring unit 12 by using the conversion table 19. Similarly, for the correction value after time t _1, a correction value for the time corresponding to the amount of change is calculated, and
Output to Here, if the value of the amount of change at time t ₀ is “−
In the case of “1”, first, the correction value γ ₀ at time t ₀ corresponding to the change amount “−1” is obtained using the conversion table 19. Then, the calculated correction value γ ₀ is output to the measuring unit 12.

Similarly, at time t ₁ , a correction value γ ₁ is calculated,
At time t _T , a correction value γ _T is calculated. This operation is repeated for a preset time t _T , and the calculated correction value is used for the averaging process.

As described above, in the AFC circuit of the present embodiment, since the conversion table 19 of the characteristics of the digital / analog converter 16 is used for calculating the correction value, the correction value can be calculated with a smaller amount of calculation. .

(Embodiment 4) An AFC circuit according to Embodiment 4 of the present invention will be described with reference to equation (2). The configuration of the AFC circuit according to the present embodiment is the same as the circuit configuration of the third embodiment shown in FIG.

The AFC circuit according to the present embodiment calculates the correction value for interpolating the error between the frequency of the received signal included in the demodulated signal and the frequency of the local oscillation signal. This is calculated by using both the equation and the conversion table 19 of the characteristics of the digital / analog converter 16. That is, the second embodiment and the third embodiment are used in combination.

Equation (2) shows the correction value calculating means in the correction value calculator 14 of the AFC circuit shown in FIG. λ = (β + αγ) / (1 + α) (2) In the equation (2), β is a correction value calculated by a mathematical expression indicating the characteristic of the digital-to-analog converter 16, and γ is the characteristic of the digital-to-analog converter 16. The correction value calculated by the conversion table 19 shown in FIG.

Next, the calculation of the correction value will be described with reference to equation (2). When the control unit 13 instructs the correction value calculation unit 14 to calculate the correction value λ at the time t, the correction value calculation unit 14 converts the correction value λ at the time t into a mathematical expression indicating the characteristics of the digital / analog converter 16 and a conversion table 19. It is calculated by using together.

The correction value calculator 14 first calculates a correction value β ₀ at time t ₀ by a function of calculating a correction value according to the characteristic equation of the digital / analog converter 16. At the same time, the correction value γ ₀ at the time t ₀ is calculated by the function of calculating the correction value using the conversion table 19 of the characteristics of the digital / analog converter 16.

Next, using the calculated correction value β ₀ and correction value γ ₀ at time t ₀ , a correction value λ ₀ is calculated by a weighted average as shown in equation (2). Here, if the correction value λ ₀ is to be an average value of the correction value β ₀ and the correction value γ ₀ , a
= 1. Then, the calculated correction value λ ₀ is
Output to 2. Similarly, for the correction value after time t _1, the correction value at that time is calculated by Expression (2) and output to the measurement unit 12. This work is performed for a preset time t _T
The calculated correction value is repeatedly used for the averaging process.

As described above, in the AFC circuit of the present embodiment, when calculating the correction value, the equation of the characteristic of the digital / analog converter 16 and the conversion table 19 of the characteristic of the digital / analog converter 16 are used together. Therefore, the correction value can be calculated by adjusting the amount of memory and the amount of calculation as needed.

The AFC circuit of each of the above embodiments is
The present invention can be applied not only to a mobile device and a base station of a mobile communication system but also to a receiver such as a television and a radio.

[0050]

As described above, according to the present invention,
The frequency of the received signal and the frequency of the local oscillation signal are obtained by using the frequency correction value obtained from the characteristics of the digital-to-analog converter in the averaging process calculated by the measurement unit until the frequency of the local oscillation signal stabilizes. Error averaging processing time can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an AFC circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an operation of the AFC circuit according to the first embodiment of the present invention;

FIG. 3 is a block diagram showing a configuration of an AFC circuit according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an AFC circuit according to Embodiment 3 of the present invention.

FIG. 5 is a diagram showing a conversion table of an AFC circuit according to Embodiment 3 of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional AFC circuit.

FIG. 7 is a diagram for explaining the operation of a conventional AFC circuit;

[Explanation of symbols]

 Reference Signs List 11 demodulation unit 12 measurement unit 13 control unit 14 correction value calculation unit 15 conversion unit 16 digital / analog converter 17 voltage controlled oscillator 18 correction value calculation unit 19 conversion table

Claims (7)

[Claims] 1. A demodulation means for demodulating a received signal and a local oscillation signal as inputs, and measuring an error between a frequency of the reception signal and a frequency of the local oscillation signal included in the demodulated signal demodulated by the demodulation means. Measuring means for averaging, a correction value calculating means for calculating a correction value corresponding to an error between the frequency of the received signal and the frequency of the local oscillation signal included in the demodulated signal demodulated by the demodulating means, Conversion means for converting the error average value into a control value for digital-to-analog conversion, digital-to-analog conversion means for converting the control value to digital-to-analog and outputting a control voltage, and a local unit having a frequency corresponding to the control voltage Voltage-controlled oscillating means for generating an oscillation signal, wherein the measuring means adds the correction value calculated by the correction value calculating means in error measurement averaging. An AFC circuit characterized by calculating an average value of errors by calculating the average value. 2. The AFC circuit according to claim 1, wherein the correction value calculating means calculates the correction value using an equation of the characteristic of the digital / analog converting means. 3. The AFC according to claim 1, further comprising a conversion table created based on the characteristics of the digital-to-analog conversion means, wherein the correction value calculation means uses the conversion table in calculating the correction value. circuit. 4. A conversion table created based on characteristics of the digital / analog conversion means, wherein the correction value calculation means uses a mathematical expression of the characteristics of the digital / analog conversion means and the conversion table in the correction value calculation. The AFC circuit according to claim 1, wherein: 5. A mobile station comprising the AFC circuit according to claim 1. 6. A base station comprising the AFC circuit according to any one of claims 1 to 4. 7. A mobile communication system comprising: the mobile device according to claim 5; and the base station according to claim 6.