JPH06216801A - Frequency correction circuit for radio terminal - Google Patents

Abstract

PURPOSE:To reduce the circuit scale and to optionally set a frequency correction range. CONSTITUTION:A 1st counter 12 counts the intermediate frequency signals in a prescribed counting cycle, and a 2nd counter 13 counts the intermediate frequency signals in a 1/N cycle (N: a natural number) of the cycle of the counter 12. A correction circuit 14 calculates the total count value of the counter 13 out of a reference range in the counting cycle of the counter 12. Then the circuit 14 outputs the count value of intermediate frequency signals, i.e., the value obtained by adding the product of the counting frequency of the counter 13 out of the reference range and the standard count value of the counter 13 to the value obtained by subtracting the total count value of the counter 13 from the count value of the counter 12. A control signal generating part 15 produces a frequency control signal based on the count value of intermediate frequency signals and the standard count value. Thus the local oscillation frequency is controlled by the frequency control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency calibration circuit for a wireless terminal, and more particularly to a frequency calibration circuit for a mobile communication type wireless terminal.

[0002] In mobile communication wireless terminals, it is necessary to improve the accuracy of the transmission frequency in order to prevent mutual interference between frequency channels. For this reason, a frequency calibration circuit is provided that causes the transmission frequency to follow the reception frequency from the base station with high accuracy. In the frequency calibration circuit of this wireless terminal, it is necessary to reduce the circuit scale.

[0003]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional frequency calibration circuit. In a wireless terminal, a system in which a transmission frequency f _{T is made} to follow a reception frequency f _R from a base station is called a frequency calibration system, and a circuit responsible for this function is called a frequency calibration circuit. In FIG. 4, the reception unit 16 frequency-converts the reception signal of the frequency f _R received by the antenna 19 from the base station in combination with the local oscillation signal of the frequency f _L generated by the synthesizer unit 17, and outputs the frequency f _IF Output as an intermediate frequency signal. The intermediate frequency signal is supplied to the counter 42 after passing through the bandpass filter 41 that selects the intermediate frequency.

The counter 42 has a frequency f of the intermediate frequency signal.
Count the _IF . The control data generation circuit 44 uses the counter 4
The count value of the frequency f _IF of the intermediate frequency signal supplied from 2 is compared with the standard value, and a value obtained by adding the error amount to the control data output last time is generated as control data.
The D / A converter 45 converts the control data supplied from the control data generation circuit 44 into an analog control voltage V _C and outputs it.

[0005] Synthesizer unit 17, according to the control voltage V _C to be supplied from the D / A converter 45 changes the reference oscillation frequency f _E of the built-in voltage controlled reference oscillator, based on the reference oscillation frequency f _E, the frequency Generate a local oscillation signal of f _L.

The transmitter 18 frequency-converts the local oscillation signal of frequency f _L to generate a transmission signal of frequency f _T ,
It transmits from the antenna 20.

Next, the operation of the frequency calibration circuit will be described in detail.
This will be described using a numerical example. Now, the reception frequency f_RMark of
Quasi value f_R= 800 MHz, α = 1 kHz shifted
It is assumed that a signal of the reception frequency is received. At this time, f_R=
It becomes 800MHz + 1kHz. In the synthesizer section 17
Frequency f of the generated local oscillation signal_LThe standard value of f _L
= 799 MHz, the intermediate frequency f of the intermediate frequency signal
_IFBecomes 1 MHz + 1 kHz as described below.

F _IF = (800 MHz + 1 kHz) −799 MHz = 1 MHz + 1 kHz When the counter 42 counts, for example, 1 sec, the count value becomes (1M + 1k). In the control data generation circuit 44, if the standard value (median value) is determined to be 1M, the error is 1 by comparison with the count value.
It becomes k.

In the control data generation circuit 44, a value obtained by adding the current error to the control data output last time is used as the control data. Since the error is now 1k, the control data is (previous control data + 1k). here,
At the previous count, the reception frequency f _R was the standard value of 800M
If the control data is Hz, and the previous control data was the standard value of 1M, the control data is (1M + 1k).

The deviation α = 1 kHz of the reception frequency f _R is
1kHz / 800MHz against the standard value of the reception frequency
= 1.25 ppm. When f _R shifts by 1.25 ppm, the local oscillation frequency f _L generated by the synthesizer unit 17 is also changed by 1.25 ppm. Therefore, for example, the conversion gain of the output voltage V _C with respect to the input control data of the D / A converter 45 is set to 1V / 1k,
The voltage control sensitivity of the reference frequency f _E of the voltage control reference oscillator incorporated in the synthesizer unit 17 is set to 1.25 ppm / 1V.

The deviation of the local oscillation frequency f _L is proportional to the deviation of the reference oscillation frequency f _E , and the sensitivity of the D / A converter 45 to the control voltage V _C is 1.25 ppm / 1V.

As described above, the conversion gain of the D / A converter 45 is set to 1V / 1k, and the D / A converter 45 is set.
When the median value of is 2.5 V (however, the control data is 1 k), the control voltage V _C is V _C = 2.5 V + 1 V when the control data is (1 M + 1 k).

Further, when a voltage control sensitivity of the reference frequency f _E is set to 1.25 ppm / 1V, the standard value of the reference frequency f _E and f _E = 10 MHz, the control voltage V _C = 2.5
At V + 1V, f _E = 10 MHz + (1.25 ppm of 10 MHz).

Since the deviation of the local oscillation frequency f _L is proportional to the deviation of the reference oscillation frequency f _E , the local oscillation frequency f _L
L is 1kH from the standard value of 799MHz as shown below.
z shift.

F _L = 799 MHz + (1.25 ppm of 799 MHz) ≈799 MHz + 1 kHz The transmission frequency f _T of the transmission signal is provided with a predetermined frequency interval with the reception frequency f _R. Now, let the transmission frequency f _T be f _T = 90
Assuming that the frequency is 0 MHz, the transmission frequency f _T will be 101 to the standard value 799 MHz of the local oscillation frequency f _L by frequency conversion.
It is obtained as a value obtained by adding MHz.

The local oscillation frequency f _L has a standard value of 799 MHz.
When it is deviated by 1 kHz, the transmission frequency f _T also deviates from the standard value of 900 MHz by 1 kHz as described below.

F _T = f _L +101 MHz = 799 MHz + 1 kHz + 101 MHz = 900 MHz + 1 kHz As described above, if the reception frequency f _R shifts by 1 kHz, the transmission frequency f _T also shifts by 1 kHz, and the transmission frequency f _T becomes the reception frequency f _R. To follow.

Next, the function of the bandpass filter 41 will be described. In mobile communication, as shown in the explanatory diagram of Rayleigh fading in FIG. 5, there is a Rayleigh fading phenomenon in which the level of the received wave changes with time. In particular, at the moment when the level of the received wave drops below the noise level, the received signal apparently becomes zero, and the frequency f _IF of the intermediate frequency signal deviates greatly from the standard value (for example, 1 MHz).

The intermediate frequency that deviates greatly from this standard value
If the counter 42 counts, it causes an erroneous count.
Reception frequency that should be received when there is no illy fading
Number f _RTransmission frequency f_TWill not follow.

In order to prevent this erroneous counting, a band pass filter 41 is provided in the conventional frequency calibration circuit. As shown in FIG. 6, the bandpass filter 41 uses the center frequency of the band as the standard value of the intermediate frequency f _IF , and the band is in the range of the frequency fluctuation of the reception frequency f _R to be tracked, that is, the frequency calibration range or more. It is spacious.

Due to Rayleigh fading, the reception level
When it falls below the noise level, the bandpass filter
The input signal of the converter 41 becomes noise and its frequency is the intermediate frequency.
Number f _IFIt greatly varies from the standard value of.

However, the signal that has passed through the bandpass filter 41 has a variation in frequency,
It is within the band of 1, and on average, its frequency is
It becomes a standard value of the center frequency of the band of the bandpass filter, that is, the intermediate frequency f _IF .

Therefore, by Rayleigh fading,
When the reception level drops below the noise level, the counter 42 counts signals with a frequency substantially close to the standard value of the intermediate frequency f _IF , and it is possible to prevent erroneous counting of the intermediate frequency due to noise.

As described above, the counter 42 normally receives the reception frequency f when the reception level is higher than the noise level.
_When the shift of _R is α, f _R + α is counted, and when the reception level drops below the noise level due to Rayleigh fading, the signal of a frequency substantially close to the standard value of the intermediate frequency f _IF is counted.

[0025]

In the conventional frequency calibration circuit shown in FIG. 4, an integrated circuit section 4 including a counter 42, a control data generation circuit 44, and a D / A converter 45 is provided.
0 can be configured as one integrated circuit.

However, the bandpass filter 41 is an analog circuit composed of, for example, a ceramic filter or the like, and must be provided as an external circuit of the integrated circuit. For this reason, there is a problem that the circuit size is increased by the amount of the bandpass filter 41. In addition, the frequency calibration range of the frequency calibration circuit is determined by the band of the bandpass filter 41, and therefore cannot be changed.

The present invention has been made in view of the above points, and a frequency calibration circuit capable of eliminating the bandpass filter to reduce the circuit scale and arbitrarily setting the frequency calibration range is provided. The purpose is to provide.

[0028]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, the synthesizer unit 17 generates a local oscillation signal based on the frequency control signal. The receiving unit 16
An intermediate frequency signal corresponding to the frequency difference between the local oscillation signal and the received signal is generated. The frequency counting unit 11 is supplied with the intermediate frequency signal and counts the frequency of the intermediate frequency signal at every predetermined cycle. The control signal generator 15 generates the frequency control signal based on the count value and the standard value. The transmission unit 18 generates a transmission signal in which the frequency is made to follow the frequency of the reception signal at constant frequency intervals based on the local oscillation signal.

The first counter provided in the frequency counter 11
The counter 12 of 1 counts the frequency of the intermediate frequency signal for each predetermined counting cycle. The second counter 13 has the first counter
The frequency of the intermediate frequency signal is counted every 1 / N (N is a natural number) of the counting cycle of the counter 12.

The correction circuit 14 includes the second counter 13 described above.
A reference range from a value below a predetermined value of the standard count value to a value above a predetermined value of the standard count value is set by the second counter 13 in each count cycle of the first counter 12 Then, the cumulative value of the count value is calculated, the cumulative value is subtracted from the count value of the first counter 12, and the count value of the second counter 13 is out of the reference range and the second counter. A value obtained by adding the product of 13 and the standard count value is output as the count value of the frequency of the intermediate frequency signal.

According to a second aspect of the invention, the correction circuit 14 is provided.
The reference range of the count value by the second counter 13 is variable.

[0032]

According to the first aspect of the present invention, since the second counter 13 and the correction circuit 14 prevent erroneous counting of the intermediate frequency due to noise, it is not necessary to provide a bandpass filter before the frequency counting section 11. .

According to the second aspect of the present invention, the frequency calibration range in which the transmission frequency follows the reception frequency is changed by changing the reference range of the count value of the second counter.

[0034]

2 is a block diagram of a frequency calibration circuit according to an embodiment of the present invention. In the figure, the same components as those in FIG. 1 and FIG. In FIG. 2, the control signal generation unit 15 includes a control data generation circuit 44 and a D / A converter 45.

The frequency counting section 11 includes a counter 22 which is a first counter, a counter 23 which is a second counter,
And a correction circuit 14. In addition, the correction circuit 14
The subtractor 24, the adder 25, the comparator 26, the subtraction value calculation circuit 27, the number counting circuit 28, and the addition value calculation circuit 29.

The receiving unit 16 receives the received signal of the frequency f _R received by the antenna 19 from the base station, and synthesizes the received signal.
The frequency conversion is performed in combination with the local oscillation signal of the frequency f _L generated in step (4), and the intermediate frequency signal of the frequency f _IF is output. The intermediate frequency signal is supplied to the frequency counting unit 11.

The frequency counter 11 counts the frequency f _IF of the intermediate frequency signal. The control data generation circuit 44 compares the count value of the frequency f _IF of the intermediate frequency signal supplied from the frequency counting unit 11 with the standard value, and adds the error value to the control data output last time to obtain a value. Generate as control data. The D / A converter 45 includes the control data generation circuit 4
The control data supplied from 4 is the analog control voltage V
Converted to _C and output as frequency control signal.

The synthesizer 17, in accordance with the control voltage V _C to be supplied from the D / A converter 45 changes the reference oscillation frequency f _E of the built-in voltage controlled reference oscillator, based on the reference oscillation frequency f _E, the frequency Generate a local oscillation signal of f _L.

The transmitter 18 frequency-converts the local oscillation signal of frequency f _L to generate a transmission signal of frequency f _T ,
It transmits from the antenna 20.

The receiving section 16, the synthesizer section 17,
The operations of the transmission unit 18, the control data generation circuit 44, and the D / A converter 45 are similar to those of the conventional frequency calibration circuit of FIG. 4, and the change of the transmission frequency f _T follows the change of the reception frequency f _R.

Next, the operation of the frequency counter 11 will be described. FIG. 3 is an explanatory diagram of a method of counting the intermediate frequency in the frequency counting unit 112. FIG. 3 (A) shows a temporal change in the reception level, and there is a moment when the noise level is lower than the noise level due to Rayleigh fading.

As shown in FIG. 3B, the counter 22 counts the frequency of the intermediate frequency signal at the counting cycle T _G1 . In contrast, the counter 23, 1 / N of the count period T _G1 (N is a natural number) counts the frequency of the intermediate frequency signal by the counting period T _G2 of. For example, as shown in FIG. 3C, N = 8 and T _G2 has a period ⅛ of T _G1 .

The standard value (median value) of the count values of the counter 23 is 1 / N with respect to the standard value (median value) of the count values of the counter 22. For example, the intermediate frequency f _IF
When the standard value of 1 is 1 MHz and the counting cycle T _G1 is 1 sec, the standard value of the count value of the counter 22 is 1M and the standard value of the count value of the counter 23 is 125k.

When Rayleigh fading occurs and the reception level becomes equal to or lower than the noise level, both the counter 22 and the counter 23 erroneously count noise. However, in the counter 23, since the counting cycle T _G2 is subdivided from the counting cycle T _G1 of the counter 22, the erroneous count value only at the moment when the reception level becomes equal to or lower than the noise level is calculated as the counting cycle T _G2. Can be taken out as the count value of.

In the comparator 26, in order to determine whether the count is wrong, a threshold value below the standard value of the count value of the counter 23 by a predetermined value β and a threshold value above the standard value β by the standard value are provided. The range of ± β is set as the reference range.

The comparator 26 compares the count value of the counter 23 with the threshold value, and when the count value is within the reference range, determines that the count value is normal, and the count value is outside the reference range. At this time, it is determined that the count is incorrect.

For example, when the standard value is 125k and the predetermined value β is 5k, the count value of the counter 23 is 12k.
If it is within the range of 0k to 130k, it is judged to be a normal count value because it is within the reference range, and if the count value is 120k or less or 130 or more, it is judged to be an incorrect count because it is outside the reference range.

The range of ± predetermined value β × N with respect to the predetermined value β that determines the reference range is the frequency calibration range in which the transmission frequency f _T follows the reception frequency f _R. For example,
Standard value of intermediate frequency f _IF is 1 MHz, N = 8, predetermined value β
Is 5k, the frequency calibration range is ± 5k × 8 = ± 4
It becomes 0 kHz.

At this time, in the comparator 26, the intermediate frequency f
_{If the IF} is within the range of 1 MHz ± 40 kHz, it is determined to be normal, and if the frequency is out of this range, it is determined to be an incorrect count. Reception frequency f _R to be tracked
The deviation is ± α, and the predetermined value β is set so that the frequency calibration range is ± α or more.

In a normal state where the reception level is higher than the noise level, the intermediate frequency f _IF is within the standard value ± α of the intermediate frequency, so the count value of the counter 23 is within the standard value ± β. It is judged to be a normal count value.

When the reception level drops below the noise level, the intermediate frequency f _IF is outside the standard value ± α of the intermediate frequency, and the count value of the counter 23 is outside the standard value ± β. , It is determined that the count value is incorrect.

The comparator 26 has a cycle T by the counter 23.
_When it is determined that the count value in _G2 is an erroneous count, the erroneous count value is given to the subtraction value calculation circuit 27.
The subtraction value calculation circuit 27 calculates the cumulative value of the false count values given from the comparator 26 in the counting cycle T _G1 .

During the counting cycle T _G1 of the counter 22, the counter 23 counts N times in the cycle T _G2 . At this time,
If M times are erroneously counted, each cycle of M times T
The cumulative value of the erroneous count values in _G2 is calculated by the subtraction value calculation circuit 27.

In the example of FIG. 3, in the period T _G1 on the left side of FIG. 3, erroneous counting occurs in the second and sixth periods. Therefore, the count value in the second cycle T _G2 and the count value in the sixth cycle T _G2 are given from the comparator 26 to the subtraction value calculation circuit 27, and the sum of the two count values is calculated. It

[0055] The subtracter 24, from the count value in the counting period T _G1 by the counter 22 subtracts the accumulated value of the erroneous count value in the counting period T _G1 supplied from the subtraction value calculating circuit 27. The data of this subtraction result is supplied to the adder 25.

The comparator 26 supplies a signal indicating an erroneous count to the number-of-times counting circuit 28 in response to the counting cycle T _{G2 in} which the count value of the counter 23 is determined to be an erroneous count.

The number counting circuit 28 is supplied with the above-mentioned signal indicating an erroneous count in the counting cycle T _G1 , and counts the number of times the erroneous count is generated by the counter 23. For example, in the cycle T _G1 , when the counter 23 makes M erroneous counts, the number counting circuit 28 counts M, which is the number of erroneous counts. The number-of-times counting circuit 28 supplies the above-mentioned count value to the addition value calculation circuit 29.

The added value calculating circuit 29 is a counter for the counter 23.
The standard value of the und value and the error supplied from the frequency counting circuit 28
Calculate the product of the number of counts. Counting cycle on the left side of Figure 3
Period T _G1Then, the second and sixth counting cycle T_G2Wrong coun
Has occurred, and the number of times counting circuit 28 counts the number of times 2.
However, in the addition value calculation circuit 29, the number of erroneous counts is 2 × the mark.
Calculate the quasi-value.

When the standard value of the intermediate frequency f _IF is 1 MHz and the counting cycle T _G1 is 1 sec, the standard value of the counter 23 is 125 k, which is 2 in the above example.
The value of × standard value is 2 × 125k = 250k. The added value calculation circuit 29 supplies the calculated data of the number of false counts × standard value to the adder 25.

The adder 25 adds the data supplied from the subtractor 24 and the data supplied from the addition value calculation circuit 29 for each counting cycle T _G1 . Therefore, in the counting cycle T _G1 , a value obtained by adding the number of false counts of the counter 23 × the value of the standard value to the value obtained by subtracting the cumulative value of the false count values of the counter 23 from the count value of the counter 22 is the adder 25. Is calculated as the count value of the intermediate frequency f _IF .

The data of the count value of the intermediate frequency f _IF calculated by the adder 25 is supplied to the control data generation circuit 44.

Intermediate frequency f calculated by the adder 25
_{The IF} count value is the count value of the counter 22 in the count cycle T _G1 in which the erroneous count when the reception level drops due to Rayleigh fading is deleted and replaced with the standard value.

Therefore, the frequency counter 11 can prevent false counting of the intermediate frequency f _IF due to noise when the reception level drops below the noise level due to Rayleigh fading.

In the frequency counting section 11, as described above, when the reception level is higher than the noise level in the normal state, the deviation of the reception frequency f _R is defined as α, and the standard value of the intermediate frequency f _IF +
The intermediate frequency signal of the frequency of α is counted, and when the reception level falls below the noise level due to Rayleigh fading, the intermediate frequency signal of the frequency of the standard value of the intermediate frequency f _IF is counted.

As described above, the counter 23 of the frequency counting unit 11 and the correction circuit 14 play the role of preventing erroneous counting of the intermediate frequency f _IF , similarly to the conventional bandpass filter of the frequency calibration times of FIG. There is.

As described above, in this embodiment, the counter 2
3 and the correction circuit 14 play the role of a bandpass filter of the conventional frequency calibration circuit, so that the bandpass filter is unnecessary. By the way, the counter 23 and the correction circuit 14
Is a digital circuit, the integrated circuit unit 10 including the counter 22, the counter 23, the correction circuit 14, and the control signal generation unit 15 can be configured as one integrated circuit. Therefore, as compared with the conventional frequency calibration circuit, the bandpass filter can be eliminated, and thus the circuit scale can be reduced.

In the comparator 26, the standard value ± predetermined value β
The upper and lower thresholds are set to, and the range of ± predetermined value β × N is
It is a frequency calibration range in which the transmission frequency follows the reception frequency. The frequency calibration range can be arbitrarily changed by changing the threshold value of the comparator 26 and changing the value of the predetermined value β. For example, if N = 8 and the predetermined value β is 5k, the frequency calibration range is ± 5k × 8 = ± 40kHz, but if the predetermined value β is 10k, the frequency calibration range is ± 10k.
It can be set to × 8 = ± 80 kHz.

Therefore, in the wireless terminal to which the present embodiment is applied, when the frequency calibration range is changed due to the change of the specification of the fluctuation range of the reception frequency f _R , it is sufficient to change the above-mentioned threshold value easily. Can respond.

[0069]

As described above, according to the invention of claim 1,
Since the second counter and the correction circuit prevent erroneous counting of the intermediate frequency due to noise, there is no need to provide a bandpass filter in front of the frequency counting unit, and the circuit scale can be reduced by the amount of the bandpass filter. It has the features that can be done.

According to the second aspect of the present invention, by changing the reference range of the count value of the second counter, it is possible to arbitrarily change the frequency calibration range in which the transmission frequency follows the reception frequency.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of a frequency calibration circuit according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of an intermediate frequency counting method.

FIG. 4 is a configuration diagram of a conventional frequency calibration circuit.

FIG. 5 is an explanatory diagram of Rayleigh fading.

FIG. 6 is a characteristic diagram of a bandpass filter.

[Explanation of symbols]

 10 integrated circuit unit 11 frequency counting unit 12 first counter 13 second counter 14 correction circuit 15 control signal generating unit 16 receiving unit 17 synthesizer unit 18 transmitting unit 19,20 antenna 22,23 counter 24 subtractor 25 adder 26 Comparator 27 Subtraction value calculation circuit 28 Number counting circuit 29 Addition value calculation circuit 44 Control data generation circuit 45 D / A converter

Claims (2)

[Claims] 1. An intermediate frequency signal corresponding to the frequency difference between a local oscillation signal generated based on a frequency control signal and a received signal is supplied, and a frequency counting unit (frequency counting unit calculates the frequency of the intermediate frequency signal every predetermined period). 11), the control signal generation unit (15) generates the frequency control signal based on the counted value and the standard value, and the frequency of the transmission signal generated based on the local oscillation signal is set to the reception signal. In a frequency calibration circuit of a wireless terminal that causes the frequency of the intermediate frequency signal to follow at a constant frequency interval, the frequency counting unit (11) counts the frequency of the intermediate frequency signal for each predetermined counting cycle.
A second counter (13) that counts the frequency of the intermediate frequency signal in each cycle of 1 / N (N is a natural number) of the counting cycle of the first counter (12); and the second counter. A reference range from a value lower than a predetermined value of the standard count value according to (13) to a value higher than the predetermined value of the standard count value is provided, and in each counting cycle of the first counter (12), a second counter ( 13) the cumulative value of the count value outside the reference range is obtained, and the count value of the second counter (13) is added to the value obtained by subtracting the cumulative value from the count value of the first counter (12). A configuration provided with a correction circuit (14) that outputs a value obtained by adding the product of the number of counts that has become outside and the standard count value by the second counter (13) as the count value of the frequency of the intermediate frequency signal. Frequency calibration circuit for wireless terminal characterized by 2. The frequency calibration circuit for a wireless terminal according to claim 1, wherein the correction circuit (14) has a variable reference range of the count value by the second counter (13).