JPH09139687A - Method and circuit for correcting reference oscillating frequency - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the circuit to perform a reference oscillation easily with high precision and to eliminate the adjustment. SOLUTION: In this circuit, a PLL circuit 19 and a voltage controlled oscillator 21 generate a local oscillation signal S7a having an upper frequency with respect to a frequency of a reception signal S1 and a local oscillation signal S7b having a lower frequency respectively in a prescribed timing to obtain a prescribed IF signal. A mixer 5 mixes the local oscillation signals S7a, S7b and the reception signal S1 in respective timings. A difference detector 14 detects the deviation (Δf) of IF signals S2a, S2b obtained as above and corrects a reference oscillating frequency of a reference oscillator 18 with a control voltage VC from a storage circuit 17 depending on the deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference oscillation frequency correction method and a reference oscillation frequency correction circuit suitable for use in a radio circuit.

[0002]

2. Description of the Related Art Conventionally, in a demodulation circuit used for a wireless communication terminal or the like, a reference oscillation signal having a predetermined reference oscillation frequency oscillated by a reference oscillator is mixed with a reception signal to obtain a desired IF (intermediate frequency). A desired signal is obtained by acquiring a signal and demodulating the IF signal. At this time, in order to eliminate the problem that the reference oscillation frequency changes due to changes in the circuit characteristics of the reference oscillator due to temperature changes, temperature compensation was performed on the crystal oscillator etc. to improve absolute accuracy. .

[0003]

However, in the conventional demodulation circuit and the reference oscillation frequency correction method, if the reference oscillation frequency is made more accurate, the variations in the elements of the individual reference oscillators cannot be absorbed and the yield is reduced. There was a problem of decrease. Therefore, it is possible to adjust each product in order to absorb the variation of the elements, but there is a problem that it takes a lot of time and effort.

Therefore, an object of the present invention is to provide a reference oscillation frequency correction method and a reference oscillation frequency correction circuit which can easily and accurately perform reference oscillation and can eliminate adjustment and the like.

[0005]

In order to achieve the above object, a reference oscillation frequency correction method according to the invention of claim 1 receives a reference oscillation signal generated by a reference oscillator and having a predetermined reference oscillation frequency. An upper local oscillation signal and a lower local oscillation signal having frequencies deviated by a predetermined amount from the frequency of the signal are generated, and the upper local oscillation signal and the lower local oscillation signal are mixed with the reception signal. A first intermediate frequency signal and a second intermediate frequency signal for each
An intermediate frequency signal and a second intermediate frequency signal and a second intermediate frequency signal
A difference between both frequencies is detected from the intermediate frequency signal, and the reference oscillation frequency of the reference oscillator is corrected based on the difference.

Further, as a preferred mode, the upper local oscillation signal and the lower local oscillation signal may be generated at different timings as described in claim 2, for example.

In a preferred mode, the upper local oscillation signal and the lower local oscillation signal may be alternately generated every N frames (N = natural number).

In the reference oscillation frequency correction circuit according to the present invention, a reference oscillation signal generating means for generating a reference oscillation signal having a predetermined reference oscillation frequency, and a reference oscillation signal generating means for generating a reference oscillation signal. Based on the oscillation signal, an upper local oscillation signal having a frequency that is deviated by a predetermined amount to the frequency of the received signal at a first timing and a lower local portion having a frequency that is deviated by a predetermined amount at the second timing. Local oscillation signal generating means for generating an oscillation signal, the upper local oscillation signal and the lower local oscillation signal generated by the local oscillation signal generating means, and the reception signal, and a first intermediate frequency signal for each. Mixing means for generating the second intermediate frequency signal, and a difference between both frequencies of the first intermediate frequency signal and the second intermediate frequency signal generated by the mixing means. A detecting means for detecting that, characterized by comprising a correction means for correcting the reference oscillation frequency of the reference oscillation signal generating means based on the difference detected by said detection means.

As a preferred mode, the detecting means frequency-detects the first intermediate frequency signal and the second intermediate frequency signal, and extracts the DC component corresponding to each frequency. The frequency detecting means and the difference detecting means for detecting the difference between the respective DC components extracted by the frequency detecting means may be provided.

According to the present invention, the upper local oscillation signal and the lower local oscillation signal having a frequency deviated by a predetermined amount from the frequency of the received signal based on the reference oscillation signal having a predetermined reference oscillation frequency generated by the reference oscillator. And a local oscillator signal. Then, by mixing the upper local oscillation signal and the lower local oscillation signal to the received signal, respectively,
A first intermediate frequency signal and a second intermediate frequency signal for each are generated. After that, the difference between both frequencies is detected from the first intermediate frequency signal and the second intermediate frequency signal, and the reference oscillation frequency of the reference oscillator is corrected based on the difference.
Therefore, it becomes possible to easily and accurately perform the reference oscillation, and it is possible to eliminate the adjustment and the like.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to the drawings as an example in which the embodiment is applied to a radio section of a mobile radio device. A. Configuration of Radio Unit FIG. 1 is a block diagram showing the configuration of the radio unit of a mobile radio according to an embodiment of the present invention. In the figure, an antenna 1 supplies a reception signal S1 having a frequency f _i (for example, a predetermined frequency in the 1.9 GHz band) to a bandpass filter 3 via an antenna switch 2 and a transmission signal S8 from a transmission unit 22. Send. The antenna switch 2 switches between transmission and reception at a predetermined timing. The bandpass filter 3 filters the received signal S1 and then supplies it to the low noise amplifier 4. The low noise amplifier 4 amplifies the received signal S1 and then supplies it to the mixer 5.

The mixer 5 has a VCO (Voltage Control Oscilater) 2 described later at a predetermined timing, in other words, at a switching timing of a PLL circuit 19 described later.
1. The local oscillation signal S7a of frequency f _L1 (> f _i ) or the local oscillation signal S of frequency f _L2 (<f _i ) supplied from
By mixing 7b and the received signal S1 described above,
An IF having an IF frequency f _IF1 at each timing by dropping from the 1.9 GHz band to 150 to 250 MHz
The signals S2a and S2b are generated and supplied to the IF amplifier 7 via the bandpass filter 6. The local oscillation signals S7a and S7b have upper and lower frequencies centered on the frequency f _i of the received signal S1 that produces the same IF signal S2.

The above-mentioned frequencies f _L1 and f _L2 have a value that is an integral multiple of the reference oscillation frequency f _OSC2 of the reference oscillation signal S6 generated by the reference oscillator 18, which will be described later. Almost matches. Therefore, if the reference oscillation signal S6 of the reference oscillator 18 shifts, the frequency f _L1 (or f _L2 ) shifts at the same rate. Here, if this deviation is Δf, the reference oscillation signal S6 of the reference oscillator 18 is deviated, so that the local oscillation signal S by the VCO 21 is changed.
7a, shifted frequency f _L1, f _L2, respectively △ f of S7b, the frequency _{f L1 + △ f, f L2} - a △ f. As a result,
I generated by the respective local oscillation signals S7a and S7b
The frequencies of the F signals S2a and S2b are also the IF frequency f _IF1 + Δf and the IF frequency f _{IF1 −Δf} , respectively. In this embodiment, the IF frequency f _IF1 + Δf and the IF frequency f _IF1 −
A deviation of Δf (actually lower IF frequency f _IF2 + Δf, IF frequency f _{IF2 −Δf} obtained in the next stage) is detected, and the reference oscillation frequency f of the reference oscillator 18 is detected according to the deviation. By controlling the _OSC2 , the frequencies of the IF signals 2a and 2b obtained in the mixer 5 are made equal, and accurate IF
I'm trying to get a signal.

The IF amplifier 7 amplifies the IF signal S2a (or 2b) and supplies it to the mixer 8. Mixer 8
By mixing the IF signal S2a (or 2b) with the local oscillation signal S3 having the local oscillation frequency f _OSC1 from the oscillator 9 to obtain a frequency of 150 to 250 MHz to 10 M
Frequency conversion to near Hz, and lower IF frequency f _IF2
Is generated and supplied to the IF amplifier 11 via the bandpass filter 10. That is, as described above, the local oscillation signal S7a,
When the frequencies f _L1 and f _L2 of S7b are shifted by Δf, the IF frequencies of the IF signals S4a and 4b are “f _IF2 + Δf” and “f _IF2 −Δf”, respectively. In addition,
The IF frequency f _IF2 + Δf is the IF frequency f _IF1 + Δf
It goes without saying that the IF frequency f _{IF2 −Δf} is proportional to the IF frequency f _IF1 −Δf. The IF amplifier 11 amplifies the IF signal S4a (or 4b) and then supplies it to the demodulation circuit (DET) 12. The demodulation circuit 12 demodulates the amplified IF signal S4a (4b),
The demodulated signal S5 is supplied to the subsequent circuit.

Next, the FM demodulation circuit 13 FM-detects the IF signal S4a having the above-mentioned IF frequency f _IF2 + Δf, which is supplied at a predetermined timing, to generate the DC voltage V1, and the difference detection circuit. Supply to 14,
The IF frequency f _IF2 - by FM detecting the IF signal S4b with △ f, to generate a DC voltage V2, and supplies the difference detection circuit 14.

The difference detection circuit 14 includes a subtracter 15 and a RAM.
The RAM 16 stores the DC voltage V1 corresponding to the IF signal S4a having the IF frequency f _IF2 + Δf, which is supplied at a predetermined timing.
To be stored. Further, the difference detection circuit 14 uses a PL described later.
At the switching timing of the L circuit 19, the IF frequency f _IF 2
When the DC voltage V2 corresponding to the IF signal S4b of −Δf is supplied from the FM demodulation circuit 13, the subtracter 15 subtracts the DC voltage V2 from the DC voltage V1 stored in the RAM 16 and supplies it to the holding circuit 17. To do. Further, the difference detection circuit 14 holds the subtraction result (V1−V2) by the holding circuit 17, and supplies the control voltage VC proportional to the subtraction result to the reference oscillator 18.

That is, if the reference oscillation frequency f _OSC2 of the reference oscillation signal S6 in the reference oscillator 18 described later is not shifted, the IF frequencies of the IF signals S4a and 4b are "f.
_IF2 ", the calculation result (V1-V2) becomes" 0 ". On the other hand, a reference oscillator 18 described later
If the reference oscillation signal S6 of is shifted, the IF signal S4
The IF frequencies of a and S4b are “f _IF2 + Δf”,
Since it becomes "f _IF2 -Δf", the subtraction result (V1-V
2), that is, the control voltage VC also has a value according to “Δf × 2”.

Next, the reference oscillator 18 outputs the control voltage V
According to C, the reference oscillation signal S6 of the reference oscillation frequency f _OSC2
Is oscillated and supplied to the PLL circuit 19. PLL circuit 19
Controls the VCO 21 with the reference oscillation signal S6 of the reference oscillation frequency f _OSC2 based on the frequency division ratio from the prescaler 20. That is, the PLL circuit 19 causes the VCO 21 to generate a local oscillation signal for transmission / reception according to the transmission / reception switching timing.
Local oscillation signals S7a and S7 having local oscillation frequencies f _L1 and f _L2
The local oscillator frequency switching control in the VCO 21 is performed so as to sequentially generate b.

Next, the VCO 21 generates a local oscillation signal for transmission / reception at the timing of transmission / reception under the control of the PLL circuit 19. Further, the VCO 21 controls the local oscillation signals S7a, S7a having the local oscillation frequencies f _L1 , f _L2 , according to the switching control of the PLL circuit 19 described above.
S7b is sequentially generated and supplied to the mixer 5 described above. In addition, the transmission unit 22, based on the local oscillation signal from the VCO21, the modulated wave supplied from the modulation circuit (not shown),
The frequency is converted to 1.9 GHz by a mixer (not shown), and the signal is radiated as a transmission signal S8 from the antenna 1 via the antenna switch 2.

B. Operation of Embodiment Next, the operation of this embodiment will be described. Here, FIG.
4 to FIG. 4 are conceptual diagrams showing the frequency distribution of signals in each unit of the wireless unit according to the present embodiment. First, the PLL circuit 19
In the VCO 21 and the reference oscillation signal S6 of the reference oscillation frequency f _OSC2 from the reference oscillator 18, the local frequency f above the frequency f _{i of the} reception signal S1 shown in FIG.
A local oscillation signal S7a having _L1 is generated and supplied to the mixer 5. Here, if the reference oscillation frequency f _OSC2 of the reference oscillation signal S6 in the reference oscillator 18 deviates, the frequency of the local oscillation signal S7a also deviates at the same rate and becomes “f _L1 + Δf”.

In the mixer 5, the received signal S1 and the local oscillation signal S7a are mixed and, as shown in FIG. 3, an IF signal S2 having an IF frequency f _IF1 + Δf shifted by Δf.
a is generated. The IF signal S2a is further mixed in the mixer 8 with the local oscillation signal S3 from the OSC 9 and converted into an IF signal S4a having a lower IF frequency f _IF2 + Δf. The IF signal S4a is demodulated by the demodulation circuit 12 and output as a demodulation signal S5 to the circuit at the subsequent stage, and the FM demodulation circuit 13 also performs FM demodulation.
The detected DC voltage V1 shown in FIG. 4 is stored in the RAM 16 of the difference detection circuit 14.

Next, at a predetermined timing, the PLL circuit 1
By changing the set frequency in 9, in the PLL circuit 19 and the VCO 21, according to the reference oscillation signal S6 of the reference oscillation frequency f _OSC2 from the reference oscillator 18,
A local oscillation signal S7b having a lower local frequency f _L2 with respect to the frequency f _i of the reception signal S1 shown in FIG. 2 is generated,
It is supplied to the mixer 5. Here, as described above, the reference oscillation frequency f of the reference oscillation signal S6 in the reference oscillator 18
_{When the OSC2} shifts, the frequency of the local oscillation signal S7b shifts at the same rate and becomes “f _L1 −Δf”.

[0023] In the mixer 5, a reception signal S1 and the local oscillation signal S7b are mixed, as shown in FIG. 3, △ f shifted by IF frequency f _IF1 - △ IF signal S2 having f
b is generated. The IF signal S2b is further mixed in the mixer 8 with the local oscillation signal S3 from the OSC 9 and converted into an IF signal S4b having an IF frequency f _IF2 -Δf. The IF signal S4a is demodulated by the demodulation circuit 12, output as a demodulation signal S5 to the circuit at the subsequent stage, and FM-detected by the FM demodulation circuit 13. As a result, the DC voltage V2 shown in FIG. 4 is obtained, which is subtracted from the DC voltage V1 stored in the RAM 16 in the subtractor 15 of the difference detection circuit 14, and the subtraction result (V1
-V2) is held in the holding circuit 17 as the control voltage VC. The control voltage VC held in the holding circuit 17 is supplied to the reference oscillator 18.

Here, if the reference oscillation frequency f _OSC2 of the reference oscillator 18 is an accurate value, the local oscillation frequencies f _L1 and f _{L2 of the} VCO 21 are also accurate values, so that the IF frequency of the IF signal S2a and the IF signal S2a are The IF frequency of S2b is
This is equal to "f _IF1 " and therefore the IF frequency of the IF signal S4a and the IF frequency of the IF signal S4b are also equal to "f _IF2 ". That is, since Δf does not occur, the subtraction result (V1−V2) becomes “0”. Therefore, the reference oscillation frequency f _OSC2 of the reference oscillator 18 is not corrected or the same control voltage VC as before is supplied as it is.

On the other hand, if the reference oscillation frequency f _OSC2 of the reference oscillator 18 is deviated, the local oscillation frequencies of the VCO 21 are "f _L1 + Δf" and "f", respectively, as described above.
_{Since L2} −Δf ”, the subtraction result (V1−V2), that is, the control voltage VC also has a value corresponding to“ Δf × 2 ”. Therefore, in the reference oscillator 18, the reference oscillation frequency f _OSC2 is corrected according to the control voltage VC. As a result,
In the PLL circuit 19 and the VCO 21, the reference oscillator 18
According to the corrected reference oscillation signal S6 of the reference oscillation frequency f _{OSC2 from} the local oscillation signals S of the local frequencies f _L1 and f _L2.
7a and S7b are generated and supplied to the mixer 5. In the mixer 5, the received signal S1 and the corrected reference oscillation signal S6
Local oscillation signal S7a (or S7 generated based on
b) and are mixed, IF with accurate IF frequency f _IF
The signal S2a (or S2b) is generated.

Since the above-described operation is performed at an appropriate interval after the power is turned on, the control voltage V is always applied to the reference oscillator 18.
C supplies the reference oscillator 18 to control the reference oscillator 18 with high accuracy.
_OSC2 is corrected.

As described above, in this embodiment, when the predetermined IF signal is obtained, the PLL circuit 19 and the VCO 21 cause the frequency f _{L1 of} the upper side and the frequency f _L of the lower side with respect to the frequency f _i of the received signal S1. Local oscillation signals S7a, S set to _L2
7b is generated at a predetermined timing, mixed with the reception signal S1 by the mixer 5, and the difference detector 14 shifts the difference between the IF signals S2a and S2b (Δf ×
2) is detected, and the reference oscillator 1
Since the reference oscillation frequency f _OSC2 of 8 is corrected,
It is possible to easily and accurately perform the reference oscillation, and it is possible to eliminate the adjustment for each product.
Further, since this frequency correction is performed so that it matches the frequency of the BS (Base Station), it is not necessary to consider the frequency deviation from the BS, and further, the reception frequency deviation hardly occurs. The pass band of a filter or the like can be narrowed to the utmost limit, and the S / N ratio at the time of reception can be improved.

[0028]

According to the present invention, based on a reference oscillation signal having a predetermined reference oscillation frequency generated by a reference oscillator, an upper local oscillation having a frequency deviated by a predetermined amount from the frequency of a received signal. A first intermediate frequency signal and a second intermediate frequency signal for each by generating a signal and a lower local oscillation signal and then mixing the upper local oscillation signal and the lower local oscillation signal with the received signal, respectively. After generating and, the difference between both frequencies is detected from the first intermediate frequency signal and the second intermediate frequency signal, and the reference oscillation frequency of the reference oscillator is corrected based on the difference. The advantage is that the reference oscillation can be performed easily and accurately, and adjustments and the like can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a wireless unit of a mobile wireless device according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a frequency distribution for explaining a local oscillation signal for obtaining an IF signal in a radio unit according to the present embodiment.

FIG. 3 is a conceptual diagram showing a frequency distribution for explaining an IF signal obtained by the local oscillation signal of the wireless unit according to the present embodiment.

FIG. 4 is a conceptual diagram showing a frequency distribution for explaining the shift of the IF signal obtained by the difference detection circuit of the wireless unit according to the present embodiment.

[Explanation of symbols]

 Reference Signs List 4 low noise amplifier 5 mixer (mixing means) 7, 11 IF amplifier 8 mixer 9 OSC 12 demodulation circuit 13 FM demodulation circuit (frequency demodulation means) 14 difference detection circuit (correction means) 15 subtractor (difference detection means, subtraction means) 16 RAM (difference detection means, storage means) 17 holding circuit (holding means) 18 reference oscillator (reference oscillation signal generation means) 19 PLL circuit 21 VCO (local oscillation signal generation means) S2a IF signal (first intermediate frequency signal) S2b IF Signal (second intermediate frequency signal) S6 Reference oscillation signal S7a Local oscillation signal (upper local oscillation signal) S7b Local oscillation signal (lower local oscillation signal) (V1-V2) Subtraction result (difference)

Claims (5)

[Claims] 1. An upper side local oscillation signal and a lower side local oscillation having a frequency that is deviated by a predetermined amount from the frequency of a received signal based on a reference oscillation signal generated by a reference oscillator and having a predetermined reference oscillation frequency. A first intermediate frequency signal and a second intermediate frequency signal for each of them by mixing the upper local oscillation signal and the lower local oscillation signal with the received signal. A reference oscillation frequency correction method comprising detecting a difference between both frequencies of a frequency signal and a second intermediate frequency signal and correcting the reference oscillation frequency of the reference oscillator based on the difference. 2. The reference oscillation frequency correction method according to claim 1, wherein the upper side local oscillation signal and the lower side local oscillation signal are generated at different timings. 3. The reference oscillation frequency correction method according to claim 1, wherein the upper local oscillation signal and the lower local oscillation signal are alternately generated every N frames (N = natural number). 4. A reference oscillation signal generating means for generating a reference oscillation signal having a predetermined reference oscillation frequency, and a received signal at a first timing based on the reference oscillation signal generated by the reference oscillation signal generating means. A local oscillation signal generating means for generating an upper local oscillation signal having a frequency deviated by a predetermined amount from the frequency and a lower local oscillation signal having a frequency deviated by a predetermined amount at the second timing; Mixing means for mixing the upper local oscillation signal and the lower local oscillation signal generated by the local oscillation signal generating means with the received signal to generate a first intermediate frequency signal and a second intermediate frequency signal for each; Detecting means for detecting a difference between both frequencies of the first intermediate frequency signal and the second intermediate frequency signal generated by the mixing means, and the difference detected by the detecting means Reference oscillation frequency correction circuit characterized by comprising a correction means for correcting the reference oscillation frequency of the reference oscillation signal generating means on the basis of. 5. The frequency detecting means for frequency detecting the first intermediate frequency signal and the second intermediate frequency signal to extract a DC component corresponding to each frequency, and the detecting means. 5. The demodulation circuit according to claim 4, further comprising a difference detection unit that detects a difference between the respective DC components.