JPH0681070B2 - Wireless communication device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication device, and more particularly to a wireless communication device of a system that corrects the frequency of a local oscillation signal based on the frequency of a received high frequency signal.

[Conventional technology]

Conventionally, this type of wireless communication device has the configuration shown in FIG. This wireless communication device is a mobile station of a mobile communication system, and communicates with a base station using a high frequency signal that is FM-modulated. The received high frequency signal S1 that has passed through the antenna and the high frequency filter section is input from the input terminal 1,
The first frequency mixer 2 mixes with the first local oscillation signal S5 generated by the first local oscillator 3 and converts it into a first intermediate frequency signal S2. Here, the first local oscillator 3 is frequency-corrected by the reference signal S7 from the reference oscillator 4. The reference signal S7 is also supplied to the transmitter 5 and serves as a reference for the transmission frequency. The first intermediate frequency signal S2 is converted into the second intermediate frequency signal S3 by the second frequency mixer 6. Here, the second local oscillation signal S6 generated by the second local oscillator 7 is used as the local oscillation signal.

The second intermediate frequency signal S3 is FM demodulated by the frequency discriminator 8 and converted into a baseband signal S4. On the other hand, the second intermediate frequency signal S3 is supplied to the frequency dividing circuit (1) 9 and divided (S8), and then input to the phase comparator 10. Further, the reference signal S7 from the reference oscillator 4 is also supplied to the frequency dividing circuit (2) 11 to be divided (S10), and then input to the phase comparator 10. Here, the respective frequency division numbers by the frequency dividing circuits 9 and 11 are selected so that the frequencies can be compared by the phase comparator 10. This phase comparator 10
Is the result of frequency (phase) comparison (also called error signal)
Is converted into a DC voltage, that is, a first analog signal S9, which is fed back to the reference oscillator 4 as a control voltage. Then, the reference signal S7 generated by the reference oscillator 4 is frequency-corrected with reference to the frequency of the received high-frequency signal S1, and according to this correction, the first local oscillator 3 generates the first signal S7.
As a result of the frequency correction of the local oscillation signal S5, the second intermediate frequency signal S3 supplied to the frequency discriminator 8 is feedback-corrected so as to have an appropriate frequency for FM demodulation.

Since this wireless communication device is a mobile station, it is required to be small and lightweight, and it is difficult to provide the reference oscillator 4 with sufficient frequency stability. Therefore, in this wireless communication device, the frequency of the reference signal S7 is corrected with reference to the received high-frequency signal with high frequency stability transmitted from the base station,
FM with good quality by eliminating frequency fluctuations of intermediate frequency signals
It enables demodulation. Here, the error signal (first analog signal S9) from the phase comparator 10 is a combination of deviations from the desired frequencies in the first local oscillation signal S5 and the second local oscillation signal S7.

[Problems to be solved by the invention]

The above-described conventional wireless communication device has a drawback in that the frequency of the reference oscillator cannot be corrected unless the received high frequency signal is present. That is, if this wireless communication device enters a tunnel or a large building, the reception of high frequency signals is interrupted, but in such a state, the frequency correction operation of the reference oscillator 4 is also interrupted, and this device again transmits the high frequency signal. Even if received, the frequency of the reference signal from the reference oscillator was not controlled at the beginning of the re-reception, and there was a risk that the device would lose good reception due to an inappropriate frequency of the local oscillation signal.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and to continue the frequency correction of the reference signal or the local oscillation signal which may have a large frequency deviation even if the input of the received high frequency signal is interrupted. Accordingly, it is an object of the present invention to provide a wireless communication device capable of extending the favorable reception period of the high frequency signal.

[Means for solving problems]

A wireless communication device of the present invention includes a frequency mixer that mixes a received high-frequency signal and a local oscillation signal to generate an intermediate frequency signal, and an oscillator that generates the local oscillation signal whose frequency is controlled by a reference signal generated by itself. A comparator for comparing the intermediate frequency signal with the reference signal to generate a first analog signal as a result of the comparison, and performing a feedback control of the frequency of the reference signal by the first analog signal. In a wireless communication device, an AD converter for converting the first analog signal into a digital signal, and updating and storing the digital signal when the intermediate frequency signal exists, and storing the digital signal when the intermediate frequency signal does not exist A memory circuit for stopping the memory update of the digital signal, and converting the stored digital signal into a second analog signal. The analog signal further comprises a D-A converter to be applied to the oscillator as the first analog signal.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.
In this wireless communication device, components having the same reference numerals as those of the conventional wireless communication device shown in FIG. 2 have the same functions as those in FIG. The received high-frequency signal S1 that has passed through the antenna and the high-frequency filter section is supplied from the input terminal 1 to the first frequency mixer 2, and the first local oscillation signal S5 from the first local oscillator 3 becomes the first intermediate frequency signal S2. To be converted.

Here, the first local oscillator 3 is frequency-corrected by the reference signal S7 from the reference oscillator 4. This reference signal S7
Is also a reference for the transmission frequency of the transmitter 5. The above-mentioned first intermediate frequency signal S2 is converted into the second intermediate frequency signal S3 by the second frequency mixer 6. The second local oscillation signal here is as described with reference to FIG.
It is generated independently by the second local oscillator 7 (S6), or the doubled output (S6a) of the reference signal S7 is used. The second intermediate frequency signal S3 is converted into a baseband signal S4 by the frequency discriminator 8.

The second intermediate frequency signal S3 is supplied to the frequency dividing circuit (1) 9 and divided (S8), and then input to the phase comparator 10. Further, after the reference signal S7 from the reference oscillator 4 is also supplied to the frequency dividing circuit (2) 11 and divided (S10),
It is input to the phase comparator 10. Here, the frequency dividing circuit 9 and
Each frequency division number by 11 is selected to be a frequency that can be compared by the phase comparator 10.

The DC voltage output from the phase comparator 10, that is, the first analog signal S9 is supplied to the AD converter 12. The first analog signal S9 is converted into a digital value (digital signal S14) by the AD converter 12, and then input to the storage circuit 13 and stored therein. In the description here, the first analog signal S9 is directly supplied to the AD converter 12 without passing through the delay circuit 16. The digital value (digital signal) S13 stored in the storage circuit 13 is the DA converter 14
Is read out, converted into an analog voltage (second analog signal) S12, and fed back to the reference oscillator 4. The frequency of the reference signal S7 generated by the reference oscillator 4 is feedback-corrected by using this feedback voltage (second analog signal S12) as a control voltage.

Here, in the memory circuit 13, the second feedback voltage to the reference oscillator 4, that is, the second voltage for controlling the frequency of the reference signal S7 is controlled.
Analog signal S12 corresponding digital signal S13, control signal
It is stored under the control of S11.

For example, when the desired input high frequency signal S1 is no longer present, such as when the input input electric field disappears, or when the frequency of the received high frequency signal S1 is abnormal, that is, the frequency discriminator 8 receives the second intermediate signal. When the frequency signal is no longer supplied, the memory circuit 13 stores the frequency correction information of the digital signal S13 received immediately before this, that is, the reference signal S7 based on the control information of the control signal S11, and the reference oscillator 4 The frequency can be constantly corrected based on the digital signal S13.

The control signal S11 is specifically the second intermediate frequency signal S
There are two states depending on the level of 3. That is, the second
When the level of the intermediate frequency signal S3 is larger than a predetermined threshold value, the control signal S11 updates the digital signal S13 stored in the storage circuit 13, while when the level is smaller than the threshold value, the storage circuit 13 Digital signal stored in S13
Stop updating.

Therefore, in this wireless communication device, when the intermediate frequency signal S3 or the received high frequency signal S1 is present, the AD converter is used.
The digital signal S14 from 12 passes through the storage circuit 13 as it is, and the DA converter 14 outputs the second analog signal S12.
And is supplied to the reference oscillator 4.

On the other hand, when the desired intermediate frequency signal S3 or the received high frequency signal S1 disappears, the updating function of the memory circuit 13 is stopped, and the stored contents (digital signal S1
3) is supplied to the reference oscillator 4 through the DA converter 14.

That is, in this wireless communication device, the frequency of the reference oscillator 4 is continuously corrected with the latest correction information.

Here, the judgment as to whether the memory update of the memory circuit 13 is continued or stopped should be made before the memory content (first digital signal S14) is inputted to the memory circuit 13. Therefore, the delay circuit 16 is provided between the phase comparator 10 and the AD converter 12.
And delays the first analog signal S9 to form a delayed analog signal S15.
The method of supplying the converter 12 and controlling the memory update of the memory circuit 13 by the control signal S11 that does not pass through the delay circuit 16 is a further development of the wireless communication device having the above-mentioned circuit configuration.

〔The invention's effect〕

As described above, according to the present invention, the first analog signal for feedback control of the reference signal is converted into a digital signal by the AD converter, and the memory circuit updates the digital signal when the intermediate frequency signal exists. Then, when the intermediate frequency signal does not exist, the memory update of the digital signal is stopped, and the D / A converter converts the stored digital signal into a second analog signal. Since the signal is added to the oscillator that generates the reference signal as the first analog signal, the advantage of using the oscillator of the reference signal having poor frequency stability in the prior art can be utilized, and the input of the desired received high frequency signal is eliminated. Even if the intermediate frequency signal disappears for a long period of time due to the above reasons, etc. It can continue to frequency correction of the reference signal, i.e. a local oscillation signal generated with the oscillator based on the digital signal stored in, and thus, there is an effect that it extends the good reception period of the received high frequency signal.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a wireless communication device of the present invention, and FIG. 2 is a block diagram of a conventional wireless communication device. 1 ... Input terminal, 2 ... First frequency mixer, 3 ... First
Local oscillator, 4 ... Reference oscillator, 5 ... Transmitter, 6 ...
2nd frequency mixer, 7 ... 2nd local oscillator, 8 ... frequency discriminator, 9 ... frequency divider circuit (1), 10 ... phase comparator, 11 ... frequency divider circuit (2), 12 ... AD converter, 13 ... memory circuit, 14 ... DA converter, 16 ... delay circuit.

Claims (2)

[Claims] 1. A frequency mixer that mixes a received high frequency signal and a local oscillation signal to generate an intermediate frequency signal, an oscillator that generates the local oscillation signal whose frequency is controlled by a reference signal generated by itself, and the intermediate signal. A radio communication device of a system which has a comparator for comparing a frequency signal with the reference signal and produces a first analog signal as a result of the comparison, and which feedback-controls the frequency of the reference signal by the first analog signal. , An AD converter for converting the first analog signal into a digital signal, and updating and storing the digital signal when the intermediate frequency signal exists, and storing the digital signal when the intermediate frequency signal does not exist. A memory circuit for stopping memory update, and a second analog signal for converting the stored digital signal into a second analog signal. Further comprising a wireless communication device and a D-A converter to be applied to the oscillator as the first analog signal. 2. A delay circuit for delaying the first analog signal is interposed between the comparator and the A / D converter, and a delay circuit is provided. Wireless communication device.