JPH07326932A - Local oscillation circuit for digital radio equipment - Google Patents

Abstract

PURPOSE:To improve communication quality by highly accurately correcting a local oscillation frequency, to simplify and miniaturize circuit constitution and to reduce cost by eliminating the need of a complicated oscillation circuit and expensive parts. CONSTITUTION:Reception frequency synthesizers 22 and 26 are provided as local oscillation means for reception frequency conversion and a frequency divider circuit 27 is provided as the local oscillation means for quadrature dentodulation. In the reception frequency synthesizers 22 and 26 and the frequency divider circuit 27, based on reference frequency signals BS generated from one reference oscillator 21, respective local oscillation signals LO1, LO2, LOI and LOQ are generated and mixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local oscillator circuit provided in a digital wireless device such as a digital automobile / mobile phone, a digital cordless phone and the like.

[0002]

2. Description of the Related Art In recent years, in wireless communication systems such as mobile wireless communication systems, systems adopting a digital modulation / demodulation system have been operated. This type of system digitally transmits not only control signals but also communication contents such as call voice signals when wireless communication is performed between a base station and a mobile station. It is possible to improve the compatibility with and effectively use radio frequency.

FIG. 2 is a circuit block diagram showing the configuration of a radio circuit section of a digital radio used as a mobile station in this type of system. In the figure, a radio frequency signal arriving via a radio line is received by an antenna 1, then input to a high frequency amplifier 3 via an antenna duplexer (DUP) 2, amplified by the high frequency amplifier 3, and further subjected to a high frequency filter. It is input to the first mixer 5 via 4. In the first mixer 5, the received radio frequency signal is mixed with the first local oscillation signal LO1 and thereby frequency-converted into the first intermediate frequency signal IF1. The first local oscillation signal LO1 has a phase difference of 90 ° with each other, and is generated by the reception frequency synthesizer 22 including a PLL circuit using the oscillation signal BS of the first crystal oscillator 21 as a reference frequency signal. The first intermediate frequency signal IF1 output from the first mixer 5 is input to the second mixer 7 after the unnecessary wave component is removed by the intermediate frequency filter 6. Then, in the second mixer 7, it is mixed with the second local oscillation signal LO2 and frequency-converted into a second intermediate frequency signal IF2 having a lower frequency than the first intermediate frequency signal IF1. The second local oscillation signal L
O2 is generated from an independent second crystal oscillator 23.

The second intermediate frequency signal IF2 output from the second mixer 7 has its unnecessary wave component removed by a band pass filter (not shown) and is amplified by an intermediate frequency amplifier, and then quadrature demodulator (Q -DEM) 8. The quadrature demodulator 8 includes a distributor 9 and two mixers 10I and 10Q. Then, the second intermediate frequency signal IF2 branched into two by the distributor 9 is supplied to each mixer 1
Local oscillation signal LO for quadrature demodulation at 0I and 10Q
Received baseband signal RS by mixing with I and LOQ
Demodulate to I and RSQ. The local oscillation signals LOI and LOQ for quadrature demodulation are generated from an independent third crystal oscillator 24. The demodulated received baseband signal RS
The I and RSQ are input to a digital signal processing circuit (DSP) 11 and decoded into data by the DSP 11.

On the other hand, the transmission baseband signal TS
The I and TSQ are input to the quadrature modulator (Q-MOD) 12. The quadrature modulator 12 includes two mixers 13I and 13I.
It has a Q and a synthesizer 14. Then, the transmission baseband signals TSI and TSQ are transferred to the mixers 13I and 1
Local oscillation signals TLI and TLQ for quadrature modulation in 3Q
Respectively, and thereby converted into a transmission radio frequency signal. Local oscillation signals TLI, T for quadrature modulation
The LQs have a phase difference of 90 ° with each other, and are the first
The oscillation signal BS of the crystal oscillator 21 is generated as a reference frequency signal by the transmission frequency synthesizer 25 including a PLL circuit. The transmission radio frequency signals output from the mixers 13I and 13Q are combined by the combiner 14 and power-amplified by the transmission power amplifier 15, and then transmitted from the antenna 1 to the wireless line via the antenna duplexer 2. It

By the way, in a digital radio equipment adopting the QPSK system as a modulation / demodulation system, if the frequencies of the receiving local oscillation signals LO1, LO2, LOI, and LOQ deviate,
There is a risk that the phase will rotate on the orthogonal plane and the data will be erroneous.
Therefore, in this type of wireless device, for example, as shown in FIG. 2, the first crystal oscillator 21 is configured by a voltage-controlled temperature-compensated crystal oscillator (VCTCXO). And DSP
In 11, the frequency error is detected from the amount of rotation of the phase of the received baseband signal, and the control voltage VS for making the frequency error zero is generated and supplied to the first crystal oscillator 21. The frequency of LO1 is corrected.

[0007]

However, when the local oscillation frequency is corrected in this way, the conventional radio device described above has the following problems. That is, the conventional radio device has the first local oscillation signal LO1, the second local oscillation signal LO2, and the local oscillation signals LOI and LO for quadrature demodulation.
Q is generated by using independent crystal oscillators 21, 23 and 24. Therefore, the DSP
In addition to the oscillation frequency error of the first crystal oscillator 21, the frequency shift detected in 11 includes the second crystal oscillator 2
Since the oscillation frequency error of the third and third crystal oscillators 24 is included, it is difficult to perform highly accurate frequency correction.

Further, the above-mentioned defect in frequency correction has a bad influence particularly on the transmission system as follows. That is, the local oscillation signal TLI for quadrature modulation supplied to the quadrature modulator 12,
The TLQ is generated by the transmission frequency synthesizer 25 with the oscillation frequency BS of the first crystal oscillator 21 as a reference frequency. Therefore, as described above, the oscillation frequency BS of the first crystal oscillator 21 is set to the local oscillation frequency LO.
If corrected by the information including the frequency error of 1, LO2, LOI, and LOQ, the frequency of the transmission radio frequency signal output from the quadrature modulator 12 becomes equal to that of the second crystal oscillator 23 and the third crystal oscillator 24. The frequency deviates from the specified frequency by an amount corresponding to the oscillation frequency error. This is very unfavorable because it causes deterioration of reception characteristics at the base station of the communication partner.

On the other hand, in order to reduce such problems,
Conventionally, for example, as shown in FIG.
Instead of the above, a reception frequency synthesizer 26 is provided, and in this reception frequency synthesizer 26, the first crystal oscillator 2
It is considered to generate the second local oscillation signal LO2 with the oscillation frequency BS of 3 as the reference frequency. With such a configuration, the first and second local oscillation signals LO1, which account for a large proportion of the frequency error detected by the DSP 13,
Since the frequency error of LO2 can be corrected at the same time, the shift width of the transmission frequency is greatly reduced.

However, even with such a configuration, an independent high-precision crystal oscillator 24 is still used as an oscillator for generating the local oscillation signals LOI and LOQ for quadrature demodulation, so that the circuit scale is large. There was a problem that it was unavoidable that the size and cost of parts increased.

The local oscillation signal LO for quadrature demodulation is used.
It is also conceivable that a frequency synthesizer is also used as an oscillator for generating I and LOQ, and the frequency synthesizer is configured to generate the local oscillation signals LOI and LOQ using the oscillation frequency BS of the first crystal oscillator 21 as a reference frequency. . However, such a configuration is not suitable for practical use because the circuit configuration becomes more complicated than when the crystal oscillator 24 is used.

The present invention has been made in view of the above circumstances. An object of the present invention is to improve the communication quality by correcting the local oscillation frequency with high accuracy, and to improve the complexity of the oscillation circuit and the cost. Another object of the present invention is to provide a local oscillating circuit for a digital radio, which can simplify the circuit structure and reduce the cost by eliminating the need for various parts.

[0013]

In order to achieve the above object, the present invention provides a baseband signal by converting a received radio frequency signal into an intermediate frequency signal by a frequency conversion circuit and then demodulating it by an orthogonal demodulation circuit. In a local oscillating circuit of a digital radio having a circuit system for reproducing, a voltage control reference oscillating means for generating a reference frequency signal having a frequency according to a control voltage is provided and a frequency controlling means is provided. A frequency error is detected from the baseband signal reproduced by the quadrature demodulation circuit, a control voltage for reducing the frequency error is generated based on the detected frequency error, and the control voltage is supplied to the reference oscillation means.
Further, a first local oscillating means for frequency conversion and a second local oscillating means for quadrature demodulation are provided, and based on the reference frequency signal generated by the reference oscillating means, the first local oscillating means A local oscillation signal for frequency conversion is generated and supplied to the frequency conversion circuit, and the reference frequency signal generated by the reference oscillation means is frequency-divided by the second local oscillation means to localize for orthogonal demodulation. An oscillating signal is generated and supplied to the quadrature demodulation circuit.

[0014]

As a result, according to the present invention, both the local oscillation signal for frequency conversion and the local oscillation signal for quadrature demodulation are generated based on the common reference frequency signal generated from one reference oscillation means. It Therefore, the frequency error included in the demodulated baseband signal is only the component due to the reference oscillating means, and can be reliably eliminated by the frequency control. Moreover, since the second local oscillating means for generating the local oscillating signal for quadrature demodulation is composed of a frequency divider, it is not necessary to use expensive circuit parts as in the case of using a crystal oscillator, and the frequency can be reduced. It does not require a complicated and large-scale circuit as in the case of using a synthesizer.
Therefore, the circuit configuration can be simplified and downsized, and the cost can be reduced.

[0015]

1 is a circuit block diagram showing the configuration of a digital radio device having a local oscillation circuit according to an embodiment of the present invention. In the figure, the same parts as those in FIG.

The local oscillator circuit of this embodiment includes one reference oscillator 21. The reference oscillator 21 is a high-precision oscillator that uses a voltage-controlled temperature-compensated crystal oscillator (VCTCXO), and generates a reference frequency signal BS having a frequency according to the control voltage VS. The reference frequency signal BS generated by the reference oscillator 21 is supplied to the reception frequency synthesizers 22 and 26 and the transmission frequency synthesizer 25, as well as to the frequency dividing circuit (÷ N) 27.

The reception frequency synthesizer 22 is responsive to a frequency division variable signal corresponding to a radio reception channel from a control circuit (not shown) to generate a first local oscillation signal based on the reference frequency signal BS generated by the reference oscillator 21. LO1 is generated, and this first local oscillation signal LO1 is supplied to the first mixer 5.

The reception frequency synthesizer 26 has a second local oscillation signal LO2 based on the reference frequency signal BS generated by the reference oscillator 21 in accordance with a predetermined frequency division number.
Is generated and the second local oscillation signal LO2 is supplied to the second mixer 7.

The frequency dividing circuit 27 divides the frequency of the reference frequency signal BS generated by the reference oscillator 21 by N to generate local oscillation signals LOI and LOQ for quadrature demodulation. The local oscillation signals LOI and LOQ have mutually orthogonal phases, and each of the mixers 1 of the orthogonal demodulator 8 is
It is supplied to 0I and 10Q.

The transmission frequency synthesizer 25 has a phase orthogonal to each other based on the reference frequency signal BS generated by the reference oscillator 21 in response to a frequency division variable signal corresponding to a radio transmission channel from a control circuit (not shown). The two local oscillation signals TLI and TLQ for quadrature modulation are generated, and the local oscillation signals TLI and TLQ for quadrature modulation are supplied to the mixers 13I and 13Q of the quadrature modulator 12, respectively.

The digital signal processing circuit (DSP) 11 performs signal processing for decoding data from the demodulated baseband signals RSI and RSQ output from the quadrature demodulator 8 and also demodulated baseband signal R.
A frequency error is detected from the phase shift between SI and RSQ.
Then, a control voltage VS for making the frequency error zero is generated based on the detected frequency error, and the control voltage VS is supplied to the reference oscillator 21.

With such a configuration, the reference frequency signal BS generated from one reference oscillator 21 is supplied to each of the reception frequency synthesizers 22 and 26 for frequency conversion and the frequency dividing circuit 27. Then, in the reception frequency synthesizers 22 and 26 and the frequency dividing circuit 27, the first and second reception local oscillation signals LO1 and LO2 and the local oscillation signal LOI for quadrature demodulation, respectively, based on the reference frequency signal BS. LOQ is generated and supplied to the mixers 5, 7, 10I, 10Q, respectively. Therefore, in the first and second mixers 5 and 7, the reception local oscillation signals LO1 and L synchronized with the reference frequency signal BS, respectively.
The radio frequency signal is frequency-converted by O2, and the mixers 10I and 10Q of the quadrature demodulator 8 receive local oscillation signals LOI and LO synchronized with the reference frequency signal BS.
Quadrature demodulation of the received intermediate frequency signal IF2 is performed by Q. The baseband signals RSI and RSQ demodulated by the quadrature demodulator 8 are decoded into reception data by the DSP 11, and frequency error information is detected.

Here, the local oscillation signals LO1, LO2, LOI, LO used for the above frequency conversion and quadrature demodulation.
Q is a common reference frequency signal B as described above.
It is generated based on S. Therefore, the frequency error components included in the demodulated baseband signals RSI and RSQ are
Only the frequency error of the reference frequency signal BS is obtained. Therefore, in the DSP 11, the demodulated baseband signal R
When the oscillation frequency of the reference oscillator 21 is corrected based on the frequency error information detected from SI and RSQ, the frequency error included in the demodulated baseband signals RSI and RSQ is almost completely erased.

Further, the reception frequency synthesizer 2 for transmission
In 5, the local oscillation signals TLI and TLQ for quadrature modulation are generated based on the corrected reference frequency signal BS. For this reason, in the quadrature modulator 12, the transmission baseband signal TSI,
The TSQ is quadrature-modulated and wirelessly transmitted. For this reason,
A transmission radio frequency signal including no frequency deviation of the local oscillation signal is transmitted to the base station.

As described above, in this embodiment, the receiving frequency synthesizers 22 and 2 are used as the local oscillating means for converting the receiving frequency.
6 and a frequency dividing circuit 27 is provided as a local oscillating means for quadrature demodulation, and in these receiving frequency synthesizers 22, 26 and frequency dividing circuit 27, a reference frequency signal BS generated from one reference oscillator 21 is generated. On the basis of this, the local oscillation signals LO1, LO2, LOI, LOQ are respectively generated and used for mixing.

Therefore, the demodulated baseband signal RS
The frequency error component contained in I and RSQ can be only the frequency error of the reference frequency signal BS, so that if the oscillation frequency of the reference oscillator 21 is variably controlled based on the frequency error, the reference of the reference oscillator 21 can be changed. It is possible to surely correct the frequency shift of the frequency signal BS. Further, by doing so, it is possible to eliminate the frequency error of the local oscillation signals TLI and TLQ for quadrature modulation generated based on the reference frequency signal BS, and thereby to prevent the frequency deviation of the transmission radio frequency signal from occurring. it can.

Further, in the present embodiment, since the frequency dividing circuit 27 is used as the local oscillating means for quadrature demodulation as described above, the cost can be reduced as compared with the case where the crystal oscillator is used. In addition, the circuit configuration can be simplified and downsized as compared with the case where the frequency synthesizer is used.

The present invention is not limited to the above embodiment. For example, although the reception frequency synthesizer 26 is used as the circuit for generating the second local oscillation signal LO2 in the above embodiment, a frequency multiplication circuit may be used instead of the frequency synthesizer. With this configuration, the circuit configuration can be further simplified and downsized.

In the above embodiment, the double superheterodyne receiver circuit has been described as an example, but the present invention can also be applied to a single superheterodyne receiver circuit.
In addition, regarding the types and configurations of digital radios,
Various modifications can be implemented without departing from the scope of the present invention.

[0030]

As described in detail above, according to the present invention, the voltage control reference oscillating means for generating the reference frequency signal having a predetermined frequency and the frequency control means are provided, and the quadrature demodulation circuit is provided by the frequency control means. A frequency error is detected from the baseband signal reproduced by, and the oscillation frequency of the reference oscillating means is feedback-controlled based on the detected frequency error, and further a first local oscillating means for frequency conversion is provided, Second local oscillation means for quadrature demodulation is provided, and the first local oscillation means generates a local oscillation signal for frequency conversion based on the reference frequency signal generated by the reference oscillation means to generate the frequency. The reference frequency signal generated by the reference oscillating means is frequency-divided by the second local oscillating means while being supplied to the converting circuit, and the local oscillation for quadrature demodulation is performed. It generates No., and the local oscillation signal is then supplied to the quadrature demodulation circuit.

Therefore, according to the present invention, the local oscillation frequency can be corrected with high accuracy, and a complicated oscillation circuit and expensive parts can be eliminated, thereby improving the communication quality and improving the circuit configuration. It is possible to provide a local oscillating circuit of a digital wireless device that enables simple size reduction and cost reduction.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a digital wireless device including a local oscillator circuit according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram showing an example of a configuration of a digital radio device including a conventional local oscillation circuit.

FIG. 3 is a circuit block diagram showing another example of the configuration of a digital radio device including a conventional local oscillation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... Antenna duplexer (DUP) 3 ... High frequency amplifier 4 ... High frequency filter 5 ... 1st mixer 6 ... Intermediate frequency filter 7 ... 2nd mixer 8 ... Quadrature demodulator (Q-DEM) 9 ... Distributor 10I, 10Q ... Mixer 11 ... Digital signal processing circuit (DSP) 12 ... Quadrature modulator (Q-MOD) 13I, 13Q ... Mixer 14 ... Combiner 15 ... Transmission power amplifier 21 ... Reference oscillator (first crystal oscillator) 22 , 26 ... Frequency conversion reception frequency synthesizer 23 ... Second crystal oscillator 24 ... Third crystal oscillator 25 ... Transmission frequency synthesizer 27 ... Dividing circuit BS ... Reference frequency signal LO1 ... First local oscillation signal LO2 ... 2 local oscillation signal LOI, LOQ ... local oscillation signal for quadrature demodulation TLI, TLQ ... local oscillation signal for quadrature modulation VS ... oscillation frequency control Pressure

Claims (1)

[Claims] 1. A local oscillating circuit of a digital radio having a circuit system for frequency-converting a received radio frequency signal into an intermediate frequency signal by a frequency conversion circuit and then demodulating by a quadrature demodulation circuit to reproduce a baseband signal. , A voltage-controlled reference oscillating means for generating a reference frequency signal having a frequency according to the control voltage, and a local oscillation signal for frequency conversion based on the reference frequency signal generated by the reference oscillating means. First local oscillation means for supplying the frequency conversion circuit to the frequency conversion circuit, and the reference frequency signal generated by the reference oscillation means is frequency-divided to generate a local oscillation signal for quadrature demodulation. Second local oscillating means for supplying to the quadrature demodulation circuit, and a frequency error is detected from the baseband signal reproduced by the quadrature demodulation circuit. Local oscillation circuit of the digital radio characterized by comprising a frequency control means for the control voltage is generated and supplied to the reference oscillation means for reducing the frequency error based on the frequency error.