KR910005652B1 - Simultaneous bidirectional fm transmitter-receiver - Google Patents

Abstract

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Description

Simultaneous 2-Way FM Transceiver

1 is a block diagram showing the configuration of one embodiment of the present invention;

2 is a block diagram showing a circuit configuration of a radio section of a mobile device of a conventional cordless telephone.

* Explanation of symbols for main parts of the drawings

1: Duplexer 2: RF Amplifier

3: bandpass filter (BPF) 4: first mixer

5: first IF bandpass filter 6: first mixer

7: second IF bandpass filter 8: IF amplifier

9: MF detector 10: AF amplifier

11: second local oscillator 12: voltage controlled oscillator (VCO)

13: Prescaler 14: Variable Divider

15: Phase Comparator 16: Low Pass Filter (LPF)

17: voltage controlled oscillator (VCO) 18: prescaler

19: variable divider 20: phase comparator

21: Low Pass Filter (LPF) 22: Reference Oscillator

23: reference divider 24: channel control circuit

25: AF amplifier 26: RF power amplifier

27: voltage controlled oscillator (VCO) 28: prescaler

29: variable divider 30: phase comparator

31: Low Pass Filter (LPF) 32: First IF Band Pass Filter

33: 2nd IF bandpass filter PLL ₁ : Receiving PLL synthesizer

PLL ₂ : Transmit PLL synthesizer (first PLL synthesizer)

PLL ₃ : PLL synthesizer for second local oscillation (second PLL synthesizer)

ANT: Antenna terminal

The present invention relates to a simultaneous two-way FM transceiver best suited for code less telephones and the like.

In recent years, there is a desire to spread a cordless telephone that can be freely carried and transported at a short distance, such as indoors.

A cordless telephone is composed of a fixing device connected to a telephone line and a mobile device connected to the fixing device wirelessly, and simultaneously performs upward wireless transmission between the fixing device and the mobile device.

As for the radio transmission frequency band used for a cordless telephone, for example, in Europe, the transmission / reception frequency from a fixed device is set to 959-960 MHz, and the transmission frequency from a mobile device is 914-915 MHz. In other words, the transmission frequency interval is 45 MHz.

As a channel, 40 channels are assigned at intervals of 25 MHz. In the channel operation, an MCA (Multi Channel Access) method is employed, and a channel control circuit for automatically selecting an empty channel and performing bidirectional transmission at the same time is incorporated in the fixed and mobile devices. Here, the outline operation at the start of connection by the MCA method will be described.

First, when the communication is not performed, the fixture and the mobile unit simultaneously display a specific channel called a control channel (for example, the transmission frequency at the fixing unit is 959.5 MHz and the transmission frequency at the mobile unit is 914.5 MHz). The receiving circuit is operated to receive, and the mobile device waits and receives a transmission signal transmitted from the fixed device by the incoming call from the telephone line.

For example, when there is an incoming call from the telephone line, the fixed channel selects an empty channel, and then the control channel selects an identification code assigned by combining the fixed group and the mobile unit, and an operating channel code specifying the selected empty channel. Transmits and switches to the operating channel.

On the other hand, the mobile device designated by the identification code receives the operation channel code, switches from the control channel to the operation channel, rings the call bell, and moves to the call state.

After that, when the call termination operation is performed on the mobile unit side, the stationary unit and the mobile unit come back to the standby state in the control channel together.

In addition, in order to reduce the congestion of the use of the control channel, the transmission time in the control channel is limited to within 1 second for transmission from the mobile device and within 4 seconds for transmission from the fixed device, and the control channel is used by other cordless telephones. If it is busy, the transmission is waited for its termination. 2 is a block diagram showing a circuit configuration of a radio section of a conventional mobile unit.

First, the reception unit will be described.

The received signal input to the antenna terminal ANT is divided by the duplexer 1 and input to the RF (high frequency) amplifier 2. The output of the RF amplifier 2 is input to the RF input terminal of the first mixer 4 through a band pass filter 3 which passes the reception frequency bands 959 to 960 MHz.

In the locally cut input terminal of the first mixer 4, the output signal of the VCO (voltage controlled oscillator) 12 constituting the receiving PLL synthesizer PLL ₁ described below is input, and frequency mixing is performed. Only a predetermined frequency component is passed through the first IF (intermediate frequency) bandpass filter 5 within the range of the output to obtain a first IF signal.

If the center frequency of the reception channel is 959.5 MHz, for example, the output frequency of the VCO 12 is 948.8 MHz, and the frequency of the first IF signal is 10.7 MHz.

The first IF signal is input to the RF input terminal of the second mixer 6 and mixed with the local oscillation signal of 10.245 MHz supplied from the second local oscillator 11.

As a result, a second IF signal of 455 KHz is obtained. Here, the second local oscillator 11 is composed of a crystal oscillation circuit, and its output is input to the local oscillation input terminal of the second mixer 6.

The second IF signal is input to the second IF band pass filter 7 to remove the interference signal in the adjacent channel band. This second IF signal is amplified by the IF amplifier 8, FM demodulated by the FM detector 9, and amplified by the AF (low frequency) amplifier 10, and then supplied to a receiver (not shown).

Next, the transmitter will be described. The output signal of the VCO 17 constituting the transmission PLL synthesizer PLL ₂ described later is a value 45 MHz lower than the reception frequency, for example, 914.5 MHz, amplified by the RF power amplifier 26, and the duplexer 1 ) Is entered.

Then, due to the branching operation of the duplexer 1, since it is not transmitted to the receiver, it is transmitted to the antenna terminal ANT as a transmission signal.

Next, the reception PLL synthesizer PLL ₁ and the transmission synthesizer PLL ₂ will be described.

The reception PLL synthesizer PLL ₁ is composed of a VCO 12, a prescaler 13, a variable divider 14, a phase comparator 15, and a low pass filter 16. 15, a reference frequency signal (frequency f _REF ) obtained by dividing the output of the reference oscillator 22 by the reference divider 23 is supplied.

If the reference frequency f _REF is 1.5625 KHz, for example, the division ratio P of the prescaler 13 is 16 and the division ratio N ₁ of the variable divider 14 is 37952, the VCO 12 The output frequency f _VCO is fixed as a frequency such that f _VCO = F _REF x P x N ₁ = 948.8 MHz.

Further, for example, by changing the division ratio N ₁ between 37932 and 37972, the output frequency f _VCO of the VCO 12 changes in 25 KHz steps between 948.3 and 949.3 MHz.

For this reason, the receiving PLL synthesizer PLL ₁ can achieve the desired function.

The PLL synthesizer PLL _{2 for} transmission is composed of a VCO 17, a prescaler 18, a variable divider 19, a phase comparator 20, and a low pass filter 21. The reference frequency signal commonly used with the reception PLL synthesizer PLL ₁ described above is supplied.

Here, when the existing frequency f _REF is 1.5625 KHz, the division ratio P of the prescaler 18 is 16 and the division ratio N ₂ of the variable divider 19 is 36580, the output of the VCO 17 is output. The frequency f _VCO is fixed at a frequency of 914.5 MHz.

Further, the frequency division ratio division ratio (N ₁₎ to (N ₂₎ as described in (37 932 to 37 972) lower than the value by (1800-428), that is, to write because varies between 36 560 to 36 600, the output of the VCO (17) The frequency f _VCO can be varied in 25 KHz steps between 914 and 915 MHz.

In addition, the value 1800 corresponds to the difference 45MHz of the reception frequency and the value 428 corresponds to the first IF frequency 10.7MHz.

The low frequency signal, which is an output signal of a transmitter (not shown), is supplied to the modulation input terminal MOD of the VCO 17 of the transmitting PLL synthesizer PLL ₂ through the AF (low frequency) amplifier 25, and this low frequency is applied. FM modulation is performed by the signal.

Further, since the time constant of the low pass filter 21 is set sufficiently larger than the period of the lowest frequency of the low frequency signal, the center frequency f _{OUT of the} modulated wave output from the VCO 17 is f _OUT = f _REF. A modulated FM wave is obtained as PLL-controlled by × P × N ₂ .

Next, the channel control circuit 24 is a circuit for selecting an empty channel at the time of transmission and reception, and is configured as an ac computer and a peripheral circuit thereof.

The channel control circuit 24 receives a state signal and a call detection signal of a hook switch (not shown), a signal proportional to the reception signal level from the IF amplifier 8, and an AF amplifier 10. The demodulation signal is input from

The output signal of the channel control circuit 24 includes a variable divider 14 and a variable divider for determining the frequency (channel) of the receiving PLL synthesizer PLL ₁ , the PLL synthesizer PLL _{2 for} transmission. 19), the use channel is selected while maintaining the relationship of division ratio N ₂ = N _1- (1800-428).

The above description of FIG. 2 is a description of the operation of the mobile station in which the reception frequency band is 959 to 960 MHz and the transmission frequency band is 914 to 915 MHz. And the circuit configuration is the same as that of FIG.

That is, in the same configuration as that in FIG. 2, the output frequency of the VCO 12 of the receiving PLL synthesizer PLL ₁ , namely. The frequency division ratio N ₁ of the variable divider 14, which determines the local oscillation frequency of the first mixer 4, is varied between 36132 and 36172, and is 903.3 to 904.3 MHz, which is 10.7 MHz lower than the reception frequency of 914 to 915 MHz. Get the local oscillation frequency of.

In addition, the division ratio N ₂ of the variable divider 19 for determining the output frequency of the VCO 17 of the transmission PLL synthesizer PLL ₂ is between 38360 and 38400, and N ₂ = N ₁ + (1800). While maintaining the relationship of +428, it is changed by the channel control circuit 24 so as to control the selection of the operating channel.

As a result, the fixing unit has a reception frequency band of 914 to 915 MHz, a transmission frequency band of 959 to 960 MHz, and bidirectional transmission is simultaneously performed with the mobile unit.

By the way, the conventional apparatus demonstrated above had the following faults.

( ₁ ) Since the first local oscillation frequency of the receiving synthesizer PLL ₁ is a frequency component close to the transmission / reception frequency, unnecessary spurious occurs.

( ₂ ) Since two PLL synthesizers (PLL ₁ ) and (PLL ₂ ) are required for reception and transmission, the circuit size becomes large (two prescalers, two variable dividers, etc. are required), and the current consumption of the circuit Grows

(3) When the transmission frequency component is mixed into its own first mixer 4 through the duplexer 1, a bead is generated due to a high level distortion of the transmission frequency component and the first local oscillation frequency component. .

In order to reduce such mixing, a high isolator value is required between the transmitting terminal and the receiving terminal of the duplexer 1.

As a result, the duplexer 1 is enlarged, and the insertion loss between the antenna terminal ANT and the transmitting terminal and between the antenna terminal ANT and the receiving terminal is increased.

The present invention has been made under such a background, and an object thereof is to provide a simultaneous bidirectional FM transceiver which solves the above problems.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention provides the 1st PLL synthesizer which outputs the 1st modulated frequency which was frequency-modulated as the low frequency signal to transmit, and the 2nd modulated wave which the frequency was modulated as the low frequency signal A second PLL synthesizer for outputting a first signal, a first mixer for inputting a first modulated wave of the first modulated wave and a high frequency received signal, and outputting a first intermediate frequency signal; and the first intermediate frequency signal and the first And a second mixer for inputting a second modulated wave and outputting a second intermediate frequency signal, wherein the carrier frequency of the first modulated wave is a transmission frequency assigned to the control channel in standby in the control channel. It is controlled to be different from.

According to the above configuration, the received signal and the first modulated wave are mixed in the first mixer, and the first intermediate frequency signal corresponding to the difference in the transmit / receive frequency is obtained.

Further, in the second mixer, the first intermediate frequency signal and the second modulated wave are mixed, and a second intermediate frequency signal is obtained.

In this manner, the first modulated signal corresponding to the transmission signal is used as the first local oscillation signal, and no bead of the transmission signal and the first local oscillation signal is generated. For this reason, the duplexer can be miniaturized.

In addition, the second PLL synthesizer that generates the second to-be-modulated wave (the second local oscillation signal) does not require a variable divider and operates at a low frequency, thereby miniaturizing and reducing power consumption. .

In addition, since the frequency of the second PLL synthesizer is far from the transmitting / receiving frequency and is low, the spurious emission as an unnecessary disturbance wave is reduced.

In addition, since the FM modulation is performed by the low frequency signal to be transmitted together with the first and second modulated waves, the amount of FM frequency shift caused by the low frequency signal included in the first intermediate frequency signal is defined as the first. In the two mixers, they are canceled out with the FM frequency deviation of the second modulated wave.

Therefore, the frequency shift amount of the second intermediate frequency signal can avoid the obstacle caused by the increase of the frequency shift amount as in the prior art (the detailed description thereof will be described later).

In addition, the frequency of the first PLL synthesizer is controlled at a frequency different from the frequency allocated to the control channel when waiting, so that it does not affect all devices in the waiting state of the control channel.

EXAMPLE

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

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In FIG. 1, the same reference numerals are used for the same parts as in the conventional example of FIG.

This embodiment differs from the prior art in that the output of the transmitting PLL synthesizer PLL ₂ is input to the local oscillation input terminal of the first mixer 4, and as the second local oscillator, a crystal oscillator circuit is provided. No PLL synthesizer (PLL ₃ ) for local oscillation is used. Therefore, the first IF frequency becomes 45 MHz, which is the difference between the transmission frequency and the reception frequency. As a result, the first IF bandpass filter 32 passes the 45 MHz band.

The first IF signal output from the first IF bandpass filter 32 is input to the second mixer 6, and is frequency-mixed with the output signal of the PL synthesizer PLL ₃ to be converted into a second IF signal.

The PLL synthesizer PLL ₃ is composed of a VCO 27, a prescaler 28, a variable divider 29, a phase comparator 30, and a low pass filter 31. A low-frequency signal applied to the modulation input terminal MOD of the PLL ₂ is commonly applied to the modulation input terminal MOD of the VCO 27. PLL _1. ) is the same configuration.

Here, for example, the reference frequency signal supplied from the reference divider 23 is 1.5625 KHz, the divider ratio P of the prescaler 28 is 16, and the divider ratio N ₃ of the variable divider 29 is represented. When it is set to 1782, the output frequency f _VCO of the VCO 27 is fixed as a frequency of 44.55MHZ.

Accordingly, the first IF signal of 45 MHz is converted into a second IF signal of 450 KHz, and is inputted to the second IF band pass filter 33 that passes the 450 KHz signal, thereby eliminating the interference signal of the adjacent channel band.

The first local oscillation signal (the first modulated wave) and the second local oscillation signal (the second modulated wave) are FM-modulated by the low-polarity signal to be transmitted, but are included in the first local oscillation signal. The FM modulation component is removed by the FM modulation component included in the second local oscillation signal, and the influence of the FM modulation by the low frequency signal is not shown in the second IF signal.

That is, the low frequency signal to be transmitted supplied to the modulation input terminal MOD of the VCO 17 (the first VCO) is also input to the modulation input terminal MDO of the VCO 27 so that the frequency shift amount of the FM modulation is applied to the VCO 17. In addition, the VCO 27 is FM-modulated to polarize the frequency shift in the second mixer 6 so as to eliminate the FM frequency shift due to the low frequency signal to be transmitted.

Further, since the time constant of the low pass filter 31 is set sufficiently larger than the synchronization of the lowest frequency of the modulated signal, the output center frequency f _OUT of the FM modulated VCO 27 is f _OUT = f _REF. The FM modulated wave is obtained as it is in the PLL controlled state at 占 R.

According to such a configuration, the maximum frequency shift amount of the received signal in the first IF signal (45 MHz) output from the first mixer 4 is the amount of FM frequency shift of the received signal and the amount of FM frequency shift of the own transmission signal. It becomes the sum of and, and the amount of deviation is twice that of the conventional example.

However, as described above, the frequency shift included in the first IF signal is eliminated by FM modulating the second local oscillation signal, and the maximum frequency shift amount of the received signal in the second IF signal is different from that of the conventional example. Similarly, the FM frequency shift amount of the received signal is obtained.

Therefore, it is not necessary to expand the passband of the second IF bandpass filter 7, the same passband as in the conventional example can be used, and demodulation can be performed without degrading the reception performance characteristic.

There is also a conventional method (not shown) which adds the self-modulated signal to the opposite polarity to the FM demodulated signal by using a fixed oscillator that does not FM modulate with the second local oscillator. It is necessary to extend the passband to a band equivalent to twice the amount of the FM frequency shift, and due to the influence thereof, reception characteristics such as adjacent channel selectivity are deteriorated. I can solve it.

Another feature of the simultaneous bi-directional FM transceiver according to the present invention lies in the frequencies of the transmission PLL synthesizer PLL ₂ and the second local oscillation PLL synthesizer PLL ₃ when waiting to receive no communication.

In other words, when waiting, the frequency of the PLL synthesizer PKPLL ₂ , in which only the function as the source of the first local oscillation signal is required, is set to a slightly different frequency compared to the transmission frequency assigned to the control channel.

For example, as in the description of the conventional example in the mobile unit, when the frequency division ratio N ₂ of the variable divider 19 is 36580, the frequency of the VCO 17 is 914.5 MHz, which is assigned to the mobile unit. Is equal to the transmitted frequency.

However, in the mobile device according to the present invention, when receiving and waiting, the division ratio N ₂ of the variable frequency divider 19 is not 36580, for example, 36581.

As a result, the frequency of the VCO 17 becomes 914.525 MHz, and the 959.5 MHz received signal is converted into a 44.975 MHz first IF signal.

At this time, the frequency of the second local oscillation PLL synthesizer PLL ₃ has the frequency division ratio N ₃ of the variable divider 29 set to 1781, so that the frequency of the VCO 27 becomes 44.525 MHz, and 44.975. The first IF signal of MHz is converted into a second IF signal of 450 KHz in the second mixer 6.

In addition, the frequency of the PLL synthesizer PLL ₂ at the time of waiting and receiving is at the transmission frequency of the control channel as long as the first IF signal generated by the frequency can pass through the bandpass filter 32 without any problem. The degree of falling is preferable, and the frequency of the PLL synthesizer PLL ₃ is set to convert the first IF signal into a second IF signal of a predetermined frequency, but the direction of increase and decrease of the frequency is determined by the PLL synthesizer PLL ₂ . The increase and decrease direction and the heterodyne method in the first mixer 4 and the second mixer 6 are set.

The control for changing the division ratios N ₂ and N ₃ of the variable dividers 19 and 29 at the time of communication in the control channel and at the time of waiting and receiving is input to the channel control circuit 24. It is made by the channel control circuit 24 in accordance with the status signal and the call detection signal of the hook switch.

In addition, the above-mentioned sharpness is a description of the mobile unit, but since the fixing unit is only a frequency relationship different from the mobile unit, the circuit configuration and operation are the same as the mobile unit.

In this way, when the output frequency of the transmission PLL synthesizer PLL ₂ in the control channel is different from the communication time when receiving and waiting, the output frequency of the transmission PLL synthesizer PLL ₂ becomes It is different from the transmission frequency, and thus it is possible to prevent the mobile and the fixed device from always in communication.

As described above, the present invention uses the first modulated wave corresponding to the transmission signal as the first local oscillation signal on the receiving side, and the second modulated wave subjected to the same modulation by the above-described transmission signal. Is used as the second local oscillation signal so that the above-described modulations of the transmission signal cancel each other, and the following effects can be obtained.

1. Since the frequency of the first local oscillation PLL synthesizer is far from the transmit / receive frequency and is a low frequency component, there is less spurious emission as an unnecessary disturbance wave.

2. A radio frequency PLL synthesizer with a variable divider is solved as one for transmission, and the second local oscillation PLL synthesizer has a low fixed frequency, so that the circuit scale is smaller than in the prior art. In addition, the circuit current consumption is also reduced.

3. Since the transmission frequency component and its first local oscillation frequency component are the same, the bead does not occur due to the high difference of distortion as in the conventional example, and the isolation required between the transmitting and receiving terminals of the duplexer is small. The size of the duplexer can be reduced, and the insertion loss can be reduced. When waiting on the control channel, the carrier frequency of the first modulated wave is controlled to be different from the transmission frequency assigned to the control channel.

4. It does not affect all devices on standby.

Claims (2)

A first PLL synthesizer PLL ₂ that outputs a first modulated frequency that has been frequency-modulated as a low frequency signal to be transmitted, and a second PLL synthesizer PLL ₃ that outputs a second modulated frequency that is frequency-modulated as the low-frequency signal And a first mixer 4 for inputting a part of the first modulated wave and a high frequency reception signal to output a first intermediate frequency signal, and the first intermediate frequency signal and the second modulated signal. And a second mixer 6 for inputting a wave and outputting a second intermediate frequency signal, transmitting the first modulated wave and demodulating a low frequency received signal from the second intermediate frequency signal. Simultaneous two-way FM transceiver. The simultaneous bi-directional FM transceiver of claim 1, wherein the carrier frequency of the first modulated wave is controlled at a frequency different from a transmission frequency assigned to the control channel when the carrier frequency waits in the control channel.

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