JPH07177051A - Fm radio telephone equipment - Google Patents

Abstract

PURPOSE:To not only improve the reception sensitivity and S/N but also effectively use the frequency by changing the local oscillation frequency so that the intermediate frequency is fixed and taking out the demodulation output from an LPF through a phase comparing circuit. CONSTITUTION:The reception signal from an antenna 1 has the amplitude limited by a limiter circuit 11 after passing the processings such as tuning, frequency conversion, and amplification, and the output has the frequency divided by a frequency dividing circuit 42 and is inputted to a phase comparing circuit 43. The reference frequency outputted from a reference frequency oscillating circuit 22 has the frequency divided by a frequency divider 44 and is inputted to the other end of the circuit 43. Phases of two frequencies are compared with each other by the circuit 43, and the output proportional to the extent of advance or delay of the output signal or the circuit 42, that is, the output including an audio signal is inputted to an LPF 45. Frequency components on the outside the audio band are eliminated by the LPF 45, and the output is inputted to a local oscillating circuit 8 as the frequency control voltage. In this constitution, the oscillation frequency of the circuit 8 is changed in accordance with the change of the reception signal in the PLL circuit consisting of circuits 8, 11, 42, 43, 45, etc., at the time of input of an FM reception signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM radiotelephone device, and more particularly to an FM radiotelephone device which can improve reception sensitivity and S / N ratio and can effectively use frequencies.

[0002]

2. Description of the Related Art Conventionally, in this type of FM radio telephone apparatus, a double super heterodyne system is generally known. FIG. 6 shows a block diagram of a receiving circuit of an FM wireless telephone device in the double super heterodyne system.

In FIG. 6, the received signal input from the antenna 1 is a band pass filter (hereinafter abbreviated as BPF).
2 is tuned by the high frequency amplifier circuit 3, mixed with the output of the first local oscillation circuit 5 by the first mixing circuit 4, and converted into the first intermediate frequency. The first intermediate frequency is mixed with the output of the second local oscillating circuit 8 in the second mixing circuit 7 via the BPF 6 and the second intermediate frequency is output.
Converted to intermediate frequency. Then, after passing through the BPF 9, the intermediate frequency amplifier circuit 10 amplifies the amplitude, the limiter circuit 11 limits the amplitude, and the demodulator circuit 12 demodulates the low pass filter 13 (hereinafter abbreviated as LPF) and the low frequency power amplifier circuit. A voice is output from the speaker 15 via 14.

As another conventional example, the one shown in FIG. 7 is known. FIG. 7 shows a block diagram of a transmission / reception circuit of an FM radiotelephone device in the double super heterodyne system. Instead of the first local oscillation circuit 5 in the reception circuit of FIG. 6, a phase locked loop (hereinafter abbreviated as PLL) circuit is shown. Is used to form the first local oscillation circuit 16.

In the first local oscillating circuit 16, the reference frequency output from the reference frequency oscillating circuit 22 and the frequency output from the voltage controlled oscillating circuit 17 (hereinafter abbreviated as VCO) are divided by the frequency dividing circuits 21 and 20, respectively. After that, it is input to the phase comparison circuit 19 and output from the phase comparison circuit 19 as an error signal. This error signal is supplied to the VCO 17 in the form of a voltage via the LPF 18, and outputs a stable frequency to the first mixing circuit 4.

On the other hand, in the transmitting circuit, the reference frequency output from the reference frequency oscillating circuit 22 is controlled by the PLL circuit, then amplified by the power amplifying circuit 34 and transmitted from the antenna 36. That is, the reference frequency output from the reference frequency oscillation circuit 22 is the frequency dividing circuit 30 and the phase comparison circuit 3.
1, the LPF 32, the VCO 33, and the power amplifier circuit 34, and the signal is transmitted from the antenna 36. At this time, VCO33
Is output to the phase comparison circuit 31 via the frequency dividing circuit 35.

[0007]

However, in the above-mentioned conventional FM radiotelephone device, the BPF 6 and the BP which are connected after the first mixing circuit 4 and the second mixing circuit 7, respectively.
The bandwidth of F9 is demodulated because the communication bandwidth required for FM waves is generally 2 (Δf _C + f _m ) or more, where Δf _C is the maximum frequency deviation and f _m is the modulation frequency. It was necessary to have a wide bandwidth above a certain value depending on the standard of output distortion.

Therefore, the sensitivity of the receiving circuit is restricted by the noise figure and the gain of the transistor in the input stage, and the receiving sensitivity cannot be improved beyond a certain value.

On the other hand, at present, improvements are being made in the direction of increasing the frequency utilization efficiency. However, if the maximum frequency deviation Δf _C and the modulation frequency f _m are left unchanged and only the bandwidth is narrowed, the distortion rate of the demodulation output will be reduced. There was a problem of deterioration.

In view of the above problems, the present invention improves the reception sensitivity and the S / N ratio without degrading the distortion rate of the demodulation output even when the bandwidth of the BPF in the intermediate frequency stage is narrowed, and the frequency It is an object of the present invention to provide an FM wireless telephone device capable of effectively utilizing the.

[0011]

In order to achieve the above object, the present invention converts the received signal into an intermediate frequency in the first and second mixing circuits by the output from the first and second local oscillation circuits, In a double super heterodyne FM radiotelephone device which outputs to a limiter circuit after being amplified by a frequency amplifying circuit, the first frequency divider divides the output of the limiter circuit.
Frequency divider circuit, a second frequency divider circuit that divides the reference frequency of the reference frequency oscillator circuit, a phase comparison circuit that inputs the outputs of the first and second frequency divider circuits, and performs phase comparison, A first low-pass filter for removing frequency components outside the voice band from the output of the comparison circuit, and inputting the output of the first low-pass filter to the second local oscillation circuit, The oscillation frequency is controlled and the output of the first low-pass filter is taken out as a demodulation output, which has a first configuration.

Further, the FM radiotelephone device of the present invention is provided with an electric field detection circuit on the output side of the limiter circuit in the above-mentioned first configuration, and the time constant of the first low pass filter is set by the output of the electric field detection circuit. It is configured to control.

Further, in the FM radio telephone apparatus of the present invention, in the above-mentioned first configuration, the first local oscillation circuit performs phase comparison between the frequency division output of the voltage controlled oscillation circuit and the frequency division output of the reference frequency oscillation circuit. Then, the error voltage is configured by a PLL circuit that feeds back to the voltage controlled oscillator circuit through a low pass filter, and an adder circuit is provided on the input side of the voltage controlled oscillator circuit of the first local oscillator circuit. Is input to one end of the adder circuit, the oscillation frequency of the first local oscillator circuit is controlled by the output added by the adder circuit, and the output of the first low-pass filter is taken out as a demodulation output. It was done.

Further, in the FM radio telephone apparatus of the present invention, in the above-mentioned first configuration, the first local oscillator circuit is phase-compared with the frequency-divided output of the voltage-controlled oscillator circuit and the frequency-divided output of the reference frequency oscillator circuit. Then, the error voltage is configured by a PLL circuit that feeds back to the voltage controlled oscillator circuit through a low pass filter, and the output of the first low pass filter is input to one end of the voltage controlled oscillator circuit of the first local oscillator circuit. Thus, the oscillation frequency of the first local oscillation circuit is controlled, and the output of the first low pass filter is taken out as a demodulation output.

Further, in the FM radio telephone apparatus of the present invention, in the above-mentioned first configuration, the first and second local oscillation circuits are provided with a frequency-divided output of the voltage-controlled oscillation circuit and a frequency-divided output of the reference frequency oscillation circuit. Of the output signal of the phase comparison circuit from the information signal of the output of the phase comparison circuit, which is composed of a PLL circuit that returns the error voltage to the voltage controlled oscillator circuit through the low pass filter. A second low-pass filter that passes a low-frequency component and a band-pass filter that passes a frequency component of an information signal among outputs of the phase comparison circuit are provided, and an output of the second low-pass filter is a first output. It is input to the voltage controlled oscillator circuit of the local oscillator circuit to control the oscillation frequency of the first local oscillator circuit and the output of the band pass filter to the second oscillator circuit.
The configuration is such that the voltage controlled oscillator circuit of the local oscillator circuit is input to control the oscillation frequency of the second local oscillator circuit, and the output of the band pass filter is taken out as a demodulation output.

Further, in the FM radio telephone device of the present invention, the first and second local oscillator circuits of the receiver circuit and the oscillator circuit of the transmitter circuit are divided into the frequency-controlled oscillator circuit and the reference frequency oscillator circuit. And the error voltage is fed back to the voltage controlled oscillator circuit through a low pass filter, and the received signal is output by the first and second local oscillator circuits to produce first and second mixed circuits. Convert to an intermediate frequency with
In a double super heterodyne FM radiotelephone device that outputs to the limiter circuit after amplification by the intermediate frequency amplifier circuit, the first frequency divider circuit for dividing the output of the limiter circuit and the reference frequency of the reference frequency oscillator circuit are A second frequency divider circuit for frequency division, a phase comparator circuit for inputting outputs of the first and second frequency divider circuits, respectively, and a frequency component lower than the information signal in the output of the phase comparator circuit. A first low-pass filter that passes, a band-pass filter that passes the frequency component of the information signal among the outputs of the phase comparison circuit, the frequency-divided output of the voltage-controlled oscillation circuit of the transmission circuit, and the division of the reference frequency oscillation circuit. The first switch circuit provided on the input side of the phase comparison circuit of the first local oscillation circuit for switching the frequency output and the divided output of the voltage controlled oscillation circuit of the first local oscillation circuit and the reference frequency generation. A second switch circuit provided on the input side of the phase comparison circuit of the transmission circuit for switching between the frequency division output of the circuit and the output of the first low-pass filter Circuit to control the oscillating frequency of the first local oscillator circuit, and the output of the bandpass filter to the voltage controlled oscillator circuit of the second local oscillator circuit to control the oscillating frequency of the second local oscillator circuit. The first and second switch circuits follow the change in the oscillation frequency of the voltage controlled oscillation circuit in the transmission circuit to change the oscillation frequency of the first local oscillation circuit and extract the output of the bandpass filter as a demodulation output. The second one
The configuration is as follows.

[0017]

In the FM radiotelephone device of the present invention having the above-mentioned structure, the oscillation frequency of the local oscillation circuit is changed so that the intermediate frequency becomes constant, and the demodulation output is provided by the phase comparison circuit instead of the general demodulation circuit. After that, it was taken out from the output of LPF or BPF.

Further, in order to capture the reception input in the initial state, an electric field detection circuit is added after the limiter circuit to facilitate the capture of the reception input.

Further, the oscillation frequency of the local oscillation circuit is also changed so that the intermediate frequency becomes constant by following the change of the oscillation frequency of the VCO in the transmission circuit.

As a result, even if the bandwidth of the BPF in the intermediate frequency stage is narrowed, the reception sensitivity and the S / N ratio can be improved without degrading the distortion rate of the demodulation output, and the frequency can be effectively used. Become.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. It should be noted that the same or similar configurations as those of the conventional example shown in FIGS. 6 and 7 are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows a block diagram of a receiving circuit in the FM radio telephone apparatus of the first embodiment. In FIG. 1, the reception signal input from the antenna 1 is tuned by the BPF 2 and the high frequency amplification circuit 3, mixed with the output of the first local oscillation circuit 5 by the first mixing circuit 4, and converted into the first intermediate frequency. The first intermediate frequency is mixed with the output of the second local oscillation circuit 8 in the second mixing circuit 7 via the BPF 6 and converted into the second intermediate frequency. Then, the signal is amplified by the intermediate frequency amplifier circuit 10 through the BPF 40, and the limiter circuit 11 limits the amplitude. The output is frequency-divided by the frequency divider 42 and input to the phase comparator 43.

The reference frequency output from the reference frequency oscillating circuit 22 is frequency-divided by the frequency dividing circuit 44 and the phase comparison circuit 4
3 is input to the other end. In the phase comparison circuit 43, 2
The phases of the two frequencies are compared, and an output proportional to the amount of advance or delay of the output signal of the frequency dividing circuit 42, that is, an output including a voice signal (modulation signal) is input to the LPF 45.
The LPF 45 removes the frequency component outside the voice band and inputs it to the second local oscillation circuit 8 as a frequency control voltage.

The second local oscillating circuit 8 is a very stable oscillating circuit such as a crystal controlled oscillating circuit. A part of the oscillating frequency determining element is a variable capacitance diode, and the oscillating frequency is changed by the applied voltage. It is a circuit, that is, a VCO.

The cutoff frequency of the LPF 45 is
Second local oscillation circuit 8, second mixing circuit 7, limiter circuit 1
1, the frequency division circuit 42, the phase comparison circuit 43, the cutoff frequency of the loop gain of the PLL circuit formed by the LPF 45 is sufficiently higher than the maximum frequency of the demodulation output.

When the FM reception signal is input in such a configuration, the PLL circuit has a sufficient loop gain at the modulation frequency thereof, and therefore the second local oscillation circuit 8 is provided.
The oscillating frequency of is changing as the frequency of the received signal changes.

Therefore, the second intermediate frequency does not change and remains constant, so that the bandwidth of the BPF 40 can be very narrow.

As a result, even if the bandwidth of the BPF is narrowed, the demodulation output can be taken out without degrading the reception distortion rate. Further, since the receiving sensitivity is proportional to the square root of the pass band width, the receiving sensitivity is also improved. However, this requires that the VCO control voltage versus frequency characteristic be linear, which is easily accomplished.

Since the frequency control input to the second local oscillation circuit 8 output from the LPF 45 is the modulated wave itself, it can be taken out as a demodulation output.

Next, how much the bandwidth of the BPF can be narrowed as compared with the conventional one will be described using mathematical expressions. Now
The frequency of the reception input is f _R , the first local oscillation frequency is f _1L ,
The second local oscillation frequency is f _2L, and their stability is p,
If q and r are set and the modulation frequency is f _m , the bandwidth f _{W of the} BPF 40 is as follows. f _W ≧ (p · f _R + q · f _1L + r · f _2L + f _m ) × 2 (1) where f _R = 900 MHz, f _1L = 810 MHz, f
_{2L = 89.5MHz, f m = 1KHz} , p = 0.5pp
If m and q = r = 1 ppm, then f _W ≧ 3.
It becomes 7 KHz.

In the conventional circuit, since f _W ≧ 8 KHz, the bandwidth can be narrowed to about 1/2.
As a result, the noise figure of the receiving circuit is also halved, so that the sensitivity is improved by about 6 dB.

In the first embodiment described above, the output of the LPF 45 is input to the second local oscillation circuit 8, but by inputting this to the first local oscillation circuit 5, the first intermediate frequency is changed. However, the bandwidths of the BPFs 6 and 40 can be narrowed.

In the above description, an example in which the reference frequency signal obtained by frequency division from the second local oscillation circuit and a reference frequency oscillation circuit separate from the second local oscillation circuit is used is shown. However, when the standard of the distortion factor is not so strict. May connect the output of the second local oscillation circuit 8 to the frequency dividing circuit 44 as shown by the broken line in FIG. 1 and use the output as the reference frequency signal.

At this point, assuming that the intermediate frequency is f _IF , the oscillation frequency of the local oscillation circuit is f _L , the modulation frequency is f _m , and the frequency dividing numbers of the frequency dividing circuits 42 and 44 are N and M, the phase comparing circuit is The frequency of the input signal is (f _L ± f _m ) / M,
(F _IF ± f _m ) / N, which is (f _L ± f
_m ) / M≈ (f _IF ± f _m ) / N, and in general f _L >.
> F _IF >> f _m , so f _L / M≈ (f _IF ± f _m ) /
This is because it becomes N and can be regarded as the same as unmodulated. With this configuration, a dedicated reference frequency oscillating circuit is not required and the circuit becomes simple.

In the above description, the bandwidth of the BPF may be very narrow, but in reality, the reception input frequency,
Since there is a deviation in the local oscillation frequency, it is necessary to consider it. This is because it is necessary to first capture the received input in the initial state. For example, when there is no reception input, the output of the limiter circuit 11 becomes a noise output and the second
The oscillation frequency of the local oscillation circuit 8 changes depending on the FM component of noise. In this case, even if there is a received input, that input cannot be captured.

In order to prevent this, it is necessary to fix the oscillation frequency of the local oscillation circuit to the center frequency of the BPF. Therefore, the electric field detection circuit 41 is added to the output side of the limiter circuit 11 so that a control signal corresponding to the magnitude of the limiter output is output, and the time constant of the LPF 45 is increased to increase the output frequency of the limiter circuit 11. The oscillation frequency of the local oscillation circuit is fixed at the average value of, that is, the center frequency of the BPF 40.

The electric field detection circuit 41 is a circuit for facilitating the capture of the received input. In the steady state after the capture, this is detected and the time constant of the LPF 45 is restored. Then the second
An example will be described. FIG. 2 shows the FM of the second embodiment.
3 is a block diagram of a receiving circuit in the wireless telephone device. In FIG. 2, the received signal input from the antenna 1 is input to the limiter circuit 11 via the same path as in FIG. The output is frequency-divided by the frequency divider 53 and input to the phase comparator 54.

The reference frequency output from the reference frequency oscillating circuit 22 is frequency-divided by the frequency dividing circuit 55 and the phase comparing circuit 5
4 is input to the other end. In the phase comparison circuit 54, 2
The phases of the two frequencies are compared, and an output proportional to the amount of advance or delay of the output signal of the frequency dividing circuit 53, that is, an output including a voice signal (modulation signal) is input to the LPF 56.
The LPF 56 removes the frequency component outside the voice band and inputs it to the switch circuit 57.

On the other hand, the first circuit composed of a PLL circuit in which an adding circuit 58 is added between the LPF 18 and the VCO 17
In the local oscillation circuit 59, the reference frequency output from the reference frequency oscillation circuit 22 and the frequency output from the VCO 17 'are input to the phase comparison circuit 19 via the frequency dividing circuits 21 and 20, respectively, and are input as an error signal to the phase comparison circuit. 19
Is output from. This error signal is input to the adder circuit 58 in the form of voltage through the LPF 18 which passes only the DC fluctuation. The demodulated output from the switch circuit 57 is input to the other end of the adder circuit 58, and is added in the adder circuit 58. By inputting the output of the adder circuit 58 to the VCO 17,
The oscillation frequency of the VCO 17 changes as the frequency of the received signal changes.

Therefore, since the first intermediate frequency is substantially constant, it does not matter if the bandwidths of the BPFs 50 and 51 are very narrow. Since the output from the LPF 56 is the modulated wave itself, it can be taken out as a demodulation output.

As a result, even if the BPF bandwidth is narrowed, the demodulated output can be taken out without degrading the reception distortion rate. Further, since the receiving sensitivity is proportional to the square root of the pass band width, the receiving sensitivity is also improved. However, this requires that the VCO control voltage versus frequency characteristic be linear, which is easily accomplished.

However, even in the second embodiment, the first
Similar to the embodiment, there is a deviation in the reception input frequency and the local oscillation frequency in practice, and it is necessary to consider them.
For example, when there is no reception input, the output of the limiter circuit 11 becomes a noise output, and the oscillation frequency of the VCO 17 'changes depending on the FM component of noise. In this case, even if there is a received input, that input cannot be captured.

Therefore, an electric field detection circuit 52 for outputting a control signal corresponding to the size of the limiter output is added to the output side of the limiter circuit 11, and when the output of the electric field detection circuit 52 is below a certain level. , VCO 17 'does not operate improperly, the switch circuit 57 operates so as to disconnect the output of the LPF 56.

In the second embodiment described above, the second local oscillator circuit 8 is provided independently, but the reference frequency oscillator circuit 2 is used.
It is also possible to multiply the output of 2 and use this as a local oscillation circuit. Next, a third embodiment will be described. FIG. 3 is a block diagram of a receiving circuit in the FM radio telephone apparatus of the third embodiment, in which the demodulated output of the switch circuit 57 in FIG. 2 is directly input to the VCO.

The difference between FIG. 3 and FIG. 2 is the first point.
The addition circuit provided between the LPF and the VCO of the local oscillator is deleted, the output of the LPF is directly input to the VCO, and the VCO is a VCO 17 'having a frequency control terminal and a PLL control terminal. That is, the output of the switch circuit 57 is input to one end of the VCO 17 ', not to the adder circuit.

In the first local oscillation circuit 60, the error voltage from the phase comparison circuit 19 is supplied to the PLL control terminal of the VCO 17 '. The demodulated output from the switch circuit 57 is input to the frequency control terminal of the VCO 17 '.

In the VCO 17 ', the phase comparison circuit 19
By inputting the error voltage from the input signal and the demodulation output from the switch circuit 57, the oscillation frequency of the VCO 17 'changes as the frequency of the received signal changes.

Therefore, since the first intermediate frequency becomes almost constant, the bandwidth of the BPFs 50 and 51 can be made extremely narrow. As a result, even if the BPF bandwidth is narrowed, the demodulation output can be taken out without degrading the reception distortion rate. Further, since the receiving sensitivity is proportional to the square root of the pass band width, the receiving sensitivity is also improved. Next, a fourth embodiment will be described. FIG. 4 shows a block diagram of a transmission / reception circuit in the FM radio telephone apparatus of the fourth embodiment. In FIG.
The received signal input from the antenna 1 is input to the limiter circuit 11 via the same path as in FIG. The output is frequency-divided by the frequency divider 72 and input to the phase comparator 73.

The reference frequency output from the reference frequency oscillating circuit 22 is frequency-divided by the frequency dividing circuit 76 and the phase comparing circuit 7
3 is input to the other end. In the phase comparison circuit 73, 2
The frequencies are compared in phase, and the frequency component lower than the information signal in the output that is proportional to the amount of advance or delay of the output signal of the frequency dividing circuit 72, that is, the output including the audio signal (modulation signal), is the LPF 74. V of the first local oscillation circuit 82
Input to CO17 '. On the other hand, the frequency component of the information signal passes through the BPF 75 and the VCO 77 of the second local oscillation circuit 83.
Entered in.

In the second local oscillation circuit 83, the reference frequency output from the reference frequency oscillation circuit 22 and the VCO 77
The frequencies output from the frequency dividing circuits 81 and 80, respectively.
Is input to the phase comparison circuit 79 and is output from the phase comparison circuit 79 as an error signal. This error signal passes through the LPF 78, which passes only the DC fluctuation component, and then the VCO 77 in the form of voltage.
Is supplied to the PLL terminal.

By inputting the error voltage from the phase comparison circuit 79 and the received signal from the BPF 75 to the VCO 77, the oscillation frequency of the VCO 77 changes as the frequency of the received signal changes.

Further, by inputting the error voltage from the phase comparison circuit 19 and the received signal from the LPF 74 into the VCO 17 ', the oscillation frequency of the VCO 17' changes as the frequency of the received signal changes.

Therefore, the second intermediate frequency becomes almost constant, and the bandwidth of the BPF 71 can be made extremely narrow.

As a result, even if the BPF bandwidth is narrowed, the demodulation output can be taken out without degrading the reception distortion rate. Further, since the receiving sensitivity is proportional to the square root of the pass band width, the receiving sensitivity is also improved. However, this requires that the VCO control voltage versus frequency characteristic be linear, which is easily accomplished.

Now, the reason why the received signal from the LPF 74 is input to the VCO 17 'to control the oscillation frequency will be described.

The received signal is largely FM-modulated at a frequency lower than that of the information signal in order to spread the energy. Therefore, in this state as it is, the bandwidth of the BPF 70 needs to be wide.

Therefore, among the outputs of the phase comparison circuit 73,
By extracting a frequency component lower than the information signal by the LPF 74 and inputting it to the VCO 17 ', the VCO 17'
The oscillating frequency is changed in synchronization with the frequency of the received signal to the same extent, so that the output frequency of the first mixing circuit 4 has a small frequency change. As a result, the bandwidth of the BPF 70 can be made narrower than the conventional one. In addition, BPF70
By narrowing the bandwidth of, it is possible to increase the number of radio waves allocated in the band, and to effectively use the frequency.

In the above, since the output from the BPF 75 has a value proportional to the amplitude of the received signal, this can be taken out as a demodulation output.

Next, this will be described using mathematical expressions.

The sensitivities of the variable capacitance diodes of the VCO 17 'and VCO 77 are α ₁ [Hz / V] and α ₂ [Hz, respectively.
/ V], the deviation of the received signal at a frequency lower than that of the information signal is V _L (t), and the deviation of the information signal is V _H (t),
When the carrier wave is f _c , the reception frequency f _r (t) becomes f _r (t) = f _c + V _L (t) + V _H (t) (2) The first mixing circuit operates so that V _L (t) = 0, and the second mixing circuit operates so that V _H (t) = 0. Assuming that the information signal is f _p (t), V _H (t) = m _f
It can be expressed as f _p (t). Note that m _f is a proportional constant.

When the output of the BPF 75 is f _BF (t), the output of the second mixing circuit operates so that V _H (t) = 0, and thus f _BF (t) · α ₂ = m _f · f _p (t).
As a result, f _BF (t) = (m _f / α ₂ ) · f _p (t) ··· (3), and since m _f and / α ₂ are constants, f _BF (t) Is a value proportional to the information signal f _p (t), which can be used as a demodulation signal.

In FIG. 4, the operation of the transmission circuit is as shown in FIG.
Since it is the same as, the description thereof will be omitted. Next, a fifth embodiment will be described. FIG. 5 shows a block diagram of a transmission / reception circuit in the FM radio telephone apparatus of the fifth embodiment.
5, the operation of the receiving circuit is basically the same as that of the receiving circuit of FIG. 4, and the difference from FIG. 4 lies in the transmitting circuit.

The first local oscillator circuit 93 includes a switch circuit 9
0 is provided, the reference frequency input from the frequency dividing circuit 21 and
The operation of switching the frequency input of the VCO 33 from the frequency dividing circuit 35 'is performed. A switch circuit 91 is also provided between the frequency divider circuit 30 and the phase comparison circuit 31 of the transmission circuit,
The reference frequency input from the frequency dividing circuit 30 and the frequency dividing circuit 20 '
To switch the frequency input of the VCO 17 'from the. The operation of the transmission circuit of this embodiment will be described below.

In FIG. 5, when the power is first turned on, both the transmitting and receiving circuits have constant waves f _T and f _R. That is, in the standby state, it is a constant wave, that is, a carrier wave. When calling the other party here, it is modulated with the other party's code and output. When the other party receives his or her code, a response signal to the code is sent. After that, when the response signal is received, the switch circuit 90 causes the frequency dividing circuit 35 to operate.
Switch to the output side from ´. In addition, the switch circuit 92
Is set to "contact" and the low frequency signal is input to the VCO 33.
The VCO 33 changes greatly according to the low frequency signal. VC
The output from O33 is superimposed on the modulation signal and the power amplification circuit 34
After being amplified by, the signal is transmitted from the antenna 36 as a transmission wave.

When a signal from the other party is received in such a state, since the switch circuit 90 is switched to the output side from the frequency dividing circuit 35 ', the oscillation frequency of the VCO 17' changes according to the oscillation frequency of the VCO 33. Therefore, it is possible to receive even if the transmission output of the other party changes according to the low frequency signal.

After that, the switch circuit 91 causes the frequency divider circuit 20 to operate.
Switch to the ´ side. When the received signal changes according to the low frequency signal, the VCO 17 'of the receiving circuit changes accordingly, and the VCO 33 of the transmitting circuit also changes accordingly. The transmission / reception circuit operates in this manner.

Since the operation described above is performed, the modulation factor can be increased within the limit of the used band, and the pass band width of the BPF 71 of the receiving circuit can be extremely narrowed, so that the receiving sensitivity and the S / N ratio can be improved. Can be improved.

If the information signal is a sine wave having a low frequency, the bandwidth of the BPFs 71 and 75 can be further narrowed, so that it is less likely to be affected by the interfering wave.

The contents described above will be described more concretely by way of examples. Now, the information signal is 1 KHz, the frequency lower than the information signal is 100 Hz, the reception frequency is 2 GHz, and the maximum frequency deviation due to the low frequency 100 Hz is ± 10 MHz,
The maximum frequency shift due to the information signal is ± 100 KHz. In this case, the bandwidth of the BPF 71 is 2 × (100 + 1) KHz = 202KH if it is the bandwidth of the conventional circuit.
z is necessary, but in the present invention, the input of the BPF 71, the second
At the output of the mixing circuit 7, the frequency shift operates so as to be almost zero, and therefore, approximately 2 × (0 + 1) KHz =
2KHz is good. That is, although the information signal S is the same, the noise is considered to be 1/100 (2 OdB), so the S / N ratio is considered to be improved by 2 OdB.

[0070]

As can be understood from the above description, in the FM radio telephone apparatus of the present invention, the oscillation frequency of the local oscillation circuit can be changed so that the intermediate frequency becomes constant. Even if the bandwidth of the BPF is narrowed, the reception sensitivity and the S / N ratio can be improved without degrading the distortion rate of the demodulation output.

Further, the narrow bandwidth means that
The unnecessary electric waves such as noise power in the band may be increased accordingly, and the number of electric waves allocated in the band can be increased, and the frequency can be effectively used. .

[Brief description of drawings]

FIG. 1 is a block diagram of a receiving circuit of an FM wireless telephone device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a receiving circuit of an FM wireless telephone device according to a second embodiment.

FIG. 3 is a block diagram of a receiving circuit of an FM wireless telephone device in a third embodiment.

FIG. 4 is a block diagram of a transmission / reception circuit of an FM wireless telephone device in a fourth embodiment.

FIG. 5 is a block diagram of a transmission / reception circuit of an FM wireless telephone device in a fifth embodiment.

FIG. 6 is a block diagram of a receiving circuit of an FM wireless telephone device in a conventional example.

FIG. 7 is a block diagram of a transmission / reception circuit of an FM wireless telephone device in another conventional example.

[Explanation of symbols]

 1, 36 antenna 2 BPF 3 high frequency amplifier circuit 4 first mixing circuit 5, 59, 60, 82, 93 first local oscillation circuit 6 BPF 7 second mixing circuit 8, 83 second local oscillation circuit 10 intermediate frequency amplification circuit 11 Limiter circuit 13 LPF 14 Low-frequency power amplifier circuit 15 Speaker 17, 17 ', 77 VCO 18, 78 LPF 19, 79 Phase comparator circuit 20, 20', 21, 80, 81 Frequency divider circuit 22 Reference frequency oscillation circuit 30, 35 , 35 'frequency divider circuit 31 phase comparator circuit 32 LPF 33 VCO 34 power amplifier circuit 40, 50, 51, 70, 71 BPF 41 electric field detection circuit 42, 44, 53, 55, 72, 76 frequency divider circuit 45, 56, 74 LPF 43, 54, 73 Phase comparison circuit 57, 90, 91, 92 Switch circuit 58 Adder circuit 75 BPF

Claims (8)

[Claims] 1. A double super output circuit for converting a received signal into an intermediate frequency by the first and second mixing circuits by outputs from the first and second local oscillation circuits, amplifying it by an intermediate frequency amplifying circuit, and then outputting it to a limiter circuit. In a heterodyne type FM radio telephone device, a first frequency dividing circuit for frequency-dividing an output of the limiter circuit, a second frequency dividing circuit for frequency-dividing a reference frequency of a reference frequency oscillation circuit, the first and second A phase comparison circuit that inputs the outputs of the second frequency dividing circuits and performs phase comparison; and a first low-pass filter that removes frequency components outside the voice band from the output of the phase comparison circuit, The output of the first low pass filter is input to the second local oscillator circuit to control the oscillation frequency of the second local oscillator circuit, and the output of the first low pass filter is taken as a demodulation output. FM radio telephone apparatus according to claim Succoth. 2. The FM radiotelephone device according to claim 1, further comprising an electric field detection circuit on the output side of said limiter circuit, and controlling the time constant of said first low pass filter by the output of said electric field detection circuit. An FM wireless telephone device characterized by the above. 3. The FM radio telephone apparatus according to claim 1, wherein the second frequency dividing circuit changes the reference frequency of the reference frequency oscillating circuit to divide the output of the second local oscillating circuit. An FM wireless telephone device characterized by the above. 4. The FM radiotelephone device according to claim 1, wherein the first local oscillation circuit compares the frequency division output of the voltage controlled oscillation circuit and the frequency division output of the reference frequency oscillation circuit in phase to determine an error voltage. A PLL circuit that feeds back to the voltage controlled oscillator circuit via a low pass filter, an adder circuit is provided on an input side of the voltage controlled oscillator circuit of the first local oscillator circuit, and an output of the first low pass filter. Is input to one end of the addition circuit, and the oscillation frequency of the first local oscillation circuit is controlled by the output added by the addition circuit.
An FM radio telephone apparatus, wherein the output of the first low pass filter is taken out as a demodulation output. 5. The FM radiotelephone device according to claim 1, wherein the first local oscillation circuit compares the frequency division output of the voltage controlled oscillation circuit and the frequency division output of the reference frequency oscillation circuit in phase to determine an error voltage. A PLL circuit that feeds back to the voltage controlled oscillation circuit via a low pass filter, and inputs the output of the first low pass filter to one end of the voltage controlled oscillation circuit of the first local oscillation circuit,
An FM radiotelephone device characterized in that the oscillation frequency of the first local oscillation circuit is controlled and the output of the first low pass filter is taken out as a demodulation output. 6. The FM wireless telephone device according to claim 4, further comprising an electric field detection circuit on an output side of the limiter circuit, and a first switch circuit on an output side of the first low pass filter. An FM wireless telephone device characterized in that the first switch circuit is controlled by an output of the electric field detection circuit. 7. The FM radiotelephone device according to claim 1, wherein the first and second local oscillator circuits are phase-compared with a frequency-divided output of a voltage-controlled oscillator circuit and a frequency-divided output of a reference frequency oscillator circuit. A PLL circuit that feeds back an error voltage to the voltage controlled oscillator circuit through a low-pass filter, changes to the first low-pass filter, and outputs a frequency lower than the information signal in the output of the phase comparison circuit. A second low-pass filter that passes a component; and a band-pass filter that passes a frequency component of the information signal among the outputs of the phase comparison circuit, the output of the second low-pass filter being the first The voltage controlled oscillator circuit of the first local oscillator circuit is controlled to control the oscillation frequency of the first local oscillator circuit, and the output of the band pass filter is inputted to the voltage controlled oscillator circuit of the second local oscillator circuit to control the oscillation frequency of the second local oscillator circuit. Two And controls the oscillation frequency parts oscillator, FM radio telephone apparatus characterized by taking out an output of the band-pass filter as a demodulated output. 8. The first and second local oscillation circuits of the reception circuit and the oscillation circuit of the transmission circuit are phase-compared with the frequency division output of the voltage controlled oscillation circuit and the frequency division output of the reference frequency oscillation circuit to determine the error voltage. A PLL circuit that feeds back to the voltage controlled oscillation circuit via a low-pass filter, and converts a received signal into an intermediate frequency by the first and second mixing circuits by the output from the first and second local oscillation circuits, In a double super heterodyne FM radio telephone device which outputs to a limiter circuit after being amplified by an intermediate frequency amplifier circuit, a first frequency divider circuit for dividing the output of the limiter circuit and a reference frequency of a reference frequency oscillator circuit. A second frequency dividing circuit for dividing the frequency, a phase comparison circuit for inputting the outputs of the first and second frequency dividing circuits and performing phase comparison, and A first low-pass filter that passes a frequency component that does not pass, a band-pass filter that passes a frequency component of the information signal among the outputs of the phase comparison circuit, and a frequency-divided output of the voltage-controlled oscillation circuit of the transmission circuit. A first switch circuit provided on the input side of the phase comparison circuit of the first local oscillation circuit for switching between the frequency division output of the reference frequency oscillation circuit and the frequency division of the voltage controlled oscillation circuit of the first local oscillation circuit A second switch circuit provided on the input side of the phase comparison circuit of the transmission circuit for switching between the output and the frequency-divided output of the reference frequency oscillating circuit, the output of the first low-pass filter being the output of the first low-pass filter. The voltage controlled oscillator circuit of the first local oscillator circuit is controlled to control the oscillation frequency of the first local oscillator circuit, and the output of the band pass filter is inputted to the voltage controlled oscillator circuit of the second local oscillator circuit. And controlling the oscillation frequency of the second local oscillator circuit, following the change in the oscillation frequency of the voltage controlled oscillation circuit in the transmission circuit by further said first and second switching circuits,
An FM radiotelephone device characterized in that the output of the band pass filter is taken out as a demodulation output as the oscillation frequency of the first local oscillation circuit changes.