JPH0884052A - Radio communication equipment with automatic frequency adjusting circuit - Google Patents

Abstract

PURPOSE: To provide a radio communication equipment provided with automatic frequency adjusting circuit where reception sensibility is excellent and an AFC function always functions. CONSTITUTION: The passing band width ±Δfb of a band filter 11 filtering the first intermediate frequency F1 after the frequency is passed through a first mixer MiX1 and the passing band width ±Δfc of a band filter 12 filtering the second intermediate frequency F2 after the frequency is passed through a second mixer MiX2 are set in a narrow band so that the signal to noise ratio may be optimum in a state that a frequency deviation does not exist. An AFC circuit 13 detects the DC voltage level of accompanied by the deviation of the center frequency of a detection output fS and performs a frequency adjustment. When an opposite signal deviates from the passing bands of the band filters 11 and 12 and the detection output fS becomes a no-signal time, a frequency deviation is adjusted so that the both of the opposite signals in the first intermediate frequency F1 and the second intermediate frequency F2 may come to the center of the passing bands of the band filters 11 and 12 by fluctuating the local oscillation frequency f01 of a first local oscillator Lo1 in a prescribed range by the control of a microcomputer 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automatic frequency adjustment using ultrashort waves.
Control; Abbreviation AFC) wireless communication device with a circuit, particularly gigahertz region (UHF, microwave region)
Signal-to-noise ratio (S / N) in the high frequency band of
Ratio) is obtained.

[0002]

2. Description of the Related Art In the current wireless communication, an increase in the number of channels accompanying an increase in the number of users has shifted to higher frequencies, and most of them use a highly stable crystal oscillator for frequency management.

However, this is approaching its limit, and even in the case of the radio communication using the existing ultra-high frequency wave (UHF) or microwave having a frequency of 1 GHz or more, even the crystal oscillator cannot be said to have sufficient stability.

That is, a commonly used crystal oscillator has an oscillation frequency variation caused by a temperature change, and its stability in the allowable temperature range of use is ± 2 PPM (± 2 KH at 1 GHz).
z) and it is difficult to realize stability other than using a constant temperature bath.

However, in recent years, in mobile radio communication (cell phones, transceivers, etc.), there is a demand for smaller size, lighter weight, and power saving type. Therefore, the specifications of the above-described constant temperature bath do not meet the requirements. There is.

In this respect, ± 2 in communication in which the operating frequency of the crystal oscillator to be the reference oscillation frequency exceeds 1 GHz.
Deviation of frequencies above PPM is a fatal problem in the receiver. (Aggravation of communication sound, reduction of communication distance, worst case inability to start communication, etc.) In order to avoid these problems, automatic frequency adjustment (AF
C) is adopted. (However, there seems to be no example that has been adopted in mobile radio communication devices, so-called transceivers.) The above AFC means that the oscillation frequency of the oscillator is automatically adjusted to match a predetermined value. The deviation of the oscillation frequency caused by the constant change due to the temperature rise of the components that make up
This means controlling the oscillation frequency of the oscillator by this voltage.

FIG. 3 shows an example of a block configuration of a super-heterodyne FM receiver with an AFC circuit. As can be seen from the figure, an incoming wave F0 received by an antenna (ANT) is first passed through a high frequency band filter (BPF1) and a high frequency amplifier ( HF
Amplify in A). This is added to the first mixer MIX1 called a mixer together with the output f01 of the first local oscillator (Lo1) to form a first intermediate frequency F1 (= F0-f01). F1
Is an inaudible sound, in order to make it an audible sound, in addition to the output f02 of the second local oscillator Lo2, a second intermediate frequency F2 (= F1-f02) is added to the second mixer MIX2, and this is detected through the bandpass filter BPF3 ( Frequency discriminator; DE
T) The detected output fs of the other party's signal is low frequency amplified (LF
A) and sound the speaker.

On the other hand, the DC voltage level ef of the detection output fS
Is input to the AFC circuit 3 through the integrator circuit 4 and the change in the DC voltage level ef corresponding to the deviation of the center frequency is fed back to the local oscillation circuit Lo1 to change the first local oscillation frequency f01 and pass through the mixers MIX1 and MIX2. Intermediate frequency F after
The frequency shift is prevented so that 1 and F2 are appropriate, and the reception state is kept optimal.

That is, in the detection circuit DET, when the input frequency deviates from the center frequency, a DC voltage level ef (which is linearly proportional) appears in accordance with the change of the frequency, so that the intermediate frequency is utilized by using the voltage ef. The first local oscillation frequency f01 is changed so that F1 is returned to the center.

As a method of changing the local oscillation frequency f01 in the AFC circuit 3 by the voltage ef, a variable capacitance diode (varicap) or a variable capacitance of the collector output capacitance of a transistor is used, and the capacitance C becomes the applied voltage ef. On the other hand, it is common to connect this to the tuning circuit of the first local oscillator Lo1 by utilizing the fact that it is inversely proportional to the power of 1/2 or 1/3.

The first local oscillator Lo1 has an input signal fi obtained by dividing the reference oscillation frequency f0 of the crystal oscillation circuit 4 (OSC) and a voltage control oscillation circuit 5 as shown in a broken line frame.
(VCO) output signal f01 (which is the first local oscillation frequency) The phase comparator 6 for comparing the phase difference of the frequency-divided signals.
And a PLL circuit 9 including a low-pass filter (LPF) 7.

[0012]

However, the bandpass filter BP in which the pass band width BP is widened beyond the frequency fluctuation that can occur in the AFC circuit 3 in the conventional FM receiver described above.
If F2 and BPF3 are not used, the AFC effect of detecting the frequency shift and adjusting the first local oscillation frequency f01 cannot be obtained.

Because the AFC function is an operation for adjusting the center frequency at the DC voltage level ef of the detection output fS, it does not operate unless the partner signal appears at the detection output fS at any time.

On the other hand, however, the bandpass filters BPF2, B
Widening the pass band width BP of the PF3 has a demerit of deteriorating the reception S / N ratio.

FIG. 4 shows the bandpass filters BPF2 and BPF.
5 is a diagram for explaining the relationship between the pass band width BP of 3 and the center frequency shift of the partner signal wave and the first intermediate wave F1. FIG.

In a receiving system equipped with a bandpass filter having a relatively narrow pass band width BPN in order to improve the receiving sensitivity as shown in FIG. 4 (b), the reference oscillation frequency of the crystal oscillator, which is the basis of the frequency management of the system. If f0 shifts by Δf to f0 ', or if there is a frequency shift (Δf) in the incoming wave F0 on the other side, the frequency shift width exceeds the passband width of the bandpass filter The signal wave also enters the attenuation band, making it impossible to detect even the presence or absence of the signal of the other party (becomes no signal).

Therefore, inevitably, S /
Band-pass filters BPF2, BP at the expense of N ratio to some extent
Under the present circumstances, the pass band width of F3 is set to be BPW wider than the optimum width so that the partner signal S always enters the detection output fS even if the center frequency f0 is deviated.

For example, in the case where the frequency used is 1 GHz and the crystal oscillator stability is ± 2.5 PPM, if the audio signal band is approximately ± 3.75 KHz, the fluctuation frequency ± 2.5 KHz that can occur in the crystal oscillator is added to this. And ±
The frequency becomes 6.25 KHz, and a filter circuit having a pass band width larger than this is required to pass the partner signal. This essentially means that a bandpass filter with an optimum passband width of about ± 4 KHz can be used when the frequency shift is zero, but a wider bandpass filter must be used. Therefore, the S / N ratio of reception is reduced. It makes it worse.

At frequencies of 1 GHz or higher, a bandpass filter having a wider pass band must be adopted in order to effectively operate the AFC circuit.

Further, even in a wireless communication device having a frequency of gigahertz or less, if there is no AFC circuit, a band filter having a slightly wide pass band is used in consideration of the frequency deviation of the crystal oscillator, and the S / N ratio is slightly sacrificed. Is the current situation.

On the other hand, in terms of cost, the crystal oscillator generally has a stability of about ± 2.5 PPM (± 2.5 KHz at 1 GHz), and a crystal oscillator having a stability higher than that (± 2 PPM or less) is very expensive. In addition, a constant temperature bath is required at several GHz.

The present invention has been made in view of the above circumstances, and is a bandpass filter having a narrow pass band (good S / N ratio).
However, the present invention provides a new wireless communication device with an automatic frequency adjustment circuit devised so as to obtain a sufficient AFC effect.

[0023]

SUMMARY OF THE INVENTION The present invention relates to a radio communication device with an automatic frequency adjustment circuit having a superheterodyne receiver, and a bandpass filter for filtering the first intermediate frequency after passing through the first mixer, and The pass band width of the band-pass filter that filters the second intermediate frequency after passing through the two-mixer is set to a narrow band so that the signal-to-noise ratio is optimum without any frequency shift, and an automatic frequency adjustment circuit Adjusts the frequency by detecting the DC voltage level due to the deviation of the center frequency of the detection output, and at the same time when the other signal deviates from the pass band of the bandpass filter and the detection output becomes no signal, the microcomputer By controlling, the local oscillation frequency of the first local oscillator is changed within a predetermined range so that the partner signals in the first intermediate frequency and the second intermediate frequency both come to the center of the pass band of the bandpass filter. It is intended to achieve the above object by providing a wireless communication device with automatic frequency adjustment circuit, characterized by automatically adjusting the displacement of the sea urchin center frequency.

[0024]

In the present invention, the band-pass filter BPF for filtering the first intermediate frequency F1 after passing through the first mixer MiX1 of the receiver.
2 and the second intermediate frequency F after passing through the second mixer MiX2
The passband width of the bandpass filter BPF3 that filters 2 is set to a narrower band than in the past so that the signal-to-noise ratio is optimized with no frequency shift, and a good S / N ratio is obtained.

Assuming that the reference oscillation frequency f0 of the crystal oscillator or the reception frequency F0 from the other side is deviated, the first intermediate frequency F1 or the second intermediate frequency F2 is changed to each band filter BPF.
2. When the BPF3 is not passed, the AFC circuit that detects no signal of the detection output fS is controlled by the microcomputer of the wireless communication device system and automatically sets the local oscillation frequency f01 of the first local oscillator Lo1 within a predetermined range. It fluctuates between high and low with ± Δfw.

Then, the partner signal in the first intermediate frequency F1 and the second intermediate frequency F2 mixed with the fluctuating local oscillation frequency f01 comes to the center of the pass band width BPN of each of the band-pass filters BPF2 and BPF3.

Then, the partner signal S appears at the detection output fS, the frequency deviation is adjusted, and thereafter, the normal AFC function by the DC voltage level ef is restored.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wireless communication device with an automatic frequency adjusting circuit according to the present invention will be described in detail below with reference to the drawings. It should be noted that the same components as those of the above-described conventional device are represented by the same reference numerals in the drawings.

FIG. 1 shows an FM of a wireless communication device according to the present invention.
It is a block circuit diagram for explaining a receiver.

FIG. 2 is a block circuit diagram for explaining three embodiments for varying the local oscillation frequency f01 of the wireless communication apparatus according to the present invention.

First, as described in the problem, in order to operate the AFC function, even if the frequency of the incoming wave F0 from the other side or the reference frequency f0 of the crystal oscillators of the local oscillators Lo1 and Lo2 is deviated, First, it is essential to catch the other party's signal as the detection output.

In the wireless communication apparatus according to the present invention, the S / N ratio should be set high in order to increase the receiving sensitivity.
Although the band-pass filters BPF2 and BPF3 having a pass band width BPN narrower than usual as in (b) of FIG. Then, the other party's signal is cut by the bandpass filter and the output cannot be taken out, and the AFC function does not work.

However, in such a case, if the local oscillation frequency f01 is moved to the side where the center frequency is deviated by the amount of frequency deviation Δf, the first intermediate wave F1 (= F0-f01) is normally centered on the pass band of the BPF2. It can be seen that the output can be taken out well because the other party's signal comes.

Based on the above, the local oscillator Lo1 will be described below.
The AFC circuit for varying the local oscillation frequency f01 of will be described in detail.

In FIG. 1, a radio communication device 10 is a radio communication device with an automatic frequency adjustment circuit having a super-heterodyne receiver, and a band for filtering the first intermediate frequency F1 after passing through the first mixer MiX1. Filter 11 (B
The bandpass filter 1 for filtering the pass band width ± Δfb of PF2) and the second intermediate frequency F2 after passing through the second mixer MiX2.
The passband width of 2 (BPF3) ± Δfc is set to a narrow band so that the signal-to-noise ratio is optimized in the absence of frequency shift, and the automatic frequency adjustment (AFC) circuit 13 sets the center frequency of the detection output fS. DC voltage level e due to deviation
When f is detected and the frequency is adjusted, the partner signal is deviated from the pass band of the band-pass filters BPF2 and BPF3, and the detection output fS becomes no signal, the first local oscillator Lo1 is controlled by the microcomputer 18. Local oscillation frequency f
01 is varied within a predetermined range to adjust the frequency shift so that the partner signals in the first intermediate frequency F1 and the second intermediate frequency F2 are both in the center of the pass band of the band-pass filters BPF2 and BPF3. It has a feature where it is.

It should be noted that a bandpass filter BPF for a high frequency range is usually used.
Since the pass band width ± Δfa of 1 is sufficiently wider than the other party's signal, the other party's signal passes without any problem even if the reception frequency F0 from the other party is deviated, and it is negligible with respect to the operation of AFC. .

Next, as a method of changing (oscillating) the first local oscillation frequency f01 within a predetermined range, (1) the first local oscillation frequency is changed by changing the frequency data of the PLL. (2) The reference oscillation frequency is switched to change the first local oscillation frequency. (3) A method of continuously varying the first local oscillation frequency or the like can be considered.

FIG. 2 is a circuit block diagram showing an embodiment of the above methods (1) to (3).

In the method (1), the divided data is controlled by the microcomputer 18, and for example, the crystal oscillator 4 (OS
When the reference oscillation frequency of C) is 12.8 MHz and the frequency division of the frequency divider b is 1/2560, 5 KHz is input to the phase comparator 6. On the other hand, if the local oscillation frequency f01 of the VCO is 1 GHz, the frequency divider a divides the frequency by 1/200000 to 5
KHz can be made. Phase synchronization (lock) is applied by comparing the above 5 kHz.

If the frequency division by 1/200000 of the frequency divider a is ± 1 (200001 or 199999), the frequency entering the phase comparator 6 tends to be 5 KHz, and the oscillation frequency f01 of the VCO is 1 GHz ± 5 KHz. .

As described above, by sequentially changing the frequency-divided data of the frequency dividers a and b by the microcomputer 18, the oscillation frequency of the VCO (that is, the first local oscillation frequency f01) can be made variable.

Next, in the method (2), the first local oscillator Lo
The reference oscillation frequency f0 of the crystal oscillator OSC of 1 is set to the crystal CR.
The capacitors C1 and C2 connected in parallel with the switch S
The local oscillation frequency f01 is fluctuated stepwise as shown in the table by switching by 1 and S2. Further, .DELTA.f can be finely changed by increasing the number of circuits ... Cn, ... Sn. The switches S1 ... Are switched by the microcomputer 18.

Next, in the method (3), the up / down counter 15 controlled by the microcomputer performs addition / subtraction at an appropriate cycle, and the D / A converter 16 obtains a triangular wave CW. When this is connected to the variable capacitance diode 17 connected to the tuning circuit of the crystal oscillator OSC, the variation of the local oscillation frequency f01, which was stepwise in (2), becomes continuous.

Since the new AFC circuit of this time is subject to the periodic fluctuation of the local oscillation frequency, if the fluctuation range is made sufficiently wider than the expected center frequency deviation, the microcomputer for controlling the system when there is no signal has a local cycle at a predetermined cycle. Oscillation frequency f
By swinging 01, even if the reference frequency f0 or the received frequency (arrival wave F0) is deviated, the partner signal S can always be taken out as the output fS of the detector DET through the band filter, and once the partner signal is detected. If this is done, thereafter, the frequency shift can be set to zero by the normal AFC function, and the communication can be maintained in the best state as it is.

According to this method, even if a narrower (optimal) band filter than usual is used for BPF2 and BPF3, the frequency shift is always detected and the AFC function is operated to catch the signal to match the frequency with the other party of communication. It becomes possible. In addition, the crystal oscillator to be used has the advantage that it can be used even if it is inexpensive and has a stability of about 2 to 3 PPM, which contributes to cost reduction.

It should be noted that the AFC function here does not have to be constantly operating, and there is no problem even if the AFC function operates at the start of communication or at regular intervals after the start.

Needless to say, the AFC operation according to the present invention can be similarly applied to the second local oscillator Lo2.

The present invention does not specify how to use the output of the AFC, but only limits the method of changing the local oscillation frequency so that the AFC function operates with a narrow filter.

[0049]

The wireless communication device with the automatic frequency adjusting circuit according to the present invention has the following excellent effects.

(1) Even though the pass band width of the band-pass filter circuit is narrower than that of the conventional one so that a high S / N ratio can be obtained, the automatic frequency adjustment function can be effectively operated in the gigahertz region where frequency deviation becomes a problem. It has an excellent effect of being able to.

(2) The stability of the crystal oscillator serving as the reference frequency does not pose any particular problem, and an inexpensive one can be used, which has an excellent effect of reducing the cost.

[Brief description of drawings]

FIG. 1 is a block circuit diagram illustrating an FM receiver of a wireless communication device according to the present invention.

FIG. 2 is a block circuit diagram for explaining three embodiments for varying a local oscillation frequency f01 of a wireless communication device according to the present invention.

FIG. 3 Superheterodyne F with conventional AFC circuit
It is an example of a block configuration of an M receiver.

FIG. 4 is a diagram for explaining a relationship between pass band widths of band-pass filters BPF2 and BPF3 and center frequency shifts of a partner signal wave and a first intermediate wave.

[Explanation of symbols]

 3, 13 Automatic frequency adjustment (AFC) circuit 4 Crystal oscillator 5 Voltage control oscillator 6 Phase comparator 7 Low-pass filter 10 Wireless communication device 11, 12 Band filter 17 Variable capacitance diode 18 Microcomputer ANT antenna BPF1 High frequency band filter BPF2, BPF3 band Filter Lo1 First local oscillation circuit Lo2 Second local oscillation circuit MIX1 First mixer MIX2 Second mixer DET Detector (frequency discriminator) HFA High frequency amplifier LFA Low frequency amplifier F0 Incoming wave F1 First intermediate frequency F2 Second intermediate Frequency f0 Reference oscillation frequency Δf Deviation frequency f01 First local oscillation frequency f02 Second local oscillation frequency fS Detection output ef DC voltage level S Opponent signal CW triangular wave

Claims (1)

[Claims] 1. A radio communication device with an automatic frequency adjustment circuit having a super-heterodyne receiver, wherein a bandpass filter for filtering a first intermediate frequency after passing through a first mixer and a bandpass filter after passing through a second mixer are provided. The passband width of the bandpass filter that filters the second intermediate frequency is set to a narrow band so that the signal-to-noise ratio is optimized with no frequency shift, and the automatic frequency adjustment circuit shifts the center frequency of the detection output. Detecting the DC voltage level corresponding to the frequency adjustment and at the same time when the other party signal is out of the pass band of the bandpass filter and the detection output is no signal, the first local oscillator Deviation of the center frequency so that the local oscillation frequency is varied within a predetermined range so that the partner signals in the first intermediate frequency and the second intermediate frequency are both in the center of the pass band of the bandpass filter A wireless communication device with an automatic frequency adjustment circuit, which automatically adjusts the frequency.