JPS6076819A - Radio receiver free from cross spurious - Google Patents

Abstract

PURPOSE:To prevent the generation of cross spurious beats by applying the voltage obtained by giving D/A conversion to the proper digit output of an up-down counter to a voltage control variable reactance element which gives a fine adjustment to the local oscillation frequency of a mixer at the next stage. CONSTITUTION:An input signal supplied through an antenna is turned into the 1st intermediate frequency of a mixer 2 of the preceding stage and then converted into the 2nd intermediate frequency by a mixer 4 of the next stage through a BPF3. The 2nd intermediate frequency is amplified and demodulated through a BPF5. The local oscillation frequency of the mixer 2 is injected from the 1st PLL oscillator 6, and the 2nd PLL oscillator 9 is used to a local oscillator of a mixer 62 within a control loop of the oscillator 6. Then the voltage which is obtained by giving D/A conversion to the proper digit output of a BCD up-down counter 10 which integrates the clock pulses given from an encoder 11 is applied to a voltage control variable reactance element 72 which controls the oscillation frequency of the mixer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is to prevent cross-snorrious beats from occurring in a communication device having a multi-frequency conversion configuration, particularly in a circuit including a PLL oscillator.

Almost all of recent communication devices are based on the sous-guetero main system, and often have multiple M conversions of double or more, and each converter (hereinafter referred to as a mixer) has a local Although it is equipped with an oscillator, PLL (Phas
e Locked Loop) control is often used.

However, PLL circuits have spurious beats that occur due to the frequency relationship of the circular part, which may interfere with reception at certain frequencies.First, we will explain the mechanism of its occurrence and the M essential point for the establishment of the present invention. The tonoft cancellation circuit, which is an element, will be explained.

FIG. 1 shows an example of the configuration of a double conversion superhetero gain receiving circuit, in which input information from antennas l and p is converted to a first intermediate frequency by a pre-stage mixer 2, and then passes through a transpantohas filter 3. It is amplified and demodulated by the downstream mixer 4 to the second intermediate frequency, which passes through the bandpass filter 5. The local oscillation frequency fLj of the front-stage mixer 2 is PLL
It is injected onto the controlled oscillation circuit. PLL oscillation circuit is 1
A pressure controlled oscillator (hereinafter referred to as VCO) generates fundamental wave oscillation, and its output is supplied to mixer 2 and mixed with the frequency of fixed oscillator 7 by internal mixer 62 to output fm. In FIG. 1, the frequency of the oscillator 7 is injected into the mixer 62 and is also used as the local oscillation frequency fL2 of the rear-stage mixer 4, so that the oscillator 7 serves as a shared oscillator for the front-stage mixer and the rear-stage mixer. This configuration can only limit the number of oscillators to one '1 by sharing the oscillator 7. Even if the oscillation frequency of the shared oscillator 7 fluctuates somewhat, the injection frequency fL of the pre-stage mixer
However, the change in the first intermediate frequency due to the fluctuation of 1 can be canceled out by the fluctuation of the injection frequency fL2 of the rear mixer, so that the 21st; 1 frequency is not affected at all. , the principle of which is well known as the drift cancellation method, so it will not be described in detail, but it is one of the essential components of the present invention.

The output frequency of the mixer 62 is passed through the divider 63 and compared with the reference frequency fR in the phase comparator 64, and the positive or negative detection voltage generated according to the phase difference is filtered into the low/high frequency filter 6.
In addition to the VCO 61 as a DC control voltage, it constitutes a control loop that stabilizes the oscillation frequency, but since the oscillation frequency basically changes in steps of the reference frequency fR, Compared to fLlV, 9 is very small, and the frequency divider output frequency whose phase should be compared with 9 is also an extremely small value. On the other hand, there is a problem that the larger the frequency division ratio of the frequency divider, the lower the control loop gain and the lower the stability of the PLL Luso.
Since it is desirable that the output f of the mixer 62il-L is a down mixer, it is desirable that the frequency is as low as possible, and because of the constraints imposed by the operable frequency of the frequency divider, fm is usually set to be much smaller than fL. . Since the cross snorious fist beat of the PLL circuit is most noticeable when the frequencies of f and fLl are in an integer ratio, the mechanism of its occurrence will be explained below.

62 is a down mixer, so if we take the above integer ratio fn and let fL, > fL2, then fm = fL, -fL2, and the mixer output has fLi ``L2'' in addition to fnI.
This includes frequencies such as fLs+fL2, which are fLs+fL2, etc.
Since it has a much higher frequency than m, it is easily removed by the filter band and mid-pass filter, and only f can be extracted. Due to the non-linearity of the mixer, harmonics of the above frequencies are generated. This harmonic itself has an i% lower frequency, so there is no problem, but in the frequency state of nfm=fL1, the nth harmonic of the output fIn has the same frequency as fLi, causing interference. This becomes a zero beat and appears outside7
1. However, if the input frequency changes by Δf, the change in the fundamental wave output is Δf, and the change in the nth harmonic output is nΔ
It becomes f. Therefore, nfm→]lfm:l:nΔf-fL, ±nΔf Taking the difference between this and the input fL1±Δf, (fL, ±nΔf)
-CfL, ±Δf) = ±(n-1)Δf From this formula, it can be seen that before and after the frequency where the input frequency is n times the output frequency in the down mixer, the difference frequency from the input frequency is (n-1). Generating twice the beat frequency in the output means that the frequency changes so that it crosses around the silo beat, so it is generally called a cross spurious beat.

This beat passes through a frequency divider with fm or modulates fm and is mixed in the output of phase comparator 64, and if it is below the cutoff frequency of filter 65, VCO 61
It is frequency-modulated to the output fL1 and becomes a streaky component. If the cut-off frequency of this filter 65 is set low, the time constant increases and the lock-up time of the PLL oscillator (the time at 1 during which the oscillation frequency is stabilized) becomes longer, which is a limitation in practical circuits. There are also spurious waves caused by the high frequency and non-linearity of the reference frequency and phase comparator, but since all of them are limited to specific frequencies, it is desirable to have a setup i4 that is frequency-related, which generates spurious spurious waves. This is not possible for wideband Genezuru Capaleno applications. The actual situation will be explained using the practical circuit example shown in FIG. The difference between this circuit and the configuration shown in Figure 1 is that the PLL
The N-RIT is responsible only for the large frequency step 0 (in this case 1d 500 kHz) that is used to set the reception/gun. However, the constant ′iδ is PL
The frequency is mixed with the local oscillator 70 frequency of the downstream mixer 4 by the mixer 8, and the P
This purpose is achieved by injecting it into the mixer 62 in LL(b)1M6. 1 and 2, the only difference in their configuration is that the mikuki 8 is added, and the drift canceling operation described in connection with FIG. 1 is also applied to FIG. (Proof omitted) The frequency configuration is [intermediate frequency 47.055 kHz,
With the second intermediate frequency of 10,700 kHz, the reception frequency can range from 0 to 30.000 kHz. The following frequencies are also in kHz to avoid confusion.
Unify the display. Local oscillation frequency fL1 of front mixer 2
is the sum of the receiving frequency and the intermediate frequency, which is 47,055
~77.055 kHz, and since the PLL 60 reference frequency is 500 kHz, the bandwidth is also 500 kHz.
It becomes z.

The band width was set to 500 kHz by amateurs.
This is because it is convenient for bands. The local oscillation frequency f, 2 of the rear mixer 4 is 36,355 kHz.
and the second oscillation frequency is 8,700 to 9,200
kHz and mixer 8, the sum frequency is 45,055
~45.555 kHz fL4 is injected into mixer 62 within PLL 6. Frequency division ratio N of frequency divider 63 = 4 to 6
4, the comparison frequency on the output side is 500 kHz, so the input of the frequency divider (also the output of the mixer 62) fr11
= 500 kHzX'N, and as explained in Figure 1, when nfm = fLl, cross
produces a beat. However, this spurious does not occur in all bands, but in the case of the above frequency relationship, the receiving frequency 1ffl, 9
Generates beats around 45kHz. Uke 48 at that time
The 14th harmonic of the local oscillation frequency fL1 and 9 for the frequency table 1 (unit: kHz) (
Table 1 shows the relationship between the frequency of the cross-surgical beat (which is constant at 49,000 kHz) and the frequency of the generated cross-surgical beat. This beat frequency is 4'9,0 of the interference quotient gradient.
00 kHz is also the generated frequency that is added to the mixer together with the local excavation fLj and detected through the intermediate frequency stage. In order to prevent cross-surgical beats occurring in this way, the present invention uses a second PLL oscillator as the local oscillator of the mixer within the loose control of the first PLL oscillator constituting the local oscillator of the pre-stage mixer.
Setting the frequency of the operating band with the first PLL oscillator,
In a wireless receiver configured to set the first digit frequency within a band using a second PLL oscillator, the temporary mixer station 75B
The oscillation frequency of the first PLL oscillator? 111 control loop to form a drift canceling circuit (7t+) and set the local oscillation frequency to λ1.
) Setting the frequency of the LL oscillator Anor Dow/・D/A converting the appropriate digit output of the counter 4
By setting f/i, the first local oscillation frequency fL1, which generates the cross sharp beat, is shifted within a range where the sharp beat can be removed by a filter in the circuit.

Since the first PLL optical oscillation optical path circuit of the above He is almost the same as that in FIG. 2, the second PLL oscillation circuit will be described below. In Figure 3, the PLL circuit is an oscillator (VC
O-2) 91 (Oscillation frequency 87,000 to 92.0
0 (l kHz), programmable frequency divider 92 (
N; 700 to 1199), phase comparator 93 (reference frequency f112 is 10 kHz), low-pass filter 94
Since the oscillation frequency of vCO~2 is very high, the frequency applied to the frequency divider υ is lowered to 7,000 to 12,000 kf (z) by the down mixer 95.

VCO-2) output is 8,700 through a l/10 divider.
~9.200 kHz as mixer 8 (symbol fd 2nd
(common with the figure), the purpose of increasing the oscillation frequency and using the frequency divider is to shorten the lock-up time of the circuit by making it possible to obtain the reference frequency as much as possible. This is due to effects such as frequency division of the output, which reduces the sharpness of the output generated within the circuit, but these are not directly related to the present invention and will not be discussed in detail.

The frequency is set using the clock supplied from the encoder 11.
BCD f down counter 10 that integrates pulses
The data is input to each digit of the branch unit. This is the commonly used frequency control method.
The appropriate digit of the data output of the down counter 10 (
In Figure 3] kHy.

The output of the oscillating crystal element 71 of the local oscillator 7 of the rear-stage mixer 4 is adjusted to a voltage <Ii1!
In addition to the controlled variable reactance element (voltage iIt controlled variable capacitance diode 1' in the figure) 72, 36, 35 in FIG.
The oscillation frequency, which was a fixed frequency of 5 kHz, was changed to 36.3
By changing the frequency between 55 and 36,365 kHz, it is possible to avoid the cross-surgical noise that occurs around the receiving frequency of 1.945 kHz, as shown in Table 1. The second column summarizes this frequency relationship in an easy-to-understand manner, and for changes in the reception frequency in the first column,
When the second local oscillation frequency fL2 is changed as shown in the second column, the first local oscillation frequency FIfL1 changes stepwise as shown in the third column, and the cross oscillation frequency changes as shown in the fourth column. Since the beat frequency does not go below 51 kHz,
The deviation can be completely removed by using a narrow band filter. At this time, the first intermediate frequency fluctuates in the order of 25 kHz], but it is corrected by the drift-cancelling principle explained earlier, so that it does not fall out of the band of the first intermediate frequency filter. Note i(C misalignment indicates operational problem).

Figure 4 is a graphical representation of the frequency relationship between Tables 1 and 2 to make it easier to see.The thick line (A) is for Table 1, and the horizontal axis In response to the received J.1 wave, the local oscillation frequency changes proportionally to 1.9
A cross-surgical beat occurs around the zero beat of 45 kHz, and the intermediate frequency is 47,055 kHz.
It can be seen that it is constant. Also, Table 2 t'', wave number (B)
As shown in Table 2, the local oscillation frequency (unit: kHz) is 1d 49,00'OkHz, and the local oscillation frequency is 10
Since the beat frequency changes stepwise in kHz, the beat frequency is constant at a minimum of 5 kHz. 49,00 at 1.940 kHz
Although it appears to intersect with 0 kHz, it is actually 1-148
,995 to 49,005 kHz, so no beat occurs. 'Furthermore, since the intermediate frequency changes in a serpentine shape with a width of 10 kHz, it can be seen that the center frequency of the filter is 47,060 kHz, which is an even better deviation. In the second case, changes are displayed at 1 kHz intervals, but in reality, changes can be made more finely, so the shape is as shown in Figure 4.

In the 282nd order, in Fig. 4, the receiving frequency and the second local oscillation frequency f, 2 are the same amount of jI, 1 wave? j1. Although it is assumed that Vj will change, it is not necessarily necessary to change it by exactly the same amount, since the change in 11j shown by the broken line in Figure H174 will only be slightly curved and will not cause any problems in practical use. ,
There is no need to worry about it becoming a bottleneck in production.

Figure 4 is a simple 156-inch diagram. Figure 1 is an example of a Glock circuit diagram of a double comparator receiver having a PLL-controlled transmitter oscillation circuit. Figures 2 and 3 are block diagrams of a circuit implementing the present invention. FIG. 4 is a graph showing the frequency behavior of the circuit of the present invention, taken in a totally symmetrical manner.

1... Antenna, 2... Pre-stage mixer, 3, 5... Band pass filter, 4... Manslaughter mixer, mutual, tan...
・PLL oscillation circuit, 61.91...VCo, 62.9
5...Internal mixer, 63.92...Glogrammaple frequency division? J, 64.93... Phase comparison Wi, 65,94
...Low-pass filter, 7.2nd/-i section oscillator, 71.. Excavation crystal piece, 72.. Variable capacitance diode, 8.. Mixer, 10.. BCD assozo down.
Counter, 11...Encoder, 12...D/A converter, fL+'fL2'fL5'fL4...Local oscillation frequency, fRl l fR2・Reference frequency.

Patent Applicant: 8N Mi1 Radio Co., Ltd. Procedural Amendment Invitation (Method) February 15, 1980 Commissioner of the Patent Office Kazuo Wakasugi, Wife) bl, Indication of Case 1984 Patent Application No. 184736 2, Invention The name of the radio receiver 3 from which cross spurious was removed, the person making the correction 4, the date of the correction order, and the name of the invention are corrected to ``Radio receiver from which cross spurious was removed.''

Claims (1)

[Claims] A second PL as a local oscillator of the mixer in the control loop of the first PLL oscillator that constitutes the local oscillator of the pre-stage mixer.
In a radio receiver configured to use an L oscillator, a first PLL oscillator sets the frequency of the operating band, and a 20th PLL oscillator sets the lower digit frequency within the band, the local oscillation frequency of the subsequent mixer is set to the second PLL oscillator. The 20th PLL oscillator is injected into the control loop of the 20th PLL oscillator to configure a seat lift cancellation circuit, and the 20th PLL oscillator frequency is set to the voltage controlled variable reactance zigzag that finely adjusts the local oscillation frequency. A radio receiver that eliminates cross-snoritious noise generated in a PLL oscillator by using a 4U configuration that applies a voltage obtained by D/Ai converting the digit output as appropriate.