JPS60204113A - Up-down tuner - Google Patents

Abstract

PURPOSE:To improve the 1st local oscillating frequency as required according to the frequency fluctuation of the 2nd oscillator by detecting the oscillating frequency of the 2nd local oscillator at the 3rd mixer so as to correct the detected frequency error at a PLL loop including the 1st local oscillator. CONSTITUTION:A reception signal applied to an input terminal 1 is fed to the 1st mixer 3 via an input BPF2, the signal is converted into the 1st IF by the local oscillating frequency of the 1st local oscillator 6, subjected to the 1st IF amplification 9 and fed to the 2nd mixer 11. The result is converted into the 2nd IF at the mixer 11 by using the local oscillating frequency of the 2nd local oscillator 12 and the 2nd IF is outputted from an output terminal 14. The frequency of the oscillator 12 is fed to the 3rd mixer 20 and converted into the 3rd IF by using the oscillation frequency of the oscillator 1. The 3rd IF is fed to a prescaler 70 and a PLL5 including the oscillator 6 is controlled by utilizing the relation of frequency between the 1st and 2nd oscillators. Further, generation of beat and spurious operation is suppressed corresponding to the frequency fluctuation of the oscillator 2.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to receiving a wideband signal (ML) and converting the received signal into a high frequency signal by a first mixer to which the output of a first local oscillator is added. The signal is converted into a first width wave signal, and then a second signal is generated using the output of the second local oscillator at a predetermined receiving frequency.
In particular, even when the oscillation frequency of the second local oscillator fluctuates, the second intermediate frequency signal is stabilized by correcting this frequency fluctuation. Concerning the up-down tuner of the Namihaku.

[Technical background of the invention and its problems]

In terms of frequency conversion ratio, etc., tuners that receive multiple channels, such as CATV, generally use an up-down channel that converts the input reception frequency to a higher frequency and then lowers it to a predetermined frequency. corner is used. Since this up-down channel is suitable for receiving multiple channels, it is applied to a system in which multiple channels are transmitted, such as CATV.

CATV is a communication signal system that has the transmission of multi-channel signals as one of its characteristics, but recently the number of transmission channels has been increasing, and the number of receiving channels can be increased without interference between multiple channels. What is desired is an up-down tuner that can be increased in number. Further, when the oscillation frequency of the second local oscillator fluctuates, the second intermediate frequency fluctuates, resulting in reception disturbances such as deterioration of reproduced images. Therefore, in the up-down tuner, it is necessary to sufficiently stabilize the frequency of the second intermediate frequency signal obtained by down-converting the one-way up-converted signal.

FIG. 1 is a circuit diagram showing a conventional up-down tuner, and shows the case where this is used for CATV. In FIG. 1, an input signal applied from an input terminal 1 is applied to a mixer 3 of part 1 via an input bandpass filter 2. The first mixer 3 includes a PLL circuit 5 that operates at a frequency division ratio set by the tuning circuit 4, a first local oscillator 6, and a prescaler that divides the oscillation outputs and supplies them to the PLL circuit 5. The output of the first local oscillator 6 whose output frequency has been stabilized by the loop No. 7 is added. As a result, the first mixer 3 converts the input signal applied to the input terminal 1 into a high frequency signal. In the state where the frequency has been converted to this high frequency, the channel selection circuit 4 sets a channel division ratio for the PLL circuit 5 to perform a channel selection operation. The output of the first mixer 3 is applied to a second mixer 11 via a first intermediate frequency band-pass filter 8, a first intermediate frequency amplifier 9, and a first intermediate frequency band-pass filter 10. The second mixer 11 receives the output of the second local oscillator 12 and frequency-converts the signal converted to the high frequency into a predetermined second intermediate frequency signal. The output of the second mixer 11 is applied to a second intermediate frequency signal passing filter 13 and then output to an output terminal 14.

The conventional up-down corner shown in FIG. 1 has the following problems. This problem will be described below, but for convenience of explanation, the reception frequency of the up-down tuner is assumed as follows.

In other words, the % receivable frequency range is 50 to 450 MHz (
Video carrier wave: 55.25MHz to 445.25MHz
z), US Channel 3 (video carrier frequency 61.25
M)lz) shall be received. At this time, the YY channel (fi
The frequency range corresponding to (2) ~ fi(YY)K is 55
．． 25MFtz~445°25 MHz; A1
Intermediate frequency flIFs First local oscillation frequency f 1 u
2) ~ f I L (YY), second intermediate station wave number f2IF
, the second local oscillation frequency f2L is as follows.

Margin table below 2 In addition, in the case of Cicona's reception channel power tool, for example, in the case of US channel 2 and channel 4, the second intermediate frequency f2IF is 55.25 and 67.25MFl, respectively.
z.

The second local oscillation frequency f2L is 668.680 ME respectively.
(The relationship between the other frequencies is 1-1 from the above table. Here, in the above table, the frequency conversion process is generalized by the following formula.

fxIp = flL-tic = tsu, z)-fi(
21=flL(W)”(i(yy))・・・・・・・・・
・(1) f2xp=f2t, -flxp ・・・・・・・・・(
2) The received signal, the first intermediate frequency, and the second intermediate frequency are subjected to frequency conversion based on the relationship shown in the above equation, but when the number of input channels increases, in other words, the input frequency range is expanded to the higher side. In this case, selection of the first intermediate frequency becomes an important factor in determining the performance of the tuner. Generally, it is desirable to set a high frequency for the following reasons (1) to (3).

(1) In FIG. 1, when the frequency of the transmission signal increases and the frequency input to the input terminal 1 increases, the first band-pass filter 8 acts as a band-pass filter on the output of the first mixer and the input signal Frequencies are close. The filter characteristics of the first intermediate frequency band-pass filter 8 are as shown in FIG. This shows the characteristics when the input frequency range is expanded by about 10 (bVHz) compared to If attenuation of unnecessary signals is insufficient at ZL, intermodulation with the frequency-converted signal and the output component of the second local oscillator 12 is likely to occur, and spurious signals to the output terminal 14 will increase.From this point of view, the channel When increasing the number, it is desirable to increase the frequency of the first intermediate frequency.

(2) Furthermore, as the number of channels increases and the input frequency range expands, the passband of the input bandpass filter 2 extends in a higher direction. In other words, among the characteristic curves in FIG. 3 showing the characteristics of the input bandpass filter 2, the characteristic curve A1 when the number of channels is not increased is compared with the characteristic curve B when 1001Vl [(z channels are added). As can be seen, when the number of channels is increased, the band of the input bandpass filter 2 must be widened.At this time, the band of the input bandpass filter 2 must be widened. Therefore, the level at which the oscillation output of the @10 local oscillator 6 leaks to the input bandpass filter 2 side increases.In this case as well, the oscillation frequency of the first local oscillator is increased to increase the frequency of the first intermediate wave number. This reduces the leakage of - to the input bandpass filter 2 side.

(3) Next, it is desirable to increase the first intermediate frequency from the viewpoint of interference beats between input signals, so-called constant beats.

In systems such as CATV where multiple channel signals are transmitted, various beat signals are generated in the first mixer, but among these beats, the beats with frequency components close to the first intermediate frequency are called fixed beats. do. The manner in which the above-mentioned constant beat occurs will be explained using the case of IN CATV in the US as an example. In the US CATV, the video carrier frequency of channel AA is 301.25 #II (z), channel BB is 307.25 ME (z), and the sum of these frequencies is 608.5 ME (z).
The video carrier frequency of is 295.25 MHz, and that of 1 channel CC is 313.25 MHz, so the sum of these frequencies is also 608.5 MF (z. Therefore, between channel crystal and BB, channel W and CC0, 6085 MHz
Generates a Hz beat. The 608.5 MHz beat also occurs in combinations other than these channel combinations. Focusing on the beat of i-g, 608.5■t, and converting it into one step, if the frequency of the channel crystal is (X-1) and the frequency of channel BB is (x+1), then the above 60
The 8.5 MHz component is generated according to the following equation.

Σ(fx-n+fz+n);"fop-...
・・・・・・・・・(3) Here 608.5 ME (z is 1
This level is within the band of the stBPF and interferes with the video and audio carriers, so it is desirable that this level be as small as possible.

However, in the current frequency range, 2 in the above equation is 2
4, but for example, the upper limit of both wavenumbers is 547.251Vf
f(If extended to z, it becomes 41, and the number of beats with the same frequency is approximately 1.7 times. As the number 2 above increases, that is, as the number of input signals increases, the beat level increases. However, if the first intermediate frequency is selected high, the number will decrease.In particular, if the first intermediate frequency is set to more than twice the upper limit of the input frequency, the number will decrease.
becomes 0 and the above beat does not occur.

For the above reasons, when increasing the number of transmission channels, it is better to select the first intermediate frequency signal frequency as high as possible.
This is particularly desirable for the reasons (1) to (3) mentioned above. In particular, for the reason (3) above, the upper limit of the input signal frequency is 2.
It is desirable to select a frequency that is at least twice as high. , In a double superheterodyne tuner for CA'rV, that is, an up-down tuner, the oscillation frequency of the first local oscillator is variable, and the second local oscillator is usually configured as a fixed frequency oscillator. As shown in FIG. 1, the output of the first local oscillator is frequency-divided by a fixed ratio in the grease scaler circuit 7, and Ii! It is generally necessary to stabilize the i1 wave number.

When the input family wavenumber range is expanded by increasing the number of input channels, the oscillation frequency of the first local oscillator increases in the direction of increasing. Furthermore, if the first local oscillator is selected to be higher, the increased frequency is added and the oscillation frequency of the first local oscillator is shifted upward.

On the other hand, the maximum divisible input frequency of the grease scaler circuit, that is, the upper limit of the frequency that can be input to the grease scaler is not infinite, but has a certain limit. Currently, the same frequency is IGH
The actual situation is that it is about 1.1 GHz or 1.1 GHz. As shown in Table 1, according to the currently commonly used frequency relationships, the frequency range of the first local oscillator is 66
8 to 1058MHz, for example, if the input frequency is 10
0MI (if z-enlarged, the same frequency is 668 to 115
The frequency becomes 8 MHz, which exceeds the current maximum frequency that can be divided, making it difficult to divide the frequency. Furthermore, if the first intermediate frequency is selected to be high, for example, more than twice the upper limit of the input signal, and set to 1112.75 h, l st
Since L and 0 are 1168 to 1658M) (z, branching is completely impossible, and a CATV chicon system cannot be realized.

As mentioned above, in an up-down tuner, as the number of channels increases, it is desirable to lower the oscillation frequency of the first local oscillator in terms of beat generation and spurious interference. In view of the frequency dividing ability of the grease scaler 7, the input frequency of the grease scaler 7 is limited, and there is a limit to increasing the first O local oscillation frequency.

Moreover, in the up-down corner shown in FIG. Reception problems such as deterioration occur.

[Purpose of the invention]

The present invention has been made in view of the above points, and it is possible to increase the oscillation frequency of the first local oscillator and to increase the oscillation frequency of the second local oscillator as necessary as the number of reception channels increases. It is an object of the present invention to provide an up-down corner that suppresses fluctuations in a second intermediate frequency signal in response to fluctuations.

[Summary of the invention]

In this invention, the first local oscillator 6 converts the input received signal into the output of the first mixer 3 into the first intermediate frequency, and the second local oscillator 12 converts the above kt into the intermediate frequency signal into the second intermediate frequency signal. A third mixer 20 is provided which converts the frequency into a second intermediate frequency signal by the mixer 11, receives the first local oscillator 6 and the second local oscillator as input, and generates a third intermediate frequency signal.

The first local oscillator 6, the third mixer 20, the third
PL
A D PLL loop is formed by the L circuit, and the frequency fluctuation of the second local oscillator is corrected by the PLL loop,
In addition, as the number of channels increases, the first intermediate frequency signal can be set higher as necessary.

[Embodiments of the invention]

FIG. 4 shows an embodiment of an up-down tuner according to the present invention, and parts having the same functions as those of the conventional example shown in FIG.

In FIG. 4, a received signal supplied from a terminal 1 is applied to a first mixer 3 via an input bandpass filter 2 and converted to a first intermediate frequency. The first intermediate frequency is applied to the second mixer 11.

The second mixer 11 uses a signal obtained by multiplying the output of the second local oscillator 12 by the multiplier 30 to generate the second intermediate frequency.
Frequency conversion to intermediate frequency signal. Second local oscillator 12
The output signal is applied to a third mixer 20, which inputs the outputs of the first local oscillator 6 and second local oscillator 12 and converts the frequency to a third intermediate frequency. This third intermediate frequency f3M has the following relationship between the oscillation frequency flL of the first local oscillator and the oscillation frequency f2L of the second local oscillator: s f3M''flL f2L. A signal with a frequency lower than the oscillation frequency fiL of the first local oscillator 6 is applied.Therefore, even though the frequency entering the grease scaler qO is low, the mixer 3 of @1 has a frequency corresponding to the increase in the number of channels. can be applied, and the first + frequency is set high to generate a beat.

The occurrence of spurious signals, etc. is suppressed. In the embodiment shown in FIG. 4, the multiplication ratio N of the multiplier 30 is set to N=2, and the frequency relationship with respect to the input frequencies shown in Table 2 above is shown in Table 4 below.

Below is a margin table. 4 The frequency conversion process itself is as follows: is a signal obtained by dividing the frequency by the grease scaler 7o.In other words, the input signal of the grease scaler 7o is
o, which is a signal converted to a low frequency by the third mixer 2o of the first local oscillator 6, and the frequency division ratio capability required of the prescaler 70 itself is relaxed. In a conventional up-down tuner, the frequency input to the grise scaler is 6.
68 to 1160 Ml (z), and there is a problem that the first intermediate frequency cannot be set high due to the problem of the branching ability of GRISCA-2, but according to the present invention, the period mantissa of the first local oscillator 6 itself is equal to the number of channels. Although it can be set higher as the frequency increases, the frequency input to the grease scaler 70 is added by the frequency difference between the first local oscillator 6 and the second local oscillator 12 due to the mixing action of the third mixer 20. According to the invention, the frequency applied to the grease scaler 70 is 331 to 823 MF1z as shown in Table 4, which is lower than the frequency applied to the input to the grease scale 270, which was 668 to 1160 MHz in the conventional case. is a wave number that has a sufficient margin as an input signal to the prescaler 70 or the PLL circuit 5, and the first intermediate frequency can be selected as high as required from the viewpoint of preventing beat disturbance and noise.

Now, assuming that the upper limit frequency of the input frequency of the grease scaler 70 is 1.1 GHz, according to the present invention, the input frequency can theoretically be further expanded by about 27 hff1z, and in this case, the frequency range is within the human frequency range. is about 50-825
It is expanded to stop 2.

In addition, as the number of channels increases, the first intermediate frequency k
If id
The output of 0 increases. As shown in FIG. 4, since a multiplier 30 is used, if the multiplication ratio of this multiplier 30 is N, the increase in the oscillation frequency of the second local oscillator 12 is equal to the increase in frequency due to the number of channels. /N is all you need. As a result.

The input frequency range has been increased to 55.25~ by increasing the number of channels.
If it is 547.25MHz, @1 intermediate frequency is 55
4FvIHz (2771Q[E (when zX2:N=2)) can be made worse than the current situation, and in this case, the first intermediate frequency can be increased to 1166.7MHz 1. In this way, the first intermediate frequency can be increased to 1166.7MHz 1. Since the intermediate frequency can be increased without compromising the division capability t of the prescaler 70, the number of channels can be increased without generating beats or spurious signals.

Note that, in consideration of the constant beat described above, it is desirable to set the first intermediate frequency to at least twice the upper limit of the incoming input frequency, but the first intermediate frequency is not limited to this frequency.

As mentioned above, in the conventional up-down channel corner, it is not possible to expand the input frequency range and raise the first intermediate frequency as the number of channels increases, but the up-down channel corner according to the present invention cannot As the number of channels increases, it becomes possible to increase the first intermediate frequency. From the current input frequency range of 55.25 to 445.25 VIHz shown in Table 1 above, the input frequency is increased by 5
Table 5 shows the frequency relationship at up and down corners according to the embodiment of the invention described above when the frequency is expanded to 5.25 to 547.25 MHz.

Margin table below 5 As can be seen from Table 5 above, as the number of receiving channels increases, the input frequency range of the up-down tuner expands.
If the first intermediate frequency is ideally set high, a conventional up-down cornerer would require a grease scaler that divides frequencies from 1168 to 1660 MHz, which is impractical because the branching ability of the grease scaler cannot keep up with this. However, according to the up-down cornerer of the present invention, the third mixer 20
is the input of the grease scaler, and its input frequency is 581~
Since it is 1073IVIE (z), it is within the branching capability of Griskey-2, so it can be used to add channels without causing problems such as beat interference.

In the up-down tuner according to the present invention, as shown in FIG. 4, vibrations in the oscillation frequency of the second local oscillator 12 result in fluctuations in the output of the third mixer 20, and this fluctuation is suppressed by the feedback action in the LL loop. The configuration is such that it is corrected. This second
The effect of correcting signal fluctuations in the intermediate frequency will be explained next.

In FIG. 4, the output signal flL of the first local oscillator 6
and the oscillation output f2L of the second local oscillator 12 are frequency-mixed in the third mixer 20, and this mixed frequency &X faM (=
ftt, -fzb) signals are input to the PLL circuit 5 directly or through the grease scaler 7o. When a frequency fluctuation occurs in either or both of the first local oscillator 6 and the second local oscillator, feedback is applied from the PLL1 path 5 to the first local oscillator circuit to adjust the oscillation output frequency of the tuner. Always keep it constant.

Note that the frequency commanded from the tuning circuit 4 to the PLL is not the conventional frequency flL, but a third frequency with a lower wave number than this.
The output frequency of the mixer 20 is (fu, -fzL).

To explain the correcting effect of the same wave number error detected by the third mixer 20, the US 11 channel will be taken as an example. Input frequency fio of US 11 channel.

is fl(1t)=199.25MI(z 1 first local oscillation frequency fIL(it)=812.00M1dz,
First intermediate frequency f IIF =612.75MHz,
W; 2nd local oscillation frequency, 2nd local oscillation frequency f
lL(11) -f2L is 245.00 (z).

Now, in the 11th channel, if the oscillation frequency of the first local oscillator 6 fluctuates by +I ME (z), the output frequency of the third mixer 20 will be 246 MHz, so the normal frequency 245'M [ (z K becomes P
LL operation is performed. In other words, the oscillation frequency of the first local oscillator 6 is lowered by I MHz.

A PLL operation is performed to correct frequency fluctuations of the first local oscillator 6. Conversely, when the oscillation frequency of the first local oscillator 6 shifts to -H4Hz, the same PLL f
The oscillation frequency of the first local oscillator is corrected by the AR operation.

Next, the oscillation wave number of the second local oscillator 12 fluctuated @
For example, if +IMHz fluctuates to 568.00MHz, the output frequency of the third mixer 7 will be 244A.
Since it is IIHz, that frequency is the regular frequency 245M.
](PI and L operate so that the oscillation frequency of the first local oscillator 6 becomes IMHz higher, that is, the oscillation frequency of the first local oscillator 6 becomes higher by IMHz.

At this time, the oscillation frequency of the first local oscillator 6 is 813.0
01VIHz, the frequency of the first intermediate frequency signal is 813.00-199.25=613.75MHz, which is 1.1VIHz higher than the normal frequency. However, the oscillation frequency of the second local oscillator is +I MHz.
Since we are assuming a fluctuating state, the signal frequency of the second intermediate frequency signal is 613.75-568.00=45-75
Mf(z), a constant frequency is always maintained, and fluctuations in the oscillation frequency of the second local oscillator 13 are corrected.

As described above, even if either the first local oscillator 6 or the second local oscillator 12 fluctuates, a frequency fluctuation correction action is performed to correct the frequency fluctuation of the second intermediate frequency signal.

In this way, by providing the third mixer 20, the frequency of one wave of the second intermediate frequency signal is maintained at a constant frequency by the PLL operation, but in the above embodiment, the second local oscillator 12
The frequency fluctuation results in the frequency fluctuation of the first intermediate frequency signal, so the bandwidth of the first intermediate frequency band-pass filter 8 corresponds to the frequency fluctuation as shown by the solid line in FIG. It is desirable to widen the frequency range by the amount taken into account.

That is, FIG. 5 shows the frequency characteristics of the first intermediate frequency band-pass filter 80, and the broken line in the figure shows the case where there is no frequency fluctuation due to frequency fluctuation correction of the second local oscillator 12 by the third mixer 20. , and the solid line indicates a characteristic in which the pass band is expanded by the frequency fluctuation caused by the frequency correction operation by the third mixer 2o. By configuring the first intermediate frequency band-pass filter 8 with the characteristic indicated by the line in FIG. Fluctuations in the oscillation frequency of the oscillator 12 can be reliably corrected.

〔Effect of the invention〕

As described above, according to the present invention, the oscillation frequency of the second local oscillator is detected by the third mixer, and the detected frequency error is corrected by the PLL loop including the first local oscillator. Even if the oscillation frequency of the second local oscillator fluctuates, the signal frequency of the second intermediate frequency signal can be kept constant.

Furthermore, even when the number of channels increases, the first intermediate frequency can be increased depending on the arrangement in order to prevent beat interference from occurring.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional up-down tuner, FIGS. 2 and 3 are characteristic diagrams showing the characteristics of FIG. 1,
Fig. 4 is a circuit diagram showing an embodiment of the present invention, and Fig. 5 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a characteristic diagram for explaining the characteristics of the circuit used in the figure. 1... Input terminal, 3... First mixer, 11... Second mixer, 6... First local oscillator, Figure 3 Frequency (MHz) Figure 4 Figure 5 Frequency (MHz)

Claims (1)

[Scope of Claims] An input terminal into which a plurality of channel signals to be received are input; a first mixer that converts the frequency into a first mixer, and a first intermediate frequency obtained at the output of the first mixer (with g as one input and an oscillation signal of a second local oscillator as the other input, a second frequency converter for converting the first intermediate frequency signal into a second intermediate frequency signal;
the oscillation frequency of the first or second local oscillator by detecting the frequency ζ of the difference between the oscillation frequency of the first local oscillator and the oscillation frequency of the second local oscillator. frequency fluctuation detection means for detecting fluctuations in the frequency fluctuation detection means; frequency control means for controlling the oscillation frequency of the first local oscillation circuit according to the output of the frequency fluctuation detection means; and deriving the output of the second mixer. said 8g even if the oscillation frequency of either one of said first and second local oscillators fluctuates.
An up-down tuner characterized by keeping the frequency of the intermediate frequency signal of No. 2 constant.