JPH0456524A - Tuner circuit - Google Patents

Abstract

PURPOSE:To reduce an interference signal generated in an RF amplifier by providing an input filter composed of an N-path filter and a pre--filter on the pre-stage of the RF amplifier. CONSTITUTION:A desired signal among plural RF signals inputted from an RF signal input terminal is selected at the input filter 2 by using a tuning volt age applied from a channel selector through a tuning voltage input terminal 9 and a local oscillation signal from a local oscillator 8 and the selected signal is amplified by an R amplifier 3. The input filter 2 consists of a pre-filter 10 and an N-path filter 11. In this case, the N-path filter 11 has a steep band characteristic and also has a flat characteristic within its pass band. Thus, the input filter 2 attenuates surely the signals other than the desired signal and only the desired signal is inputted to the RF amplifier 3. Thus, an interfer ence signal generated in the RF amplifier 3 is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a television signal (hereinafter referred to as a TV signal).
The present invention relates to a tuner circuit that can receive cable television signals (hereinafter referred to as CATV signals).

[Conventional technology]

Conventional tuner circuits that receive TV signals and CATV signals are of the single superheterodyne type for boat fishing, and include an input tuning filter, an RF amplifier, an interstage tuning filter, a mixer, a local oscillator, an IF amplifier, and an IF filter. The input RF multiplied signal is converted into an IF multiplied signal and outputted.

Here, the tuning filter has a two-stage configuration of an input tuning filter and an interstage tuning filter, which has a Q of up to the high frequency band.
This is to obtain a highly tuned filter.

Incidentally, in recent years, with the development of consumer CyaAs devices and high-frequency Si devices, tuner circuits that were conventionally composed of individual components (that is, composed of discrete circuits) have become more integrated, and mixers,
Local oscillators, IF amplifiers, etc. are being integrated.

However, filters such as input tuning filters and interstage tuning filters are still composed of individual components such as inductors and capacitors, so in order to obtain similar band characteristics over a wide frequency range, it is necessary to Complex adjustments to inductors, capacitance, etc. were required.

Therefore, in order to obtain a filter with high performance (that is, the same band characteristics can be obtained over a wide range of frequencies) and without adjustment, it is desired to integrate filters. One method of integrating filters is to use an N-pass filter, which can be constructed from operational amplifiers, resistors, and the like, and has a plurality of signal paths.

In addition, as a conventional example of filter integration using such an N-pass filter, for example, Japanese Patent Laid-Open No. 61-1
Examples include those described in Japanese Patent No. 50416. This conventional example discloses a method for reducing image signals that are generally problematic interference signals in radio receivers.

Note that the N-pass filter will be explained in detail later.

[Problems to be Solved by the Invention] As described above, the conventional example discloses a method for reducing image signals in a wireless receiver,
The target is the case where a single-channel signal is input, and no consideration is given to the case where multi-channel signals such as TV signals and CATV signals are input.

Therefore, the above conventional example can be used as is for TV signals and CATV signals.
When applied to a tuner circuit that receives signals, interference signals other than image signals such as second-order distortion and third-order distortion may be generated in the RF amplifier.

Moreover, in the conventional example described above, since the purpose is to reduce the image signal, even if interference signals other than the image signal (i.e., interference signals such as second-order distortion and third-order distortion) occur, they are ignored. It was not possible to reduce the interference signal.

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a tuner circuit using an N-pass filter that can reduce interference signals generated in an RF amplifier.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention includes a tuning device that outputs a tuning voltage, a tuning device that outputs a local oscillation signal, and a tuning voltage from the tuning device that is input, and a tuning device that outputs a local oscillation signal. A first local oscillator in which the frequency of a local oscillation signal changes; an input filter that receives an RF multiplied signal and outputs the signal by passing only a signal within its passband; and an output signal from the input filter. an RF amplifier that amplifies and outputs the signal; a local oscillation signal from the first local oscillator and an output signal from the RF amplifier are input; the signal is frequency-converted by the local oscillation signal; A mixer that outputs the IF multiplied signal, an IF amplifier that receives the IF multiplied signal from the mixer, amplifies and outputs the signal, and inputs the output signal from the IF amplifier, and among the signals, In a tuner circuit consisting of an F filter that only passes and outputs signals within its passband,
The input filter includes a pre-filter or a post-filter that inputs a tuning voltage from the channel selection device and whose pass band changes according to the tuning voltage, and a post-filter or post-filter of the pre-filter. An N-pass filter is disposed at the front stage, receives a local oscillation signal from the first local oscillator, and has a pass band that changes depending on the frequency of the local oscillation signal.

Further, a second local oscillator is provided which inputs the tuning voltage from the tuning device and changes the frequency of the local oscillation signal according to the tuning voltage, so that the frequency of the local oscillation signal from the first local oscillator changes. Alternatively, a local oscillation signal from the second local oscillator may be input to the N-pass filter.

[Effect]

Before explaining the present invention, the configuration and operation of the N-pass filter will be explained.

FIG. 11 is a block diagram showing the configuration of a general N-pass filter.

In the figure, 15 is a local oscillation signal input terminal, 20.2
1 is a signal terminal, 22 is a phase shifter, 23 and 25 are mixers for the first signal path, 24 is a first pass filter, 26.28
is the mixer of the second signal path, 27 is the second pass filter, 29.31 is the mixer of the third signal path, 30 is the third pass filter, 32.24 is the mixer of the Nth signal path,
33 is an Nth pass filter.

Typically, the mixers and pass filters of the first to Nth signal paths each have equal characteristics.

Further, the phase shifter 22 has a phase shift amount of 0.0, respectively, from the local oscillation signal input from the local oscillation signal input terminal 15 with respect to the local oscillation signal (period T). T/N, 2T/N,...
..., (N-1)T/N are generated and applied to the mixers of each signal path.

Note that the frequency of the local oscillation signal input from the local oscillation signal input terminal 15 is fc.

Now, the band characteristics of this N-pass filter are shown in Figure 12 and Figure 1.
This will be explained using Figure 3.

First, with reference to FIG. 12, a case will be described in which a bandpass filter whose pass band has a center frequency of 10 is used as the pass filters 24, 27, 30, and 33 in FIG. 11.

Figure (a) shows the band characteristics of each pass filter, with a center frequency fo and a pass band from fo-f to f. +f5.

The band characteristic of an N-pass filter consisting of this pass filter and a mixer of each signal path into which a local oscillation signal of frequency fc is input is shown in FIG. 2(b).

The passband of the N-pass filter is the passband of the passfilter, fc, and the passband whose center frequency is fc fo and whose bandwidth is equal to that of the passfilter, fc+f.

A passband with a center frequency of , and a bandwidth equal to that of the pass filter, and a harmonic order passband of these appear.

Next, with reference to FIG. 13, a case will be described in which low-pass filters with a passband of f are used as the pass filters 24, 27, 30, and 33 in FIG. 11.

Figure (a) shows the band characteristics of the pass filter, where the pass band is f,
It is a low pass filter.

The band characteristic of an N-pass filter consisting of this pass filter and a mixer for each signal path into which a local oscillation signal of frequency fC is input is shown in FIG. 2(b).

The passband of the N-pass filter includes a passband of the passfilter, a passband with fc as the center frequency and a bandwidth of 2 fs, which is twice that of the passfilter, and a passband of its harmonic order.

As mentioned above, the passband of the N-pass filter is determined by moving only the center frequency on the frequency axis at the frequency fC of the local oscillation signal injected into the mixer of each signal path, without changing the band characteristics of the pass filter. It is possible to obtain band characteristics similar to those described above. Therefore, even in a high frequency band where relatively steep (that is, high Q) band characteristics are difficult to achieve, it is possible to achieve a high Q band characteristic that can be achieved in a low frequency band.

Furthermore, since the band characteristics of each pass filter are maintained at any center frequency, there is little deviation within the band. Therefore,
When this N-pass filter is used in a tuner circuit, the PC tilt (level difference between the video carrier and color subcarrier due to in-band deviation), which is a relatively problematic problem in the tuner circuit, is reduced, and the PC tilt variation between channels is reduced. Similarly, when receiving TV signals such as high-definition television, the performance of the channel equalizer at the subsequent stage can be reduced.

The above is an explanation of the configuration and operation of the N-pass filter.

Now, the present invention will be explained.

In the present invention, since the input filter placed before the RF amplifier is configured with an N-pass filter having steep band characteristics, the input filter can reliably attenuate signals other than the desired signal, and the RF amplifier Only desired signals can be input to the RF amplifier and mixer, thereby reducing interference signals generated by the RF amplifier and mixer.

Furthermore, the present invention eliminates the need for an interstage filter (i.e., interstage tuning filter), which was conventionally provided to compensate for the band characteristics of the input filter (i.e., input tuning filter), and simplifies the circuit configuration of the tuner circuit. It is also possible to reduce the number of parts.

Further, since the local oscillation signal from the first local oscillator is input to the N-pass filter, the present invention can be incorporated into a conventional tuner circuit relatively easily.

On the other hand, when the local oscillation signal from the second local oscillator is input to the N-pass filter, the frequency of the local oscillation signal input to the N-pass filter can be arbitrarily selected. The degree of freedom in designing the pass filters constituting the filter increases, it becomes possible to use a low-pass filter as the pass filter, and it is possible to obtain a filter with steeper band characteristics.

〔Example〕 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a tuner circuit as a first embodiment of the present invention, and this embodiment is used in a television receiver.

In the same figure, 1 is an RF signal input terminal, 2 is an input filter, 3 is an RF amplifier, 4 is a mixer, 5 is an IF amplifier, and 6
7 is an IF filter, 7 is an IF signal output terminal, 8 is a local oscillator, and 9 is a tuning voltage input terminal.

Among the multiple RF signals input from the RF signal input terminal 1, the input filter 2 receives the tuning voltage applied from the tuning device (not shown) via the tuning voltage input terminal 9 and the local oscillation from the local oscillator 8. A desired signal is selected based on the signal and then amplified by the RF amplifier 3. Then, this desired signal is mixed with the local oscillation signal from the local oscillator 8 in the MISC 4 and converted into an IF multiplied signal. This IF multiplied signal I
The signal is amplified by the F amplifier 5 and output from the IF signal output terminal 7 through the IF filter 6.

Here, the configuration of the input filter 2 will be explained using FIGS. 2 and 3.

FIG. 2 is a block diagram showing one specific example of the input filter in FIG. 1, and FIG. 3 is a block diagram showing another specific example of the input filter in FIG. 1.

In these figures, 1 is an RF signal input terminal, 10 is a pre-filter, 11 is an N-pass filter, 12 is a post-filter, 13 is a tuning voltage input terminal, 14 is an output terminal, and 15 is a local oscillation signal input terminal. .

As described above, the N-pass filter 11 has, in principle, a pass band that is formed as a subsidiary in addition to the desired pass band.

Therefore, in order for the input filter 2 to form a single passband, at least the prefilter 10 or the postfilter 12 must be
It is necessary to select the required band according to the following.

FIG. 2 shows a specific example in which the prefilter 10 is used, and FIG. 3 shows a specific example in which the postfilter 12 is used.

Since the desired band characteristic is determined by the N-pass filter 11, the prefilter IO and the postfilter 12 can be configured with a low Q filter having a relatively wide band, that is, a low-order simple filter. For example, 5allen-Key
(Salen-Key) circuits and low-order ladder circuits.

Prefilter 10 or postfilter 1 having such a configuration
2, a tuning voltage is input from the tuning voltage input terminal 9 of FIG. 1 through the tuning voltage input terminal 13, and the band to be selected is controlled by the tuning voltage.

Further, a local oscillation signal from the local oscillator 8, which is the same as the local oscillation signal input to the mixer 4, is input to the N-pass filter 11 via a local oscillation signal input terminal 15.

In a specific example using the prefilter 10 shown in FIG.
Since the signal band input to the N-pass filter 11 can be limited by the prefilter 10, the interference rejection ability required of the N-pass filter 11 can be reduced.

In addition, in the specific example using the post-filter 12 shown in FIG. 3, it is possible to reduce the local oscillation signal leaking to the N-pass filter 11 through the mixer 4 and RF amplifier 3. Unnecessary signals (interfering signals) generated within the filter 11 can be reduced.

Next, the configuration of the N-pass filter 11 will be explained using FIG. 4.

FIG. 4 is a block diagram showing a specific example of the N-pass filter in FIGS. 2 and 3. FIG.

In the figure, 35 and 36 are band pass filters.

This specific example is an N-pass filter when N=2, and is an N-pass filter when bandpass filters 35 and 36 are used as the pass filters.

Therefore, this specific example has the band characteristics shown in FIG.

In FIG. 4, the local oscillation signal input from the local oscillation signal input terminal 15 is the same local oscillation signal output from the local oscillator 8 as the local oscillation signal input to the mixer 4, as described above.

Therefore, if the center frequency of the RF signal band selected by the input filter 2 is flIF+the center frequency of the intermediate frequency signal band output from the mixer 4 is flF, the frequency fC of the local oscillation signal is fc=f, I, +f ,.

becomes.

Next, this local oscillation signal is converted to 0° and 18° by a phase shifter 22.
The signals are converted into two signals with a 0° phase shift and applied to mixers 23 and 25 and mixers 26 and 28, respectively.

On the other hand, a bandpass filter 35.3 which is a pass filter
6, the passband of the N-pass filter 11 is f, as shown in FIG.
Bandpass filter 35.36 with center frequency at IF
Its own passband, a passband with its center frequency at fcflF, that is, fllF, and a passband with its center frequency at r, 10r, , are obtained, respectively. If a passband having flF as the center frequency is selected by the prefilter 10 or the postfilter 12, a single band characteristic can be obtained.

Using the US channel arrangement as an example, from the center frequency of the second channel signal band fllLF to 57M) (z,
The frequency f of the local oscillation signal for it. is 101M)t
z, the center frequency flF of the intermediate frequency signal band is 44MHz
So, if the center frequency f0 of the bandpass filter 35.36 is 44 MHz (-f IF), then 101M7-
A passband of an N-pass filter having a center frequency of 44M7=57Mce (fc f+v=f+ty) can be obtained. This makes it possible to select only the second channel signal.

Here, the other passband, that is, fc+flF=1
The band with a center frequency of 45 MHz is generally an image signal band, and when the frequency is converted by the mixer 4 in the subsequent stage, the frequency flF of the IF signal is determined by the difference from the frequency fc of the local oscillation signal.
This results in interference with the desired IF signal. Therefore, it is necessary to sufficiently attenuate this band using the prefilter 10 or the postfilter 12. In addition, it is also possible to suppress the image signal by adjusting the phase of the image signal using an image cancellation mixer.

In addition, in FIG. 4, the phase shift amount of the local oscillation signal in the phase shifter 22 is set to 0° and 90° instead of the above-mentioned Oo and 180@, and the mixer 23, 25 of the first signal path 0° to
, when a 90° phase-shifted signal is applied to the mixers 26 and 28 of the second signal path, the image signal is phase-shifted by 180° in the second signal path, and is canceled out by the opposite phase at the signal terminal 21. . By using this phase relationship, the degree of attenuation in the image signal band of the prefilter 10 or the postfilter 12 can be reduced.

Up to this point, the frequency relationship when receiving the second channel has been described, but with this method, a filter having the same band characteristics up to the highest receiving frequency in the UHF band of 800 MHz or higher can be realized.

The pass filter is a band pass filter whose center frequency is 44M) [35.36, and its pass band is lower than the frequency band of the RF signal, so it can be easily configured with an integrated circuit consisting of an operational amplifier, resistor, capacitor, etc. be.

The above has described the case where N = 2, but when N is 3 or more, by giving a phase shift amount of period/N to the N outputs of the phase shifter 22, a wide frequency range can be achieved. , a variable filter with constant band characteristics can be obtained.

As explained above, the N-pass filter has steep band characteristics and can obtain flat characteristics within the passband, and in this embodiment, such an N-pass filter is used as the input filter 2. This allows the input amplifier 2 to reliably attenuate signals other than the desired signal, and allows only the desired signal to be input to the RF amplifier 3. Therefore, the interference signal generated in the RF amplifier 3 (i.e., 2
RF distortion, third-order distortion, etc.) can be reduced.
Since the amplifier 3 itself does not need to take care to prevent the generation of interference signals, the configuration can be simplified accordingly.

Further, since the interstage tuning filter conventionally provided between the RF amplifier 3 and the mixer 4 to compensate for the characteristics of the input filter is no longer necessary, the circuit can be made smaller and the number of components can be reduced by two.

Furthermore, since the pass filter (original filter) in the N-pass filter 11 can have a relatively low pass band, the filter, which was conventionally constructed with a discrete circuit consisting of an inductor and a capacitor, can be replaced with an operational amplifier. It can be configured with an integrated circuit consisting of resistors, capacitors, etc., and therefore the circuit can be further miniaturized, and its performance can be improved.
It is possible to eliminate the need for adjustment.

Next, FIG. 5 is a block diagram showing a tuner circuit as a second embodiment of the present invention.

In this figure, the same components as in FIG. 1 are given the same reference numerals. Additionally, 40 is a second local oscillator.

In this embodiment, a second local oscillator 40 is provided separately from the local oscillator 8 in the embodiment shown in FIG. The phase shifter 22 of the N-pass filter 11 is manually operated.

Therefore, in the first embodiment, the local oscillation signal input to the phase shifter 22 is the same local oscillation signal from the local oscillator 8 as the local oscillation signal input manually to the mixer 4,
The frequency fc is determined by fRF, which is the center frequency of the RF signal band, and flF, which is the center frequency of the intermediate frequency signal band.
c=f*r+f+y, but in this embodiment, since the local oscillation signal input to the phase shifter 22 is the local oscillation signal from the second local oscillator 40, its frequency fc is the second local oscillation signal. can be arbitrarily selected using the local oscillator 40.

Therefore, in the embodiment shown in FIG. 1, the local oscillation signal from the local oscillator 8 is phase-shifted by the phase shifter 22 via the local oscillation signal input terminal 15, as shown in FIG.
, 25, 26, and 28, when obtaining the desired pass band, the image signal band appeared simultaneously on the high frequency side with the frequency fc of the local oscillation signal in between. , the frequency f of the local oscillation signal input to the phase shifter 22 via the local oscillation signal input terminal 15.

can be arbitrarily selected by the second local oscillator 40, so it is also possible to attenuate the image signal band.

That is, in FIG. 12, the pass band with fc fa as the center frequency is defined as the RF signal band (center frequency fi
) by selecting the frequency f of the local oscillator signal to be different from the frequency of the local oscillator signal from the local oscillator 8, fc +f.

It is possible to make the pass band with the center frequency different from the image signal band.

Alternatively, the frequency f of the local oscillation signal may be selected so that the pass band having the center frequency fc+fo matches the RF signal band (center frequency fIIF).

In addition, in this embodiment, the frequency f of the local oscillation signal,
can be arbitrarily selected by the second local oscillator 40, which increases the degree of freedom of the pass filter.

That is, as the pass filters constituting the N-pass filter 1, the band-pass filters 35 and 36 shown in FIG.
It is also possible to use a low-pass filter instead.

FIG. 6 is a block diagram showing another specific example of the N-pass filter constituting the input filter in FIG.

In the figure, 37, 38, and 39 are low-pass filters.

This specific example is an N-pass filter when N=3, and the low-pass filters 37, 38, 39
This is an N-pass filter when using . Therefore, this specific example has the band characteristics shown in FIG.

That is, in FIG. 6, the local oscillation signal from the second local oscillator 40 is input to the phase shifter 22 via the local oscillation signal input terminal 15, and the phase shifter 22 outputs 0' 12
The signal is converted into three signals phase-shifted by 0° and 240' and applied to mixers 23, 25°, 26.2B, and 29.31 of each signal path, respectively.

As a result, as shown in FIG. 13, the pass band of the low pass filter, the band where the low pass filters face each other with fc as the center, and the pass bands of harmonic orders thereof are obtained. Here, as shown by the broken line in FIG.
Alternatively, a single passband can be selected with the postfilter 12.

According to this specific example, the low pass filter 3 is used as the pass filter.
By using 7, 38, and 39, a steeper band characteristic can be realized, and since the band characteristic is folded back against fc, the passband is flat and the band on the high and low sides is flat. The outer damping layer can also be made equal. Furthermore, since the pass filter can be designed in a low frequency range, it is easy to configure the filter, which used to be a discrete circuit, with an integrated circuit.

Next, FIG. 7 is a block diagram showing a tuner circuit as a third embodiment of the present invention.

In this figure, the same components as in FIGS. 1 and 2 are given the same reference numerals.

In this embodiment, instead of the input filter 2 in the first embodiment, the prefilter 10 and the N-pass filter 11 shown in FIG. 2 are divided into the input side and output side of the RF amplifier 3. I tried to place it.

Therefore, since the RF amplifier 3 is placed before the N-pass filter 11, it is possible to compensate for the decrease in gain in the N-pass filter 11, and to reduce the influence of noise generated in the N-pass filter 11 on the overall noise figure of the tuner. I can do it, S/
A tuner circuit with less N deterioration can be realized.

Furthermore, since the prefilter 10 limits the signal band input to the RF amplifier 3, interference signals such as second-order distortion and third-order distortion caused by the nonlinearity of the RF amplifier 3 can be reduced.

Furthermore, it also has the effect of reducing local oscillation signals leaking from the N-pass filter 11 to the RF signal input terminal 1 side.

Next, an example in which the above configuration is applied to the example shown in FIG.
It is shown in FIG.

FIG. 8 is a block diagram showing a tuner circuit as a fourth embodiment of the present invention.

In this figure, the same components as in FIGS. 5 and 2 are given the same reference numerals.

In this embodiment, by using the second local oscillator 4o, the frequency f0 of the local oscillation signal input to the phase shifter 22 of the N-pass filter 11 can be arbitrarily selected, so as shown in FIG. A low-pass filter can be used as the pass filter in the N-pass filter 11, and a steeper and better band characteristic can be obtained.

In addition, since the RF amplifier 3 is placed before the N-pass filter 11, it is possible to compensate for the decrease in gain in the N-pass filter 11, and the influence of noise generated in the N-pass filter 11 on the overall noise figure of the tuner is reduced. Yes, S/N
A tuner circuit with less deterioration can be realized.

Furthermore, since the prefilter 10 limits the signal band input to the RF amplifier 3, interfering signals such as second-order distortion and third-order distortion caused by the nonlinearity of the RF amplifier 3 can be reduced.

Furthermore, it also has the effect of reducing local oscillation signals leaking from the N-pass filter 11 to the RF signal input terminal 1 side.

Next, FIG. 9 is a block diagram showing a tuner circuit as a fifth embodiment of the present invention.

In this figure, the same components as in FIG. 7 are given the same reference numerals. Additionally, 42 is a filter section, and 43 is a band switching terminal.

In this embodiment, the filter section 42 is composed of a plurality of band pass filters, and the N pass filter 11
The hands are divided so as to remove unnecessary passbands other than the desired passband generated in the transmitter, and the hands can be switched as appropriate according to the frequency of the desired signal to be received by a signal applied to the hand switching terminal 43.

Therefore, in this embodiment, in addition to obtaining the same effect as the embodiment shown in FIG. There is no need to consider
No adjustments will be made.

Next, an example in which the above configuration is applied to the example shown in FIG.
It is shown in FIG.

FIG. 10 is a block diagram showing a tuner circuit as a sixth embodiment of the present invention.

In this figure, the same components as in FIGS. 8 and 9 are given the same reference numerals.

Therefore, in this embodiment, the embodiment of FIG. 8 and the embodiment of FIG.
The same effect as the embodiment shown in the figure can be obtained.

In the embodiment shown in FIG. 9 and the embodiment shown in FIG. 10, the filter unit 42 is composed of a plurality of band-pass filters, but conditions such as the structure of the N-pass filter 11 and the channel arrangement of the desired reception band, etc. Depending on the case, the same effect can be obtained even if a low-pass filter or a bypass filter is used.

〔Effect of the invention〕

As explained above, in the present invention, the following effects can be obtained.

In other words, since an N-pass filter has a steep band characteristic, by providing an input filter consisting of an N-pass filter and a pre-filter or a post-filter before an RF amplifier, the input filter can eliminate signals other than the desired signal. can be reliably attenuated, allowing only the desired signal to be input to the RF amplifier, and therefore reducing the interference signal generated by the RF amplifier. Also,
Since the interstage filter (i.e., interstage tuning filter) that was conventionally provided to compensate for the band characteristics of the input filter (i.e., input tuning filter) is no longer required, the circuit configuration of the tuner circuit can be simplified, and the number of components can be reduced. It is also possible to reduce the number of points.

In addition, a pre-filter or a band-switchable filter is provided before the RF amplifier, and an N
When a pass filter is provided, the band of the signal input to the RF amplifier can be limited by a pre-filter or a band-switchable filter, so the R
Interfering signals generated by the F amplifier can be reduced.

Furthermore, it is possible to compensate for the decrease in gain in the N-pass filter, reduce the influence of noise generated in the N-pass filter on the overall noise figure of the tuner, and realize a tuner circuit with less S/N deterioration.

In addition, N-pass filters allow the pass filters inserted into each signal path to be designed in a relatively low frequency band, so the filters, which were conventionally constructed with discrete circuits consisting of inductors and capacitors, can be replaced with operational amplifiers, resistors, capacitors, etc. It can be configured with an integrated circuit consisting of, etc. Therefore, there is no need for the circuit area or circuit adjustment required for the inductor.
Further miniaturization of the circuit can be achieved, and high performance and no adjustment can be achieved.

In addition, N-pass filters have constant pass filter characteristics and constant band characteristics for all reception channels, so there is little in-band deviation, which reduces PC tilt and reduces PC tilt between channels. The variation in is also reduced.

Furthermore, if the same local oscillation signal input to the N-pass filter is used as the local oscillation signal manually input to the mixer, this can be easily achieved by making relatively simple changes to the conventional tuner circuit. can.

In addition, as a local oscillation signal input to the N-pass filter,
When using a signal different from the local oscillation signal input to the mixer, the frequency of the local oscillation signal input to the N-pass filter can be arbitrarily selected, so it can be set to a pass band that does not overlap with the image signal band. It is also possible to do so. In addition, the degree of freedom in designing the pass filters that make up the N-pass filter increases, making it possible to use a low-pass filter as a pass filter, allowing design in a lower frequency band, and thus further increasing the integration of filters. It becomes easier.

Furthermore, in the N-pass filter, it is also possible to cancel out the image signal by appropriately adjusting the phase shift amount of a phase shifter that shifts the input local oscillation signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a tuner circuit as a first embodiment of the present invention, FIG. 2 is a block diagram showing an integrated example of the input filter in FIG. 1, and FIG. 3 is a block diagram showing the input filter in FIG. 4 is a block diagram showing another example of the N-pass filter in FIGS. 2 and 3, and FIG. 5 is a block diagram showing a tuner circuit as a second embodiment of the present invention. FIG. 6 is a block diagram showing another specific example of the N-pass filter constituting the input filter in FIG. 7, and FIG. 7 is a block diagram showing a tuner circuit as a third embodiment of the present invention. , FIG. 8 is a block diagram showing a tuner circuit as a fourth embodiment of the invention, FIG. 9 is a block diagram showing a tuner circuit as a fifth embodiment of the invention, and FIG. 10 is a block diagram showing a tuner circuit as a fifth embodiment of the invention. A block diagram showing a tuner circuit as the sixth embodiment, FIG. 11 is a block diagram showing the configuration of a general N-pass filter, and FIG. 12 shows a case where a band-pass filter is used as the pass filter in FIG. 11. , a characteristic diagram showing the band characteristics of the pass filter and the N-pass filter, and FIG. 13 is a characteristic diagram showing the band characteristics of the pass filter and the N-pass filter when a low-pass filter is used as the pass filter in FIG. 11. . Explanation of symbols 2...Input filter, 3...RF amplifier, 4...
Mixer, 5... IF amplifier, 6... IF filter,
8... Local oscillator, 10... Prefilter, 11.
・・N-pass filter, 12 ・Post-filter, 22・
・・Phase shifter, 23.25, 26.2B, 29.31・・
・Signal path mixer, 35.36... Band pass filter, 36° 38.39... Low pass filter, 40
. . . second local oscillator, 42 . . . filter section. II Figure Agent Patent Attorney Akio Namiki) 12 Figure 3 Figure 4 Figure 6 Rei 5! ! i! @7 Figure 8 Figure 9 Figure 11

Claims (1)

[Claims] 1. A tuning device that outputs a tuning voltage, and a tuning device that outputs a local oscillation signal and inputs the tuning voltage from the tuning device,
a first local oscillator in which the frequency of the local oscillation signal changes according to the tuning voltage; an input filter that receives an RF signal and passes and outputs only a signal within the passband of the signal; An RF amplifier inputs an output signal from the input filter, amplifies and outputs the signal, and inputs a local oscillation signal from the first local oscillator and an output signal from the RF amplifier, and outputs the signal. A mixer that converts the frequency using the local oscillation signal and outputs it as an IF signal, an IF amplifier that inputs the IF signal from the mixer, amplifies and outputs the signal, and inputs the output signal from the IF amplifier. , an IF filter that passes and outputs only the signal within the passband of the signal, and the input filter inputs a tuning voltage from the tuning device and outputs the tuning voltage. a prefilter whose pass band changes according to the voltage, and which inputs the RF signal and passes and outputs only the signal within the pass band of the signal; A local oscillation signal is input, and its pass band changes according to the frequency of the local oscillation signal, and an output signal from the prefilter is input, and only the signal within the pass band is passed. A tuner circuit comprising: an N-pass filter that outputs the signal. 2. A tuning device that outputs a tuning voltage, outputting a local oscillation signal, and inputting the tuning voltage from the tuning device,
a first local oscillator in which the frequency of the local oscillation signal changes according to the tuning voltage; an input filter that receives an RF signal and passes and outputs only a signal within the passband of the signal; An RF amplifier inputs an output signal from the input filter, amplifies and outputs the signal, and inputs a local oscillation signal from the first local oscillator and an output signal from the RF amplifier, and outputs the signal. A mixer that converts the frequency using the local oscillation signal and outputs it as an IF signal, an IF amplifier that inputs the IF signal from the mixer, amplifies and outputs the signal, and inputs the output signal from the IF amplifier. , and an IF filter that passes and outputs only the signal within the passband of the signal, wherein the input filter receives a local oscillation signal from the first local oscillator. , an N-pass filter whose passband changes according to the frequency of the local oscillation signal, and which inputs the RF signal and passes only signals within the passband among the signals and outputs the filter; A tuning voltage from the station equipment is input, and its pass band changes according to the tuning voltage, and an output signal from the N-pass filter is input, and only the signals within the pass band are passed. A tuner circuit comprising: a post-filter that outputs the signal. 3. The tuner circuit according to claim 1 or 2,
A second local oscillator is provided that outputs a local oscillation signal, inputs a tuning voltage from the tuning device, and changes the frequency of the local oscillation signal in accordance with the tuning voltage,
The tuner circuit is characterized in that the N-pass filter receives a local oscillation signal from the second local oscillator instead of the local oscillation signal from the first local oscillator. 4. A tuning device that outputs a tuning voltage, outputting a local oscillation signal, and inputting the tuning voltage from the tuning device;
A first local oscillator whose frequency of the local oscillation signal changes according to the tuning voltage, and a tuning voltage from the tuning device are input, and the pass band changes according to the tuning voltage, and the RF signal a prefilter that inputs the signal, passes only the signal within the passband and outputs the signal, and an RF amplifier that inputs the output signal from the prefilter, amplifies the signal, and outputs the signal. , inputs a local oscillation signal from the first local oscillator, the pass band of which changes according to the frequency of the local oscillator, inputs an output signal from the RF amplifier, and inputs the output signal from the RF amplifier; An N-pass filter that passes only signals within a passband and outputs the signal; a local oscillation signal from the first local oscillator and an output signal from the N-pass filter are input; A mixer that converts the frequency and outputs it as an IF signal; an IF amplifier that inputs the IF signal from the mixer, amplifies and outputs the signal; and an IF amplifier that inputs the output signal from the IF amplifier and outputs the signal. , and an IF filter that passes only signals within its passband and outputs the filter. 5. The tuner circuit according to claim 4, wherein a second tuner circuit outputs a local oscillation signal and inputs a tuning voltage from the tuning device, and changes the frequency of the local oscillation signal in accordance with the tuning voltage. A tuner circuit characterized in that a local oscillator is provided, and the N-pass filter inputs a local oscillation signal from the second local oscillator instead of the local oscillation signal from the first local oscillator. 6. a tuning device that outputs a tuning voltage; and a tuning device that outputs a local oscillation signal and inputs the tuning voltage from the tuning device;
It has a first local oscillator whose frequency of the local oscillation signal changes according to the tuning voltage, and a plurality of fixed band filters, and a desired one of the fixed band filters is selected by an input switching signal. Along with selecting
A filter that inputs an RF signal, passes only the signal within the passband of the selected fixed band filter, and outputs the signal; inputs the output signal from the filter, amplifies and outputs the signal. An RF amplifier is input with a local oscillation signal from the first local oscillator, and its pass band changes depending on the frequency of the local oscillation signal, and an output signal from the RF amplifier is input, and the signal is Among them, an N pass filter that passes only signals within the pass band and outputs the filter, a local oscillation signal from the first local oscillator, and the N pass filter.
a mixer that inputs the output signal from the pass filter, converts the frequency of the signal using the local oscillation signal, and outputs it as an IF signal; inputs the IF signal from the mixer, amplifies the signal, and outputs the signal; A tuner circuit comprising: an IF amplifier; and an IF filter that receives an output signal from the IF amplifier, passes only signals within the passband of the signal, and outputs the passed signals. 7. The tuner circuit according to claim 6, wherein a second tuner circuit outputs a local oscillation signal and inputs a tuning voltage from the tuning device, and the frequency of the local oscillation signal changes according to the tuning voltage. A tuner circuit characterized in that a local oscillator is provided, and the N-pass filter inputs a local oscillation signal from the second local oscillator instead of the local oscillation signal from the first local oscillator. 8. The tuner circuit according to claim 3, 5 or 7, wherein the frequency of the local oscillation signal in the second local oscillator is set to the center frequency of the RF signal band desired to be received. A tuner circuit that changes according to the tuning voltage. 9. The tuner circuit according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the N-pass filter is a first mixer that converts the frequency of an input signal using an oscillation signal and outputs the frequency-converted signal. , a bandpass filter that inputs the output signal from the first mixer, passes only the signal within the IF signal band and outputs the signal, and inputs the output signal from the bandpass filter, and A second mixer that frequency-converts the signal using an oscillation signal and outputs the signal is connected in parallel, and the input local oscillation signal is phase-shifted so that the signal is at a position of approximately 180° from each other. Two signals having a phase difference are generated in a one-to-one correspondence with the two signal paths, and the two generated signals are respectively input to the first and second mixers of the corresponding signal paths as the oscillation signal. A tuner circuit characterized in that it has a phase shifter that inputs . 10. The tuner circuit according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the N-pass filter is a first mixer that converts the frequency of an input signal using an oscillation signal and outputs the frequency-converted signal. , a bandpass filter that inputs the output signal from the first mixer, passes only the signal within the IF signal band and outputs the signal, and inputs the output signal from the bandpass filter, and A second mixer that frequency-converts the signal using an oscillation signal and outputs the signal is connected in parallel, and the input local oscillation signal is phase-shifted so that the signal is at a position of approximately 90° from each other. Two signals having a phase difference are generated in a one-to-one correspondence with the two signal paths, and the two generated signals are respectively input to the first and second mixers of the corresponding signal paths as the oscillation signal. A tuner circuit characterized in that it has a phase shifter that inputs . 11. The tuner circuit according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the N-pass filter is a first mixer that converts the frequency of an input signal using an oscillation signal and outputs the frequency-converted signal. , a bandpass filter that inputs the output signal from the first mixer, passes only the IF signal band signal among the signals, and outputs the signal; It has N (N is an integer of 3 or more) signal paths connected in parallel, each consisting of a second mixer that converts the frequency using an oscillation signal and outputs the signal. The phase of the local oscillation signal is shifted by (period of the local oscillation signal)/N, and N signals are generated in one-to-one correspondence to the N signal paths, and the generated N signals are connected to the corresponding signal paths. A tuner circuit comprising a phase shifter that inputs the oscillation signal to the first and second mixers. 12. The tuner circuit according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the N-pass filter is a first mixer that converts the frequency of an input signal using an oscillation signal and outputs the frequency-converted signal. , a low-pass filter that inputs the output signal from the first mixer, passes only the signal within the passband of the signal, and outputs the signal; It has three signal paths connected in parallel, consisting of a second mixer that converts the frequency based on the oscillation signal and outputs the signal, and also shifts the phase of the input local oscillation signal so that the phase difference is approximately 120° from each other. three signals having a one-to-one correspondence to the three signal paths, and inputting the three generated signals to the first and second mixers of the corresponding signal paths as the oscillation signals, respectively. A tuner circuit comprising a phase shifter. 13. In the tuner circuit according to claim 1, 2, 3, 4, 5, 6, 7, or 8, the N-pass filter is a first mixer that converts the frequency of an input signal using an oscillation signal and outputs the frequency-converted signal. , a low-pass filter that inputs the output signal from the first mixer, passes only the passband signal of the signal, and outputs the signal; N (N is an integer) signal paths are connected in parallel, and the input local oscillation signal is converted to T (T is the period of the local oscillation signal). )/
By shifting the phase by N, N signals are generated in one-to-one correspondence with the N signal paths, and the generated N signals are:
A tuner circuit comprising a phase shifter that inputs the oscillation signal to the first and second mixers of corresponding signal paths. 14. A tuning device that outputs a tuning voltage; and a first tuning device that outputs a local oscillation signal and inputs the tuning voltage from the tuning device, and the frequency of the local oscillation signal changes according to the tuning voltage. A local oscillator, a tuning voltage from the channel selection device, and a local oscillation signal from the first local oscillator are input, and the pass band changes according to the frequency of the local oscillation signal and the tuning voltage, inputting the RF signal;
an input filter that passes and outputs only the signal within the passband among the signals; an RF amplifier that receives the output signal from the input filter, amplifies and outputs the signal;
a mixer that inputs a local oscillation signal from the first local oscillator and an output signal from the RF amplifier, converts the frequency of the signal using the local oscillation signal, and outputs the signal as an IF signal; and an IF signal from the mixer. An IF amplifier that inputs a signal, amplifies and outputs the signal, and an IF filter that inputs the output signal from the IF amplifier and passes and outputs only the signal within the passband of the signal. A tuner circuit comprising: 15. The tuner circuit according to claim 14, wherein the second tuner circuit outputs a local oscillation signal and receives a tuning voltage from the tuning device, and changes the frequency of the local oscillation signal in accordance with the tuning voltage. A tuner circuit comprising a local oscillator, and the input filter inputs a local oscillation signal from the second local oscillator instead of the local oscillation signal from the first local oscillator.