JPH0360225A - Receiver circuit - Google Patents

Abstract

PURPOSE:To simplify circuit configuration by making the carrier frequencies of the VHF low band of L-system and the VHF high band of L-system as well as a UHF band coincident with each other. CONSTITUTION:A frequency conversion circuit 21 is provided between a tuner 1 and surface wave filters 24, 25, and an intermediate frequency signal outputted from the tuner 1 is frequency-converted, and the frequency of a video signal (video carrier frequency) in the intermediate frequency signal after frequency conversion is made into the same frequency independently of the system and the received band of the received signal. Accordingly, the carrier frequency at the time of L-system VHF low band reception and the carrier frequency at the time of L-system VHF high band and UHF band reception coincide with each other. Thus, the changeover switch and the variable capacitor of tuning frequency become unnecessary, and the circuit configuration is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a branch channel for receiving signals (including video signals and audio signals) transmitted by different systems.

Conventional technology] Conventionally, in order to reduce the circuit scale when receiving signals transmitted by a system to the L system and B/G or D/, a method has been proposed in which an integrated circuit for video detection can be used in combination. has been proposed (Japanese Unexamined Patent Publication No. 65-245184)
.

FIG. 5 is a block diagram showing the main parts of a conventional receiving circuit, and FIG. 4 is a characteristic diagram showing the relationship between band characteristics and carrier frequency of the surface wave filter shown in FIG.

Furthermore, in the fourth prisoner, number 12 (t=1-5) is the video key? ') TJitli number, fct (i = i
~5) is the color subcarrier frequency, fsi(i =
1 to 3) represent audio carrier frequencies, respectively.

In the conventional example shown in FIG. 3, the surface wave filter 2 has a flat characteristic that passes from the video carrier frequency 15<fpt of the B/C system to the audio carrier frequency fsl. On the other hand, the audio surface wave filter 3 is the VH of the L system.
F high band and UHF band audio carrier frequency fs
It has a bimodal characteristic with passbands near z and near the audio carrier frequency fsa of the rHFo-band of the L system. Further, the pass band of the audio surface wave filter 3 exists outside the cutoff point of the surface wave filter 2.

In addition, by turning on and off the switch 9 connected to the video detection IC 4, the tuning frequency can be changed to fps, fP, and c.
= fc), and by turning on and on the switch 15 connected to the audio detection IC 5, the tuning frequency becomes fs! and jsl.

Therefore, for example, when receiving the VHF low band of the L system, use Swift 9y! - turn on switch 15
By turning off the desired video and audio signals can be obtained.

[Problem to be solved by the invention]

In the conventional example described above, there is no need for a special chainer with a so-called lower % a mechanical structure where the local frequency required for L system reception is lower than the carrier frequency, and there is an advantage that the video detection IC can also be shared. .

However, in the conventional example described above, each carrier frequency is the VHFcx-band of the L system, the VHF high band and the UHF band (or B/
G system), so for example, V of the L system
When switching from HF high band and UKF hand (or B/G system) to VHF low band of L system, it is necessary to switch the tuning frequency.
A switch and a highly accurate variable capacitor are required. In particular, the video detection circuit requires a video detection tuning circuit and an AFC tuning circuit, both of which need to switch the PJl&i1 frequency, resulting in a complicated circuit configuration.

In addition, among the carrier frequencies, in particular, the audio carrier frequency is different between the L system's VHFQ-pantodo, the L system's VHF high band, and the UHF band, so a special audio carrier frequency is used to pass the two different audio carrier frequencies. A surface wave filter is required, leading to an increase in the chip size and cost of the surface wave filter.

Also, among the carrier frequencies, the magnitude relationship between the video carrier frequency and the color subcarrier frequency is reversed between the VEFcx-band of the L system and the VHF high band and UHF band of the L system, so # - The delay characteristics are different, and the image quality changes between when receiving the L system (DVHFcx-/(Grot) and when receiving the VHF high band and UHF band of the L system.

The purpose of the present invention is to solve the problems of the prior art described above,
In a receiving circuit that receives signals transmitted between the L system and B/G or D/K% other systems,
At least the VEF low band of the L system and the VHF biband and UEF bands of the L system are made to match each carrier frequency.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an oscillator capable of oscillating at two different oscillation frequencies between the chainer and the surface wave filter, and the chip. A mixer that converts the frequency of the intermediate frequency signal output from the island with the oscillation output from the oscillator and outputs the resulting signal to each of the surface wave filters, and a frequency conversion circuit that converts the frequency of the signal and outputs the same to the surface wave filters are provided.

[Effect]

The frequency conversion circuit selects one of the two oscillation frequencies depending on the system or reception band of the received signal.
By causing the oscillator to oscillate at one of the oscillation frequencies, the frequency of the video signal included in the signal output from the frequency conversion circuit is the same regardless of the system or reception band of the received signal. Frequency conversion is performed so that the frequency becomes the same.

Example,tJf,,L system VHF bipan)',UEF
When receiving other systems such as band and B/G or D/, the intermediate frequency signal output from the IrtI chainer is set to the oscillation number of 8 of the oscillator as fl, and the intermediate frequency output tuning in the chainer is 1gjw1. When receiving the L system VHFcx-band by converting the frequency out of the band, the intermediate frequency signal output from the above-mentioned chip is
The oscillation frequency of the oscillator 'fpJ is set as f, and the frequency is converted to outside the band. At this time, the frequency f, and f
! is set so that the frequency of the video signal in the intermediate frequency signal after frequency conversion (i.e., video carrier frequency) is the same for the former and the latter.

As a result, in the intermediate frequency signal after frequency conversion, at least the L system VHFCI-band receiver 1g
In addition to the video carrier frequency, the color subcarrier frequency and the audio carrier frequency can be made to match each other when receiving signals in the VEF and UHF bands of the L system.

As a result, an IC for image 4a detection, which was previously required.

It is possible to eliminate the switch and variable capacitor for switching the PLL harmonic wave number of the tuning circuit of the audio detection IC, and the audio table bm filter only needs to pass a single frequency, so the filter configuration can be changed. This solves the problem that the image quality changes due to the group delay characteristic changing between the bands of the L system.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

In Fig. 1, 1 is a chainer, 4 is a video signal of the L system, and an ICl 3 for video detection for demodulating video signals and audio signals of other systems such as B/G or D/ is AM modulated by the L system. ICs for audio detection for demodulating the audio signal, 6 and 7 are each composed of a tuning coil and a capacitor for video detection, 10 and 11 are each a tuning coil and a capacitor for audio detection, and 21 is composed of a mixing circuit 22 and an oscillation circuit 23. 24 is a surface wave filter (SiF2) for selecting a video signal etc., and 25 is a surface wave filter (SiF4) for selecting an audio signal of the L system.

The frequency IX conversion circuit 21 is L system VHF high band,
f when receiving UHF band and other systems such as B/G.
= At the oscillation frequency, the intermediate frequency signal obtained from the chime output is converted to Tjde, and the L system VHFH is obtained.
- When the band is used, the frequency is converted at an oscillation frequency of f.

If the video intermediate frequency of the different output at the time of EGG reception is fl1, and the -color subcarrier convergence intermediate frequency is fCI, then L
System VEFr: oscillation frequency f at x-band receiver 6
By setting , to the relationship expressed by equation (1),
L system VHFCI-band frequency converted video carrier frequency, color subcarrier frequency, audio carrier frequency and L system VHF high band, UHF band frequency converted video carrier frequency 9 color subcarrier frequency, audio carrier frequency and It is possible to match the size relationship of

f2 = l fpt +jcx -h l ・-
(1) FIG. 2 shows an example of the frequency relationship of the intermediate frequency signal from the Chener output to the inspection IC input and the band characteristic of the surface wave filter in this embodiment.

In FIG. 2, reference numeral 26 indicates the 8-wave number relationship of the intermediate frequency signal at the Chener output when the BAG system receiver is 96.

27 is the frequency relationship of the intermediate frequency signal at the tuner output when receiving the L system VHF high band and UHF band, 28 is the frequency change relationship of the intermediate frequency signal at the tuner output when receiving the L system VBPCI-band, 29,
l is the oscillation circuit 2 when receiving B/G system and L system VHF high band and UHF, respectively.
3 oscillation frequency and L system VBFC! 51 and 52.55 indicate the frequency relationships after the intermediate frequency signals at the outputs of 26 and 27.28 are frequency-converted by the frequency conversion circuit 21, respectively; 54 is the i-band characteristic of the surface wave filter (SAFE) 24 for selecting the video signal, and 55 is the surface wave filter (SAW"4) 25 for selecting the L system audio f1.
The band characteristics are as follows.

With this configuration, it is possible to match the video intermediate frequency i number (video carrier frequency) and the audio intermediate frequency a ridge (audio carrier frequency) when receiving the L system VHFCX-band and when receiving other bands of the L system. , video demodulation I
The same g@ path of C only needs to operate at a single frequency,
There is no need for a switch and a variable capacitor to switch the tuning frequency as in the conventional technology, and the surface wave filter for selecting the audio signal when receiving the L system only needs to have a single peak characteristic, which simplifies the configuration of the surface wave filter. It is not necessary to switch the tuning circuit for audio demodulation.

Furthermore, since the magnitude relationship of the video carrier frequency and the color subcarrier frequency is the same when receiving the L system Ω-band and when receiving the other band signal 1B- of the L system, the conventional technology It is possible to eliminate changes in image quality due to changes in group delay characteristics due to the reversal of the magnitude relationship of the subcarrier frequency for one color of the video carrier frequency when receiving 4G and when receiving other bands, making it possible to obtain high-quality images. can.

In Figure 2, for example, jl is set lower than the intermediate frequency at the output of the chime, j2 is set higher,
Furthermore, the converted intermediate frequency is set lower than the intermediate frequency at the Chainer output, but as long as the relationship in equation (1) is satisfied, C and h can be set in any way, and they can be set at frequencies that do not cause interference. Just do it.

〔Effect of the invention〕

As explained above, in the present invention, a frequency conversion circuit is provided between the chainer and the surface wave filter, and the intermediate frequency signal outputted from the circuit is frequency converted, and the intermediate frequency signal after the frequency conversion is System and reception f6 of the signal in which the frequency of the video signal (video carrier frequency) in the frequency signal is received
By making the frequency the same regardless of the band, at least when receiving the L system VIiFC1-band and when receiving the VHF high band and UHF band of the L system, in addition to the video carrier frequency, the color subcarrier frequency , audio carrier frequencies can be set respectively.

This eliminates the need for a switch and a variable capacitor for switching the tuning frequencies of the video detection IC and the audio detection IC, which were conventionally necessary, thereby simplifying the circuit configuration.

Further, since the audio surface translation filter only needs to pass a single frequency, the configuration of one surface wave filter is simple, and the chip size and cost of the surface wave filter can be reduced.

In addition, since the magnitude relationship of the video carrier frequency and 9 color subcarrier frequencies is the same when receiving and receiving the VHFO band of the %L system and when receiving the VHF high band and UHF band of the L system, the magnitude relationship of the subcarrier frequencies of the 9 colors is the same, so it depends on the group delay characteristics between the bands. Changes can be removed and good image quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of a receiving circuit as an embodiment of the present invention, and FIG. FIG. 3 is a diagram showing the main part of a conventional receiving circuit, and FIG. 4 is a characteristic diagram showing the relationship between the band characteristic and the carrier frequency of the conventional surface wave filter shown in FIG. 1...Chi tool 4.5-$IL technical IC
6, 10... Tuning coil 7.11... Tuning coil 21 - Frequency conversion circuit 24, 25... Surface wave filter 41 - Figure 2

Claims (1)

[Claims] 1. A tuner capable of receiving signals transmitted by the L system and signals transmitted by other systems, and a video signal transmitted by the L system from the signal output from the tuner. A first surface wave filter selects and outputs the video signal and audio signal transmitted by the other system, and a second surface wave filter selects and outputs the audio signal transmitted by the L system from the signal output from the tuner. a first demodulation circuit that demodulates the video signal output from the first surface wave filter transmitted by the L system and the video signal and audio signal transmitted by the other system; a second demodulation circuit that demodulates the audio signal output from the second surface wave filter and transmitted by the L system, between the tuner and the first and second surface wave filters; An oscillator capable of oscillating at two different oscillation frequencies, and a signal output from the tuner mixed with the oscillation output from the oscillator to convert the frequency and generate the first and second surface waves. A frequency conversion circuit consisting of a mixer outputting to each filter is provided, and in the frequency conversion circuit, one of the two oscillation frequencies is selected depending on the system or reception band of the received signal.
By oscillating the oscillator at one of the oscillation frequencies, the frequency of the video signal included in the signal output from the frequency conversion circuit is the same regardless of the system or reception band of the received signal. A receiving circuit characterized by performing frequency conversion so that.