JPH0918364A - Double super tuner - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to suppress spurious interference in a double super tuner. In a double super tuner, a second frequency converter 7 for converting a first intermediate frequency signal into a second intermediate frequency signal, and a second local oscillator 8 for outputting an oscillation signal to the second frequency converter 7. Between the first local oscillator 2
A double super tuner comprising a filter circuit 9 comprising a trap circuit having a pole at the fundamental frequency thereof or its higher order frequency or the higher order frequency of the second local oscillator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double super tuner used for a television tuner, a CATV converter or the like.

[0002]

2. Description of the Related Art In recent years, double super tuners have been used as tuners for television tuners and CATV converters.

A conventional double super tuner will be described below. FIG. 5 shows a circuit configuration of a conventional double super tuner. In FIG. 5, 1 is a first frequency converter, 2 is a first local oscillator, 3 is a low pass filter (LPF), 4 is a first band pass filter (BPF1), and 5 is a first intermediate frequency amplifier. , 6 is a second band pass filter (BPF2), 7 is a second frequency converter, and 8 is a second local oscillator. The modulated high-frequency signal is converted into an oscillation signal of the first local oscillator 2 and a first intermediate frequency signal of 612.75 MHz by the first frequency converter 2, and then the oscillation signal of the second local oscillator 8 and The second frequency converter 7 frequency-converts and outputs the second intermediate frequency signal of 58.75 MHz. The first and second bandpass filters 4 and 6 band-limit the frequency-converted signal and attenuate the image frequency.

[0004]

However, in the above-mentioned configuration, the oscillation signal of the first local oscillator 2 and the oscillation signal of the second local oscillator 8 are the integer multiple signals of the second oscillation signal.
The local oscillator 8 distorts the pseudo second local oscillation signal (5
52.5 to 558.5 MHz), and there is a problem that the first intermediate frequency signal is frequency-converted into the second intermediate frequency signal band by the second frequency converter 7 as an interference signal. The above-mentioned interfering frequency is the first system. Second
If the intermediate frequency is determined, the jamming channel. The generation frequency can be specified. FIG. 4 shows the interference frequency-related values in the above conventional system.

An object of the present invention is to provide a double super tuner which can easily solve the above conventional problems.

[0006]

In order to achieve this object, a double super tuner according to the present invention includes a fundamental frequency and a high frequency of a first local oscillator between a second frequency converter and a second local oscillator. A trap circuit is arranged as a filter for attenuating the next higher harmonic frequency.

In order to achieve this object, the double super tuner of the present invention comprises a fundamental frequency of the first local oscillator and higher harmonic frequencies between the second frequency converter and the second local oscillator. A low-pass filter is arranged as a first filter for attenuating the.

[0008]

With this configuration, the first filter can obtain a certain degree of attenuation at the fundamental frequency of the first local oscillator and the harmonic frequencies of several orders, and can be input to the second local oscillator. It is possible to suppress the signal levels of the fundamental frequency and the frequencies of several orders of one local oscillation signal, and to suppress spurious interference in a stable manner.

With this configuration, the low-pass filter as the first filter can obtain a certain degree of attenuation at the fundamental frequency of the first local oscillator and the harmonic frequencies up to the high order, and the second pass filter. The signal levels of the fundamental frequency and the several-order frequencies of the first local oscillation signal input to the local oscillator can be suppressed, and spurious interference can be suppressed stably.

[0010]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

1 and 2, parts having the same functions as those in FIG. 5 are designated by the same reference numerals. FIG. 4 shows a frequency relation table of spurious interference generation in the above conventional system. In FIG. 1, 1 is a first frequency converter, 2 is a first local oscillator, 3 is a low pass filter (LPF), 4 is a first band pass filter (BPF1), and 5 is a first intermediate frequency amplifier. , 6 is a second band pass filter (BPF2), 7 is a second frequency converter, 9 is a first filter, and 8 is a second local oscillator. FIG. 2 shows the second local oscillator 8 and the first
The actual circuit of the filter 9 of FIG. 16 is a resonance circuit section, 17
Is a coupling capacitor for the oscillation transistor 21 and the resonance circuit portion 16, 17 and 18 are bias resistors for the transistor 21, 24 is an emitter resistor, 20 is a capacitor for grounding high frequency components of the oscillation frequency band, 22 and 23 are capacitors, 2
Reference numeral 5 is a coupling capacitor, 26, 27, and 28 are resistors, which form a resistance attenuator, 29 is an inductance, which is a matching inductance between the second local oscillator 8 and the second frequency converter 7, and 34 is an inductance, which is a second intermediate frequency signal ( 58.75 MHz) is shorted.

36 is a second intermediate frequency bandpass filter,
30.37.39 is the inductance, 31.38.40
Is a capacitor. The operation of the double super tuner configured as above will be described below.

The first local oscillator 2 has a frequency of 704.5 MHz.
It oscillates up to 1162.5MHz and the level of the reference signal is 1.
5 dBm, the oscillation signal is mixed with the RF signal by the first frequency converter 1, and the first intermediate frequency signal (612.
The frequency is converted to 75 MHz). LPF4 has a cut-off frequency of 1 GHz and an out-of-band characteristic of 2 GHz or more is -40.
dB or more. First bandpass filter (BPF
1) 4 is an attenuation of image frequency (495.25 MHz) of 10 dB and an attenuation of 1 to 2 GHz of 20 dB. The first intermediate frequency signal after passing through the three filters is amplified by the first intermediate frequency amplifier 5, and then band-limited (1 GHz or more attenuation 30 or more) by the second band-pass filter (BPF2) 6.
2 dB or more) and mixed by the second frequency converter 7 with the oscillation signal (554 MHz) of the second local oscillator 8
The frequency is converted into an intermediate frequency signal (58.75 MHz).

A first filter 14 consisting of an inductance 30.37.39 and a capacitor 31.38.40.
The pole frequency of the trap of is the oscillation signal of the second local oscillator (5
54MHz) 2.3.4 times higher harmonics (1.1GHz,
1.66 GHz, 2.22 GHz), attenuation 15d
Secure at least B. The pole frequency 1.10 GHz of the trap of the first filter 9 is the fundamental frequency of the oscillation signal of the first local oscillator of the C68 channel, and the pole frequency 1.66 GHz of the trap of the first filter 9 is 12 channels. A harmonic of twice the oscillation signal of the first local oscillator,
The pole frequency of the trap of the first filter 14 is 2.22.
GHz is a triple harmonic of the oscillation signal of the first local oscillator of the C16 channel and a double harmonic of the oscillation signal of the first local oscillator of the C68 channel.

(Embodiment 2) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, the same elements as those in FIG. 1.2.5 are designated by the same reference numerals. FIG. 3 shows a real circuit of the second local oscillator 8 and the first filter 9. FIG. 4 shows a frequency relation table of spurious interference generation in the above conventional system. Reference numeral 16 is a resonance circuit section, and 17 is an oscillation transistor 21.
And a coupling capacitor of the resonance circuit section 16, 17 and 18 are bias resistors of the transistor 21, 24 is an emitter resistor,
20 is a capacitor for grounding the high frequency component of the oscillation frequency band,
22 and 23 are capacitors, 25 is a coupling capacitor, 26
27 and 28 are resistors, which constitute a resistance attenuator, 29 is an inductance, which is a matching inductance between the second local oscillator 8 and the second frequency converter 7, and 34 is an inductance, which shorts the second intermediate frequency signal (58.75 MHz). To do. 36 is a second intermediate frequency bandpass filter, 4
1.42.43 is an inductance of 44.45.46.
47.48.49 is a capacitor. The operation of the double super tuner configured as above will be described below.

A first filter 14 consisting of an inductance 41.42.43 and a capacitor 44.45.46.
The parallel resonance trap has a pole frequency of 1.10 GHz,
By setting the cutoff frequency of the first filter 9 to 600 MHz and the band attenuation attenuation of 35 dB or more from 1 to 6 GHz, the cutoff frequency is set to 1.66 GHz and 3.32 GHz. The pole frequency of the trap of the first filter 9 is 1.
10 GHz is the fundamental frequency of the oscillation signal of the first local oscillator of the C68 channel, and the pole frequency of 1.66 GHz of the trap of the first filter 9 is twice the harmonic of the oscillation signal of the first local oscillator of the 12 channels. Wave, the pole frequency of 3.32 GHz of the trap of the first filter 14 is C
It is a triple harmonic of the oscillation signal of the 68-channel first local oscillator and a 4-fold harmonic of the oscillation signal of the 12-channel first local oscillator.

[0018]

As described above, according to the present invention, the fundamental frequency of the oscillation signal of the first local oscillator 2 and the harmonics of several orders are provided between the second frequency converter 7 and the second local oscillator 8. By arranging the trap in the first filter 9 that decrements the frequency, a constant attenuation can be obtained at the fundamental frequency of the first local oscillator 2 and harmonic frequencies of several orders, and the second local The distortion component generated by the difference between the oscillation signals of the first local oscillator 2 and the oscillation signal of the second local oscillator 8 in the oscillator 8 can be suppressed, and thereby spurious interference can be stably suppressed. be able to.

As described above, according to the present invention, between the second frequency converter 7 and the second local oscillator 8, the fundamental frequency of the oscillation signal of the first local oscillator 2 and the harmonic frequencies up to several orders. By arranging a low-pass filter as the first filter 9 for attenuating, the constant attenuation can be obtained at the fundamental frequency of the first local oscillator 2 and higher harmonic frequencies, and The first local oscillator 2 in the local oscillator 8 of
Distortion signal generated by the difference between each of the oscillation signals of 1 and the oscillation signal of the second local oscillator 8 can be suppressed, and thereby the spurious interference can be suppressed stably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a double super tuner according to an embodiment of the present invention.

FIG. 2 shows the first trap and the second trap of the first embodiment of the present invention.
Of the real circuit of the local oscillator and the second frequency converter

FIG. 3 is a first trap and a second trap of the first embodiment of the present invention.
Of the real circuit of the local oscillator and the second frequency converter

FIG. 4 is a diagram showing a frequency relation table of spurious interference occurrence.

FIG. 5 is a block diagram of a conventional double super tuner.

[Explanation of symbols]

1 1st frequency converter 2 1st local oscillator 3 low pass filter (LPF) 4 1st bandpass filter (BPF1) 5 1st intermediate frequency amplifier 6 2nd bandpass filter (BPF2) 7 2nd Frequency converter 8 Second local oscillator 9 First filter 16 Resonance circuit section 17 25 Coupling capacitor 18 19 Bias resistor 20, 22, 23, 31, 38, 40, 44, 45, 4
6, 47, 48, 49 Capacitor 21 Oscillation transistor 24 Emitter resistance 26 27 28 Resistance 29, 30, 37, 40, 41, 42, 43 Inductance 36 Second intermediate frequency bandpass filter

Front page continuation (72) Inventor Takaaki Konishi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A first frequency converter for inputting a high-frequency signal to convert the frequency into a first intermediate frequency signal, and a first local oscillator for generating an oscillation signal to be input to the first frequency converter, A second frequency converter for inputting the first intermediate frequency signal and converting the frequency into a second intermediate frequency signal; a second local oscillator for generating an oscillation signal for inputting to the second frequency converter; A second frequency converter and the second
Between the local oscillators, the filter comprising a trap circuit having a pole at the fundamental frequency or higher order frequency of the first local oscillator or the higher order frequency of the second local oscillator. Super tuner. 2. The double super tuner according to claim 1, wherein the filter is a low-pass filter.