KR820002284B1 - Output circuit of tuner - Google Patents

Abstract

An output circuit of VHF tunner using FET devices in a mixed terminal has a good characteristic of beat and has a high gain. The dual gate MOSFET devices are used in the mixed terminal of VHF tunner and intermediate frequency signal is produced by these devices. The second dual gate MOSFET device combines these signals through a filter of double tuned circuit and then output circuit having a amplified characteristics is offered to gain a desired high level. The frequenvy conversion system which combines an output signal to an image circuit of a television set is applied.

Description

Tuner Output Circuit

1 and 2 are block diagrams showing the conventional tuner output circuit system.

3 is a block diagram of a tuner circuit system according to the present invention.

4 is an output circuit diagram of an essential part of a VHF tuner according to the present invention.

The present invention relates to an output circuit of a tuner, in particular an output circuit of a VHF tuner using a FET element in a mixing stage. Conventionally, mixing using a dural gate type MOSFET as a mixing element has the advantage of exerting an excellent effect on the bead characteristic, while the linearity of the output characteristic is strong, so that the desired gain can be obtained. There was a flaw that it could not be held high.

Therefore, in order to eliminate these drawbacks and increase the gain, it is proposed to amplify by using a bipolar transistor at the rear end, but due to the nonlinearity of the amplification characteristics by the transistor elements, the specific bead disturbance is generated again at the rear end side. It turned out to be practical. Therefore, it has been desired to provide a tuner output circuit that improves intermodulation, has no specific bead interference, and obtains a sufficiently high gain.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above, and an object thereof is to provide a tuner output circuit which facilitates defects with a television set while achieving wider output.

According to the present invention, in the television VHF tuner, a duo-alter MOSFET element is used for the mixing stage and a second duo-gate MOSFET is used to convert an intermediate frequency signal, which is frequency-converted by mixing, through a filter of a double modulation circuit. An output circuit is provided that is coupled to the device and amplified to achieve a desired level of gain here.

In other words, the first duo-alter MOSFET element is mainly used as the mixing element in the front end of the mixing stage of the VHF tuner, and the second duo-gate MOSFET element in the rear stage for amplifying the mixed intermediate frequency signal through the double-tuning filter circuit. In addition, a frequency conversion method is provided, which obtains an output signal having a predetermined gain and couples the output signal to a video circuit of a television set as a stable signal over a wide band. In such a conversion scheme, specific bead disturbances, for example. U.S. The color bead interference of the sixth channel is suppressed, and the output signal having a desired gain can be stably obtained even in a wide bandwidth of 10 MHz or more by improving the intermodulation characteristics.

In addition, it is possible to provide a tuner output circuit that is extremely stable against changes in the bias voltage and ambient temperature of the FET element and that reduces unnecessary radiation from the intermediate frequency output terminal despite a wide variation on the output side.

In other words, when the MOSFET element is used in the mixing stage, the conversion gain of the improved bead characteristic is lowered, causing other problems.

SUMMARY OF THE INVENTION The present invention discloses a novel and improved VHF tuner mixing stage that can satisfactorily achieve the gain required of a tuner rotor while improving intermodulation and characteristics.

It should be noted that in addition to using a bipolar transistor or simply adding a FET as a gain raising means, the front end is attenuated to exclude unnecessary signals of the received signal or the local oscillating signal component remaining on the output side of the mixing FET device. A means, specifically, a double-tuning filter circuit for an intermediate frequency signal is inserted so as to input only a desired intermediate frequency output component to the rear-end amplification MOSFET element.

This is extremely important in that the desired intermediate frequency signal component as the output of the mixed element, as well as the disturbed component such as the amplified local oscillation signal component, remains, preventing it from being mixed and generating the disturbed output in the post amplifier.

In addition, the prevention of the disturbance output requires sufficient attenuation of the local oscillation signal or the received signal that has passed through the front end, but this must be achieved simply and effectively.

For example, even if the amplification element is a bipolar transistor, even if the attenuation of 30 dB is obtained, if the local oscillation signal component is 1 V, it becomes about 30 mV and is input to the rear transistor element to cause a mixing action to generate an interference signal.

However, if the rear end is a MOSFET device as in the present invention, since no mixing action occurs at 30 mV, no interference signal is generated. Therefore, the configuration in which the two-stage MOSFET is combined as a double tuning circuit is extremely effective, and in particular, U.S. The sixth channel bead countermeasure is also effective.

Hereinafter, the present invention will be described in detail with reference to the drawings in accordance with the conventional and the present invention block and specific embodiments.

Prior to the description of the drawings, a specific color bead generation mechanism will be described.

For example, U.S. It is well known that there is color bead interference in the sixth channel according to the channel allocation method and in the second channel according to the Australian channel Haldal method.

U.S. In case of the sixth channel, a spurious intermediate frequency (IF) signal approaching a color signal carrier of 42 MHz is generated at a median frequency (SIF) of 41.25 MHz of an audio carrier and 45.75 MHz of an image carrier. It is considered that such spurious signals are generated due to the secondary nonlinearity and the third nonlinearity.

Therefore, these two main factors are described for the spurious occurrence in each case, and the method of suppressing such specific color bead disturbance is examined.

(i) The output current is given by the exponential series of input voltages when there is nonlinearity in a device with respect to spurious due to secondary nonlinearity.

What is given as e _in is represented as three signals of the image carrier V, the audio carrier 5 and the local oscillation (0).

Summarizing the above formula with respect to paragraph 3 of i

From this, when unidirectionalized in the second nonlinearity, the doubled and the added and decaying spectra are generated, respectively.

If feedback is present here, in the case of emitter ground (G.E), the second, third, and fourth terms of Eq. (3) assume α as an integer, and the input is as follows.

When this is mixed with the fundamental wave, 19 spectra are generated (the second and subsequent feedbacks are ignored because they are small), but there is a spectra in one of them (ω _s + ω _v -ω _o ).

this is

It is by.

This is 42 MHz when f _v = 83.25 MHz, f _s = 87.75 MHz, and f _o = 129 MHz.

(Ii) Substituting Formula (2) into a ₃ ein ³ in Clause 4 of Formula (1) for the spurious resulting from the third nonlinearity.

에 의하여 구하여지는 스펙트럼이 발생한다.As a result

The spectrum obtained by is generated.

(Iii) Inhibition of Beads

As described above, it is apparent that spurious disturbances are caused by secondary nonlinearity and feedback coupling or tertiary nonlinearity, and thus, devices having a low third order nonlinearity, in other words, strong linearity elements. What is necessary is just to use the thing with few feedbacks.

In order to exhibit these two characteristics, there is a dual gate MOS type FET, and the use of the mixing circuit 1 by the MOSFET element as shown in FIG. 1 makes it possible to suppress the above-mentioned beads. The drawback was that the circuit could not gain enough.

Here, RF is a reception signal input, OSC is a local oscillation signal, and IF is an intermediate frequency output signal.

On the other hand, the sum of the spectra produced by (i) and (ii) becomes as follows.

And where a ₂ and a _3> 0, α> hapjung of the spectrum in the case where 0 is a ₃ -3αa by ₂ = 0, the bias point is present.

This bias is very sharp, which means that the B voltage needs to be suppressed with very slight fluctuations, for example within ± 1%, and it is also very critical against ambient temperature changes, making it practical. This is not it.

Therefore, a circuit configuration must be made to eliminate these defects.

Here, an output circuit using bipolar transistors for amplification (see FIG. 2) in addition to the mixed circuit of the MOSFET alone shown in FIG. 1 and an output circuit using a second duo gate MOSFET for amplification ( A coupling circuit is proposed.

In each of these circuit type VHF tuners, the 75 Ω terminating antenna input terminal has the above-described voltage intensities of the video signal V: 60 dB and the audio signal S: 54 dB from two signal generators. When a signal corresponding to the sixth channel is input, the characteristics as shown in the following table are obtained on the output side, respectively.

Where the D / U ratio is the spectral analyzer

(Note 1) D / U ratio changes greatly with respect to bias change that gain change can neglect and is very weak against temperature change.

When the output side is widened, for example, in the 20 MHz band, the radiation from the IF terminal on the output side is greatly increased.

(Note 2) It is extremely strong against bias and temperature change, and passes through the double-tuning filter, so there is little radiation from the IF terminal even when the output is wideband. It is about 30dB compared with the above.

As is apparent from the respective tuner output circuit schemes shown in FIGS. 1 and 3 and the above table showing the characteristics thereof, the circuit scheme of FIG. 3 according to the present invention has a D / U ratio and gain indicative of color beads. In addition to the characteristics, the stability of the output circuit is distinguished as both the first and second figures and the superiority of the characteristics.

In Figs. 1 to 3, the mixed circuits are each configured as a dual gate MOSFET 1, and the reception signal RF and the local oscillation signal OSC are input to the input side thereof, and the intermediate frequency to the output side thereof. The signal IF is output.

In addition, the bipolar transistor amplifier 2 in FIG. 2 is connected to the duo-al gate MOSFET amplifier 3 in FIG. 3 as a rear end of the mixing circuit.

4 is a high frequency equivalent circuit diagram in which the circuit system of FIG.

Here, the MOSFFT amplifier 3 is inserted into the rear end of the mixing circuit of the first dual gate MOSFET 1 for mixing.

Since the amplifier is constituted by the double tuning circuit filter 4, the second and duo gate MOSFETs 5, and the output side tuning circuit 6, an interference signal or a local oscillation signal other than a specific color bead in the filter 4 is used. The passage of can be blocked. In addition, B is a B power supply terminal for operating the two MOSFETs 1 and 5, and is used in a common source method, and the second gate is properly biased with respect to the first gate input.

Such a configuration effectively prevents the carbidoid disturbance of the tuner as described above, and also improves intermodulation characteristics in addition to obtaining a desired gain.

In addition, the widening of the output side facilitates the coupling with the rear end circuit, thereby stabilizing the characteristics.

Moreover, practical effects are large, such as suppressing the radiation from an output side terminal. For example, the output bandwidth of the conventional 4.5 MHz bandwidth is expanded to 20 MHz to facilitate the coupling with the set, and also to suppress unnecessary radiation.

Claims (1)

A VHF tuner mixing stage for mixing an RF signal and a predetermined local oscillation signal to generate an intermediate frequency signal, wherein the mixing stage includes a first duo-gate MOSFET element 1 for mixing a reception signal and an oscillation signal. And a second demodulation filter for the intermediate frequency signal combining the second duo-gate MOSFET element 5 for amplifying the intermediate frequency signal generated by the element to a predetermined level and the first and second MOSFET elements. And a circuit (4), characterized in that the attenuator signal component is attenuated by the filter circuit described above.

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