JPH0738536B2 - RF converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an RF converter for displaying signals of a video tape recorder, a video disk, a microcomputer, etc. on a television receiver.

SUMMARY OF THE INVENTION The present invention is an RF converter for displaying a signal of a video tape recorder, a video disc, a microcomputer, or the like on a television receiver, while modulating a common carrier signal with a video signal and an audio signal. By adding and synthesizing the differential output of the differential amplifier to be added and synthesized by the differential amplifier, it is possible to suppress the base band feed-through, components, high frequency components, etc., and simplify the external accessory circuit. is there.

[Conventional technology]

Conventionally, in video equipment such as video tape recorders,
The video output and audio output are converted into an empty channel television signal by an RF converter and supplied to a monitor receiver.

In general, RF converters have conventionally been offered as integrated circuits (ICs) such as balanced mixers for video signal modulation and balanced mixers for audio signal modulation. Further, by adding and synthesizing, the target television signal is converted.

[Problems to be solved by the invention]

Generally, in RF converters, the baseband feed-through components and harmonic components are factors that determine the circuit size of the external accessory circuit, and it is necessary to keep the baseband feed-through components and harmonic components small. is there. In the conventional RF converter, the modulated output of the video signal and the modulated output of the audio signal are added and synthesized outside the IC, so that the wiring of the external accessory circuit is troublesome and the mounting space is large. There were problems such as.

Considering the mounting space and wiring of the external accessory circuit in this way, it is desirable that the means for adding and synthesizing the modulated output of the video signal and the modulated output of the audio signal be integrated with each modulating means. Baseband feed-through components and harmonic components become factors that determine the circuit scale of the external accessory circuit, and it is necessary to keep the baseband feed-through components and harmonic components small.

Therefore, in view of the above problems, the present invention provides an RF converter having a novel configuration in which the feedthrough component, the harmonic component, and the like of the baseband are suppressed to be small and the circuit scale of the attached circuit can be reduced. That is the purpose.

[Means for solving problems]

In order to solve the above-mentioned problems, the RF converter according to the present invention includes a first differential amplifier to which a carrier signal is commonly supplied and an emitter current path of the first differential amplifier. A third differential amplifier connected to which a video signal is input; a fourth differential amplifier connected to an emitter current path of the second differential amplifier to input an audio signal; and the first and second And a fifth differential amplifier to which each output of the differential amplifier is supplied.

[Action]

In the RF converter according to the present invention, the first and second differential amplifiers modulate the signal level of the carrier signal with the signal level of the input video signal and the signal level of the input audio signal, and add and synthesize them. Further, the third and fourth differential amplifiers operate as signal input means for supplying video signals and audio signals to the first and second differential amplifiers. Further, the fifth differential amplifier is
The modulated combined outputs output from the first and second differential amplifiers are further added and combined to output an RF converted output signal.

〔Example〕

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

In the embodiment shown in FIG. 1, the modulated carrier signal S _C is supplied between the first input terminals 1, the audio signal S _V is supplied between the third input terminals 3, and The video signal S _A is supplied between the input terminals 2 of.

The first input terminal 1 is connected to the bases of the pair of transistors Q ₁₁ and Q ₁₂ that form the first differential amplifier 10, and also forms the second differential amplifier 20. The bases of the pair of transistors Q ₂₁ and Q ₂₂ are connected to each other. The second input terminal 2 is connected to the bases of a pair of transistors Q ₃₁ and Q ₃₂ forming the third differential amplifier 30. Furthermore, the third input terminal 3 is connected to the bases of a pair of transistors Q ₄₁ and Q ₄₂ that form a fourth differential amplifier 40.

In each of the transistors Q ₁₁ and Q ₂₂ constituting the first and second differential amplifiers 10 and 20, each collector is connected to the power supply V _CC through a common resistor R _C1 , and It is connected to the base of one transistor Q ₅₁ which constitutes the fifth differential amplifier 50. Further, the other transistor Q constituting each of the first and second differential amplifiers 10 and 20.
₁₂ and Q ₂₁ are connected to the power source V _CC through a resistor R _C2 that is common to each collector.
Is connected to the base of the other transistor Q ₅₂ which constitutes the fifth differential amplifier 50.

Further, in the transistors Q ₃₁ and Q ₃₂ which form the third differential amplifier 30, each emitter has a constant current source 31, 32, respectively.
_Grounded through and connected to each other through a resistor R _E3 . Then, each of the above transistors Q ₃₁ , Q
_One of the collectors of ₃₂ is connected to the emitters of the transistors Q ₁₁ and Q ₁₂ that form the first differential amplifier 10, and the other is connected to the power supply V _CC .

Here, the constant current sources 31 and 32 have the same current I
₁ is set to flow.

Further, in the transistors Q ₄₁ and Q ₄₂ constituting the fourth differential amplifier 40, the emitters thereof are constant current sources 41 and respectively.
It is grounded via 42 and is also connected to each other via a resistor R _E4 . Then, the transistors Q ₄₁ ,
One of the collectors of Q ₄₂ is connected to the emitters of the transistors Q ₂₁ and Q ₂₂ that form the second differential amplifier 20, and the other is connected to the power supply V _CC .

Here, the constant current sources 41 and 42 have the same current I
₂ is set to flow.

Then, each transistor that constitutes the fifth differential amplifier 50.
Q ₅₁ , Q ₅₂ are connected to each other via resistors R _E5 , and each collector is connected to each other via resistors R _C3 and R _C4 . Connected to the power supply V _CC through. Further, an output terminal 5 is provided at a connection point between the collector of one of the transistors Q ₅₁ which constitutes the fifth differential amplifier 50 and the resistor R _C4 .

In the embodiment having the above-mentioned configuration, if the signal level of the video signal S _V is x, the signal level of the audio signal S _A is y, and the signal level of the carrier signal S _C is z, the first differential amplifier 10 In the emitter current path of the above video signal
I corresponding to S _V signal level x of _{1 = I 1 · (1 +} x) current i ₁ flows consisting, i ₁₁ in each of the transistors Q11, Q12 = (1 + x ) · (1 + z) · I 1/2 i 12 = ( Currents i ₁₁ and i _{12 of} (1 + x) · (1−z) · I _1/2 flow.

Further, the emitter current path of the second differential amplifier 20, the audio signal S i according to the signal level x of _{A 2 = I 2 · (1} + y) current i ₂ flows made, the transistors Q _21, Q _{22 i 21 = (1 + y)} · (1 + z) · I 2/2 i 22 = (1 + y) · (1-z) · I 2/2 becomes current i _21, i ₂₂ flows.

Therefore, in the resistor R _C1 connected to the collectors of the transistors Q ₁₁ and Q ₂₂ of each of the first and second differential amplifiers 10 and 20, I ₀₁ = i ₁₁ + i ₂₂ = (1 + x). _{(1 + z) · I 1} /2 + (1 + y) ·
_{(1-z) · I 2} /2 becomes the current I ₀₁ flows, and each other of the transistors Q _12, Q
The resistor R _C2 connected to the collector of _{21, I 02 = i 12 +} i 21 = (1 + x) · (1-z) · I 1/2 + (1 + y) ·
_{(1 + z) · I 2} /2 becomes the current I ₀₂ flows.

That is, in this embodiment, the first and second differential amplifiers 10 and 20 convert the signal level z of the carrier signal S _{C into} the signal levels x and y of the video signal S _V and the audio signal S _A , respectively. The operation of modulating and adding and synthesizing is performed.

Then, in the fifth differential amplifier 50 to which the outputs of the first and second differential amplifiers 10 and 20 are supplied, I ₀ = I ₀₁ −I ₀₂ = (1 + x) · (1 + z) · I _{1/2 + (1 + y} ) · (1
-Z) ・ I ₂ / 2- (1 + x) ・ (1-z) ・ I ₁ / 2- (1+
y) · (1 + z) · I 2/2 = 2z · (1 + x) · I 1 / 2-2z · (1 + y) · I 2/2 = xz · I 1 -yz · I 2 + (I 1 -I 2 ) .Z current I ₀ will flow through transistor Q ₅₁ .

Therefore, the common carrier signal S _C is modulated by the input video signal S _V and the audio signal S _A from the signal output terminal 5 provided in the collector of the transistor 51 which constitutes the fifth differential amplifier 50. A combined RF conversion output signal can be obtained.

In this embodiment, the first and second differential amplifiers
The degree of modulation of the common carrier signal S _{C in} 10, 20 depends on the current that is steadily flowed in each emitter current path of each of the differential amplifiers 10, 20 described above.
It is determined by the current setting value I ₁ of each constant current source 31, 32 provided in 30 and the current setting value I ₂ of each constant current source 41, 42 provided in the above-mentioned fourth differential amplifier 40. Then, the degree of modulation by the video signal S _V in the first differential amplifier 10 is set smaller than the degree of modulation by the audio signal S _A in the second differential amplifier 20 so that 100% modulation is not performed. . That is, the current I ₁ of each constant current source 31, 32 provided in the third differential amplifier 30 and the current I ₂ of each constant current source 41, 42 provided in the fourth differential amplifier 40 described above are Set to different values.

The first and second differential amplifiers 10 and 20 operate as so-called double balanced mixers, and when the steady-state value of each emitter current, that is, each of the currents I ₁ and I ₂ is equal, the baseband component is Although it does not leak to the modulation output, if the respective currents I ₁ and I ₂ are set to different values as in this embodiment, the baseband component leaks to the modulation output. However, in this embodiment, each of the differential amplifiers 10 and 2 described above is
By supplying the respective modulated outputs from 0 to the fifth differential amplifier 50 and combining them, it is possible to cancel the leakage of the baseband component.

Here, the measurement results of the spectrum distribution of the output obtained at the signal output terminal 5 in the above-mentioned embodiment are shown in FIGS. 2A and 3A, and the fifth differential amplifier 50 in the above-mentioned embodiment is shown. FIGS. 2B and 3B show the measurement results of the spectrum distribution when the modulation output from the first differential amplifier 10 is directly taken out without being provided.

In this embodiment, as compared with the case where the fifth differential amplifier 50 is not provided, as shown in FIGS. 2A and 2B, the secondary spurious is improved by -21 dB and the RF output level is + 5d.
B can be elevated, and also FIGS. 2A and 2B
As shown in, the leakage of the baseband component could be improved by -28 dB.

Further, when the fifth differential amplifier 50 is not provided, the differential phase (DP) characteristic is remarkably changed when the ratio of the currents I ₁ and I ₂ is changed, and the differential phase (DP) characteristic is changed. Could not be made sufficiently small, but in the above example,
Even if the ratio of the currents I ₁ and I ₂ was changed, the differential phase (DP) characteristic did not change so much, and the differential phase (DP) characteristic could be suppressed sufficiently small.

As described above, in this embodiment, the secondary spurious component included in the RF conversion output signal obtained at the signal output terminal 5 can be suppressed to a small level, and the feed-through, that is, the leakage of the baseband component can be eliminated. By connecting a simple band-pass filter (BPF) with a small sharpness Q as an external accessory circuit, only the necessary RF conversion output signal component can be input to the television receiver.

〔The invention's effect〕

As is apparent from the above description of the embodiments of the present invention,
In the RF converter, the secondary spurious component contained in the RF converted output signal can be suppressed to a small level, and the feed-through, that is, the leakage of the baseband component can be eliminated. By connecting a bandpass filter (BPF), only the necessary RF conversion output signal components can be input to the television receiver. Moreover, the differential phase (DP) characteristic can be suppressed sufficiently small, and an RF converted output signal with good quality can be obtained.

In addition, the base band signal is a signal component of 3.58MHz and 4.5MHz in the case of an NTSC television signal. In Japan, 1ch (91.25MHz) or 2ch is used by the RF converter.
Although the conversion to ch (97.25MHz) television signals is performed, in the United States the RF carrier frequency is 55MHz, which is close to the frequency of the baseband signal, making it difficult to design the bandpass filter (BPF). Therefore, it is extremely effective to apply the present invention to video equipment for the United States.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an RF converter according to the present invention. FIG. 2A is a spectrum distribution diagram showing the results of actual measurement of the harmonic signal components contained in the RF conversion output signal according to the above embodiment, and FIG. 2B does not include the fifth differential amplifier in the above embodiment. FIG. 3A is a spectrum distribution diagram showing the result of actually measuring the harmonic signal component contained in the RF converted output signal when the modulated output from the first differential amplifier is directly taken out as the RF converted output signal. FIG. 3B is a spectrum distribution diagram showing the result of actually measuring the leakage component of the base band included in the RF conversion output signal according to the above embodiment, and FIG. 3B shows the first differential amplifier without the fifth differential amplifier in the above embodiment. FIG. 4 is a spectrum distribution diagram showing the result of actual measurement of the baseband leakage component included in the RF conversion output signal when the modulation output from the differential amplifier of is directly extracted as the RF conversion output signal. 10,20,30,40,50 ... Differential amplifier

Claims (1)

[Claims] 1. A first and a second differential amplifier to which a carrier signal is commonly supplied, and a third differential amplifier which is connected to an emitter current path of the first differential amplifier and receives a video signal. A fourth differential amplifier connected to the emitter current path of the second differential amplifier and receiving an audio signal, and a fifth differential amplifier to which the outputs of the first and second differential amplifiers are supplied. RF converter consisting of a differential amplifier.