JPS6218112B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an RF converter circuit.

RF converters are used in video equipment such as video tape recorders (hereinafter referred to as VTRs) for connection with television receivers. this
An RF converter is a circuit that converts video and audio signals from a VTR, etc. into RF signals that are the same as broadcast waves.
The output signal is input from the antenna terminal of the television receiver, and can be received by the television receiver in the same way as broadcast waves. A conventional RF converter circuit has a configuration as shown in FIG. 1 or 2.

To explain the RF converter circuit shown in Figure 1, an audio signal input from input terminal 1 is converted into an FM wave with a center frequency of 4.5MHz by FM modulation circuit 2, and then input from input terminal 4 by mixing circuit 3. Mixed with video signal. Further, this output is frequency-converted by the frequency conversion circuit 5 using a carrier from the carrier wave oscillation circuit 6, and converted into an RF signal. The output signal of the frequency conversion circuit 5 includes upper and lower sideband waves of the video and audio FM signals around the carrier frequency. Among these, the lower sideband wave due to the high frequency component of the video signal has a relatively low level, so that the interference to the lower adjacent channel is slight. However, since the level of the lower sideband of the audio FM signal is relatively high, interference with the lower adjacent channel becomes a problem, and an audio lower sideband trap 7 is used to remove this frequency band. The RF signal that has passed through the audio lower side wave trap 7 is outputted to an output terminal 9 through a bandpass filter 8 to remove unnecessary spurious components.

By the way, the bandpass filter 8 has a relatively wide band characteristic sufficient for consumer use, so there is no particular need for adjustment, but the audio lower side wave trap 7 is required to have a steep characteristic and requires critical adjustment.

FIG. 2 is a block diagram showing another conventional example of an RF converter circuit. A video signal input from the input terminal 4 is converted into an RF signal by the AM modulation circuit 10. On the other hand, the audio signal input from the input terminal 1 is subjected to FM modulation in the FM modulation circuit 2, frequency-converted in the frequency conversion circuit 5, and lower-side wave trap 7 as described in the previous example. Lower side waves that interfere with adjacent channels are removed. and
The output of the AM modulation circuit 10 and the output of this trap 7 are mixed in a mixing circuit 3 and outputted at an output terminal 9 via a bandpass filter 8.

In the circuit shown in FIG. 2 described above, the audio FM signal and the video signal are converted into RF signals separately, so beat interference is less likely to occur, and this circuit is often used as a consumer RF converter circuit. However, as with the previous conventional example, interference of the lower side band of the audio FM signal to the lower adjacent channel becomes a problem.
An audio lower sidewave trap is required to remove this frequency band. In recent years, the development of surface acoustic wave resonators has made it possible to eliminate carrier wave oscillation circuits without adjustment, but this audio lower side wave trap still requires critical adjustment, and it is not possible to perform audio lower side wave removal without adjustment. There was a strong demand for a circuit that

The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide an RF converter circuit which, in principle, does not generate lower sideband waves after RF conversion of an audio FM signal.

The present invention generates an audio FM signal and a video carrier signal each at a frequency twice the fundamental frequency,
By dividing these positive polarity signals and reverse polarity signals by 1/2, a signal with a 90° phase difference can be generated without the need for a special phase shift circuit. Then, by adding these signals to the first, second, and two balanced modulators, and appropriately adding and subtracting the output signals of these modulators in a coupling circuit, only the upper sideband of the audio FM wave converted to an RF signal is generated. It was designed to be taken out.

The present invention will be explained below based on illustrated embodiments.

FIG. 3 is a block diagram showing an embodiment of the RF converter circuit according to the present invention. 20 is an audio signal input terminal, and 21 is an FM modulation circuit. This FM modulation circuit performs FM modulation with a center frequency of 9MHz, which is twice the center frequency of a normal audio FM modulation wave of 4.5MHz. 22 is a limiter, 23 is a first inverting circuit, and 24 and 25 are first and second frequency dividing circuits, respectively, which frequency divide the input signal by 1/2. 26 and 27 are filters, and 28 and 29 are first and second balanced modulators, respectively.

30 is a carrier wave oscillation circuit, which has a frequency twice the desired carrier wave frequency (for example, in JA2ch,
It oscillates at a frequency of 194.5MHz, which is twice this frequency (97.25MHz), and generates a video carrier wave. 31 is a limiter, 32 is a second inversion circuit, and 33 and 34 are third and fourth frequency dividing circuits, respectively, which input the input signal.
It divides the frequency by 1/2. 35 is a video signal input terminal, and 36 is an AM modulation circuit. 37 is a combination circuit that subtracts and mixes two inputs; 38 is a mixing circuit;
39 is a bandpass filter, and 40 is an output terminal.

Next, the operation of this circuit will be explained.

The audio signal input from the audio signal input terminal 20 is subjected to FM modulation in the FM modulation circuit 21 with a center frequency of 9MHz, which is twice the normal frequency. This FM modulation output is input to an inverting circuit 23 through a limiter 22, and the signal is inverted. The output of the limiter 22 is also input to the frequency divider circuit 25, where the frequency is divided by 1/2. The signal input from the inverting circuit 23 to the frequency dividing circuit 24 is similarly frequency-divided by 1/2. The outputs of the frequency dividing circuits 24 and 25 are input to balanced modulators 28 and 29 via filters 26 and 27, respectively. The filters 26 and 27 are for reducing spurious signals, and may be, for example, 4.5 MHz ceramic solid filters. In practice, this filter is not always necessary. Here, the frequency dividing circuit 24,
The output of No. 25 will be explained. Figure 4 a, b,
c, d are A, A', B, B', respectively in Figure 3.
It is a figure which shows the waveform of each point C, C', D, D'. As can be seen from this figure, the output of the frequency divider circuit 24 (waveform at point D) is 90° ahead of the output from the frequency divider circuit 25 (waveform at point C).

On the other hand, the video carrier wave is generated by a carrier wave oscillation circuit 30, and is oscillated here at a frequency twice the desired carrier wave frequency. One of the outputs of this oscillation circuit 30 is inputted to an inverting circuit 32 through a limiter 31 and inverted, and the other output is inputted to a frequency dividing circuit 34 and 1/2
The frequency is divided. The output of the inverting circuit 32 is further input to a frequency dividing circuit 33, where the frequency is divided by 1/2. Here the fourth
As shown in Figures c and d, the output of the frequency divider circuit 33 (waveform at point D') is the output of the frequency divider circuit 34 (waveform at point C').
The phase is 90° ahead. The output of the frequency dividing circuit 34 is a video carrier wave of a desired frequency, and is input to the AM modulation circuit 36. The video signal input from the video signal input terminal 35 is subjected to AM modulation by the AM modulation circuit 36 using the output signal of the frequency dividing circuit 34.

The outputs of the frequency dividing circuits 33 and 34 are outputted by the balanced modulator 28,
29 respectively. Here the modulator 28,
The operation of No. 29 will be explained. To simplify the explanation, the signals corresponding to the outputs of the frequency divider circuits 24 and 25, which are modulation inputs, are respectively expressed as Em sin (pt+π/2) and Em sinpt. Also, the frequency divider circuit 3 which is a carrier
Ec sin(ωct+
π/2), Ec sinωct. The output E ₁ of the first balanced modulator 28 is E ₁ =K ₁ EcEm{cos(ωc−p)t+cos(ωc+
p)t}. Here, Em is the amplitude of the modulated input signal, Ec is the carrier amplitude, ωc is the angular frequency of the carrier, p is the angular frequency of the modulated input signal,
K ₁ is the proportionality constant of the balanced modulator 28.

The output E ₂ of the second balanced modulator 29 is E ₂ =K ₂ EcEm{cos(ωc-p)t-cos(ωc+
p)t}. Here, K ₂ is the proportionality constant of the balanced modulator 29. When E ₁ and E ₂ are subtracted and mixed in the coupling circuit 37, the output E ₀ is E ₀ = E ₁ − E ₂ = EcEm {(k ₁ − k ₂ ) cos (ωc − p) t + (k ₁ + k ₂ ) cos(ωc+p)t}. Here, if K ₁ =K ₂ =K, then E ₀ =2KEcEmcos(ωct+p)t, and since only the upper sideband is present, there is no need in principle for a trap to remove the lower sideband.

The output of the combining circuit 37 is mixed with the video RF signal, which is the output of the AM modulation circuit 6, in a mixing circuit 38, and is outputted to an output terminal 40 via a bandpass filter 39.

In addition, in the explanation of the above-mentioned embodiment, the outputs of the first frequency dividing circuit 24 and the third frequency dividing circuit 33 are used as signals with a phase lead of 90 degrees, but depending on the timing when the power is turned on, the output may be reversed. . FIG. 5 shows an example of a circuit in which initialization is performed so that the phase always reaches the desired phase. That is, FIG. 5 is a diagram showing a specific circuit in which this initializing circuit is added to the inverting circuit and frequency dividing circuit of FIG. 3.

In FIG. 5, 41 is an inverting circuit, 42, 43, and 44 are flip-flops, and 45 is an RS flip-flop. Points A, B, C, and D in the figure correspond to points A, B, C, D, and points A', B', C', and D' in FIG. 3, respectively. Next, the operation of the circuit shown in FIG. 5 will be explained using the timing chart shown in FIG. FIGS. 6a to 6f show waveforms at points A and F in FIG. 5, respectively. When the power is turned on, Figure 6 c, d
Suppose that the output of the flip-flop 42 (corresponding to the first and third divided outputs) is delayed in phase by 90 degrees from the output of the flip-flop 44 (corresponding to the second and fourth divided outputs) as shown in FIG. . At this time, the output pulse width of the R-S flip-flop 45 is
Since this is 1.5 cycles of the CK pulse, the flip-flop 43 detects the falling edge of the CK pulse and inverts it.
The flip-flop 42 is preset by its Q output (FIG. 6f). As a result, the output of the flip-flop 42 (FIG. 6d) is greater than the output of the flip-flop 44 (FIG. 6c).
The phase advances by 90°. Once it is initialized in this way, it continues to operate in this state.

By the way, the present invention can also be implemented by balanced modulating the outputs of the first and second frequency dividers shown in FIG. 3 with the outputs of the fourth and third frequency dividers, respectively. FIG. 7 is a block diagram showing an embodiment of the RF converter circuit according to the present invention in this case.

The first difference from the RF converter circuit in Figure 3 is
The output of the frequency dividing circuit 24 is supplied to the second balanced modulator 29, and the output of the second frequency dividing circuit 26 is supplied to the first balanced modulator 28, and the coupling circuit 46 and the outputs of the second balanced modulators 28 and 29 are added and mixed. As in the previous example,
Let the signals corresponding to the outputs of the frequency dividing circuits 24 and 26 be Em sin (pt+π/2) and Em sinpt, respectively. Furthermore, the output signals of the frequency dividing circuits 33 and 34, which are carriers, are assumed to be Ec sin (ωct+π/2) and Ec sinωct, respectively. At this time, the output E ₃ of the first balanced modulator 28 is E ₃ =K ₁ EcEm{sin(ωc+p)t−sin(ωc−
p)t}, and the output E ₄ of the second balanced modulator 29 is E ₄ =K ₂ EcEm{sin(ωc+p)t+sin(ωc−
p)t}. The coupling circuit 46 adds and mixes these signals and outputs the resultant signal. The output E ₅ is E ₅ = E ₃ + E ₄ = EcEm {(k ₁ + k ₂ ) sin (ωc + p)
t+( _k2 - _k1 )sin(ωc-p)t}. Here, if K ₁ =K ₂ =K, E ₅ =2KEcEm sin(ωc+p)t, and only the upper sideband wave can be extracted as in the previous embodiment.

As described above, according to the present invention, the lower sideband of the audio FM RF signal is not generated in principle, and the conventionally required non-sideband trap becomes unnecessary. Therefore, critical adjustment of this trap is also eliminated. In addition, conventional RF converters in the UHF band cannot make the trap sharpness sufficiently high, so audio FM
The lower side wave of the RF signal could not be attenuated, but according to the present invention, it is theoretically possible to remove the lower side wave of the audio FM RF signal even in the UFH band, and an RF converter circuit with great practical value can be realized. can be provided.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams showing conventional RF converter circuits, Figure 3 is a block diagram showing an embodiment of the RF converter circuit according to the present invention, and Figure 4 is a main part of the circuit shown in Figure 3. 5 is a diagram showing the waveform of the circuit of FIG. 3, with an initialization circuit added to the inversion circuit and frequency dividing circuit, FIG. 6 is a timing chart of FIG. 5, and FIG. 7 is a diagram of the circuit of the present invention. FIG. 3 is a block diagram showing another embodiment. 21...FM modulation circuit, 23, 32...Inversion circuit, 24, 25, 33, 34... Frequency division circuit, 2
8, 29...Balanced modulator, 30...Carrier wave oscillation circuit, 36...AM modulation circuit, 37...Coupling circuit,
38... Mixed circuit.

Claims (1)

[Claims] 1 RF converts video and audio signals into RF signals
2 of the desired center frequency in the converter circuit.
an FM modulation circuit that performs FM modulation of an audio signal at a double center frequency; a first inversion circuit that inverts the output of this circuit; a first frequency division circuit that divides the frequency of this inversion output into 1/2; a second frequency dividing circuit that divides the output of the modulation circuit by 1/2, an oscillation circuit that oscillates at a frequency twice the desired video carrier frequency, and a second inversion circuit that inverts the output of the oscillation circuit. , a third frequency divider circuit that divides the inverted output by 1/2, and a fourth frequency divider circuit that divides the output of the oscillation circuit by 1/2;
an AM modulation circuit that performs AM modulation on the video signal using the output of the third or fourth frequency divider circuit; and an AM modulation circuit that modulates the video signal using the output of the third or fourth frequency divider circuit;
Alternatively, first and second balanced modulators that perform balanced modulation using the outputs of the fourth and third frequency dividing circuits, respectively, and a coupling circuit that adds or subtracts the outputs of these first and second balanced modulators; The output of the coupling circuit and the AM
An RF converter circuit characterized by comprising a mixing circuit that mixes the output of the modulation circuit.