JP3309054B2 - Frequency conversion circuit for television broadcasters - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit for a television broadcaster, and more particularly, to a phase control loop (hereinafter referred to as a "phase control loop") for preventing spurious frequency components from being generated in any television channel during television broadcasting. (Referred to as "PLL").

[0002]

2. Description of the Related Art Conventionally, a digital television broadcaster has a digital modulation section for generating a digital modulation signal for television broadcasting modulated by a digital signal, and a digital modulation signal having an intermediate frequency of a higher frequency by a first local oscillation signal. A first frequency conversion circuit for converting to a frequency signal;
A second frequency conversion circuit for converting the intermediate frequency signal into a television broadcast signal of a predetermined channel by the second local oscillation signal.

In such digital television broadcasting, since a low phase noise characteristic is usually required for a broadcast signal, a first voltage controlled oscillator for generating a first local oscillation signal and a second local oscillation signal are generated. The second voltage-controlled oscillating unit is coupled to a first PLL and a second PLL whose phases are controlled based on a frequency reference signal, and keeps the frequencies of the first local oscillation signal and the second local oscillation signal stable. I am trying to be.

[0004] In this case, in digital television broadcasting used in CATV broadcasting and CS broadcasting, a large number of digital television broadcasting machines having different transmission frequencies are used, and these digital television broadcasting machines are used. Many broadcast signals are added and sent out.

[0005]

In the known digital television broadcaster, the frequency reference signal supplied to the first PLL may be supplied to the first frequency conversion circuit together with the first local oscillation signal. A frequency reference signal component may be output together with the intermediate frequency signal from one frequency conversion circuit. In this case, the frequency of the intermediate frequency signal is high, and the frequency reference signal component is transmitted without being removed by the band-pass filter provided on the output side of the first frequency conversion circuit. A spurious frequency component is generated at a frequency position which is separated by the frequency of or a multiple frequency thereof.

[0006] In particular, when a large number of broadcast signals are synthesized and sent out, such as in CATV broadcasts and CS broadcasts, spurious frequency components generated by one broadcaster are generated in the frequency band of any television channel. Therefore, when selecting the frequency of the frequency reference signal supplied to the first PLL, it is necessary to prevent the frequency reference signal of the broadcaster from entering any other television channel as a spurious frequency component.

However, in CATV broadcasting and CS broadcasting,
Since the entire broadcast frequency band covers a wide band of about 1 GHz,
In order to prevent the frequency reference signal of the broadcast machine from entering another television channel, it is necessary to select the frequency of the frequency reference signal to be 1 GHz or more. Thus, a stable frequency reference signal having a high frequency is obtained. That is technically difficult.

[0008] The present invention improves on such a point, and an object of the present invention is to increase the frequency of the frequency reference signal supplied to the PLL without increasing the spurious signal caused by the frequency reference signal in any television channel. It is an object of the present invention to provide a frequency conversion circuit for a television broadcaster, which does not enter the system.

[0009]

In order to achieve the above object, a frequency conversion circuit for a television broadcast according to the present invention comprises:
When a digitally modulated television broadcast signal is frequency converted by a local oscillation signal into a higher frequency intermediate frequency signal, a frequency reference supplied to a phase control loop (PLL) used to control the frequency of the local oscillation signal Means is provided for selecting a signal to have a frequency that is の of the frequency bandwidth allocated to one channel of television broadcasting.

According to the above means, the first-order spurious frequency component based on the frequency of the frequency reference signal occurs at the frequency boundary between the self-channel and the adjacent channel, and is included in the frequency band of both the self-channel and the adjacent channel. Do not enter. Also, among the higher-order spurious frequency components based on the frequency of the frequency reference signal, the odd-order spurious frequency components are generated at the frequency boundary portions of adjacent channels adjacent to each other, like the first-order spurious frequency components. It does not penetrate into the frequency band of the channel, and even-order ones occur near the center frequency of the adjacent channel, but have a lower level than the odd-order spurious frequency components, so that substantial interference is prevented. Does not occur.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention, a frequency conversion circuit for a television broadcaster receives a digitally modulated television broadcast signal and a local oscillation signal to input the frequency of the television broadcast signal. A frequency converter that outputs a higher-frequency intermediate frequency signal, a voltage-controlled oscillator that generates a local oscillation signal, a frequency reference signal generator that generates a frequency reference signal, and a phase shifter between the local oscillation signal and the frequency reference signal. A phase control loop for generating an error voltage by comparison, and controlling the frequency of the local oscillation signal based on the error voltage, wherein the frequency reference signal has a frequency of １ ／ of the frequency bandwidth allocated to one channel of television broadcasting. I have chosen.

In a preferred embodiment of the present invention, a band-pass filter for extracting an intermediate frequency signal is connected to an output terminal of the frequency conversion unit.

According to these embodiments of the present invention, the frequency reference signal generated by the frequency reference signal generation unit is set to have a frequency of に な る of the frequency bandwidth allocated to one channel of the television broadcast. I have chosen. For this reason,
Among the spurious frequency components based on the frequency of the frequency reference signal mixed into the intermediate frequency signal, the first-order spurious frequency components are generated at the frequency boundary between the self-channel and the adjacent channel, and the self-channel and the adjacent channel Without entering any of the frequency bands
Also in the higher-order spurious frequency components, the odd-order spurious frequency components are generated at the frequency boundaries between adjacent channels adjacent to each other, like the first-order spurious frequency components, and are included in the frequency band of any channel. Further, even-order spurious frequency components occur near the center frequency of the adjacent channel, but are lower in level than the odd-order spurious frequency components, so that no substantial interference occurs. .

[0014]

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

FIG. 1 is a block diagram showing an embodiment of a frequency conversion circuit for a television broadcaster according to the present invention.

As shown in FIG. 1, a frequency conversion circuit 1 for a television broadcaster according to the present embodiment includes a first frequency conversion section 2 and a first voltage controlled oscillation section (hereinafter, referred to as a first VCO).
3 and a first phase control loop (hereinafter, referred to as a first PLL)
4, a first loop filter 5, a frequency reference signal generator 6, a first signal amplifier 7, a first bandpass filter 8,
And a digital modulation signal generator 9 for television broadcasting. Here, the digital modulation signal generation unit 9 for television broadcasting includes a digital frequency conversion unit 10.
And a modulation signal generator 11 and a digital modulated signal generator 12. Further, the frequency conversion circuit 1
A second frequency conversion circuit 13 is connected to the next stage,
The frequency conversion circuit 13 includes a frequency reference signal generation unit 6 shared with the frequency conversion circuit 1, a second frequency conversion unit 14,
Second voltage controlled oscillator (hereinafter referred to as second VCO) 15
And a second phase control loop (hereinafter, referred to as a second PLL) 1
6, a second loop filter 17, and a second signal amplifier 18
And a second band-pass filter 19.

In the frequency conversion circuit 1, the first
The frequency converter 2 has a first input terminal connected to the output terminal of the digital modulation circuit 9 for television broadcasting, a second input terminal connected to a first output terminal of the first VCO 3, and an output terminal connected to the first signal amplifier. 7 is connected to the input terminal. The first VCO 3 has a second output terminal connected to the first input terminal of the first PLL 4, and a control terminal connected to the output terminal of the first loop filter 5. First
The PLL 4 has a second input terminal connected to the output terminal of the frequency reference signal generator 6, and an output terminal connected to the input terminal of the first loop filter 5. The first band pass filter 8 has an input terminal connected to the output terminal of the first signal amplifying unit 7, and an output terminal connected to the input terminal of the succeeding second frequency conversion circuit 13. In the digital modulation circuit 9 for television broadcasting, the modulator 10 has a first input terminal connected to the output terminal of the digital signal source 11, a second input terminal connected to the output terminal of the carrier generator 12, and an output terminal. It is connected to the output terminal of the digital modulation circuit 9 for television broadcasting.

In the second frequency conversion circuit 13,
The second frequency converter 14 has a first input terminal connected to the input terminal of the second frequency conversion circuit 13 and a second input terminal connected to the second VCO.
15 is connected to the first output terminal, and the output terminal is connected to the input terminal of the second signal amplifier 18. The second VCO 15 has a second output terminal connected to the first input terminal of the second PLL 16 and a control terminal connected to the output terminal of the second loop filter 17. Second
The PLL 16 has a second input terminal connected to the output terminal of the frequency reference signal generator 6, and an output terminal connected to the input terminal of the second loop filter 17. The second bandpass filter 19 is
The input terminal is connected to the output terminal of the second signal amplifying unit 18, and the output terminal is connected to the transmission output terminal 20.

In this case, the frequency of the frequency reference signal generated by the frequency reference signal generator 6 is one of the ones of the television broadcast.
For example, when the frequency bandwidth of one channel is 8 MHz, the frequency is set to 4 MHz so as to be equal to half the frequency bandwidth allocated to the channel.

The frequency conversion circuit 1 for a television broadcaster according to the present embodiment having the above-described configuration operates as follows.

Digital modulation circuit 9 for television broadcasting
, A modulation unit 10 modulates a carrier generated by a carrier generation unit 12 with a digital signal obtained from a digital signal source 11 such as a video disk (VD) or a video tape recorder (VTR). Is generated and supplied from the output terminal of the digital modulation circuit 9 to the input terminal of the frequency conversion circuit 1.

In the frequency conversion circuit 1, the first frequency conversion unit 2 includes a digital modulation signal supplied to an input terminal of the frequency conversion circuit 1 and a first local oscillation signal whose frequency supplied from the first VCO 3 is stabilized. And, for example,
An intermediate frequency signal having a frequency of 1.3 GHz is generated. In such an operation, the first PLL 4 controls the phase of the frequency of the first local oscillation signal generated by the first VCO 3 by a frequency reference signal generated by the frequency reference signal generator 6, for example, a frequency of 4 MHz, and compares the phase. The phase error voltage generated at the time of
This is supplied to the control terminal of the VCO 3 to stabilize the frequency of the first local oscillation signal generated by the first VCO 3.
Next, the 1.3 GHz output from the first frequency conversion unit 2
The intermediate frequency signal of z is amplified to a predetermined level by the first signal amplifying unit 7, and only the 1.3 GHz intermediate frequency signal component is selectively extracted by the first band-pass filter 8.
Is supplied to the input terminal of the next second frequency conversion circuit 13.

In the second frequency conversion circuit 13, the second frequency conversion section 14 includes an intermediate frequency signal of 1.3 GHz supplied to an input terminal of the second frequency conversion circuit 13 and a second VCO
And a second local oscillation signal having a stabilized frequency supplied from the mixer 15 to generate a broadcast signal. In this case, the frequency of the broadcast signal is selected to be, for example, one of a number of channels divided by a frequency band of 8 MHz within a frequency range of 50 to 860 MHz. Also during this operation, the second PLL 16 sets the frequency of the second local oscillation signal generated by the second VCO 15 to
The phase is compared with a frequency reference signal having a frequency of, for example, 4 MHz obtained by the frequency reference signal generator 6, and the phase error voltage obtained at the time of the phase comparison is passed through the second loop filter 17 to the control terminal of the second VCO 15. To the second V
The frequency of the second local oscillation signal generated by the CO 15 is stabilized. Subsequently, a broadcast signal of a predetermined frequency having a bandwidth of 8 MHz output from the second frequency conversion unit 14 is amplified to a predetermined level in the second signal amplifying unit 18, and only the broadcast signal of the predetermined frequency is amplified in the second bandpass filter 19. Is selectively extracted and supplied to the transmission output terminal 20. The broadcast signal supplied to the transmission output terminal 20 is then sent out via a communication cable or an antenna (not shown).

Here, also in this embodiment, the frequency reference signal generated by the reference frequency signal generator 6 is supplied to the first frequency converter 2 together with the first local oscillation signal. A frequency reference signal component is output together with the signal, and the frequency reference signal component is not sufficiently attenuated by the first band-pass filter 8 and supplied to the succeeding second frequency conversion circuit 13.
3 is not sufficiently attenuated, and is transmitted from the transmission output terminal 20 in a state of being superimposed on the broadcast signal. At this time, the present embodiment sets the frequency of the frequency reference signal to 1
Frequency bandwidth allocated to the channel, eg, 8 MH
Since the frequency is selected and set to be half the frequency of z, that is, 4 MHz, there is no influence of spurious frequency components based on the frequency reference signal as described below.

FIG. 2 is a characteristic diagram showing the relationship between the own channel, the adjacent channel and the adjacent channel, and the generated spurious frequency components in the embodiment shown in FIG.

In FIG. 2, the horizontal axis is the frequency in MHz, and the vertical axis is the output level.

As shown in the characteristic diagram of FIG. 2, the frequency of the frequency reference signal is selected so as to be a frequency bandwidth assigned to one channel of the television broadcast, for example, a frequency of 1/2 MHz, that is, 4 MHz. If set, among the spurious frequency components based on the frequency reference signal, the first-order spurious frequency component occurs at the frequency boundary between the own channel and the adjacent channel, and is within the frequency band of both the own channel and the adjacent channel. Without getting in,
Also in the higher-order spurious frequency components, the odd-order spurious frequency components are generated at the frequency boundaries between adjacent channels adjacent to each other, like the first-order spurious frequency components, and are included in the frequency band of any channel. Furthermore, even-order spurious frequency components are generated near the center frequency of the adjacent channel and the adjacent channel, but are substantially lower than the levels of the odd-order spurious frequency components. Does not occur.

In this embodiment, the frequency bandwidth allocated to one channel of the television broadcast is 8 MHz.
z and the example in which the frequency of the frequency reference signal is selectively set to 4 MHz has been described. However, the present invention is not limited to this example, and the frequency bandwidth allocated to one channel may be different. Of course, any frequency may be used as long as the frequency of the frequency reference signal is 1/2 of that frequency.

[0029]

As described above, according to the present invention, the frequency of the frequency reference signal generated by the frequency reference signal
Instead of selecting a high frequency of about 1 GHz or more, the frequency is selected to be a half of the frequency bandwidth allocated to one channel of television broadcasting. Therefore, among the spurious frequency components based on the frequency reference signal mixed into the intermediate frequency signal, the primary spurious frequency component is
Occurs at the frequency boundary between the self-channel and the adjacent channel, does not enter any of the frequency bands of the self-channel and the adjacent channel, and also in the higher-order spurious frequency components, the odd-order spurious frequency components are: Like the first-order spurious frequency component, it occurs at the frequency boundary between adjacent channels adjacent to each other, does not enter the frequency band of any channel, and further, the even-order spurious frequency component is Although generated near the center frequency, the level is lower than the level of the odd-order spurious frequency component, so that there is an effect that substantial interference does not occur.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a frequency conversion circuit for a television broadcaster according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a self channel, an adjacent channel and a nearby channel, and generated spurious frequency components in the embodiment shown in FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 frequency conversion circuit for television broadcaster 2 first frequency conversion unit 3 first voltage controlled oscillation unit (first VCO) 4 first phase control loop (first PLL) 5 first loop filter 6 frequency reference signal generation unit 7 first Signal amplification unit 8 First bandpass filter 9 Digital modulation circuit 10 Modulation unit 11 Digital signal source 12 Carrier generation unit 13 Second frequency conversion circuit 14 Second frequency conversion unit 15 Second voltage controlled oscillator (second VCO) 16 Second Phase control loop (second PLL) 17 second loop filter 18 second signal amplifier 19 second bandpass filter 20 transmission output terminal

Claims (2)

(57) [Claims] A frequency converter for inputting a digitally modulated television broadcast signal and a local oscillation signal and outputting an intermediate frequency signal having a frequency higher than the frequency of the television broadcast signal; A frequency control signal generator for generating a frequency reference signal, and a phase comparison between the local oscillation signal and the frequency reference signal to generate an error voltage. A phase control loop for controlling the frequency of the signal, wherein the frequency reference signal is selected to have a frequency that is １ ／ of the frequency bandwidth allocated to one channel of the television broadcast. Frequency conversion circuit. 2. The frequency conversion circuit according to claim 1, wherein a band-pass filter for extracting the intermediate frequency signal is connected to an output terminal of the frequency conversion unit.