JPH0455035B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a modulated television channel signal generator, and particularly relates to a multi-channel signal generator suitable for adjusting or measuring the reception characteristics of a receiver. be.

[Background technology and its problems]

FIG. 1 is a block diagram showing an example of a conventional multi-channel signal generator. 1 is a composite TV signal source that generates a video signal and an audio signal in a standard TV signal, such as the NTSC system or the PAL system. Contains test pattern and color pattern signals. 2 is a voltage controlled oscillator (VCO) whose frequency is variable by the composite TV signal source 1, and this voltage controlled oscillator (VCO) 2 is frequency controlled so that the average value of its output frequency is constant. A circuit 3 is provided. 4 is a crystal oscillation element X ₁ ,
A crystal oscillator that can set different reference frequencies (channel frequencies in this case) by selecting X _{2 ,} A filter 7 is a second frequency mixer, which together with an oscillator 8 that forms a carrier wave and a frequency selection filter 9 constitutes a frequency conversion circuit.

Since this conventional multi-channel signal generating device is configured as described above, it can be used, for example, as a channel signal generating device for adjusting a converter that receives TV radio waves from a satellite. That is, a TV signal (for example, a standard pattern) converted into an FM signal by the voltage controlled oscillator 2 is converted to a specific channel frequency by the first frequency mixer 5, and then converted to a specific channel frequency by the second frequency mixer 7.
In the broadcasting satellite transmission frequency band (12GHz)
is converted to

Therefore, if the crystal oscillator elements X ₁ , X ₂ , X ₃ ... are selected according to the channel of the receiver (comparator) to be adjusted or measured, the frequency of the 12 GHz carrier wave is modulated to the predetermined channel. The received TV signal is output and various characteristics of the receiver can be checked.

However, such a multi-channel signal generating device has the disadvantage that when generating multi-channel signals in accordance with characteristic tests for each channel of the receiver, channel switching is required, making measurement work complicated.

In addition, as a receiver measurement or adjustment method, the separation characteristics of adjacent channels,
In some cases, the characteristics of the S/N ratio are investigated when the channel frequency is slightly shifted, but such tests are performed using conventional multi-channel signals in which the output channel selects a single channel signal defined by a crystal oscillator. There is a problem in that this cannot be done with a signal generator.

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a modulated television channel signal generator capable of simultaneously outputting a plurality of arbitrary channel signals to an output terminal.

[Embodiment] Hereinafter, an embodiment of the modulated television channel signal generator of the present invention will be described with reference to the block diagram of FIG.

In FIG. 2, common symbols excluding subscripts a, b, and c indicate circuit blocks having the same function, and this circuit example is a block diagram in which signals for three channels are formed.

In this figure, 11, a, b, and c are respectively
A TV signal processing circuit that processes TV screen and audio signals; 12, a, b, and c are voltage-controlled oscillators whose frequencies are modulated by the composite TV signal; 13 is the voltage-controlled oscillator 12, a, b, and c; This is a frequency control circuit (average value AFC circuit) that is provided so that the average frequency of is constant, and these circuits together form modulated wave circuits 10, a, b, and c.

The outputs of the modulated wave circuits 10, a, b, c are input to mixers 14, a, b, c, and frequency controlled oscillators 15, a, b, c (for example,
It is mixed with the output of an oscillator (in this example a microwave oscillator) whose frequency can be controlled by voltage.

The mixing frequencies of the mixers 14, a, b, and c are controlled to match the reception channel frequency of the receiver to be measured, as will be described later.
6 and bandpass filter 17 within a predetermined frequency band.

Subsequently, the frequency controlled oscillator 15,a,
The control circuits b and c will be explained.

21 is a reference oscillator whose frequency changes under the control of a central processing circuit (CPU) 26; 22 is a harmonic mixer for forming an intermediate frequency; and 23 is a counter for measuring the output frequency of the harmonic mixer 22. , 24 are the respective frequency controlled oscillators 15a, 15
oscillation output of mixer 14, a,
A switch 25, a, which sequentially takes in the outputs of b and c in a time-division manner and supplies them to the harmonic mixer 22.
b, c are the frequency controlled oscillators 15, a, b, c
This is a frequency setting device (digital-to-analog converter with a signal holding function) that controls the oscillation frequency of the oscillation frequency. Incidentally, indicates that the control signal of the central processing circuit 26 is supplied.

27 is a target value setting circuit for setting the target frequency of each channel; 28 is a time division control means for sending time division signals to the switch 24 and the frequency setting devices 25, a, b, and c; 29 is the target value setting circuit; 2
7, the counter measurement value, and the output value of the reference oscillator 21, the calculation means 29 and the time division control means 28 constitute a central processing circuit 26. It is something.

Next, the operation of this circuit block will be explained based on the waveform diagram of FIG.

Each modulated wave circuit 10a, 10 surrounded by a dashed line
b, 10c are TV signals (audio signals are
(sometimes converted to PCM) is frequency modulated.
FM/TV signals are formed, and each mixer 14a, 14
b, 14c.

Now, each frequency controlled oscillator 15a, 15b, 15
If the oscillation frequencies of c are _a , _b , _c , and the frequency of the FM/TV signal is _TV , each mixer 14a, 1
The mixed frequency of 4b and 14c is | _a ± _TV |, | _b ±
It is output as _TV |, | _c ± _TV |.

Therefore, the oscillation frequencies _a , _b , and _c are set by the target value setting circuit 27 so that _a − _b = Δ _{, b} − c = Δ.
If set by , each modulated wave circuit 10a,
The frequencies of the FM/TV signals formed by 10b and 10c are input to the synthesizer 16 at channel intervals of Δ, and are outputted to the output terminal 18 via the bandpass filter 17 as a multi-channel signal.

In this case, the channels become adjacent multi-channel signals, but depending on the settings of _a , _b , _{and c} , each modulated wave circuit 10a, 10b, 10
It can output FM/TV signals of c.

On the other hand, the frequency controlled oscillator 15, a, b, c
The oscillation outputs e _a , e _b , e _c are sequentially controlled by the time division control means 28 of the central processing circuit 26 through the switch 24 during the periods T _a , T _b , and T _c as shown in FIG. It is taken into the harmonic mixer 22.

Further, in accordance with the periods T _a , T _b , T _c , the reference oscillator 21 generates different reference frequencies _ra , rb , _rb , as shown in FIG. The switch 24 transmits _{the rc} signal to the frequency controlled oscillators 15, a, b, c.
The oscillation outputs e _a , e _b , and e _c are outputted to the harmonic mixer 22 in synchronization with the respective capture.

The harmonic mixer 22 has, for example, a reference frequency _ra ,
An intermediate frequency i which is the difference between the n times (n=1, 2, 3...) harmonics of _rb , _rc and the oscillation frequencies ( _a , b, c) of the frequency control oscillators 15, a, _b , _{c .}
It is configured to generate.

Therefore, if each reference frequency ( _ra , _rb , _rc ) is set to a predetermined value, a constant intermediate frequency such as _a −n _ra = _b −n _rb = _c −n _rb = _i will be output. It turns out.

This intermediate frequency _i is measured by the counter 23, input to the central processing circuit 26, and stored.

The calculation means 29 of the central processing circuit 26 each have
Within the period of T _a , T _b , T _c , the count value of the counter 23 of the intermediate frequency _i is calculated from the target value of the intermediate frequency [from the target value of the oscillation frequency to the frequency n times each reference frequency (n _ra , n _rb , n _rc )], and the frequency setting devices _25a , _25b , _25b ,
25c, respectively.

For example, if the target value of _a is 1000MHz, the output signal n _ra (n = 1, 2, 3...) of the reference oscillator 21 is 990M
Hz, if the measured value of the counter 23 is 9MHz, the calculation means 29 calculates the target value as 990+9.
A correction signal S _a of 1000×1000/999 is calculated from 1000 and output as a digital signal.

Further, if the measured value of the counter 23 is 11 MHz, the calculation means 29 calculates a correction signal _{S a of} 1000×1000/1001 from 990 MHz + 11 MHz and the target value of a 1000 MHz, and sends the same digital signal to the frequency setting device 25 a. Output.

Similarly, the counter 23 is used for the correction signals S _b and S _c .
are calculated based on the measured values of and output to the respective frequency setting devices 25b and 25c.

And each frequency setting device 25a, 25b, 2
Each frequency controlled oscillator 15 is controlled by an analog signal output from a digital-to-analog converter 5c.
Oscillation frequency of a, 15b, 15c (a, b, c)
are controlled respectively.

In this case, for example, the corrected signal S _a is input to the frequency setting device 25a controlling the frequency controlled oscillator 15a during the period T _a , and during the other periods T _b ,
At _Tc , the signal S _a is controlled to remain latched by the frequency setting device 25a.

Therefore, each frequency controlled oscillator 15a, 15
b, 15c receives control signals from the time division control means 28 of the central processing circuit 26 during periods T _a , T _b , and T _c , and during other periods, the oscillation frequency is maintained based on the control signals. Control is divided.

The frequency setting devices 25a, 25b, and 25c each receive the measurement value and the target value sent out, perform calculations in the same manner as in the above case, and generate correction signals S _a , S _b , and S _{c .}
is output to each digital-to-analog converter.

And each frequency setting device 25a, 2
The frequency controlled oscillators 15a, 1
5b and 15c to correct the target frequency.

In the above embodiment, a signal generator for three channels has been described, but by increasing the number of block circuits with subscripts, it is possible to output even more channel signals at the same time.

In the embodiment of the present invention, the intermediate frequency _i is measured by the counter 23, so the signal to be controlled and taken in by the switch 24 is the output of the mixer 14, a, b, c as shown by the dotted line. You can also use it as

In this case, the frequency modulated frequency (,a,
b, c± _TV ) is input, but when measured by the counter 23, the average value of the modulation frequency is output, so there is no problem unless the time division periods T, a, b, c are extremely short. It will never be.

FIG. 4 shows that the channel frequency is set in the central processing circuit 26 based on the settings of the target value setting circuit 27, and the frequency control oscillator 15,
This is a flowchart for adjusting and maintaining a, b, and c. When the channel frequency consisting of a, b, and c is read in the central processing circuit 26, first the reference of the reference oscillator 21 corresponding to the channel frequency is Frequencies ( _ra , _rb , _rc ) are set.

Next, the D/A value of the a channel is output, and the oscillation frequency ' _a of the frequency control oscillator 15a is measured by measuring _{the intermediate frequency i ,} and the difference signal or The corrected signal is output to the D/A converter.

In this way, the frequency control oscillators 15, a, b, and c are time-divisionally feedback-controlled via the counter 23 to bring the frequency closer to the target value.

Below, D/A with the oscillation frequencies _b and _c having predetermined values in the b channel and c channel as well.
A value (target value) is set, and thereafter this value is used as the target value, and the frequency control oscillators 15, a, b, and c are controlled as described above while detecting the difference from the intermediate frequency _i .

〔Effect of the invention〕

As explained above, the modulated television channel signal generator of the present invention generates a plurality of channel signals output from a synthesizer by mixing signals from N modulated wave circuits and N frequency controlled oscillators. When doing so, the output of the frequency controlled oscillator is supplied to the harmonic mixer via a switch, and the harmonics of the reference signal source outputting N different frequencies to the harmonic mixer are The signals are given sequentially.

Then, the output frequency of the harmonic mixer is counted as an intermediate frequency by a counter, and the oscillation frequency of the frequency control oscillator is determined by performing arithmetic processing between this counted value and the target frequency set and input to the central processing circuit. Since the control correction signal is output, the loop gain that controls each channel frequency is always constant, and the response characteristics when switching to perform time division control are constant for each channel. the result,
This has the effect of reducing frequency fluctuations between channel frequencies. In addition, multiple (3) TV channel frequencies can be output at the same time, so
This is useful when testing the channel separation characteristics of BS tuners and converters, and the S/N characteristics when the channel frequency is slightly shifted.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional multi-channel signal generating device, FIG. 2 is a block diagram of a multi-channel signal generating device showing an embodiment of the present invention, FIG. 3 is a waveform diagram for explaining the operation, and FIG. Figure 4 is a flowchart of the central processing circuit. In the figure, 10 is a modulated wave circuit, 14, a, b, c are mixers, 15, a, b, c are frequency controlled oscillators,
16 is a synthesizer, 21 is a reference oscillator, 22 is a harmonic mixer, 23 is a counter, 24 is a switch, 2
5, a, b, and c are frequency setting devices, 26 is a central processing circuit, 27 is a target value setting circuit, 28 is time division control means, and 29 is calculation means.

Claims (1)

[Claims] 1. N including voltage controlled oscillators 12a, 12b, 12c for frequency modulating and outputting a television signal.
independent modulation wave circuits 10a, 10b, 10c
and N independently controlled frequency controlled oscillators 1
5a, 15b, 15c, a switch 24 that sequentially selects and outputs each output signal of the frequency controlled oscillator or a frequency-converted signal of this output signal, and a switch 24 that outputs N different reference frequencies in synchronization with the switch. a reference signal oscillator 21 that sequentially generates a signal; a harmonic mixer 22 that mixes the signal output from the switch and the signal output from the reference signal oscillator and outputs an intermediate frequency signal; It is equipped with a counter 23 for counting, and a calculation means for setting a target oscillation frequency of each of the frequency controlled oscillators and calculating a correction signal value of the frequency controlled oscillator between the target frequency and the count value of the counter. The central processing circuit 26 and each of the N frequency controlled oscillators are respectively provided, and in synchronization with the switch, receive a correction signal from the central processing circuit to sequentially form a feedback loop. When disconnected, N frequency setting devices 25a, 25b, 25c hold correction signal values of the central processing circuit to control the frequency of the frequency controlled oscillators; and output signals of the N frequency controlled oscillators. and N mixers 14a, 14b, 14c that mix the output signals of the N modulated wave circuits, respectively, and a combiner 16 that combines and outputs the output signals of the mixers. A modulated television channel signal generator capable of simultaneously outputting N modulated television channels.