JPH036070Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an IC (integrated circuit) of a television tuner and a television channel selection device whose manufacturing can be easily automated.

Generally, television tuners that use variable capacitance diodes as tuning elements are widely used. The tuning circuit of this tuner requires an inductor in addition to the variable capacitance diode, so the circuit
There are difficulties in converting to IC. Further, since the density of the inductance coil is used to adjust the high frequency input tuning circuit and the high frequency/mixing stage double tuning circuit, adjustment work is required during the tuner manufacturing process.

In recent years, television receivers have tended to be used for personal use, and television channel selection devices are often incorporated into VTRs (video tape recorders), so only the main circuit of the television receiver is required. Therefore, there is a demand for a smaller television receiver. Furthermore, although the manufacturing of television receivers has been largely automated, the automation has been delayed because the manufacturing of television receivers requires the above-mentioned adjustment work. In order to make television tuners smaller and to automate their manufacturing, it is necessary to develop tuners that do not use inductance, and to make tuners IC-free and non-adjustable.

The present invention aims to provide a television channel selection device using a synchronous reception method, in order to implement an IC television channel and eliminate adjustment.

FIG. 1 shows a block diagram of an embodiment of the present invention.
In the figure, 1 is a high frequency input section such as a high frequency amplifier, 2 is a voltage controlled local oscillator, 3 is a mixer,
4 is a signal low-pass filter, 5 is a signal amplifier, 6 is a 90° phase shifter, 7 is a mixer, 8 is a signal low-pass filter, 9 is a signal amplifier, 10 is a phase comparator, 11 is a PLL low-pass The filter 12 is an analog switch, and these constitute a PLL (phase lock loop). 13
is a pulse oscillator, 14 is a gate circuit, 15 is a binary counting circuit, and 16 is a digital-analog (D-
A) converters, these are analog switches 1
2, voltage controlled local oscillator 2, mixer 3, signal low pass filter 4, signal amplifier 5, video signal low pass filter 1
7, synchronous separation circuit 18, synchronous signal tuning circuit 19,
Together with the rectifier circuit 20, it constitutes a search circuit that searches for television broadcast waves. 21 is a control input device, 22 is a channel selection control circuit, 23 is an analog switch, 24 is a video output device, 25 is an audio intermediate frequency amplifier, 26 is a frequency discriminator, and 27 is an audio output device.

A plurality of television broadcast waves are input to the high frequency input section 1 . Let the video carrier wave of a certain channel among them be V _V (t), and the audio carrier wave be V _S (t).

Since V _V (t) is modulated by residual sideband, V _V (t)=R _e {[I(t)+jQ(t)] expj[ω _V t
+
φ _V ]}=I(t) cos[ω _V t+φ _V ]−Q(t) sin
[ω _V t+φ _V ] ...(1) It can be expressed as follows. Here, R _e is the real part of the expression in { },
I(t) includes a video signal with an amplitude of an in-phase component with respect to a carrier wave. I(t) includes a video signal with an amplitude of an in-phase component with respect to a carrier wave. Q(t) is the amplitude of the component orthogonal to the carrier wave, ω _V is the angular frequency of the video carrier wave, φ _V
is the phase of the video carrier.

The output of the voltage controlled local oscillator 2 is V _O (t) = A _O cos (ω _O t + φ _O ) ...(2), and this is combined with the video carrier wave V _V (t) of equation (1), which is composed of a voltage multiplier. When added to mixer 3, its output
V _PV (t) is V _PV (t) = {I (t) cos [ω _V t + φ _V ] − Q (t)
sin[ω _V t+φ _V ]} A _O cos[ω _O t+φ _O )=A _O I(t)cos[ω _V t+φ _V
]cos[ω _O t+φ _O ) −A _p Q(t) sin[ω _V t+φ _V ]cos[ω _O t+φ _O )
=A _O I(t)/2 {cos[(ω _V +ω _O )t+φ _V +φ _O ]+cos[(ω _V
−ω _O )t+φ _V −φ _O ]} −A _O Q(t)/2{sin[ω _V +ω _O )t+φ _V +φ
_O ] + sin [(ω _V − ω _O ) t + φ _V − φ _O ]}...(3) Now, when the local oscillator output is synchronized with the video carrier wave, ω _O = ω _V , so V _PV (t) = A _O I(t)/2{cos[2ω _V t+φ _V +φ _O
]+cos[φ _V −φ _O ]} −A _O Q(t)/2{sin[2ω _V t+φ _V +φ _O ]+sin
[φ _V −φ _O ]}……(4) The output that has passed through the low-pass filter that removes 2ω _V is V _PV (t) = A _O I (t)/2 cosφ − _{A O} Q (t)/ 2sinφ...(5) Here, φ is _{φV −φO} , which is the difference between the video carrier and the local oscillator output. If φ=0, V _PV (t)=A _O I(t)/2 (6). In this way, the amplitude of the in-phase component with respect to the video carrier wave is obtained as a detection output. However, the amplitude of the component orthogonal to the video carrier is not detected. The detection output A _O I(t)/2 is output as a video detection output through a signal low-pass filter 4 , amplified by a signal amplifier 5 , and outputted through a video signal low-pass filter 17 to a video output device 24 . The filtering characteristics of the signal low-pass filter 4 are shown in FIG. The video signal is filtered at baseband X as shown in this figure. Since this video signal is demodulated from vestigial sideband modulation, the detection output in the low frequency range is twice that when filtered using Nyquist filtering characteristics. The frequency characteristics of this detection output are corrected by a video signal low-pass filter 17. Since the audio carrier wave of television broadcasting is frequency modulated, V _S (t) can be expressed as V _S (t) = A _S cos [{ω _S + S (t)} t + φ _S ] (7). where A _S is the amplitude of the audio carrier,
ω _S is the angular frequency of the audio carrier, S(t) is the audio signal, and φ _S is the phase of the audio carrier.

When this V _S (t) and V _O (t) of equation (2) are added to the mixer 3, the output V _PS (t) is V _PS (t) = A _S cos [{ω _S + S (t) }t+φ _S ]A _O co
s(ω _O t+φ _O ) =A _S A _O /2cos[(ω _S +ω _O )t+S(t)t+φ _S
+φ _O ] +A _S A _O /2cos [(ω _S −ω _O )t+S(t)t+φ _S
−φ _O ]……(8) When the frequency component of ω _S +ω _O is removed by the signal low-pass filter 4, V _PS (t)=A _S A _O /2cos[(ω _S −ω _O )t+S(t )
t+φ _S −φ _O ] = A _S A _O /2cos[{ω _IF +S(t)}t+φ _IF ]...
…(9) Here, ω _IF is ω _S −ω _O , the audio intermediate angular frequency, φ _IF
is φ _S −φ _O which is the phase of the audio intermediate frequency carrier.
Equation (9) is nothing but a conversion of the high frequency audio carrier shown in Equation (7) into an intermediate frequency audio carrier.

The filtering characteristics of the signal low-pass filter 4 are designed to cover the frequency ω _IF of the intermediate frequency audio carrier Y, as shown in FIG. ω _IF is set at 4.5MHz, but this figure is an example of the NTSC system, and the frequency is different for other systems. The intermediate frequency audio carrier passes through this signal low pass filter 4 and is amplified by a signal amplifier 5 and an audio intermediate frequency amplifier 25. The output is detected by the frequency discriminator 26, and the audio signal S
(t) is obtained. S(t) is output to the audio output device 27.

In the above explanation, it is assumed that there is no difference between the phase of the video carrier wave V _V (t) and the phase of the output V _O (t) of the local oscillator 2, that is, φ = 0. can be obtained.

The output of the voltage controlled local oscillator 2 is applied to a mixer 7 via a 90° phase shifter 6. The output of 90° phase shifter 6 is
Assuming V _Q (t), V _Q (t) = A _O sin (ω _O t + φ _O ) ...(10) This is combined with the image carrier V _V (t) in equation (1) to mixer consisting of a voltage multiplier. 7, its output V _PQ
(t) is V _PQ (t) = {I(t) cos[ω _V t+φ _V ]−Q(t)
sin[ω _V t+φ _V ]} A _O sin[ω _O t+φ _O )=A _O I(t)cos[ω _V t+φ _V
]sin[ω _O t+φ _O ) −A _O Q(t) sin[ω _V t+φ _V ]sin[ω _O t+φ _O )
=A _O I(t)/2 {sin[(ω _V +ω _O )t+φ _V +φ _O ]−sin[(ω _V
−ω _O )t+φ _V −φ _O ]} −A _O Q(t)/2{−cos[(ω _V +ω _O )t+φ _V +
φ _O ]+cos[(ω _V −ω _O )t+φ _V −φ _O ]} Since ω _O =ω _V , V _PQ (t)=A _O I(t)/2{sin[(2ω _V t+φ _V +
φ _O ]−sin[φ _V +φ _O ]} −A _O Q(t)/2{−cos[2ω _V t+φ _V +φ _O ]+c
os(φ _V −φ _O )} When the 2ω _V signal is removed by the signal low-pass filter 8, V _PQ (t)=−A _O I(t)/2sinφ−A _O Q(t)/2
cosφ……(11) is obtained. This V _PQ (t) is amplified by a signal amplifier 9 and applied to a phase comparator 10.

The control voltage V _C (t) is obtained by voltage-multiplying V _PV (t) and V _PQ (t) obtained from equations (5) and (12) using the phase comparator 10.

V _C (t)=V _PV (t)・V _PQ (t)={A _O I(t)/2
cosφ−A _O Q(t)/2sinφ} {−A _O Q(t)/2sinφ−A _O Q(t)/2cosφ}
=-A _O ² /8 {I(t) ² -Q(t) ² }θ-A _O ² /4{I(t)
Q(t)}...(12) Here, θ=2φ.

Since the video carrier wave V _V (t) has vestigial sideband characteristics, the in-phase component I(t) is always larger than the quadrature component Q(t). Therefore, −A _O /8{I(t) ² −Q(t) ² }≠0.

At this time, if the noise bandwidth of the loop is narrow enough to eliminate -A _O ² /4 {I(t)Q(t)}, the voltage controlled local oscillator 2 is controlled so that θ=0. Ru. That is, the synchronous reception system is controlled so that φ=0.

When φ=0, as already shown in equation (6), the amplitude of the in-phase component with respect to the video carrier wave is obtained as the detection output.

Next, the search for television broadcast waves will be explained. So far, we have described the phase control of the voltage-controlled local oscillator 2, assuming that the oscillation frequency ω _O (t) of the voltage-controlled local oscillator 2 is equal to the input video carrier frequency ω _V (t). The aforementioned PLL not only performs phase locking, but also performs negative feedback operation regarding frequency within the PLL's pull-in range. The television broadcast wave search circuit is provided to bring the local oscillation frequency within this pull-in range. The channel selection control device 22 opens the gate circuit 14 in response to a channel selection command inputted from the control input device 21 . The output pulses of the pulse oscillator 13 pass through a gate circuit 14 and are applied to a binary counting circuit 15. 2
The output of the decimal counting circuit 15 is applied to the D-A converter 16, and its analog output is applied to the analog switch 12.
It is applied to the voltage controlled local oscillator 2 via the . Since the analog output is determined by the binary counting result in the binary counting circuit 15, it is a kind of sweep voltage. The output frequency of the voltage controlled local oscillator 2 is also swept by this sweep voltage. The swept local oscillation frequency approaches the video carrier frequency ω _V (t) of a certain channel and enters the PLL pull-in range, and then, just before the phase lock is reached, the mixer 3 begins to generate a video detection output. This video detection output passes through a signal low-pass filter 4, a signal amplifier 5, and a video signal low-pass filter 17, and is applied to a synchronization separation circuit 18, where the synchronization signal is separated. If the tuning frequency of the synchronization signal tuning circuit 19 is set equal to the horizontal synchronization frequency, a sine wave having a frequency equal to the synchronization signal frequency is obtained when the video detection output is present. This is added to the rectifier circuit 20 and rectified to obtain a DC signal. This DC signal is used as a control signal for the gate circuit 14, and the gate circuit 14 is closed.

The output of the rectifier circuit 20 is also supplied to the tuning control circuit 2.
2, the analog switch 12 and the analog switch 23 are controlled to open the search circuit loop.
Close PLL. Just before the search circuit loop opens, the output voltage of the D-A converter 16 is applied to the voltage controlled local oscillator 2 via the analog switch 12, but at the same time, the output voltage of the D-A converter 16 is applied to the PLL low-pass filter 11 via the analog switch 23. It has also been added to However, the analog switch 12 cuts off the output terminal of the PLL low-pass filter 11 and the voltage-controlled local oscillator 2. Next, analog switch 12 is PLL
At the same time as connecting the low-pass filter 11 and the voltage-controlled local oscillator 2, the analog switch 23 is cut off. Before the voltage applied from the D-A converter 16 to the PLL low-pass filter 11 is discharged, the previously obtained voltage-controlled local oscillator control voltage V _C (t) from the phase comparator 10 is Added. After this switching operation, the PLL becomes a closed circuit.

As described above, first, the television broadcast wave search circuit loop searches for the video carrier wave ω _V (t) of the desired station, and then the PLL searches for the voltage-controlled local oscillator output V _O (t). The frequency ω _O (t) and phase φ _O (t) of are controlled to be equal to the video carrier frequency ω _V (t) and phase φ _V (t), respectively, and a mixer 3 consisting of a voltage multiplier controls the frequency ω O (t) and phase φ O (t) of , enters the reception state with a synchronous reception system that performs synchronous detection for video carrier waves and frequency conversion for audio carrier waves. Note that GaAs transistors as high-mobility devices are used for the high-frequency input section 1 and the mixer 3, and these parts can be combined with a 90° phase shifter and the like into one IC.

As described above, according to this embodiment, the phase of the oscillation output of the voltage-controlled local oscillator is synchronized with the phase of the video carrier wave of the desired station to obtain a video signal and an audio intermediate frequency signal. Therefore, it is possible to select and receive the desired station from the television broadcast waves, and compared to the tuning method that uses an inductor and variable capacitance diode like the television tuner, it is easier to integrate into an IC, and the manufacturing process of the tuner is easier. No adjustment can be achieved. In this case, the oscillation frequency of the voltage controlled local oscillator 2 must be within the pull-in range of the PLL, but in this embodiment a television broadcast wave search circuit is used. This configuration has the advantage that a prescaler is not required compared to the method using a PLL frequency synthesizer.

In addition, the video signal demodulated to baseband,
The audio intermediate frequency signal converted to an intermediate frequency is
By using a configuration in which the signal is filtered by the signal low-pass filter 4 having filtering characteristics as shown in the figure, and both are amplified by the signal amplifier 5, it is possible to amplify the video signal and the audio intermediate frequency signal with one amplifier. Regardless, the video signal is
There is no interference with the audio signal. This is especially advantageous when broadcasting music in stereo using audio multiplexing.

In addition, recently, on TV Jiyeon Chiyuna
There have been attempts to apply GaAs-based variable capacitance diodes and high-frequency transistors, but these remain in the traditional tuning method using variable capacitance diodes and inductors;
It is not a method that can be configured only by applying devices. Although this embodiment cannot be constructed using conventional Si devices, a television channel selection device with the various effects described above can be realized for the first time by applying high mobility devices such as GaAs devices. The focus is on

As described above, according to the present invention, the phase of the oscillation output of the voltage controlled local oscillator is synchronized with the phase of the video carrier wave of the desired station to obtain the video signal and the audio intermediate frequency signal. You can select and receive the desired station from the television broadcast waves, compared to the tuning method that uses an inductor and variable capacitance diode like the conventional television tuner.
It becomes easy to integrate into IC, and also eliminates the need for adjustment in the tuner manufacturing process. Furthermore, since the present invention uses a television broadcast wave search means, it does not require a prescaler and can have a simpler configuration than when a PLL frequency synthesizer is used.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.
FIG. 2 is a filtering characteristic diagram of the signal low-pass filter in the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... High frequency input part, 2... Voltage controlled local oscillator, 3... Mixer, 4... Signal low pass filter, 5...
...Signal amplifier, 6...90° phase shifter, 7...Mixer,
8... Signal low pass filter, 10... Phase comparator, 1
1...PLL low-pass filter, 15...binary counting circuit,
16...D-A converter, 18...Synchronization separation circuit,
27...Audio intermediate frequency amplifier.

Claims (1)

[Scope of utility model registration request] a first mixer that multiplies the output from the high-frequency input section into which television broadcast waves are input by the output of the voltage-controlled local oscillator; and a 90° phase shifter that shifts the phase of the output of the voltage-controlled local oscillator by 90°. a second mixer that multiplies the output of the high frequency input section and the output of the 90° phase shifter; and a second mixer that multiplies the output of the high frequency input section and the output of the 90° phase shifter, and multiplies the outputs of the first and second mixers to determine the phase of the television video carrier wave. a phase comparator that detects a phase difference between the voltage-controlled local oscillators; and by controlling the voltage-controlled oscillator with the output of the phase comparator, the phase of the output of the voltage-controlled local oscillator is determined by the high-frequency input section. a phase lock loop for synchronizing the phase of one video carrier among the outputs of the voltage controlled local oscillator; a sweep voltage generating means for generating a sweep voltage for sweeping the output frequency of the voltage controlled local oscillator; television broadcast wave searching means having a synchronization separation circuit that separates a synchronization signal from the video detection output that is generated, and a sweep voltage control means that controls the sweep voltage based on the synchronization signal; a switching means for switching between the output of the phase comparator and the output of the sweep voltage generating means and outputting one to the voltage controlled local oscillator; and a signal responsive to the output of the synchronization separation circuit; 1. A television channel selection device comprising a control means for controlling a switching means.