JPS5816807B2 - Channel number counting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel number counting device using a surface acoustic wave filter.

The following example is known as a channel number counting device using a surface acoustic wave filter (hereinafter referred to as a SAW filter).

FIG. 1 is a diagram showing an example of this, in which 1 is an electronic tuning tuner (hereinafter referred to as an electronic tuner), 2 is an SA
W filter, 3 is a high frequency amplification circuit, 4 is a detection amplification circuit,
5 is a waveform shaping circuit, 6 is a frequency divider by 3 circuit, 7 is a counter, 8
9 is a channel number display device, 9 is a tuning voltage reset circuit,
10 is a tuning voltage generation circuit, and 11 is a tuning circuit.

Here, the SAW filter 2 will be explained using FIGS. 2 and 3.

12, 12' in FIG. 12″ is the input lead wire,
13, 13', 13" are output lead wires, VHF
When receiving band signals, a local oscillation signal is input from the VHF tuner to the input leads 12, 12'.
When receiving a band signal, a local oscillation signal is input from the UHF tuner to the input lead wire 12''.

When receiving a UHF band signal, the local oscillation signal is converted into a surface wave at the input electrode 12''a and reaches the output electrodes i3''a and i3''b.

However, the output electrode 13''a, which is closer to the input electrode 12''a,
Since the phases of the surface waves arriving at the far output electrode 13''b are different, the surface waves strengthen each other where they are in phase.
They weaken each other when they are out of phase.

That is, if the signal at the output electrode 13''a near the input electrode 12'4 is AeJωt (2πff: frequency), and the delay time at one output electrode 13''b is τ, then Aej
ct (=1τ).

Therefore, this sum signal is output to the lead wire 13'' of the SAW filter 2, and the absolute value IVI of the output signal is IVI=
lAejωt+AeJ'L (1τ) l=Av': t=σ, which results in a filter having a peak point at f=n/τ (n: integer).

Therefore, if T=1/2 usec is selected, a comb filter having a peak every 2 MHz can be obtained.

The same applies to the characteristics of the VHF band.

In Japan, the local oscillation frequencies for each band are as follows.

vHF mouth → Kundo (1~3ch): 150~162
MHzvHF hinoside (4-12ch): 230-
276MHz UHF band (13-62ch): 530
~824MHz, so each band has 146
If the center frequency and bandwidth of the SAW filter 2 are set to match .about.162.degree. 226.about.276.526.about.824.times., the frequency characteristic will be as shown in FIG.

Figure 8 is a diagram showing frequency on the horizontal axis and amplitude characteristics on the vertical axis.
F biband, FIG. 3C shows the UHF band.

The reason why the two sets of filters for the 5t VHF band are connected in parallel as shown in FIG. 2 is that the two bands do not share each other's bands and are unlikely to interfere with each other.

Next, the operation of the channel counting device will be described.

When the input to the tuning circuit 111 is applied, the tuning voltage generating circuit 1
0) Generate a predetermined tuning voltage for the iron.

The tuning voltage generating circuit 10 may be of a variable resistor type or a type of a semiconductor memory and a DA converter.

At the same time, the tuning voltage reset circuit 9 operates to once set the tuning voltage to O2 (volts) and then increase it to a predetermined value.

Therefore, the local oscillation frequency of the voltage-controlled local oscillator in the electronic tuner 1 is swept.

This output is input to the SAW filter 2, amplified to a sufficient level by the high frequency amplifier circuit 3, and detected by the detection amplifier circuit 4.

By counting the number of peak points of the output of the SAW filter 2, it can be determined how many times the local oscillation frequency has passed through the peak points of the SAW filter 2.

Therefore, the output of the detection amplifier circuit 4 is waveform-shaped by the waveform shaping circuit 5, divided by 3 by the divide-by-8 circuit 6, sent to the counter 1, counted, and displayed by the channel number display device 8 to know the channel number. be able to.

Note that since the initial channel numbers of the VHF low band, biband, and UHF band are 1 and 4.13, respectively, it is necessary to preset 0, 3, and 12 in the counter at the start of channel selection.

In such a channel number counting device.

There were problems that needed to be resolved as described below.

That is, at the time of tuning, the tuning circuit 11 (this input is applied) and a predetermined tuning voltage is generated in the tuning voltage generating circuit 10.

In order to sweep this voltage, the tuning voltage reset circuit 9 is operated to once remove the tuning voltage from OVl.

At this time, the tuning voltage drops from the predetermined voltage to O■ in a short time, resulting in a high-speed reverse sweep, and at this time, the signal generated by the reverse sweep is output from the detection amplifier circuit 4 as an unnecessary signal. n1 counter 7 is operated by this unnecessary signal,
The channel number display device gives an incorrect display.

In addition, after tuning sweep, temperature changes, power supply voltage fluctuations, changes over time, etc. may occur, and external noise may cause fluctuations in the local oscillation frequency of the electronic tuner 1, and the signal lines before and after the detection amplifier circuit 4 may change. Channel number display devices often display incorrect information when interference due to noise is present.

For example, if the local oscillation frequency fluctuates, as can be seen from Figure 3, the local oscillation frequency will fluctuate at a point that deviates from the peak point, and if it deviates further from the peak point, the amplitude will change significantly, and in some cases When the threshold value of the waveform shaping circuit 5 is exceeded and the local oscillation frequency fluctuates, the waveform shaping circuit 5 outputs a signal repeatedly and is counted by the counter 7, causing the channel number display device to display an incorrect value.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to eliminate unnecessary signal interference (caused by counters) from outside the board during tuning voltage sweep.

In order to achieve the above object, the present invention includes a gate circuit so that a signal is applied to the counter only during the tuning voltage sweep, and controls the gate signal in synchronization with the sweep. Remove unnecessary signals.

The present invention will be explained in detail below using examples.

FIG. 4 is a block diagram showing one embodiment of the present invention.

In the figure, 21 is a timing generation circuit, and 22 is a gate circuit.The feature of the present invention is that the timing generation circuit 21 and the gate circuit 22 are provided.

Further, FIG. 5 shows the voltage waveform of the main part of FIG. 4.

5A shows the tuning signal input from the tuning circuit 11 to the timing circuit 21, FIG. 5 shows the tuning voltage which is the output signal of the tuning voltage generation circuit 10, and FIG. 5C shows the tuning voltage reset circuit 9. 5d is the electronic tuner input tuning voltage applied from the tuning voltage reset circuit 9 to the electronic tuner 1, and FIG. 5e is the gate signal applied from the timing generation circuit 21 to the gate circuit 22. 5
FIG. f shows the detection output output to the detection amplifier circuit 4 when the electronic tuner input tuning voltage d is applied to the electronic tuner 1.

When the channel selection circuit 11 is instructed to select a new channel at time t1, the channel selection signal a is input to the timing generation circuit 21, and the timing generation circuit 21 is reset at the timing shown in FIG. A signal C is applied to the tuning voltage reset circuit 9.

At this time, the electronic tuner input tuning voltage d is the reset signal C
OVI continues while t is added, time t.

Thereafter, the voltage is swept to a predetermined voltage E.

On the other hand, following the reset signal C, the timing generation circuit 21 supplies the gate signal e having a predetermined time longer than the sweep time of the electronic tuner input tuning voltage d to the gate circuit 22, thereby opening the gate of the gate circuit 22.

At this time, the detection output f is outputted from the detection amplifier circuit 4, and this detection output f is shaped into a pulse waveform by the waveform shaping circuit 5 and sent to the counter 1 via the gate circuit 22.3 frequency dividing circuit 6. The channel number is added, counted, and displayed as a channel number by the channel number display device 8.

Thereafter, the gate signal e supplied to the gate circuit 22 stops at time t3, and the gate of the gate circuit 22 closes.

Therefore, when the tuning voltage reset circuit 9 is reset after time t2, the electronic tuner input tuning voltage changes (OV), and as a result, the local oscillation frequency changes and the output signal of the SAW filter 2, which is generated after time t3, The gate circuit 22 (thereby makes it possible to block noise generated due to frequency fluctuations, etc.) until the next channel selection.

FIG. 6 shows a timing generation circuit 2 which is the main circuit of the present invention.
1 and a specific example of the gate circuit 2 will be shown.

In the figure, 41 is an input terminal 42 for the tuning signal a, a detection input terminal to which a detected pulse shaped into a pulse by the waveform shaping circuit 5 is added, 43 is a reset output terminal for outputting a reset signal C, and 44 is a gate circuit 22. gate output terminal,
51 to 55 are inverter circuits, 56.57 are capacitors, 58° and 59 are diodes, 61 to 66 are resistors, 2
2 is an AND gate circuit.

In the figure, when a channel selection signal is input to the channel selection signal input terminal 40, the capacitor 56 A reset signal C determined by the time constant of the resistor 61 and the like is generated and output from the reset output terminal 43.

On the other hand, this reset signal C is inverted by an inverter circuit 58, and is connected to a capacitor 57, a resistor 64, and a diode 5.
9 is input to the rising differential circuit Riko, and resistors 65, 6
6 and inverter circuits 54 and 55, a gate signal e is generated in synchronization with the rise of the reset pulse and determined by the time constant of the capacitor 57 and the resistor 64.

This gate signal e controls the AND gate circuit 22 to take out the n signal applied from the detection input terminal 42, outputs it to the gate output terminal 44, and supplies it to the frequency divider circuit 6.

As described above, according to the present invention, unnecessary signals other than those during tuning voltage sweep can be cut off, so the channel number display device does not display errors and the channel number counting device operates stably.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional channel number counting device.
FIG. 2 is a diagram showing a SAW filter, FIG. 3 is a characteristic diagram showing its band characteristics, FIG. 4 is a configuration diagram showing an embodiment of a channel number counting device according to the present invention, and FIG. 6 is a voltage waveform diagram of the main part of the figure, and FIG. 6 is a circuit diagram of a timing generation circuit and a gate circuit in the present invention. 1: Electronic tuner, 2: SAW filter, 4: Detection amplifier circuit, 7: Counter, 8: Channel number display device, 9:
Tuning voltage reset circuit, 10: Tuning voltage generation circuit, 11
: Tuning circuit, 21: Timing generation circuit, 22: Gate circuit.

Claims (1)

[Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator, a surface acoustic wave filter into which the output signal of the electronically tuned tuner is input, a detection amplifier circuit that detects the output signal of the surface acoustic wave filter, and the electronically tuned tuner. A channel number counting device comprising a sweeping means for sweeping the local oscillation frequency of the detector, and a counter for counting the number of output signals obtained by the detection amplifier circuit, wherein a gate circuit is provided between the detection amplifier circuit and the counter. A channel number counting device characterized in that, in this gate circuit, the output signal of the detection amplification circuit is gated by a gate signal synchronized with the output signal of the sweep means and supplied to the counter.