Switching control apparatus for tuning system

A switch control apparatus for a tuning system includes a station selecting unit which has an analog to digital converter to which a first signal indicative of the reception state of a receiver and a second information signal independent of the first signal are inputted. A switching circuit selects one of the two input signals to the analog to digital converter in accordance with the on or off state of a power supply of the receiver. A control circuit controls the switching circuit such that when the power supply is on, the first signal indicative of the reception state is inputted to the analog to digital converter while when the power source is off, the second information signal is input to the analog to converter.

BACKGROUND OF THE INVENTION 
The present invention relates to tuning control systems used in television 
receivers including video tape recorders (VTRs) and AM FM radio receivers, 
and more particularly, to such apparatus which, in turn, includes an 
analog to digital converter. 
Recently, a tuning control system with a controllable electronic tuner has 
its main portion made of multi-function ICs. The IC of one chip is used 
not only for control of tuning, but also for control of on and off 
operations of a power supply of a television receiver or for adjustment of 
acoustic volume. The multi-function IC which serves its central role is 
desired to be used in many kinds of apparatus in terms of productiveness 
and cost. 
A conventional tuning control system will now be described with reference 
to the drawings. FIG. 1 is a block diagram of a tuner of a conventional 
television receiver. A reference numeral 1 denotes an automatic frequency 
regulator (AFT) of the television receiver. The AFT voltage signal 
corresponding to the output signal of the well-known AFT 1 is inputted to 
an analog to digital (A/D) converter 3 of a tuning control IC 13 to be 
converted into an AFT digital signal, which is then input to a central 
processing unit (CPU) 5 where the digital AFT signal is processed by 
control software stored in a read only memory (ROM) 6. The resulting data 
signal is outputted from an output port 7 connected to CPU 5 so as to 
correct the reception frequency of an electric tuner 9. 
A DC power source voltage E.sub.0 has series connected voltage dividing 
resistors 11 and 12 having resistance values R.sub.11 and R.sub.12, 
respectively. If R.sub.11 =R.sub.12, a voltage signal of E.sub.0 /2 is 
applied to the A/D converter 4. The voltage levels set by the resistors 11 
and 12 correspond to three operational modes, as shown in FIG. 3. 
If a key switch 15 which selects one of television and video inputs is 
pressed so as to select a video mode, the input signal voltage to the 
input port 14 drops from E.sub.0 (volts) to 0 (volts). The control 
software stored in the ROM 6 is programmed so as to be expressed by a 
flowchart shown in FIG. 2. As will be understood from the flowchart, when 
the input voltage level to the input port 14 becomes 0 volts, CPU 5 takes 
the data signal from the A/D converter 4. Applied to the input of the A/D 
converter 4 is a voltage signal of E.sub.0 /2 (volts) indicating that the 
number of video input terminals is 1 (unity). Therefore, a binary 
operational-mode selective signal (TV mode: H, and VTR mode: L 
corresponding to the initial set mode L) when the number of video input 
terminals is 1 (unity) is output to the output port 8 to thereby control 
the television/video input switching circuit 10. The operational mode 
signal is circulated in the order of a television mode.fwdarw.a video 
mode.fwdarw.the television mode. While the operation of the tuning control 
system having a single video input terminal has been described, the 
operation of a tuning control system having two video input terminals is 
as follows. The initial setting by the resistors 11 and 12 is made such 
that the set voltage is between 2E.sub.0 /3 and E.sub.0. Under such 
conditions, when the key switch 15 is pressed, processing is performed as 
in the initial setting mode mentioned above, and a mode selective signal 
which circulates the operational mode is outputted from the output port 8 
in the order of television mode.fwdarw.video mode.fwdarw.television mode. 
In this way, the station selecting apparatus is able to set three kinds of 
initial modes: a non-video input terminal mode, a single-video input 
terminal mode, and a two video input terminal mode in accordance with 
voltage levels set by combinations of resistors 11 and 12. In addition, 
the apparatus is usable in three kinds of television receivers. 
However, in the conventional device, at least two A/D converters are 
employed in the tuning control IC; namely, the A/D converter for reception 
of the AFT voltage signal and the A/D converter for reception of a mode 
setting voltage signal must be provided. The A/D converter occupies a 
relatively large area when it is designed so as to include IC circuits, so 
that only provision of many A/D converters would bring about a large-scale 
IC and increase the cost. There is a known multiplexing technique which 
realizes an apparatus using a single A/D converter. In this case, however, 
the number of IC pins is required to increase only for multiplexing 
control purposes. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a tuning control system 
which is usable in three kinds of television receivers operating in a 
no-video input terminal mode, a single-video input terminal mode and a 
two-video input terminal mode without increasing the number of A/D 
converters for tuning control purposes and without increasing the number 
of IC pins. 
In order to achieve the above object, the tuning control system according 
to the present invention includes a switching circuit for selecting an 
input to the A/D converter in accordance with the on or off state of a 
power supply of a television receiver such that the A/D converter receives 
an AFT signal when the power supply is on, and second information on the 
number of video terminals when the power supply is off and such that the 
station selecting IC receives the AFT signal when the power supply is on, 
and second information when the power supply is off. 
Therefore, according to the tuning control system of the invention, a 
single A/D converter suffices for the station selecting IC and hence the 
number of IC pins is reduced. Thus, the tuning control IC is reduced in 
scale and cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of the present invention will now be described with 
reference to the drawings. FIG. 4 is a block diagram of a tuning control 
system as one embodiment of the present invention. In FIG. 4, reference 
numeral 1 denotes an AFT of a television receiver whose output comprises 
an AFT voltage signal which is inputted to a central processing unit (CPU) 
5 via an A/D converter 3. CPU 5 has a control software ROM 6 connected 
thereto. The control software stored therein operates the system which 
comprises CPU 5 as the hub. Reference numeral 20 denotes a key switch 
which turns on and off the main power supply of the television receiver; 
21, a key switch for selecting between television and video inputs. Both 
the switches 20 and 21 are connected via input ports 23 and 22, 
respectively, to CPU 5. The key switch 21 is a push switch which generates 
a pulse signal when pressed. The control output signal from CPU 5 is 
supplied to an electronic tuner 9 via an output port 7, to a circuit 10, 
which selects between television and video inputs, via an output port 8 
and to a transistor 16 which drives a power supply relay 17 via an output 
port 11 and a resistor 13. The output signal from the output port 11 is 
supplied to a transistor 15 which selects an input to the A/D converter 3 
via a resistor 12. 
CPU 5 delivers data corresponding to a channel to be selected to a tuning 
voltage generator 101. Tuning voltage generator 101 generates a tuning 
voltage corresponding to the data delivered thereto, and supplies the 
tuning voltage to an electronic tuner 9. Tuner 9 selects a channel 
corresponding to the tuning voltage, and supplies an output to an IF 
amplifier 102. The amplified signal is detected by a detector 103 and a 
video signal is taken out. The video signal is supplied to TV/VIDEO input 
selector 10 as a TV input. 
On the other hand, a carrier component amplified by IF amplifier 102 is 
supplied to an AFT circuit 1, and an output voltage corresponding to a 
frequency deviation is generated. This output voltage is inputted to A/D 
converter 3 of tuning control IC 2. 
The present invention thus includes a switching circuit which changes over 
two different kinds of input signals, i.e., first and second input 
signals, and one of the two input signals is supplied to a single A/D 
converter of a tuning control system. The switching circuit is controlled 
by ON and OFF states of a power supply to a receiver. The first input 
signal to the A/D converter can be an AFT (AFC) voltage, and AGC voltage, 
etc., representing a receiving state, and the second input signal can be a 
control signal which controls the tuning control system. The first input 
signal is inputted when the power supply to the receiver is turned ON, and 
the second input signal is inputted when the power supply to the receiver 
is turned OFF. Thus, two kinds of information can be supplied to a single 
A/D converter by changing over therebetween. 
In operation, assume that the power main supply is off. The output signal 
from the output port 11 is rendered low on a control command from CPU 5 in 
the tuning control IC 2 in an operative state due to power supplied by a 
sub-power supply an on state. Therefore, the base current in the 
transistor 15 flows through the resistor 12 to thereby render transistor 
15 conductive. At this time, the AFT 1 outputs no AFT voltage signal 
because the main power supply is off and a voltage of E.sub.0 
.times.Z.sub.0 /(R.sub.14 +Z.sub.0) volts is inputted to the A/D converter 
3 where R.sub.14 is the resistance value of the resistor 14, and Z.sub.0 
is the impedance seen from the output terminal because the transistor 15 
is on. 
Assume now that Z.sub.0 =R.sub.14, and the input voltage is E.sub.0 /2. As 
shown in the flowchart of FIG. 5, CPU 5 receives a data signal from the 
A/D converter 3 when the main power supply is off, and stores it in an 
internal RAM 24. 
If the main power supply on-off key switch 20 is pressed, the signal level 
to the input port 23 changes high to low and CPU 5 changes the output from 
the output port 11 from low to high. As a result, a power supply relay 17 
is turned on because the transistor 16 is rendered conductive, and the 
main power supply of the television receiver is turned on. Since the base 
of the transistor 15 is changed simultaneously to high via the resistor 
12, so that the transistor 15 is turned off and the AFT voltage output 
signal from the AFT 1 as it is inputted to the A/D converter 3. Therefore, 
CPU 5 performs AFT processing using the input to the A/D converter as an 
AFT voltage signal, as shown in the flowchart of FIG. 5, to thereby 
correct the reception frequency in the electronic tuner 9. 
Under such conditions, if the television-video input switching key 21 is 
pressed, the signal level to the input port 22 is changed from high to low 
for the time interval corresponding to the width of a pulse generated by 
the pressing of the key 21, and CPU 5 detects the reception of a trigger 
pulse signal thereto, reads a voltage value stored in RAM 24 when the main 
power supply is off, determines which of the ranges of 0-E.sub.0 /3, 
E.sub.0 /3 -2E.sub.0 /3 and 2E.sub.0 /3-E.sub.0 the read value is in, and 
outputs a mode selective signal to the output port 8 in accordance with 
the read voltage value. 
In the present embodiment, data on the voltage E.sub.0 /2 generated across 
the resistor 14 when the main power supply is off and the sub-power supply 
is on is stored in RAM 24. Thus, CPU 5 outputs to the output port 8 a mode 
selective signal which requires to change the mode from the television 
input to the video input in accordance with the trigger pulse signal which 
is a signal requiring to switch between the television mode and the video 
mode, and the data on E.sub.0 /2 is read out of RAM 24. The mode selective 
signal is realized, for example, by a 2-bit binary signal. More 
specifically, the television mode is "01" while the video mode is "10". 
Assume herein that the "10" mode selective signal is input to the 
television/video switching circuit 10. As a result, the switching circuit 
10 selects the input signal from the video tape recorder, etc., in place 
of the currently selected signal from the television receiver circuit, and 
supplies it to the subsequent signal processor (not shown). 
The switching operation from the video mode to the television mode is 
performed as follows. If the television/video input switching key 21 is 
pressed when the main power supply is on and the operational mode is the 
video mode, a trigger pulse signal is generated in a manner similar to 
that mentioned above and input signal to the input port 22. In response to 
this pulse signal, CPU 5 reads the data on the voltage value corresponding 
to E.sub.0 /2 stored in RAM 24 and processes it in order to determine 
which of the television and VTR modes should be selected as the 
operational mode and which of the three initial settable modes the initial 
set mode is. As a result, the 2-bit code signal "01", requiring the 
operational mode to be the television mode, is outputted to the output 
port 8. Thus, CPU 5 reads an AFT signal from AFT 1 using a control signal 
and tunes the electronic tuner 9 so as to receive a desired signal. 
As mentioned above, the initial setting and the selection of the 
operational modes (TV, VTR) of the television receiver having a single 
video input terminal are performed. 
When the IC 2 is used in a television receiver having no video input 
terminals, R.sub.14 is selected so as to be larger than 2Z.sub.0 on the 
basis of E.sub.0 .times.Z.sub.0 /(R.sub.14 +Z.sub.0)&lt;E.sub.0 /3. 
If it is used in a television receiver having two video input terminals, 
R.sub.14 is selected so as to be smaller than Z.sub.0 /2 on the basis of 
E.sub.0 .times.Z.sub.0 /(R.sub.14 +Z.sub.0)&gt;2E.sub.0 /3. 
As described above, in the tuning control system according to the present 
invention including an A/D converter, a switching circuit is provided for 
selecting one of a voltage signal indicative of the reception state and a 
second information signal indicative of the number of video terminals used 
for selecting between television and video inputs to the A/D converter in 
accordance with the on or off state of the main power supply. Namely, when 
the main power source is on, a voltage signal indicative of the reception 
state is inputted to the A/D converter while when the power source is off, 
the second information signal is input. Therefore, a single A/D converter 
suffices for the apparatus to thereby facilitate the formation of an 
apparatus of ICs. 
While, in the particular embodiment described above, information on the AFT 
voltage and on the number of terminals for selecting between the 
television and video inputs is taken in, the AGC voltage and the voice 
multi-broadcasting mode may be used as the signal indicative of the 
reception state while whether the television receiver can receive voice 
multi-broadcasting or not and whether the receiver can receive satellite 
broadcasting or not may be used as the second information.