JP2687345B2 - Tuning control circuit - Google Patents

Description

The present invention relates to a channel selection control circuit. [Summary of the Invention] In the present invention, in the tuning control circuit, band switching data and channel data are separated from serial tuning data and taken out in parallel, and the data consisting of the taken out predetermined number of bit strings is directly extracted. By forming the band switching voltage and the tuning voltage, the characteristics can be improved and the number of parts can be reduced to simplify the configuration. [Prior Art] Electronic tuning tuner circuits used in TV receivers and VTRs require a band switching voltage for switching the reception band to the VHF low band, the VHF high band, or the UHF band. In addition, a tuning voltage is needed to select the channel in the switched receive band. Therefore, the tuning control circuit is configured as shown in FIG. 3, for example. That is, in the figure, (1) is an electronic tuning type tuner circuit, which has band switching terminals U, H, L and a tuning terminal CH. In this case, the terminal U corresponds to the UHF band, the terminal H corresponds to the VHF high band, and the terminal L corresponds to the VHF low band. For example, U = “1” level, H =
Band switching voltage at "0" level and L = "0" level
When V _B is supplied, it corresponds to the terminal U which is at “1” level
The band corresponding to the "1" level terminal is defined as the reception band such that the UHF band is defined as the reception band. Further, the analog tuning voltage V _C is supplied to the terminal CH, and a channel corresponding to the magnitude of the tuning voltage V _C is selected in the band selected by the band switching voltage V _B. And (2) is a one-chip IC microcomputer for tuning, and from now on, the band switching data BAND and the tuning pulse P _C according to the tuning operation of the user.
Is output. In this case, the band switching data BAND
Is 2-bit binary data having a value corresponding to the reception band. Also, tuning pulse P _C is a PWM pulse which is formed by a microcomputer incorporated in (2) the PWM generator (2P). That is, 14-bit data for tuning voltage is formed in the main part of the microcomputer (2), and this data is supplied to the generator (2P) to generate the fourth voltage.
As shown in the figure, a PWM pulse P _C having a period of 0.25 ms and a pulse width that can change over 2 ¹⁴ steps is formed. The pulse width of the pulse P _C, in addition to tuning operation AFT
It also changes depending on the movement. The band data BAND is decoded is supplied to the voltage V _B to the decoder (3), the voltage V _B is supplied to the terminal U~L the tuner circuit (1). Also, the tuning pulse
P _C is supplied to an integrator circuit (4) having a transistor Q ₁ for buffer and converted into a tuning voltage V _C having a magnitude corresponding to the pulse width of the pulse P _C , and this voltage V _C is converted into a tuner circuit (1 ) Terminal CH. Therefore, the reception band is selected according to the band data BAND, and the channel is selected according to the pulse P _C. [Problems to be Solved by the Invention] However, in the control circuit described above, since the tuning voltage V _C is formed by integrating the pulse P _C , when the channel is switched, the voltage V _C follows (changes). ) Causes a delay of about 0.1 seconds, at which time the screen is disturbed, so it is necessary to mutate the screen for at least 0.1 seconds. The microcomputer in order to form a PWM pulse P _C (2) is PWM
A special circuit called a generator (2P), which is not found in general microcomputers, must be built in. Furthermore, since the integrating circuit (4) is composed of discrete parts, it is not preferable in terms of the number of parts and the mounting area. The present invention seeks to eliminate these problems. [Means for Solving the Problems] Therefore, in the present invention, the band switching data and the channel data are serially output from the microcomputer, and the band switching voltage and the channel data are separated in the shift register, and then the band switching voltage and the channel data are directly output. It is adapted to be converted into a tuning voltage. [Operation] Band switching data and channel data are separated from serial tuning data and extracted in parallel, and directly from the extracted data consisting of a predetermined number of bit strings,
A band switching voltage and a tuning voltage are formed. [Embodiment] In FIG. 1, (5) shows a microcomputer for forming tuning data which is made into a one-chip IC, and when this user (5) performs a tuning operation,
When the AFT operation is performed, for example, as shown in FIG. 2, 16-bit tuning data SLCT is serially output in synchronization with the clock CLK. In this case, the first two bits of data SLCT is a band switching data BAND described above, 14-bit data when the pulse P _C and PWM modulation to remain, i.e., a channel data CHNL specifying the channel. Further, when this data SLCT is output, the microcomputer (5) also outputs a strobe signal STRB indicating that the data SLCT is being output, as shown in FIG. Further, (6) is a 16-bit serial input / parallel output shift register to which the data SLCT is input, and the clock CLK and the strobe signal STRB are also supplied. Then, the outputs of the two stages [1] and [2] on the opposite side of the input stage [16] of the shift register (6) are supplied to the decoder (3), and the decoded output is supplied to the terminal U of the tuner circuit (1). ~ L is supplied to the tuner circuit (1) as the band switching voltage V _{B and} the remaining 14 stages [3] of the register (6) ~
The output of [16] is supplied to the D / A converter (7) and its D
The / A output is supplied to the terminal CH of the tuner (1) as the tuning voltage V _C. According to such a configuration, at the time of channel switching (and at the time of AFT operation), the signal (CLK, SLCT, STRB) is supplied from the microcomputer (5) to the register (6) and the register (6) is synchronized with the clock CLK. The signal SLCT is latched (loaded) by the signal STRB. Then, at this time, the leading 2-bit BAND of the signal SLCT is decoded into the band switching voltage V _B by the decoder (3) and supplied to the tuner circuit (1), and the remaining 14-bit CHNL of the signal SLCT is A / D. The tuning voltage V _C is D / A converted by the converter (7) and supplied to the tuner circuit (1). Therefore, in the tuner circuit (1), the voltage V _B
And V _C , the channel of the receiving band, that is, the channel of the receiving band according to the bits BAND and CHNL of the tuning data SLCT is selected. EFFECTS OF THE INVENTION Thus, according to the present invention, the channel selection operation is performed. In this case, in particular, according to the present invention, the microcomputer (5)
There is almost no time delay from the output of the tuning data SLCT from the output of the voltage V _B , V _C to the supply of the tuner circuit (1), thus minimizing the screen muting period against the screen disturbance. You can In addition, the microcomputer (5) simply uses 16 as the tuning data SLCT.
It suffices to output individual bit strings, which can be executed by a general output port in a very ordinary manner. As in the case of FIG. Since it does not require any configuration or function, a general IC can be used as the microcomputer (5). Also, the load on the CPU of the microcomputer (5) is reduced. Further, the integrating circuit (4) is not necessary, which is advantageous in terms of the number of parts and the mounting area.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection diagram of an example of the present invention, and FIGS. 2 to 4 are diagrams for explaining the same. (1) is a tuner circuit, (5) is a microcomputer, (6) is a shift register, and (7) is an A / D converter.

Claims (1)

(57) [Claims] A tuning control circuit that supplies an electronic tuning tuner circuit with a band switching voltage for switching the receiving hand and an analog tuning voltage for specifying a tuning frequency in the reception band switched by the band switching voltage. Sometimes, a microcomputer for channel selection, which serially outputs channel selection data consisting of digital data consisting of a predetermined number of bit strings designating the reception band and digital data consisting of a predetermined number of bit strings designating the tuning frequency, A serial input-parallel output shift register that latches the serial tuning data and converts the serial tuning data into parallel tuning data, and a predetermined one that specifies the reception band of the parallel tuning data output from the shift register. Decode digital data consisting of several bit strings into the above band switching voltage Of the parallel tuning data output from the shift register, a decoder and a D / A converter that directly D / A converts digital data consisting of a predetermined number of bit strings that specify the tuning frequency to the tuning voltage. Tuning control circuit having.