JPS6377209A - Filter tuner for tuner input stage - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the disturbance excluding capability by fetching an RFAGC voltage into a comparator at channel selection and using a microcomputer so as to control a D/A converter thereby compensating the deviation of tuning of an input stage tuning circuit. CONSTITUTION:A down-convert output terminal 14 of a down-convert section 3 is connected to a VIF circuit 31, where video detection is executed. Then an output being the result of video detection is fed to an RFAGC circuit 32 and an IFAGC circuit 33, in which an IFAGC voltage and an RFAGC voltage are changed depending on the quantity of a detection output. Then the RFAGC voltage is fetched by a comparator 34 at the channel selection, digital information given to a D/A conversion circuit 35 is detected by varying an output of the comparator 34 by the control of a microcomputer 17. Thus, the microcomputer 17 applies correction to input tuning voltage information of a channel being in channel selection and stored in a digital memory 16 in advance as a prescribed electric field strength so as to correct the tuning deviation of an input stage tuning circuit thereby preventing the deterioration in the disturbance excluding capability of the input stage tuning circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tuning device for an input stage filter of an up-conversion tuner.

Conventional technology In general, existing ATV converters are up-converters that cascade together an up-convert method in which the local oscillation frequency is higher than the receiving frequency, and a down-convert method to convert to a specific channel for connection to an existing TV receiver.・
Down conversion (UP/DOWN CON
V) Method C') Receiving method 75: In recent years, as the number of CATV channels has increased, the 11th F (fil,) has been set higher, and electronic In the tuner, when a common tuning voltage is applied to both the first local oscillator and the input stage tuning filter, the frequency change ratio in the variable range of both becomes constant. Since this increases the tracking error of the input tuning frequency, untuned BPFi is often used as the input stage filter. On the other hand, if the input stage filter is untuned, interference characteristics such as cross modulation and intermodulation will be bad, so as a means of tuning the input stage filter, an input stage tuning voltage memory independent of the tuning voltage of the first local oscillator is used. A channel selection device with this function has been proposed.

FIG. 3 shows a block diagram of a tuning device using an input stage filter. Hereinafter, a conventional up/down conversion type channel selection device will be described with reference to the drawings.

In FIG. 3, 2 is an up-conversion section, and 3 is a down-conversion section, and the down-conversion section 3 is connected to the output of the former up-conversion section 2.

The desired reception frequency (fd) tuned by the input stage tuned filter 5 is extracted from the signal received by the antenna input terminal 4, amplified by the RF amplifier 6, and input to the input signal terminal of the first mixer 7. Note that the MUGC voltage is applied to the RF amplifier 6 from the terminal 16. A variable capacitance diode for tuning of the first local oscillator 8 is connected to a local oscillator voltage control terminal 9.
When the first part F is (fif,), a tuning voltage is applied so that the first local oscillation frequency (f LOs) becomes fLo, = f part f, +fd, and its output is the local oscillator of the first mixer 7. Enter the number terminal. The 11th F (fif,) converted by the first mixer 7 is amplified by the 11th F amplifier 10 and then enters the input signal terminal of the second mixer 11. In the second local oscillator 12, when the second IF is (f, f2), the second local oscillation frequency (fl, 02) is fLo2=fift f2C7 is fLo2=fi
It is a fixed frequency oscillator that oscillates at f1+fif2),
The output enters the local oscillator signal terminal of the second mixer 11. Second
The 21st F signal (fif2) converted by the mixer 11 is amplified by the second IF amplifier 13 and output from the terminal 14.

By the way, the RF tuning frequency Cfd) can be obtained by the following procedure. When a channel selection command is input to the microcomputer 17, the microcomputer 17 retrieves arbitrary channel data and its input stage tuning voltage information from the digital memory 16 which stores the data in advance, and performs arithmetic correction for each channel. The calculation correction is performed as follows. Let the local tuning voltage at the time of receiving a certain RF multiplied signal ay) be (BTLO), the tuning voltage of the input stage tuning filter at this time be (BTRF), and when receiving the newly selected RF multiplied signal fRF'), The local tuning voltage (
BTLO'), the tuning voltage (BTRF') of the input stage tuning filter is fif1', where the first IP is fif1'. As described above, the input stage tuning voltage information that has been calculated and corrected for each channel by the microcomputer 17 is
It is converted into an analog voltage by the D/A conversion circuit 18, and is applied from the input stage filter tuning voltage control terminal 19 via the low resistor 20 to the variable capacitance diode of the input stage tuning filter 5, and is applied to the desired input tuning frequency (fd). It is configured to be in tune with the

Problems to be Solved by the Invention However, the digital information stored in the digital memory is a set value at a predetermined electric field strength, and in the market, the electric field strength varies for each channel.
There is a problem in that the input capacitance of the pRF amplifier changes depending on the RFAGC voltage applied to the tuner, causing the tuning of the input stage tuning circuit to shift.

The present invention is intended to solve these conventional problems, and is intended to prevent tuning deviation of the input stage tuning circuit and to prevent deterioration of the interference rejection ability of the input stage tuning circuit.

Means for Solving the Problems The tuner input stage filter tuning device of the present invention includes a first D/A conversion circuit that supplies a tuning voltage to a variable capacitance diode and is controlled by first digital information, and an RFAGCi.
A comparator is provided to compare the voltage with an analog voltage which is an arbitrary reference potential obtained through a second D/M conversion circuit controlled by second digital information, and the channel is selected and the local oscillation frequency is determined. After stabilization, the second D/A conversion circuit is controlled by the second digital information to detect the output of the comparator, and a correction value according to the second digital information is added to the first digital information. It has become.

Operation The input stage filter tuning device of the present invention corrects the digital information of the input tuning voltage, which is set in advance at a predetermined electric field strength, by detecting the RFAGC voltage, and corrects tuning deviation due to changes in the input capacitance of the RF amplifier. It is complementary.

Embodiment Hereinafter, a tuner input stage filter tuning device according to an embodiment of the present invention will be explained with reference to the drawings. In FIG. 1, the same parts as those in the conventional configuration shown in FIG. 3 are given the same numbers.

In Figure 1, the second IF is for domestic video carriers at 68.75 MHz! /! : selected and connected to the down-convert output terminal 14iV IF circuit 31,
Detect video. Image detected output RFAGC circuit 3
2 is applied to the IFAGC circuit 33, and depending on the magnitude of its detection output, the IFA (, C voltage, RF
AGG voltage changes.

In the case of FIG. 2, an example of IFAGC, RFAGC, and (-S AGO) is shown. and comparator 34 are RFA
A GC voltage is connected to one terminal of the comparator 34, and the other + terminal is connected to a D/A conversion circuit 35, which is controlled by the microcomputer 1γ.

The output of the comparator 34 is connected to the input port P of the microcomputer 17.

In the tuner input stage filter tuning device configured as described above, when selecting a channel, the RFAGC voltage is input to the comparator 34, and the microcomputer 17 inputs the RFAGC voltage.
By controlling the A conversion circuit 36 and detecting the digital information given to the D/M conversion circuit 35 in which the comparator output changes, the microcomputer 17 converts the digital memory 16 into
In this method, the input tuning voltage information of the selected channel, which is stored in advance at a predetermined electric field strength, is corrected.

Effects of the Invention As described above, the tuner input stage filter tuning device of the present invention applies the RFA (, C voltage) to the tuner, thereby adjusting the RF
It is possible to correct a shift in input stage tuning due to a change in the input capacitance of the amplifier, and this provides an effect without impairing the desired interference rejection ability that the input stage tuning circuit should originally have.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tuner input stage filter tuning device according to an embodiment of the present invention, FIG. 2 is an AGO characteristic diagram of the same device, and FIG. 3 is a block diagram of a conventional device. 17...Microcomputer, 18.35.
...D/A conversion circuit, 34...Comparator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (2)

[Claims] (1) A first D/A conversion circuit that supplies a tuning voltage to a variable capacitance diode, which is a tuning element of the tuner's input stage filter, and is controlled by first digital information, and controlled by second digital information. The second D/A conversion circuit is equipped with a comparator that takes as input the analog voltage obtained through the second D/A conversion circuit and the RFAGC voltage, and after selecting the channel and stabilizing the local oscillation frequency, the second D/A conversion circuit A tuner characterized in that the A conversion circuit is controlled by second digital information, the output of the comparator is detected, and a correction value according to the second digital information is added to the first digital information. Input stage filter tuning device. (2) A tuner input according to claim 1, wherein the tuner input is configured such that a microcomputer performs control of the first and second digital information, detection of the comparator output, and calculation of the digital information. Stage filter tuning device.