JPH11163684A - Auto-tuning circuit and receiver using the circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give no influence to the sweep rate despite a very large time constant of a smoothing circuit by converting the DC voltage acquired by the smoothing circuit into the digital voltage to calculate the counter value and setting and holding the calculated value by a counter. SOLUTION: The DC voltage TU outputted from a smoothing circuit 3 is sent to a tuning voltage generation circuit 4 and also to an A/D conversion circuit 6. Then the voltage TU is converted into the digital value in a quantization bit number, e.g. 14 bits equal to that of a counter contained in a tuning control circuit 2'. At the same time, the count value of the circuit 2' that is equivalent to the original PWM signal of the voltage TU outputted from the circuit 3 is calculated and sent to the circuit 2'. If the circuit 2' decides that the voltage of an AFT signal is approximate to the local oscillation frequency, the circuit 6 fetches the digital value acquired from the voltage TU outputted from the circuit 3. Thus, the digital value is newly held and set in place of the old value and accordingly the influence of the delay value is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auto-tuning circuit applied to, for example, a portable radio receiver or a liquid crystal television set, and a receiver using the same.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a general auto-tuning circuit employed in a portable liquid crystal television device or the like. In FIG. 1, when a signal for instructing tuning up or tuning down by key operation is input, the tuning control circuit 2 increases or decreases a built-in counter, and a PWM having a resolution of, for example, 14 bits corresponding to the count value. A (pulse width modulation) signal is sent to the smoothing circuit 3.

[0003] The smoothing circuit 3 is composed of a low-pass filter, and smoothes the received PWM signal to thereby reduce the DC voltage TU.
The obtained DC voltage TU is sent to the tuning voltage generation circuit 4. The tuning voltage generation circuit 4 amplifies the DC voltage TU to obtain a tuning voltage BT necessary for a channel selection operation, and supplies the tuning voltage BT to the tuner 1.

[0004] The tuner 1 performs a tuning operation in accordance with a given tuning voltage BT, converts a television reception signal into an intermediate frequency signal IF, and outputs the intermediate frequency signal IF to the intermediate frequency amplifier circuit 5. The intermediate frequency amplifying circuit 5 amplifies the intermediate frequency signal IF and outputs the amplified signal to a video detection circuit (not shown). The AFT signal and the composite synchronization signal C-SYNC obtained by performing the AFT detection are sent to the tuning control circuit 2. Send out.

The tuning control circuit 2 includes an AFT signal from the intermediate frequency amplification circuit 5 and a composite synchronization signal C-SYNC.
When the broadcast station is determined, the content of the PWM signal to the smoothing circuit 3 is fixed and the channel selection operation is terminated.

[0006]

In the configuration of the auto-tuning circuit as described above, the PWM signal output from the tuning control circuit 2 is converted into a smoothing circuit having a large time constant in consideration of frequency fluctuation due to ripple. 3 to obtain a DC voltage TU.
, And a value of a built-in counter which is a reference for generating a PWM signal by the tuning control circuit 2 has a time lag.

Therefore, when the sweep speed is increased, the amount of the above-mentioned shift increases, and the AFT signal and the composite synchronous signal CS obtained from the intermediate frequency signal IF from the tuner 1 are increased.
When the sweep operation is terminated at the discretion of the broadcasting station by YNC,
This causes a problem that the receiving frequency is significantly deviated. Therefore, it is impossible to perform a sweep operation too fast, and there is a limit in improving the sweep speed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a voltage synthesizer type auto-tuning circuit using a pulse width modulation signal for smoothing the pulse width modulation signal. Even if the time constant of the circuit to be set is set to be very large in consideration of the frequency fluctuation due to ripple, it does not affect the sweep speed, so that the sweep speed can be increased even with stable operation It is an object of the present invention to provide a circuit and a receiving device using the same.

[0009]

According to the first aspect of the present invention,
In a voltage synthesizer type auto-tuning circuit for generating a tuning voltage from a pulse width modulation signal corresponding to a counter value, a smoothing for generating a DC voltage used for generating the tuning voltage by smoothing the pulse width modulation signal Circuit, a digital conversion circuit that digitizes the DC voltage obtained by the smoothing circuit to calculate the value of the counter, and control means for setting and holding the value calculated by the digital conversion circuit in the counter. Features.

According to a second aspect of the present invention, in a receiving apparatus using a voltage synthesizer type auto-tuning circuit for generating a tuning voltage from a pulse width modulation signal corresponding to a counter value, the pulse width modulation signal is smoothed. A smoothing circuit that generates a DC voltage used to generate the tuning voltage, a digital conversion circuit that digitizes the DC voltage obtained by the smoothing circuit to calculate the value of the counter, and a digital conversion circuit that calculates the value of the digital conversion circuit. Control means for setting and holding the value in the counter.

In any of the above constructions, even if the time constant of the smoothing circuit for smoothing the pulse width modulation signal is set to be very large in consideration of the frequency fluctuation due to the ripple, The sweep speed is not affected, so that the sweep speed can be increased even in a stable operation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an automatic tuning circuit of a liquid crystal television set will be described below with reference to the drawings. FIG. 1 shows the circuit configuration, which is basically the same as that shown in FIG. 5 above. Therefore, the same portions are denoted by the same reference numerals and description thereof will be omitted.

The DC voltage TU output from the smoothing circuit 3 is sent to the A / D conversion circuit 6 in addition to the tuning voltage generation circuit 4. The A / D conversion circuit 6 digitizes the DC voltage TU with the same number of quantization bits as the counter incorporated in the tuning control circuit 2, for example, 14 bits, so that the smoothing circuit 3 outputs at that time. The count value in the tuning control circuit 2 corresponding to the original PWM signal of the DC voltage TU is calculated, and the calculated count value is sent to the tuning control circuit 2 '.

The smoothing circuit 3 is constituted by an integrating circuit including a resistor R and a capacitor C as shown in FIG. 2, for example, to obtain a DC voltage TU by smoothing a PWM signal from a tuning control circuit 2 '. The values of the resistor R and the capacitor C are set so as to increase the time constant in consideration of the fluctuation of the frequency.

With the above configuration, the voltage delay state in the smoothing circuit 3 will be described first with reference to FIG. In the figure, when the tuning control circuit 2 'outputs a value B of the PWM signal that is in line with the theoretical value A, the smoothing circuit 3 has a large time constant as described above.
The smoothing circuit 3 always outputs a DC voltage TU having a value C following the constant delay amount Vdelay shown in the figure.

The delay amount Vdelay is a slope of the theoretical value A,
That is, it is proportional to the product of the sweeping speed and the resistance R and the capacitor C, and it can be seen that the magnitude is exactly three count values of the PWM value B in this figure. Assuming that the smoothing circuit 3 has such a delay characteristic, the output DC voltage TU is amplified by the tuning voltage generation circuit 4 and applied to the tuner 1 as the tuning voltage BT.

FIG. 4 shows the relationship between the AFT signal obtained from the tuner 1 and the synchronization detection signal generated from the composite synchronization signal C-SYNC. As shown in FIG.
The tuning control circuit 2 determines the reception of the broadcasting station based on the FT signal and the synchronization detection signal.

That is, the reference voltages Va and Vc (Va> Vc) are used for the AFT signal shown in FIG.
Higher than the reference voltage Va (shown as “AFT-H” in the figure)
Or lower than the reference voltage Vc (shown as “AFT-L” in the figure), so that the existence of the AFT signal curve as shown is confirmed, and the reference voltage Vb (= (Va + Vc)
/ 2) to determine the vicinity of the local oscillation frequency.

At this time, due to the influence of the delay caused by the smoothing circuit 3, the value of the counter incorporated in the tuning control circuit 2 'becomes the same as that of the original PWM signal of the DC voltage TU output from the smoothing circuit 3. Since it has advanced by three in comparison with the value, the delay amount Vde with time remains unchanged.
The tuning voltage BT rises by the amount of lay, and settles out of the local oscillation frequency.

Therefore, when the tuning control circuit 2 'determines that the voltage of the AFT signal is near the local oscillation frequency, the A / D conversion circuit 6 obtains the digital value obtained from the DC voltage TU output from the smoothing circuit 3. The effect of the delay amount Vdelay is eliminated, and the deviation of the tuning voltage BT is reliably avoided by taking the acquired value and setting it again in the built-in counter instead of the previously held value. Things.

By performing such an operation by the tuning control circuit 2 ', even if the time constant of the smoothing circuit 3 is set to be very large in consideration of the fluctuation due to the frequency due to the ripple, the delay according to the sweeping speed is reduced. The tuning voltage BT does not fluctuate due to the amount Vdelay, and the tuning position does not shift. Therefore, the sweep speed can be set to a large value with a stable operation.

Although the above embodiment has been described with reference to the case where the present invention is applied to an auto tuning circuit of a liquid crystal television apparatus, the present invention is not limited to this, and generates a tuning voltage from a pulse width modulation signal corresponding to a counter value. Any receiving device using a voltage synthesizer type auto-tuning circuit that performs automatic sweeping can be similarly applied to a radio receiver and the like. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0023]

According to the first and second aspects of the present invention, even if the time constant of the smoothing circuit for smoothing the pulse width modulation signal is set to be very large in consideration of the fluctuation of the frequency due to the ripple, the sweep speed is reduced. There is no effect, and therefore, the sweep speed can be increased even in a stable operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a specific configuration of a smoothing circuit in FIG. 1;

FIG. 3 is a diagram illustrating an operation according to the embodiment.

FIG. 4 is a diagram illustrating an operation according to the embodiment.

FIG. 5 is a block diagram showing a configuration of a general auto-tuning circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tuner 2, 2 '... Tuning control circuit 3 ... Smoothing circuit 4 ... Tuning voltage generation circuit 5 ... Intermediate frequency amplification circuit 6 ... A / D conversion circuit

Claims (2)

[Claims] 1. A voltage synthesizer type auto-tuning circuit for generating a tuning voltage from a pulse width modulation signal corresponding to a value of a counter, wherein a direct current used to smooth the pulse width modulation signal and generate the tuning voltage. A smoothing circuit for generating a voltage, a digital conversion circuit for digitizing a DC voltage obtained by the smoothing circuit to calculate the value of the counter, and a control means for setting and holding the value calculated by the digital conversion circuit in the counter. An auto-tuning circuit comprising: 2. A receiving apparatus using a voltage synthesizer type auto-tuning circuit for generating a tuning voltage from a pulse width modulation signal corresponding to a value of a counter, wherein the tuning voltage is generated by smoothing the pulse width modulation signal. A smoothing circuit for generating a DC voltage used for this purpose; a digital conversion circuit for digitizing the DC voltage obtained by the smoothing circuit to calculate the value of the counter; and setting the value calculated by the digital conversion circuit to the counter A receiving device comprising: a control unit for holding the information.