JPH0448020Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a channel selection device for, for example, a television, radio, wireless device, etc., and particularly relates to an improvement of a channel selection device using digital control means.

[Description of prior art]

Voltage synthesizers and PLL synthesizers are generally known as devices that perform channel selection operations through digital control. Among these, when using a voltage synthesizer to generate the tuning voltage necessary to obtain a specific reception frequency, the user gradually changes the tuning voltage and determines the optimal tuning point by sight or ear. This is done by making judgments. In addition, in order to reduce the annoyance of the user,
The tuning device itself searches for a specific broadcasting station and determines the optimal tuning point; in this case, AFT
(Automatic Fine Tuning) The tuning device judges the signal and performs this.

On the other hand, with a PLL synthesizer, the receiving frequency can be accurately specified in advance, so there is no need for the troubles that occur with a voltage synthesizer. However, if the transmission frequency deviates from the specified value, the reception side must finely change the reception frequency accordingly, and if this is done by the tuning device, an AFT signal is still required. .

As mentioned above, the digitally controlled channel selection device
When using an AFT signal, since the AFT signal is originally an analog signal, it is necessary to convert it into a digital signal. This configuration is shown in FIG.

In FIG. 1, 1 is an electronic tuner, 2 is a digital tuning circuit that controls the electronic tuner 1, and 3 is a digital tuning circuit that controls the electronic tuner 1.
AFT signal 7 is binarized and digital tuning circuit 2
It is a window comparator for adding to.
AFT signal 7 is binarized by a comparator,
The signal becomes an up signal 5 and a down signal 6 and is input to the digital channel selection circuit 2. For example, if the received frequency is shifted lower than the optimum tuning point, an up signal 5 is output, and if it is shifted higher than the optimal tuning point, a down signal 6 is output. Furthermore, if the receiving frequency is equal to the optimum tuning point, neither signal is output. The tuning circuit 2 receives these signals, applies a tuning voltage signal 4 to the electronic tuner 1, and performs broadcast signal detection and fine tuning operations during auto search.

However, when the AFT signal is binarized and processed as described above, there is a drawback that the tuning circuit cannot judge the degree of deviation from the optimum tuning point. For this reason, it is difficult to perform fine-grained processing such as, for example, in a fine adjustment operation, if the deviation is large, the adjustment is made fast, and if the deviation is small, the adjustment is made slow to avoid synchronization deviation.

[Purpose of invention]

The purpose of this invention is to eliminate the above-mentioned drawbacks,
The present invention provides a digital channel selection device that makes signal processing easier and more reliable.

[Key points of the idea]

This invention uses an electronic tuner that controls the reception frequency by changing the voltage applied to a varactor diode, and is designed to make the tuning operation easier and more reliable in a tuning device that performs the reception operation by digital control. The present invention is characterized in that when an AFT signal is used, the AFT signal is converted into a digital signal by an A/D converter and processed.

[Explanation based on examples]

Hereinafter, the present invention will be explained based on the drawings.

FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention.

In FIG. 2, 1 is an electronic tuner, and 2 is a digital tuning circuit. 8 is an A/D converter, which has three or more conversion steps.
The AFT signal is converted into a digital data signal 9 by the A/D converter 8 and output to the digital tuning circuit 2. The digital tuning circuit 2 processes the received digital data signal 9, applies a tuning voltage signal 4 to the electronic tuner 1, and performs tuning.

Next, this process will be explained in detail. As an example, the operation when a 4-bit A/D converter is used will be described.

The AFT signal looks like the graph shown in Figure 3. The A/D conversion of this is the data shown on the right side of Figure 3, where the optimal reception frequency c is "1000", the upper limit frequency u is "0001", and the lower limit frequency _L
Suppose that it is “1110”. When the channel selection circuit 2 performs a receiving operation, an operation as shown in FIG. 4 can be considered as an example. In FIG. 4, the selected frequency is rapidly changed between t ₁ and t ₂ . The operation is slightly slowed down between t ₂ and _{t 3} , and further slowed down between t ₃ and _{t 4} to perform careful channel selection. Then, the channel selection operation ends at time _t4 when the optimum tuning point is obtained. The above switching of operations is performed based on the digital data signal 9 output from the A/D converter 8. According to this digital data signal 9, the degree of deviation from the optimum receiving frequency c can be easily and accurately determined, so that detailed tuning as described above becomes possible.

Note that the above example is just an example, and it goes without saying that the channel selection device is not limited to the two types of voltage synthesizer and PLL synthesizer.

[Effect of idea]

As explained above, the present invention uses an A/D converter instead of a comparator to determine the degree of deviation from the optimum tuning point, thereby realizing a more precise and reliable tuning operation. Furthermore, by integrating the A/D converter with the digital channel selection device into an LSI, a digital channel selection IC with advanced functions can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional device. FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention. Figure 3 is
A diagram showing an example of an AFT signal. FIG. 4 is a diagram explaining the channel selection operation. 1...Electronic tuner, 2...Digital tuning circuit, 4...Tuning selection voltage signal, 7...AFT signal, 8
...A/D converter, 9...Digital data signal.

Claims (1)

[Scope of claim for utility model registration] In a digital tuning device that controls the receiving frequency by changing the tuning voltage applied from a digital tuning circuit to an electronic tuner according to an input AFT (automatic fine tuning) signal, Equipped with an A/D converter that converts a quantity into a digital quantity, this A/D converter can perform the above
The AFT signal is digitized and fed to the digital tuning circuit, and when the deviation from the optimum receiving frequency of the AFT signal is large, the speed of change of the tuning frequency is increased, and when the deviation is small, the speed of change of the tuning frequency is increased. 1. A digital channel selection device characterized in that the channel selection voltage is changed by the digitized AFT signal so as to reduce the channel selection voltage.