JPS62204609A - Preset tuner - Google Patents

Abstract

PURPOSE:To attain the use of a D/A converter with a few bit number and to improve the temperature characteristic by using a control signal of a variable reactance for local oscillation circuit and a tracking error correcting signal stored in a nonvolatile memory. CONSTITUTION:A signal to control reactance element for a local oscillation circuit obtained from a frequency synthesis circuit 20 is fed to high frequency tuning circuits 14, 16 via adder circuits 21, 22. The signal is used to apply coarse adjustment to a varactor diode included in the tuning circuits 14, 16. The tracking error correction digital signal obtained from a nonvolatile memory 25 is read while an address suited to a reception frequency by a signal fed to a channel selection signal input terminal 13 and the capacitance of the varactor diode included in the tuning circuits 14, 16 via D/A converters 23, 24 is adjusted accurately to a required value. Thus, the temperature characteristic of the varactor diodes is compensated to improve the temperature characteristic. Further, bit number of the D/A converters 23, 24 is reduced.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a preset tuner.

Conventional technology In recent years, semiconductor technology has made remarkable advances and cost reductions, and in the field of receivers, so-called electronic tuners, which generate local oscillation signals from superheterodyne receivers using frequency synthesis technology, have become mainstream in order to ensure reliable tuning. began to occupy

Generally, in this electronic tuner, a varactor diode whose capacitance value can be changed by its reverse voltage is often used in the local oscillation circuit and high frequency tuning circuit section, and the control of the varactor diode for the local oscillation circuit generated by the frequency synthesis technology described above is used. The voltage was also applied as is to the varactor diode for the high frequency tuning circuit.However, in receivers with this type of configuration, tracking adjustment is generally troublesome due to large variations in the characteristics of the varactor diode. There have been problems such as the fact that the high frequency tuning circuit cannot simply be used in a perfect state because it cannot be used essentially over the receiving frequency band.

In order to deal with the above problem, the control signal information of the variable reactance element for the high frequency tuning circuit is stored in a non-volatile memory over the entire reception frequency band, and when selecting a 91 station, the address of the memory is specified and the For example, a method of reading control signal information and converting it into an analog control signal by D/A conversion is disclosed in Japanese Patent Publication No. 56-328.
20 “Tuner Tuning Method”.

Figure 2 shows its basic part, where IA to IIl are tuning circuits including variable reactance elements, and 2A to 2D are D
A converter (hereinafter referred to as D/A), 3 is a non-volatile memory, and 4 is a selection section for specifying a memory address.

In FIG. 2, the tuning information stored in the non-volatile memory 3 is selected by the tuning section 4, and controls the variable reactance elements of each tuning circuit via the D/A, thereby completely adjusting the tuning circuit. It will be done.

Problems to be Solved by the Invention Examples of things that can be used as a variable reactance element with the above-described configuration include the aforementioned varactor diode or a varimu inductor whose characteristic value can be changed by a DC superimposed current. However, all of these elements have so-called temperature characteristics whose characteristic values change with changes in temperature. For example, in the case of a varactor diode, the value is approximately 300 ppm/'c.

Therefore, with the above configuration, there is a problem in that the tuning frequency shifts due to temperature changes.

Further, the above configuration has another problem in that the number of bits required for D/A becomes large, which is disadvantageous for IC implementation.

For example, considering the FM broadcast band, in Japan, 76M
Although the reception frequency band is from Hz to 90 MHz, it is generally desirable to be able to adjust the reception frequency in increments of at least 100 KHz. Therefore, in the 76MHz to 90MHz band, 14
0 channel j is required, but considering the non-linearity of the voltage vs. capacitance characteristic of the varactor diode, the D/A
is required to be at least 10 bits. With the current technology, it is difficult to realize the above-mentioned /A, which does not include ripple components on the output side, at a reasonable cost, that is, as a low-cost IC integrated into a single chip.

The present invention aims to solve the above two problems and realize a preset tuner that has good temperature characteristics and can use a D/A with a smaller number of bits.

Means to Solve the Problem In order to control the tuning frequency of the superheterodyne receiver high-frequency tuning circuit, the variable reactance elements included therein are stored in nonvolatile memory in advance as tracking error correction signals according to each receiving frequency. It is controlled by a signal that is synthesized from the current signal and the control signal for the variable reactance element for the local oscillation circuit generated by frequency synthesis technology.

Effect of the present invention With the above configuration, the temperature characteristics of the variable reactance element included in the high frequency tuning circuit can be changed from the above tuning circuit.
Assuming that the same type of variable reactance element is used in the local oscillation circuit, compensation is performed using frequency synthesis technology applied to the local oscillation circuit, and furthermore, the control signal of the variable reactance element for the local oscillation circuit is used for coarse adjustment of the tuning circuit. Since the scale is regarded as a signal for use, the frequency adjustment range of the tuning circuit controlled by the read signal from the non-volatile memory can be significantly reduced, and the number of bits required for the D/A can be significantly reduced. To enable one-chip IC for cost reduction.

Embodiment Hereinafter, one embodiment of the preset tuner of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the preset tuner of the present invention. In FIG. 1, 1) is a high frequency signal input terminal, 12 is an intermediate frequency signal output terminal, 13 is a tuning signal input terminal, and 14, 15, and 16 are high frequency amplification circuits arranged before and after the circuits, and varactors are installed inside them. - a tuned circuit including a diode, 17 a mixer circuit, 18.
Reference numeral 19 collectively constitutes a local oscillation circuit, 19 is a tuning circuit containing a varactor diode inside to determine the oscillation frequency, and 20 is a local oscillation circuit that receives the signal from the local oscillation circuit. Generally, crystal oscillators, programmable frequency dividers,
A frequency synthesis circuit mainly consisting of a phase control loop consisting of a phase comparator etc. 21.22 is a D/A converter that converts the control signal obtained from the frequency synthesis circuit and the tracking error correction digital signal obtained from the non-volatile memory. an adding circuit for adding signals converted into analog signals by
23- and 24 are the above D/A.

25 is the above-mentioned nonvolatile memory.

In FIG. 3, the high frequency signal applied to the high frequency signal input terminal 1) is frequency selected by the tuning circuit 14 controlled by the output signal from the adder circuit 21, and then amplified. Frequency selection is performed by a tuning circuit 16 controlled by the output signal and applied to a mixer 17.A local oscillation signal obtained from a local oscillation circuit constituted by 18 and 19 is further applied to the mixer 17, and an intermediate frequency An intermediate frequency signal is obtained from the signal output terminal.

The oscillation frequency setting of the above local oscillation circuit is similar to that of a conventional electronic tuning tuner, and the frequency division ratio of the programmable frequency divider included in the frequency synthesis circuit 20 is determined by the digital signal applied to the tuning signal input terminal 13. This is done by setting .

The signal for controlling the actance element for the local oscillation circuit obtained from the frequency synthesis circuit 20 is applied to the high frequency tuning circuit 14, 16 via the adder circuit 21, 22, and this signal is applied to the varactor diode included in the tuning circuit. Used for rough adjustment. The digital signal for tracking error correction obtained from the non-volatile memory is read out by selecting an address that matches the receiving frequency by a signal applied to the channel selection signal input terminal 13, and is read out from the D/A (23, 2
4) The varactor included in the tuning circuit 14.16 via
Adjust the capacitance of the diode exactly to the required value.

The means for storing the necessary tracking error correction digital signals in the nonvolatile memory 25 can be easily realized using ordinary tracking adjustment techniques, and therefore detailed description thereof will be omitted.

In the above embodiments, consider the case where the temperature changes.

As mentioned above, when the temperature changes, the varactor diode has a temperature characteristic of about 300 ppm/'C, so if a constant control voltage is applied to the varactor diode, its tuning frequency and oscillation will change. Frequency changes. However, here, since the frequency synthesis circuit and the local oscillation circuit form a closed loop, as long as the loop is in a linear operating region, no change in the local oscillation frequency can occur due to temperature changes. This ultimately means that a correction voltage is applied to the varactor diode that eliminates the effects of temperature changes. In the embodiment shown in FIG. 1, this correction voltage is directly applied to the high frequency tuning circuit via the adder circuit, so that the varactor diode included therein is also subjected to temperature compensation.

Next, consider the number of bits required for D/A.

As mentioned above, the varactor diode control voltage included in the local oscillator circuit can be used for coarse adjustment of the high frequency tuning circuit.

Therefore, the range in which the tuning frequency of the tuning circuit can be adjusted using the signal obtained from the non-volatile memory is small; for example, considering the FM broadcast wave band in Japan, at most 2M11z is sufficient.

Therefore, if adjustment is to be performed in units of 100 KHz as described above, 6 to 8 bits is sufficient even if the nonlinearity of the voltage vs. capacitance characteristic of the varactor diode is taken into consideration. This facilitates the realization of a one-chip IC with D/A.

In the above explanation, a case has been shown in which a varactor diode is used as the variable reactance element, but it goes without saying that a varimu inductor can also be used in exactly the same way.

Also, when considering cost, it is natural that it is better to have a low capacity nonvolatile memory, but to achieve this, for example, rather than providing independent memory for tracking error correction signals for all reception channels, it is necessary to Needless to say, it is also possible to divide the data into several blocks and provide a tracking error correction signal memory for each block.

Effects of the Invention As described above, the present invention controls a high frequency tuning circuit using a signal for controlling variable reactance for a local oscillation circuit generated by frequency synthesis technology and a tracking error correction signal stored in a nonvolatile memory. It can eliminate the problem of tuning frequency shift due to the temperature characteristics of variable reactance elements,
Furthermore, the number of bits when D/A'ing the tracking error correction signal can be reduced, and it is also possible to use a chip IC, which has extremely great practical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a preset tuner according to the present invention, and FIG. 2 is a block diagram showing an example of the configuration of a preset tuner using a conventional nonvolatile memory. IA~ID... Tuned circuit, 2A~2゜...
...D/A, 3...Nonvolatile memory, 4...
...Tuning section, 1) ...High frequency signal input terminal,
12...Intermediate frequency signal output terminal, 13...
... Tuning signal input terminal, 14.16 ... Tuning circuit, 15 ... High frequency amplification circuit, 17 ...
・Mixer, 18...Local oscillation circuit, 19...
...Tuning circuit for local oscillation circuit, 20... Frequency synthesis circuit, 21.22... Addition circuit, 23
．． 24...DA converter (D/A), 25...
...Non-volatile memory.

Claims (2)

[Claims] (1) In a receiver in which the local oscillation signal of a superheterodyne receiver is generated by frequency synthesis technology using a variable reactance element whose characteristic value can be changed by electronic means, the tuning frequency of the high frequency circuit is generated by electronic means. Adjustment is performed using a variable reactance element whose characteristic value can be changed, and the adjustment control signal is combined with a signal previously stored in a nonvolatile memory as a tracking error correction signal according to each reception frequency, and a frequency A preset tuner is characterized in that it synthesizes from a control signal of a variable reactance element for a local oscillation circuit generated by a synthesis technique. (2) Subdividing the receiving frequency band, storing a tracking error correction signal in a non-volatile memory corresponding to one representative receiving frequency in each subdivided frequency band, and When receiving a signal of a receiving frequency different from the representative receiving frequency in the receiver, the tracking error correction signal stored corresponding to the representative receiving frequency is used as the tracking error correction signal. A preset tuner according to claim (1).