JP3514962B2 - Electronic tuner circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuner circuit device for receiving high frequency waves such as VHF.

[0002]

2. Description of the Related Art In an electronic tuner circuit device having a wide reception band, a single block having a common amplifier is used in both the high frequency band and the low frequency band of the VHF band. However, there is a disadvantage that various performances are different between when a low frequency band signal is received and when a high frequency band signal is received. The deviation of the power gain as shown in FIG. 3 is one of them. However, in the electronic tuner circuit device as described above, there is a tendency that a sufficient gain cannot be obtained for a low frequency signal included in a high frequency band due to the characteristics of the circuit. Therefore, conventionally, a gain correction is performed by inserting a peaking circuit for increasing the gain at a low frequency where the gain cannot be obtained in the high frequency band.

As is well known, the peaking circuit has a function of increasing a gain by adding a tuning circuit of a frequency that needs correction in addition to the normal tuning circuit, and is included in the high frequency band of the VHF band. When correcting the gain at a low frequency, a peaking frequency is set between the low frequency band and the high frequency band, and the power gain is increased at the peaking frequency. FIG. 2 is a diagram showing a circuit configuration of a tuner device in which a peaking circuit is provided between the input tuning circuit T1 and the RF amplifier circuit Q1. here,
The received signal received by the input tuning circuit T1 is amplified by the amplifier circuit Q1 composed of an FET (field effect transistor) connected via the coupling capacitor C2, and input between the input tuning circuit T1 and the amplifier circuit Q2. Capacity Ci
The peaking circuit T2 is composed of ss and the coil L1. In addition, C1 is a capacitor for removing direct current, and is 1 nF or 10 nF.

As described above, in the tuner circuit, the received signal received by the input tuning circuit T1 is amplified by the amplifier circuit Q1 and output. At this time, the input capacitance Cis
The frequency to be corrected set by s and the coil L1, that is, the gain of the low frequency included in the high frequency band that tends to decrease is corrected as shown in FIG.

[0005]

By the way, in the tuner device, since the input tuning circuit T1 is connected to the input side of the peaking circuit T2, as high a frequency as possible between the tuning circuit T1 and the peaking circuit T2. It is necessary to avoid such coupling, and the capacitance of the coupling capacitor C2 needs to be as small as about 5 pF or less. However, when the coupling capacitor C2 is set to a small capacity as described above, the peaking circuit T2 and the like are sufficient for the reception signal of the frequency to be corrected, that is, the reception signal in the high frequency band, which is sufficient. However, in the low frequency range, the gain is less than the required amount due to the small capacity of the coupling capacitor C2, which is conversely low (see FIG. 4).

That is, in the circuit shown in FIG. 2, even if the coupling capacitor C2 in the drawing is set to a small capacity, if the peaking circuit T2 utilizing the input capacitance Ciss of the FET is formed, the high frequency range including the frequency to be corrected is formed. Although a sufficient gain can be obtained with respect to all the signals, the signal in the low band has a problem that the amount of coupling of the received signal input via the coupling capacitor C2 is reduced. This depends on the characteristics of the condenser. That is, the lower the frequency is, the higher the impedance of the capacitor is, and the impedance Z is represented by Z = 1 / 2πfC.

Therefore, in the conventional electronic tuner circuit,
It is necessary to set the capacity of the coupling while paying attention to the function of avoiding the high frequency coupling between the peaking circuit T2 and the input tuning circuit T1 and the function of ensuring a sufficient coupling amount for the received signal in both the high and low bands. And its settings are
There was no choice but to find a compromise while sacrificing both functions, and as a result, sufficient performance was not obtained for both functions, and the setting operation was complicated and difficult.

The present invention has been made by paying attention to the above-mentioned problems of the prior art. It is possible to obtain a good gain for a received signal over a wide band, improve the gain deviation, and combine with a tuning circuit. An object of the present invention is to provide an electronic tuner circuit that can avoid adverse effects due to high-frequency coupling with a circuit in the subsequent stage coupled via a capacitor.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a tuning circuit for tuning to a signal of a desired frequency within the VHF band and a VHF band within the VHF band received by the tuning circuit and coupled to the tuning circuit via coupling capacitance. A signal amplifying circuit for amplifying a received signal and a high frequency band in the VHF band inserted between the tuning circuit and the signal amplifying circuit and output from the tuning circuit.
For low frequencies where gain cannot be obtained within the frequency range
On the other hand, there is provided a gain correction circuit for increasing the gain, and a capacitance change circuit for changing the coupling capacitance connecting the tuning circuit and the gain correction circuit according to the frequency of the received signal output from the tuning circuit. Indicates that the received signal is VHF
When the gain correction circuit set within the band is included in the high frequency band that acts to increase the gain, the coupling capacitance is a small capacitance that does not cause high frequency coupling between the tuning circuit and the gain correction circuit. set, the when the reception signal is included in the low frequency band set in the VHF band, particularly sets the coupling capacitance such that binding occurs between said tuning circuit and the gain correction circuit in capacity Yo
In most of the VHF band, stable profit
This is to make it possible to obtain benefits .

In the above configuration, when the received signal is a signal in the low frequency band set in the VHF band, the coupling capacitance is set to a large value and the impedance in the coupling capacitance is reduced, so that the received signal is reduced. Does not decrease, and good gain can be obtained. Further, when the received signal is a signal in the high frequency band set in the VHF band, the coupling capacitance has a small value, so that the input tuning circuit and the gain correction circuit in the subsequent stage are coupled by high frequency. Does not occur. Moreover, even if the coupling capacitance is small, the frequency of the received signal is high, so the impedance in the coupling capacitance does not increase significantly, and the coupling amount of the received signal output from the input tuning circuit is sufficiently maintained. It Moreover, in the frequency band to be corrected in which the gain tends to decrease in the high frequency band, the gain correction circuit sufficiently increases the gain, so that good frequency characteristics can be obtained.

Further, the capacitance changing circuit has a first capacitive reactance element connected in series with the switching element and a capacitance different from the first capacitive reactance element, and the first capacitive reactance element and the switching element. And a second capacitive reactance element that is connected in parallel to a series circuit of the switching element and a switching control circuit that switches between conduction and non-conduction of the switching element according to the frequency band of the received signal. Conceivable. Also,
It is conceivable that the gain correction circuit is configured by connecting an inductive reactance element and a capacitive reactance element, the signal amplification circuit is composed of an FET, and the switching element is composed of a switching diode.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. In the figure, T21 is VH
This is an input tuning circuit for selectively receiving a signal of a desired channel from a plurality of channels in the F band, and a DC cut capacitor C21 for removing a DC component and a coupling are provided at a stage subsequent to the input tuning circuit T1. A signal amplification circuit Q21 is coupled via the capacitance change circuit C20.
The signal amplification circuit Q21 is composed of an FET. Further, the FET that constitutes the signal amplification circuit Q21.
A coil (inductive reactance element) L2 is provided at the gate of
1, and a DC cut capacitor C24 for removing a DC component is connected in series to the coil L21. The coil L21 constitutes a peaking circuit T22 as a gain correction circuit together with the input capacitance Ciss of the signal amplification circuit Q21.

The peaking circuit T22 acts to increase the power gain of a preset frequency band to be corrected, and the frequency band to be corrected here is a low frequency band within the VHF band. The frequency to be corrected (peaking frequency) is set by selecting the input capacitance Ciss and the coil L21.
However, since the input capacitance Ciss is determined by the FET to be used, the peaking frequency is actually set by selecting the value of L21.

On the other hand, the coupling capacitance changing circuit C20 provided between the peaking circuit T22 and the input tuning circuit T21 is constructed as follows. That is, the capacitance changing circuit C20 includes a large-capacity capacitor C22 connected to the output side of the input tuning circuit T21 via a DC-cutting capacitor C21 and a switching diode (switching element) connected in series to the large-capacity capacitor C22. ) D21, a small-capacitance capacitor C23 connected in parallel to a series circuit composed of the large-capacity capacitor C22 and a switching diode, and a switching control circuit for controlling conduction (ON) and non-conduction (OFF) of the switching diode D21. It consists of D20. The small-capacity capacitor C23 is, for example, 5 pF.
It is conceivable that the capacitance is set to about 10 pF or about 103 pF as the large-capacity capacitor. This switching control circuit D
Reference numeral 20 includes bias resistors R21 and R22 for supplying a switching current to the switching diode D21, and a power source (not shown) connected to one end of the resistor R22.
This power supply generates a voltage when the low frequency band in the VHF band is selected as described above.

In the electronic tuner circuit configured as described above, when the input tuning circuit T21 receives a signal in the high frequency band of the signals in the VHF band, the power source in the switching control circuit D20 outputs the voltage. It is in the OFF state where it is not generated. Therefore, in the capacitance changing circuit C20, the switching current is not supplied to the switching diode D21, the switching diode D21 is turned off, and the received signal output from the DC tuning capacitor C21 from the input tuning circuit T21 passes through the small capacitance capacitor C23. The signal is amplified by the signal amplifying circuit Q21 at the subsequent stage via the output, and then output.

When the frequency of the received signal is a signal in a relatively low frequency band included in the high frequency band, the gain in the signal amplification circuit Q21 tends to decrease, but for this frequency band Since the peaking circuit T22 acts to increase the gain, the signal output from the signal amplification circuit is amplified to a sufficient level. In addition, as described above, the switching diode D
When 21 is OFF, capacitors C23 and C21 are placed between the input tuning circuit T21 and the peaking circuit T22.
Since there is a relatively small coupling capacitance formed by combining and, it is possible to avoid occurrence of high frequency coupling between both circuits.

If the signal received by the input tuning circuit is within the low frequency band, a power source (not shown) generates a predetermined voltage to turn it on and supply a switching current. Switching diode D21 is O
The N state is established, and the large capacity capacitor C22 is connected.
As a result, the input tuning circuit T21 and the peaking circuit T22
There is a large coupling capacitance formed by combining the capacitors C22, C23, and C21 between
The coupling capacitance is significantly increased as compared with the state where the switching diode D21 is turned off. As a result, the impedance in the coupling capacitance decreases, a sufficient amount of coupling can be obtained for the signal output from the input tuning circuit T21, and a signal of a necessary and sufficient level can be obtained by the signal amplification circuit Q21. Therefore, according to the electronic tuner circuit of this embodiment, a good gain can be obtained even in the low frequency band of the VHF band.
As shown in, in almost the entire VHF band,
A stable gain can be obtained.

In the above embodiment, the DC cut capacitor C21 is provided between the input tuning circuit T21 and the capacitance changing circuit C20, but it may be removed. Further, the capacitance changing circuit is not limited to the one shown in the above-described embodiment, and other types can be used. For example, in the circuit shown in FIG. 1, a switching element may be provided in front of each of the capacitors C22 and C23 so that both capacitors C21 and C22 are appropriately turned on alternately, and the present invention is not limited to the above invention. Not something.

[0019]

As described above, according to the present invention, the coupling capacitance is set to a small capacitance when the received signal is included in the high frequency band set in advance in the VHF band, and is set to the low frequency band when it is included in the low frequency band. Since the coupling capacitance is set to a large capacitance, it is possible to avoid high frequency coupling between the input tuning circuit and the gain correction circuit, and obtain sufficient gain even in the low frequency band. It is possible to obtain a stable gain over the entire VHF band, and the frequency deviation is greatly improved. Further, unlike the conventional case, it is possible to set the coupling capacitance extremely easily without requiring complicated and difficult work such as finding a compromise while sacrificing the function in setting the coupling capacitance.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an electronic tuner circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional electronic tuner circuit.

FIG. 3 is a diagram showing frequency characteristics of power gain by an electronic tuner circuit having no conventional gain adjustment circuit.

FIG. 4 is a diagram showing frequency characteristics of power gain by an electronic tuner circuit having a conventional gain adjustment circuit.

5 is a diagram showing frequency characteristics of power gain according to the embodiment of the present invention shown in FIG.

[Explanation of symbols]

C20 capacity change circuit Ciss capacitive reactance element D20 switching control circuit D21 switching element L22 First capacitive reactance element L23 Second capacitive reactance element L21 Inductive reactance element Q21 coupling capacity Q21 signal amplification circuit T21 tuning circuit T22 gain correction circuit

Claims (5)

(57) [Claims] 1. A tuning circuit for tuning a signal of a desired frequency within a VHF band, and a signal amplifier circuit which is coupled to the tuning circuit via a coupling capacitor and amplifies a received signal within the VHF band received by the tuning circuit. And a gain correction circuit that is inserted between the tuning circuit and the signal amplifying circuit and increases the gain with respect to a low frequency in which the gain is not obtained in the high frequency band of the VHF band output from the tuning circuit. And a capacitance changing circuit that changes the coupling capacitance that connects the tuning circuit and the gain correction circuit according to the frequency of the received signal output from the tuning circuit. When the gain correction circuit set in the above is included in a high frequency band that acts to increase the gain, a coupling capacitance is provided between the tuning circuit and the gain correction circuit. Set a small volume does not bind due to high frequency occur, the received signal is VHF
When included in the low frequency band set within the band,
By setting the coupling capacitance to a large capacitance so that coupling may occur between the tuning circuit and the gain correction circuit, the VHF
An electronic tuner circuit characterized by obtaining stable gain over almost the entire band. 2. The capacitance changing circuit includes a first capacitive reactance element connected in series with a switching element, and a capacitance different from the first capacitive reactance element. A second capacitive reactance element connected in parallel to a series circuit with the switching element; and a switching control circuit for switching between conduction and non-conduction of the switching element according to a frequency band of a received signal. The electronic tuner circuit according to claim 1, wherein: 3. The electronic tuner circuit according to claim 1, wherein the gain correction circuit comprises an inductive reactance element and a capacitive reactance element connected to each other. 4. The electronic tuner circuit according to claim 1, wherein the signal amplification circuit is composed of a FET. 5. The switching element comprises a switching diode.
2. The electronic tuner circuit device according to 2.