JPH03179819A - Uhf/vhf compatible electronic tuner - Google Patents

Abstract

PURPOSE:To reduce the gain deviation of UHF channels and to improve the reception state by providing a switching diode for inter-channel gain deviation correction turned on at the reception of a UHF between a base of a mixer transistor(TR) and a connecting point of tuning coils. CONSTITUTION:A switching diode VSX is provided, which corrects an inter- channel gain deviation with respect to a UHF reception signal to be turned on at the reception of a UHF between the base of a mixer TR 6 and the connecting point of tuning coils L1-L4. Thus, a varactor diode VT3 for coupling is short-circuited at the reception of a UHF wave, then a parallel resonance circuit comprising the tuning coils L3, L4 and the tuning varactor diode VS2 is formed between the base of the mixer TR 6 and ground. Thus, the gain difference between the output stage of a UHF mixer circuit and the input stage of a VHF mixer circuit is decreased more as the channel is higher and the gain difference of channels is reduced at the output side of the VHF mixer circuit at the time of receiving the UHF wave.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to UHF/
V HF integrated electronic tuning tuner, especially U I
-Related to improving inter-channel gain deviation during IF reception.

(Prior Art) As shown in Fig. 1, a conventional electronic tuning tuner of this type has a UHF side circuit between the input terminal IN+ and the output terminal OUT, and a circuit between the input terminal IN2 and the output terminal OLJT. By providing a V HF side circuit on each side, the U This will be explained in detail separately with reference to the figure for HF reception.

U II given to the input terminal INI via the antenna when receiving U I-I P
Among the F received signals, Ul-[F
After the received signal is selectively amplified by the UHF selection amplifier circuit 2, which is composed of an input tuning circuit, a high frequency amplification circuit, and a crotch tuning circuit, the UHF selection amplification circuit 2 that matches the desired receiving channel is used.
;'U HF' from the local oscillation circuit 4 Together with the local oscillation signal [J HF mixer circuit 6, the frequency is mixed and converted into a predetermined intermediate frequency signal.

This intermediate frequency signal is filtered by the UHFIF filter 8, and then used for coupling and a switching diode VS3 that operates to turn on when receiving LJHF, and for gain deviation correction of the U I-I F' and V HF' received signals. V via capacitor C4 for
1-IF Provided to the mixer circuit 10.

When receiving VHF, this VHF mixer circuit lO
V along with the HF local oscillation signal from the local oscillation circuit 12
It acts as a mixer circuit that converts the frequency of the HF received signal, but when receiving the U I-IF, it acts as an amplification circuit for the intermediate frequency signal of U I
Amplify the F intermediate frequency signal. This VIIF mixer circuit width-width UHF' intermediate frequency signal is further filtered by an F filter 14 and then sent to an output terminal OUT.
is output from.

At the time of V II F reception, on the other hand, at the time of VHF reception, among the V HF reception signals given to the input terminal IN2 via the antenna, the V HF reception signal of the desired reception is V After being selectively amplified by the HF selection amplification circuit 16, the VHF tuning circuit (interstage tuning circuit) 18
The synchronization is selected.

This VHF tuning circuit 18 tunes the VHF to be received.
If the received signal is in the low channel, switching diodes VSl and VS2 are turned off to turn off the tuning coil L.
The configuration of a tuning circuit including l-L4, tuning capacitors CI and C2, and tuning varactor diodes VTI and VT2 selects and outputs a low channel VHF reception signal, and if the desired VHF reception signal is a high channel. By turning on the switching diodes VSI and VS2, the tuning coil L2. Short-circuit L4 and tune coil L
1, L3, tuning capacitors CI, C2, and tuning varactor diodes VTI, VT2, the tuning circuit is configured to selectively output the high channel VI-(F reception signal).

In this way, the high channel or low channel VHF reception signal selected by the VHF tuning circuit 18 passes through the coupling varactor diode VT3 to
-IF' is output to the mixer circuit IO.

In this VHF mixer circuit 10, the frequency is mixed together with the local oscillation signal from the VHF' local oscillation circuit 12 and converted into a predetermined VHF intermediate frequency signal. Output terminal OUT after being filtered by F filter 14
is output from.

(Problem to be solved by the invention, 1) In the above conventional electronic tuning tuner, V I-I F
As is well known, the coupling varactor diode VT3 provided between the output stage of the tuning circuit I8 and the input stage of the vHF mixer circuit 1O is provided for the purpose of enabling wide (1+f) range reception of VHF. It is something that was given.

Such a varactor diode VT3 is U I-IF
At the time of reception, the following problems arise.

This problem will be explained with reference to FIGS. 2 to 4. In this electronically tuned tuner, the power gain of the U HP between the INI and the IP filter 8 is, for example, 1 as shown in FIG.
The gain increases as you move from low channels to high channels, such as 14 dB for 3 channels and 17.5 dB for 62 channels, resulting in the maximum gain deviation ΔGI between channels. becomes 3.5dB.

On the other hand, the gain of the UHF intermediate frequency signal between the IF' filter 8 and the VHF' mixer circuit 10 increases as the channel becomes higher, as indicated by the dotted line ■ in FIG. This is connected to each coupling and tuning varactor diode VT2. which is inserted in series between the input stage of the vHF mixer circuit IO and the ground. This is because the tuning voltage applied to the capacitance of VT3 varies depending on the channel. In this case, the maximum gain deviation ΔG2 between channels is 2.6 dB.

Therefore, when the power gain of the U HF output from the V HF mixer circuit 10 includes the gain of the V HF mixer circuit 10 itself, the power gain of the U HF output from the V HF mixer circuit 10 is equal to
■ The maximum gain deviation ΔG between channels is as follows.
3, it reaches as much as 6.4 dB.

In this way, in conventional electronically tuned tuners, the flI gain deviation between channels during UHF reception differs greatly, but even if the gain deviation is compensated for by the AGC circuit, the &li compensation ability is However, there was a drawback in that the UHF reception condition worsened.

Therefore, in the present invention, U[(U H at the time of receiving F
The purpose is to improve the UHF reception condition by reducing the gain deviation between F channels.

(Means for Solving the Problems) In order to achieve such an object, in the electronically tuned tuner of the present invention, the output stage of the VII F tuning circuit in the VHF open road and the input stage of the vHF mixer circuit are connected. The VHF' mixer circuit receives an input from the UHF mixer → no circuit in the UHP opening path via the coupling capacitor when receiving 011F. It is used for amplifying the intermediate frequency signal of the U II F, and the V I-I
The F tuning circuit includes at least two identical coils for low band and high band and connected in series with each other,
The VHF mixer circuit includes a parallel circuit with a tuning varactor diode, and both varactor diodes are connected in series between the base of a mixer transistor constituting an input stage of the VHF mixer circuit and the ground,
The present invention is characterized in that a switching diode is provided between the base of the mixer transistor and the connecting portion of both the surrounding network coils, which is turned on during UHF reception and operates to correct gain deviation between UHF channels.

(Function) By turning on when receiving UHF between the base of the mixer transistor and the connection part of both tuning coils, the UHF
Since a switching diode is provided to correct the gain deviation between channels for the received signal, U I-I
During reception, the coupling varactor diode is short-circuited, so that a parallel resonant circuit consisting of the tuning coil and the tuning varactor diode is formed between the base of the mixer transistor and the ground. Therefore, by setting the resonant frequency of this parallel resonant circuit to be higher than the intermediate frequency of U HF, U i
The gain deviation between the output stage of the f F mixer circuit and the input stage of the V HF mixer circuit can be made smaller as the channel becomes larger.

From this, as the channel becomes larger, U H
F The output gain of the mixer circuit increases and its U
As the gains of the HF mixer and the V 11 F mixer circuit become smaller as the channel becomes larger, their gain deviations cancel each other out, and as a result,
The gain deviation at the output side of the V I (F" mixer circuit during U HF reception is reduced between channels).

Muo, when receiving VHF, L3. Since vSX is reverse biased and turned off by the voltage at the L4 connection, no adverse effects occur.

(Example of length) Hereinafter, the embodiment of the present invention will be explained in detail by referring to the drawings.

In the electronic tuning tuner of the present invention, in the conventional electronic tuning tuner shown in FIG. A coupling varactor diode VT3 is connected between the
The present invention is characterized by the provision of a switching diode vSX that corrects the gain deviation between the UHF channels by short-circuiting the UHF channels, and the other configurations are the same as those of the conventional example.

The effects of providing the fl gain deviation correction capacitor vSX described above are as follows.

That is, the connection between the tuning coils L 3 and L 4 and V
The base of the mixer transistor of the HF mixer circuit IO is connected to the switching diode vSx for correcting the gain deviation.
If this switching diode vSX is turned on at the time of U
When viewed from the output end of the FIF filter 8, the tuning coil L3. A parallel resonant circuit is formed by L4 and the tuning varactor diode VT2.

Then, the resonant frequency of this parallel resonant circuit is set so that it is higher than the UHP intermediate frequency even if the UHF channel is changed.

Thereby, the gain deviation between the UHF mixer circuit 6 and the VHF mixer circuit 10 can be made smaller as the channel becomes larger. From this, it can be seen that as the channel becomes larger, the output gain of the Ul-IF' mixer circuit 6 becomes larger and that the UHF
Coinciding with the fact that the gain between the 'mixer circuit 6 and the V HF' mixer circuit 10 decreases as the channel becomes thicker, their gain deviations cancel each other out, and as a result, v+
The gain deviation at the output side of the tp mixer circuit 10 will be reduced between channels.

In other words, in both the conventional example and the embodiment, the power gain at the output of the F filter circuit 8 changes for each channel as shown by ■ in FIG. 2, and the maximum gain deviation is ΔGl.
In the conventional example, the gain of the intermediate frequency signal between the IP filter circuit 8 and the VI-IF mixer circuit IO changes as shown in ■ in Fig. 3, and the maximum gain deviation is ΔG2. In the example, the change is as shown in ■, and the maximum II resultant change is ΔG2'. Therefore, v ■−
The inter-channel gain of the UHF signal at the output of the t F mixer circuit 10 is as shown in ``+■'' in FIG. 4 in the conventional example, whereas it becomes ``+■'' in the embodiment. Therefore, while the maximum fl gain deviation is ΔG3 in the conventional example, it is ΔG3' in the embodiment. This means that the UHF reception condition is improved in the embodiment than in the conventional example.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
Since a switching diode for inter-channel gain deviation correction that is turned on when receiving UHF is provided between the base of the mixer transistor constituting the VHF mixer circuit and the connection part of the tuning coil constituting the UHF tuning circuit, Of the coupling and tuning varactor diodes connected in series between the base of the mixer transistor and the ground, the coupling varactor diode is short-circuited by its switching diode when receiving UHF. A parallel resonant circuit including a tuning coil and a tuning varactor diode is formed between the base of the mixer transistor and the base of the mixer transistor. Therefore, by setting the resonant frequency of this parallel resonant circuit to be higher than the UHF intermediate frequency, U I-I
The gain deviation of 11 between the output stage of the F mixer circuit and the input stage of the vHF mixer circuit can be made smaller as the channel becomes larger. From this,
As the channel becomes larger, the power output from the UHF mixer circuit increases, and the UHF
As the gain between the F mixer circuit and the v tt F mixer circuit decreases as the channel becomes larger, their gain deviations are canceled out, and as a result, UH
The gain deviation on the output side of the V HF mixer circuit during F reception is reduced between channels.
The gain deviation between UHF channels during UHF reception is reduced, making it possible to improve the UHF reception condition.

[Brief explanation of drawings]

FIG. 1 shows the circuit configuration of an electronic tuning tuner according to an embodiment of the present invention when a switching diode for gain deviation correction is provided, and the circuit configuration of an electronic tuning tuner according to a conventional example when the switching diode is not provided. The diagrams showing the configuration, FIGS. 2 to 4, are diagrams for explaining the gain deviation at the time of UHF reception in the conventional example and the present invention, respectively. IN+...U HF reception signal input terminal, IN2...
V11F reception signal reception input terminal, OUT...U I-I
F and V HF intermediate frequency signal output terminals, 2...
U HF selection amplifier circuit, 4 U tl F local oscillation circuit, 6... U tl F mixer circuit, 8... UHFI
F filter, IO...Vor;" mixer circuit, 12.
...V tl F local oscillation circuit, 18...V HF tuning circuit, VS2...switching diode, C4...
・Compaction capacitor, L3L 4...Tuning coil, VT2...Tuning varactor diode, VT
3...Varactor diode for coupling, ■SX
-Swiss isolating diode for gain deviation correction.

Claims (1)

[Claims] (1) Output stage of VHF tuning circuit in VHF side circuit and VH
The VHF mixer circuit is connected to the input stage of the F mixer circuit via a coupling varactor diode, and when receiving UHF, the VHF mixer circuit receives input from the UHF mixer circuit in the UHF side circuit via a coupling capacitor. and the VHF tuning circuit includes a parallel circuit of at least two tuning coils, one for low band and one for high band, connected in series with each other and a tuning varactor diode. and a UHF/VHF integrated electronic tuning tuner in which both of the varactor diodes are connected in series between the base of a mixer transistor constituting the input stage of the VHF mixer circuit and the ground; A UHF/VHF integrated electronic tuning tuner, characterized in that a switching diode is provided between the connecting portions of both tuning coils and is turned on during UHF reception to correct gain deviation between UHF channels.