JPS5821248Y2 - All channel channel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an all-channel tuner having an up-converter (frequency conversion circuit).

In a VHF tuner, it is not possible to cover the entire frequency band from low channel to high channel by changing the capacitance of one variable capacitance element, so normally the inductance value that determines the tuning frequency is changed in addition to changing the capacitance of the variable capacitance element. There is.

Therefore, a switching diode for band switching, a switching signal forming circuit, etc. are required.

On the other hand, since a UHF tuner handles a high frequency, the frequency change rate itself is lower than that of a VHF tuner, and the entire band can be covered by changing the capacitance of a single variable capacitance element.

Therefore, as mentioned above, switching diodes for band switching and the like are not required, and the circuit configuration is simpler than that of a VHF tuner.

Therefore, recently, it has been considered to replace the VHF tuner with a UHF tuner.

In such an all-channel tuner, ■When receiving an HF signal, the frequency of this VHF signal is first converted into a UHF signal, and this converted signal is supplied to a UHF tuner in the same way as the UHF signal to obtain the desired VHF signal. What is necessary is just to configure it so that it can receive signals.

Therefore, the UHF tuner is configured to be able to receive signals in a band wider than the regular UHF band.

With this configuration, it is possible to receive VHF signals without using a VHF tuner, thereby avoiding the bottlenecks associated with electronic tuning.

Such a frequency conversion circuit is generally called an up-converter, and an outline of an all-channel tuner including an up-converter is shown in FIG.

In the figure, 1U is a UHF antenna, 1■ is a VHF antenna, and the UHF signal sU is sent to the UHF antenna via the signal switching circuit 2.
The signal is supplied to the F tuner 10.

As is well known, the tuner 10 has a high frequency amplification circuit 11, a local oscillation circuit 12, and a mixing circuit 13, and the output of the mixing circuit 13 is supplied to an intermediate frequency amplification circuit 15.
A MHz intermediate frequency signal is extracted and amplified.

After the VHFHF signal S is supplied to the up-converter 20 described above and converted into the desired UHF signal SIF,
The signal is supplied to the tuner 10 via the switching circuit 2.

The up converter 20 includes an attenuation circuit 21 and a local oscillation circuit 2.
2. It is composed of a mixing circuit 23 and a filter 24, and the VHFHF signal S to be received is all UHF with a constant frequency fIF.
It is converted into signal SIF.

This example is for an upper sideband upconverter, so the wave number for the VHFHF signal S is set to f■, and the local oscillation circuit 2
When the oscillation frequency of 2 is fOV, the sum frequency component (
Only the converted output (mixed output) SIF of fv+fov) is extracted by the subsequent filter 24.

FIG. 2 shows the frequency band relationship between the UHFHF signal S-side wave number conversion and the UHF signal SIF.

In Japan, the UHF signal sU and frequency band are 470-7
Since it is up to 70 MHz, the frequency fIF of the UHF signal SIF after frequency conversion is 890 MHz in this example.
z is selected.

Now, it is not necessary to provide the above-mentioned switching circuit 2 in principle, and the signal SIF from the up-converter 20 and the signal sU from the UHF antenna 1U may be supplied to the UHF tuner 10 in a mixed state.

However, as a practical matter, if the signal line from the upconverter 20 and the signal line from the UHF antenna 1U are simply connected, the signal SIF from the upconverter 20 will be
Since it is supplied not only to the HF tuner 10 but also to the UHF antenna 1U, a portion of the signal SIF is lost, and a component of the signal SIF is radiated from the antenna 1U, resulting in unnecessary radiation.

. Similarly, a part of the signal SU from the UHF antenna 1U flows to the up converter 20, resulting in a signal loss.

For this reason, it is necessary to provide the switching circuit 2 so that the signal line from the up-converter 20 and the signal line from the UHF antenna 1U are not directly connected in a straight line, as described above.

Incidentally, the signal switching circuit 2 for switching between the UHF signal sU and the frequency-converted UHF signal SIF may be configured with a mechanical switch, but generally a diode switch is often used.

Figure 3 shows a typical example of this, in which the UHF signal sU supplied to the terminal 2U is connected to a capacitor C that blocks the DC signal.
1 and output terminal 2 through switching diode D1.
Supplied to S.

Similarly, the frequency-converted UHF signal SIF obtained at terminal 2■ is connected to capacitor C2 and switching diode D.
2 to the terminal 2S.

In addition, the control type 11 selected by the changeover switch 25
VD is a high frequency signal blocking coil L1. The signal is supplied to the connection points 11 and 12 via L2, and the transmission path is closed only to the side to which the control voltage VD is applied, and the signal is transmitted to the terminal 2S side.

For example, when the changeover switch 25 is switched as shown in the figure, the diode D2 is off, so ideally the U
It is thought that the HF signal SIF does not leak to the output terminal 2S side, but signal leakage occurs due to the capacitance between the anode and cathode of the diode D2, and even if the diode D1 is on, the presence of an external resistance between the anode and cathode However, it has the disadvantage that the signal transmission characteristics deteriorate.

Additionally, this circuit includes a mechanical or electronic switch 25.
Requires.

The present invention takes these points into consideration and proposes an all-channel tuner that does not particularly cause signal leakage and does not cause deterioration of transmission characteristics.

FIG. 4 is a connection diagram showing an example of the mixing circuit 20 which is the main part of the present invention, and has two first resonance systems and a second resonance system 2B connected in series, and the connection point l. .

An output terminal 2S is derived from this. The UHF signal sU is supplied to the two input terminals 2U of the first resonance system, and the UHF signal SIF is supplied to the input terminal 2■ of the second resonance system 2B.

The first resonant system consists of a first series resonant circuit SX that resonates at a first frequency, in this example near the highest frequency of the UHF signal band (about 770 MHz), and a second series resonance circuit SX that resonates at a second frequency, in this example a UHF signal SIF. If the first parallel resonant circuit SA is a parallel circuit of a coil LA and a capacitor C as shown in the figure, the first series resonant circuit Sx is This parallel circuit is configured as a series circuit of the capacitor CA.

The first parallel resonant circuit SA has a low Q and therefore has relatively broad resonance characteristics (FIG. 5A).

The second resonant system 2B includes a second series resonant circuit SY that resonates with the UHF signal SIF (second frequency fIF), and a third frequency, which in this example is approximately an intermediate frequency in the frequency band of the UHF signal SU. and a second parallel resonant circuit sB that resonates at 600 to 630 MHz.

In this case, the second series resonant circuit SY is constituted by a series circuit of the second parallel resonant circuit SB and the coil LY.

Note that, as with the resonance characteristics of the two first resonance circuits, the Q of the second parallel resonance circuit sB is selected to be low (FIG. 5B).

In this configuration, UHF signals s are applied to terminals 2U and 2V, respectively.
When U and SIF are supplied at the same time, first and second parallel resonant circuits SA and SB exist, so first, the resonant impedance of the first parallel resonant circuit SA for the frequency-converted UHF signal SIF is Since it is infinite, UHF
The signal SIF does not leak to the terminal 2U side (see FIG. 5A, however, the vertical axis in the figure is the response).

Similarly, for the UHF signal sU, the resonant impedance of the second parallel resonant circuit sB becomes infinite, and the UHF signal sU becomes infinite.
The F signal sU is completely prevented from being transmitted to the terminal 2■ side (see FIG. 5B).

Then, for the UHF signal sU, the first series resonant circuit S
Since the resonant impedance of
transmitted to the side.

The same applies to the frequency-converted UHF signal SIF, so it can be transmitted to the terminal 2S without signal leakage or transmission loss.

Note that the first and second resonance systems 2A and 2B are provided with first and second series resonance circuits SX and SY in addition to the first and second parallel resonance circuits SA and SB. The reason is as described below.

Regarding the first resonant system of two people, when the Q of the first parallel resonant circuit SA is lowered, the resonance characteristics are as shown by curve 27a in FIG. 5A, with large attenuation near the highest frequency in the UHF band.

Therefore, if left as is, the output transmission level of the UHF signal SU in the vicinity of channel 60 will decrease.

Therefore, a first series resonant circuit SX is provided to compensate for the attenuation near the highest frequency.

The curve 27b is the resonance characteristic of the circuit SX.

Based on the same idea, the second resonant system 2B is also provided with a second series resonant circuit Sy.

That is, when the second irregular resonant circuit SB with a low Q is used, its resonance characteristics become as shown by the curve 28a in FIG. 5B,
Attenuation in the UHF signal SIF after frequency conversion becomes large.

In order to compensate for this, a second series resonant circuit SB having a resonant frequency near 890 MHz is provided, and the resonant characteristics can be improved as shown by curve 28b.

According to the configuration of the present invention described above, the UHF signals SU and SIF can be transmitted to the output terminal 2S side without loss or distortion.

Moreover, according to this circuit, the switching diode D1
．． Since neither D2 nor the selector switch 25 is required, there is an effect that the circuit configuration can be simplified.

[Brief explanation of the drawing]

Figure 1 is a system diagram of an all-channel tuner with an up-converter, and Figure 2 is a diagram showing frequency bands. Third
FIG. 4 is a connection diagram showing an example of a conventional circuit, FIG. 4 is a connection diagram showing an example of the main part of the present invention, and FIG. 5 is a diagram showing the resonance characteristics of the circuit. 20 is a mixed circuit, 2A, 2B are first and second resonance systems, SA, sB are first and second parallel resonance circuits, Sx,
Sy is a first and second series resonant circuit.

Claims (1)

[Scope of utility model registration request] An up-converter that converts a VHF signal in the VHF broadcast band to an intermediate frequency signal with a higher frequency than the UHF broadcast band, and a mixing circuit that mixes the intermediate frequency signal from the up-converter and the UHF signal in the UHF broadcast band from the UHF signal input terminal. , the output of the mixing circuit is supplied, and the UHF signal is capable of receiving both the intermediate frequency signal and the UHF signal of the UHF broadcasting band.
The mixing circuit, which has an F tuner and is connected between the output terminal of the up-converter and the UHF signal input terminal, includes a first resonance system and a second resonance system.
The resonant systems are connected in series, and an output is supplied to the UHF tuner from the connection point of the first and second resonant systems, and the first resonant system is connected to a second resonant system that is approximately equal to the intermediate frequency signal. a first parallel resonant circuit that resonates at the frequency of UH;
a first series resonant circuit that resonates at a first frequency near the highest frequency of the F broadcast band;
An all-channel tuner comprising: a second parallel resonant circuit that resonates at a third frequency approximately in the middle of an HF broadcast band; and a second series resonant circuit that resonates at the second frequency.