JPS628602Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuner device used in television receivers and the like.

In tuner devices for relatively wide bands, the power gain of the radio frequency amplifying transistor is lower when receiving high bands than when receiving low bands, and the local oscillation signal supplied to the frequency conversion circuit is large, making it difficult to obtain the gain. Deterioration is likely to occur. For this reason, in the conventional example shown in FIG. 1, the oscillation power of the local oscillation circuit 4 is increased as much as possible. However, when the oscillation power is increased, the fluctuations in the oscillation frequency with respect to fluctuations in the power supply voltage become large, which causes problems such as not only the characteristics of the oscillation circuit being inferior but also the oscillation state becoming unstable as a whole. Furthermore, it cannot be ignored that leakage of local oscillation signals (unnecessary radiation) increases. In FIG. 1, 6 is an input terminal of the tuner device, 1 is an input tuning circuit 2 is a radio frequency amplification circuit, TR ₁ is an amplification transistor, 3 is an interstage amplifier, 5 is a frequency conversion circuit,
TR ₂ is a frequency conversion transistor, 4 is a local oscillator circuit C ₁ is a first coupling capacitor that couples the radio frequency reception signal to the base of the frequency conversion transistor TR ₂ , and C ₂ is a frequency converter for the output of the local oscillation circuit 4. a second coupling capacitor coupled to the base of the transistor _TR2 .

In general, the input capacitance C ₀ of the frequency conversion transistor TR ₂ is a bipolar transistor and is as large as about 30 PF, while the first coupling capacitor C ₁ is 3 to 6 PF,
The second coupling capacitor _C2 is about 1-2PF,
Therefore, the impedance on the radio frequency signal supply side including the capacitor C ₁ (in the illustrated example, the impedance of the interstage tuning circuit 3) is considerably larger than the input impedance of the transistor TR ₂ , and similarly the second coupling capacitor C ₂ The impedance on the oscillation signal supply side including the transistor _TR2 is also considerably larger than the input impedance of the transistor TR2. This is particularly noticeable in high bands. Of course, it is only necessary to select the interstage tuning circuit 3 and the local oscillation circuit 4 so as to sufficiently match the impedance with the frequency conversion circuit 5 side, but these circuits 3 and 4 are mainly determined from the aspect of tuning frequency setting. , it is unavoidable that the impedance matching is insufficient.

The present invention is based on the recognition that signal loss occurs (especially at high bands) due to insufficient impedance matching between the input of the frequency conversion circuit 5 in the tuner device and the circuit that supplies the signal. By reducing this loss, it is intended to prevent a decrease in gain at high bands.

For this purpose, the present invention inserts an inductance coil L for impedance matching between the base electrode of the frequency conversion transistor TR ₂ and the first and second coupling capacitors C ₁ and C ₂ as shown in FIG. Moreover, the value of this inductance coil is selected so as to sufficiently achieve the above-mentioned impedance matching at high bands. For example, the aforementioned C ₀ , C ₁ , C ₂
The value of inductance coil L is 37nH for the value of
It shall be selected accordingly. Note that the same effect can be obtained when a FET transistor is used instead of a bipolar transistor as the frequency conversion transistor _TR2 . Further, the present invention can be applied to both mechanical switching tuners and electronic tuning tuners (tuners using variable capacitance diodes as tuning elements).

As explained above, according to the present invention, the signal loss during high band reception is reduced, so the gain deviation from the low band can be narrowed by that amount, and the conventional method that degrades local oscillation characteristics can be reduced. This is far more useful than measures to prevent gain deviation.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional tuner device, and FIG. 2 is a block circuit diagram of a tuner device according to the present invention. 1... Input tuning circuit, 2... Radio frequency amplification circuit, 3... Inter-stage tuning circuit, 4... Local oscillation circuit,
5... Frequency conversion circuit, C ₁ ... First coupling capacitor, C ₂ ... Second coupling capacitor, TR ₂ ...
Transistor for frequency conversion, L...Inductance coil for impedance matching.

Claims (1)

[Scope of utility model registration request] A first and second coupling capacitor having a capacitance sufficiently smaller than the input capacitance of the transistor is arranged in parallel on the input electrode side of the frequency conversion transistor, and a VHF band radio frequency reception signal is transmitted through the first coupling capacitor. In the tuner device, a local oscillation signal is applied to the input electrode and also a local oscillation signal is applied to the input electrode via a second coupling capacitor,
A tuner device characterized in that an inductance coil is inserted between an input electrode of the transistor and the first and second coupling capacitors for performing impedance matching with the input capacitance during high band reception of the VHF band.