JPH05284050A - Tuner circuit - Google Patents

Abstract

PURPOSE:To provide the tuner circuit having high jamming excluding ability against jamming signals lower than a desired frequency band by forming a variable voltage trap circuit at a point coupled from an inter-step tuner circuit to the input side of a mixer circuit. CONSTITUTION:Since the joining capacity of variable capacity diodes 10 and 11 in an inter-step tuner circuit 2 is changed corresponding to a tuning voltage supplied from a terminal 12, the stepwise tuner circuit 2 is tuned to received signals. Concerning a local oscillation circuit 4, the resonance frequency is changed, the frequency of local oscillated signals is turned to a prescribed value, and those signals are inputted to a mixer circuit 3. Thus, the inputted received signals are amplified by a high frequency amplifier circuit 1, band- selected by the inter-step tuner circuit 2 and inputted to the mixer circuit 3. In the mixer circuit 3, the local oscillated signals outputted from the local oscillation circuit 4 and the received signals are mixed, and intermediate frequency signals 5 are generated. The tuning voltage supplied from the terminal 12 is supplied from the inter-step tuner circuit 2 to a coupling capacitor 9 at a gap to the mixer circuit 3, and the joining capacity is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner circuit for extracting a received signal from an interstage tuning circuit by mutual inductive coupling and inputting the received signal to a mixer circuit. The present invention relates to a tuner circuit having improved rejection characteristics of an interference signal generated in.

[0002]

2. Description of the Related Art In a conventional tuner circuit, a reception signal is taken out from an interstage tuning circuit by mutual inductive coupling and input to a mixer circuit via a coupling capacitor.

FIG. 2 shows a conventional tuner circuit.

The conventional tuner circuit includes a high frequency amplifier circuit 1, an interstage tuning circuit 2, a mixer circuit 3, a local oscillator circuit 4,
Intermediate frequency signal output 5, interstage primary resonance line 6, interstage secondary resonance line 7, mixer circuit coupling line 8, coupling capacitor 9, variable capacitance diodes 10 to 11, tuning voltage supply terminal 12, interstage primary tuning Capacitor 13 and interstage secondary tuning capacitor 14.

[0005]

In the above-mentioned prior art, as shown in FIG. 2, the interstage tuning circuit 2 constituted by the interstage primary resonance line 6 and the interstage secondary resonance line 7 is connected to the mixer circuit coupling line. The band of the received signal was taken out by 8 and input to the mixer circuit 3. In the extracted received signal, frequency components other than the desired frequency band are attenuated by the selection characteristics up to the interstage tuning circuit to remove various interferences. However, it is difficult for the selection characteristics of the interstage tuning circuit to be good over the entire receiving channel, and in particular, the amount of attenuation such as the lower local interference frequency generated near the center frequency is not sufficient. Therefore, when a signal having an excessive level is input to a band near the center frequency, the signal becomes an interfering signal, which is a problem.

An object of the present invention is to provide a circuit which has a simple circuit structure and which forms a trap for the out-of-band characteristic on the lower side of a desired frequency band and has a good lower channel interference rejection characteristic.

[0007]

To achieve the above object, in the present invention, the coupling capacitor between the interstage tuning circuit and the mixer circuit is a variable capacitance diode, and a reverse bias voltage is supplied to the variable capacitance diode. As a result, the junction capacitance continuously changes, so that a circuit is provided in which the resonance point generated by the junction capacitance and the inductance of the mixer circuit coupling line is used as a trap.

[0008]

The trap circuit is formed of a coupling capacitor (variable capacitance diode) connected in series with the mixer circuit coupling line of the interstage tuning circuit. By supplying a reverse bias voltage to this coupling capacitor (variable capacitance diode), the junction capacitance is continuously changed, a trap is formed in the lower band of the desired frequency band, and the trap is varied by the tuning voltage.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing a tuner circuit as an embodiment of the present invention. In this embodiment, a high frequency amplifier circuit 1, an interstage tuning circuit 2, a mixer circuit 3, a local oscillator circuit 4, an intermediate frequency circuit are provided. It includes a signal output 5, an interstage primary resonance line 6, an interstage secondary resonance line 7, a mixer circuit coupling line 8, a coupling capacitor 9, variable capacitance diodes 10 to 11, and a tuning voltage supply terminal 12.

The junction capacitance Cj of the variable capacitance diodes 10 to 11 of the interstage tuning circuit 2 changes according to the tuning voltage supplied from the terminal 12. As a result, the interstage tuning circuit 2 is tuned to the received signal. In the local oscillation circuit 4, the resonance frequency changes and the frequency of the local oscillation signal becomes a predetermined value and is input to the mixer circuit 3.

As a result, the input reception signal is amplified by the high frequency amplifier circuit 1, band-selected by the interstage tuning circuit 2 and input to the mixer circuit 3. In the mixer circuit 3, the local oscillation signal output from the local oscillation circuit 4 and the received signal are mixed, and the intermediate frequency signal 5 is output.

The tuning voltage supplied from the terminal 12 is also supplied to the coupling capacitor (variable capacitance diode) 9 between the interstage tuning circuit 2 and the mixer circuit 3 and the junction capacitance Cj.
Changes.

Further, the operation of this embodiment will be described in detail.

As a recent trend, the number of broadcasts using the UHF band of tuners is increasing, and in particular, it is necessary to remove the interference with the signal of the channel broadcast adjacent to the desired signal. For that purpose, it is indispensable to improve the band characteristic of the interstage tuning circuit over all the receiving channels.

The signal whose band is selected by the interstage tuning circuit 2 is taken out by the mixer circuit coupling line 8 and input to the mixer circuit 3 via the coupling capacitor 9. At this time, a resonance point due to the inductance of the mixer circuit coupling line 8 and the junction capacitance of the coupling capacitor (variable capacitance diode) 9 is formed as a trap in the signal, and an excessive level signal other than the desired frequency band is input. In case of out-of-band trap.

Consider now the interstage tuning circuit and the trap circuit of the present invention. When the capacitance of the interstage primary tuning capacitor 13 is C, the inductance of the interstage primary resonance line 6 is L, and the junction capacitance of the variable capacitance diode 10 is Cj, the resonance frequency fo is

[0018]

[Equation 1]

It is calculated by Regarding the trap circuit, the inductance of the mixer circuit coupling line 8 is L ′, and the junction capacitance of the variable capacitance diode 9 which is a coupling capacitor is C.
j'is the trap frequency ft,

[0020]

[Equation 2]

Is calculated by Considering ideally the case where the coils are tightly coupled, if L = L ′ and a variable capacitance diode having a junction capacitance having the same change ratio as the variable capacitance diode 10 of the tuning circuit is selected as the coupling capacitor 9, C
j = Cj '. From the above equation, the relationship between the resonance frequency fo and the trap frequency ft is as follows.

[0022]

[Equation 3]

Therefore, the relationship of ft≤fo is maintained. That is, the trap frequency ft can be formed below the reception frequency as shown in FIG. The junction capacitance Cj of the variable capacitance diode is large at the low tuning point and small at the high tuning point. The reception frequency is low when the tuning voltage is low, and the reception frequency is high when the tuning voltage is high. At this time, the trap frequency shown in the above equation is always ft ≦
Since it is fo, it moves with a certain fixed relationship in all the reception frequency bands shown in FIG.

The tuning bias voltage of the tuner is used as the reverse bias voltage of the coupling capacitor (variable capacitance diode) 9 forming the trap circuit. In this embodiment, the reception frequency is fo = 474 to 858 MHz and the tuning voltage is 2
When it changes by ˜20 V, the junction capacitance Cj of the variable capacitance diode 9 continuously changes by about 15 to 3 pF.

3 and 4 are characteristic diagrams showing the characteristics of one embodiment of the present invention.

In this embodiment, the tuning voltage of the tuner circuit can be used to increase the amount of attenuation below the desired frequency before the frequency is converted by the mixer circuit 3.

[0027]

According to the present invention, a large amount of attenuation can be obtained below the reception frequency, so that it is possible to realize a tuner circuit having an excellent capability of eliminating interference with respect to an interference signal lower than a desired frequency band.

[Brief description of drawings]

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

FIG. 2 is a tuner circuit diagram showing a conventional example of the present invention.

FIG. 3 is a characteristic diagram showing an example of the present invention.

FIG. 4 is a characteristic diagram showing an example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency amplifier circuit, 2 ... Inter-stage tuning circuit, 3 ... Mixer circuit, 4 ... Local oscillation circuit, 5 ... Intermediate frequency output, 6 ... Inter-stage 1
Next resonance line, 7 ... Interstage secondary resonance line, 8 ... Mixer circuit coupling line, 9 ... Coupling capacitor, 10-11 ... Variable capacitance diode, 12 ... Tuning voltage supply terminal, 13 ... Interstage primary tuning capacitor, 14 ... Interstage secondary tuning capacitor, 15 ...
Lower trap forming part.

Claims (2)

[Claims] 1. A high frequency amplifier circuit for inputting a received signal, amplifying the signal and outputting the same, and an interstage tuning circuit for inputting an output signal from the high frequency amplifier circuit and selecting and outputting a desired band. A local oscillation circuit that generates and outputs a local oscillation signal, and a mixer circuit that mixes the output signal from the interstage tuning circuit and the local oscillation signal from the local oscillation circuit to output an intermediate frequency signal. The interstage tuning circuit and the local oscillator circuit are supplied with a tuning voltage to each of the variable capacitance diodes forming the resonance circuits of the interstage tuning circuit and the local oscillation circuit, and the tuning voltage is changed. In the tuner circuit capable of changing the band to be selected, a voltage variable trap circuit is formed at a point formed by coupling the interstage tuning circuit to the input side of the mixer circuit. Anna circuit. 2. The inter-stage tuning circuit according to claim 1, wherein the inter-stage tuning circuit comprises a double-tuning circuit, and the inter-stage tuning circuit comprises an inter-stage primary tuning circuit on the input side and an inter-stage secondary tuning circuit on the output side. A trap in which a reception signal is taken out by mutual inductive coupling between a circuit and a mixer circuit coupling line, is input to the mixer circuit, and a mutual inductor and a capacitor are connected in series in an appropriate band other than a desired frequency band of the reception signal. Forming a circuit,
A tuner circuit comprising a circuit for synchronizing the trap with an interstage tuning circuit to attenuate the level of a signal that causes spurious interference.