JPH0955677A - Electronic tuner circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stably a selectivity characteristic and a power gain and to obtain a high inter-modulation performance without being affected by an impedance of a post-stage intermediate frequency amplifier circuit. SOLUTION: An output terminal O1 of a balanced output of a balanced output form U/V integrated circuit (U/VIC) 15 is connected to a parallel resonance circuit 32 consisting of a capacitor CO5 and a coil L02 being a single tuning circuit via a series circuit 31 consisting of a resistor R3 and a capacitor CO1. An intermediate frequency signal extracted by the parallel resonance circuit 32 is outputted from an output terminal 20 via a buffer circuit 33 consisting of a transistor(TR) QO2 of common emitter. On the other hand, the other signal of balanced outputs of the U/VIC 15 is connected to ground by a series circuit 30 consisting of a resistor R4 and a capacitor CO2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuning tuner circuit suitable for use in a television signal receiving circuit.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the structure of a conventional UHF / VHF integrated electronic tuning tuner circuit.
In the figure, of the UHF and VHF signals supplied to the input terminal 10, the UHF channel signal is selected by the single tuning circuit 11, and the VHF channel signal is selected by the single tuning circuit 12. UH selected by single tuning circuit 11
The signal of the F channel is amplified by the high-frequency amplifier circuit 13, passes through the double tuning circuit 14, and then the U / V integrated circuit (hereinafter referred to as U / V).
VIC) 15. On the other hand, single tuning circuit 1
The signal of the VHF channel selected in 2 is amplified by the high frequency amplifier circuit 16 and passes through the double tuning circuit 17, and then the U / V
Input to IC15. This U / VIC15 is UHF,
It is an integrated circuit having a local oscillation circuit and a mixing circuit dedicated to each VHF, and converts an input signal into an intermediate frequency signal and outputs it in a balanced manner. U / VIC on the output side of U / VIC15
A balanced / unbalanced conversion circuit 18 for converting the balanced output of 15 into an unbalanced output is connected, and a single tuning circuit 19 is connected to the output side of the balanced / unbalanced conversion circuit 18. The intermediate frequency signal from the single tuning circuit 19 is input to the next stage intermediate frequency amplifier circuit (not shown) via the output terminal 20.

FIG. 4 is a diagram showing a detailed configuration of the balanced / unbalanced conversion circuit 18 and the single tuning circuit 19 provided on the output side of the U / VIC 15. As shown in FIG. 4, the winding ratio is N: 1. One end of the primary winding of the conversion transformer To1 is connected to one output end O1 of the U / VIC 15 via the coupling capacitor Co1, and the other end of the primary winding is connected to the other end of the U / VIC 15 via the coupling capacitor Co2. Is connected to the output terminal O2. On the other hand, one end of the secondary winding of the conversion transformer To1 has an intermediate frequency resonance coil Lo1 and a capacitor Co.
It is connected to the output terminal 20 via 3 and the other end of the secondary winding is grounded. The capacitor Co4 is connected between the capacitor Co3 and the output terminal 20 and the ground. The conversion transformer To1 converts the balanced output of the U / VIC 15 into an unbalanced output.
Impedance conversion is performed by a turn ratio of 1 (N: 1). Further, the conversion transformer To1, the intermediate frequency resonance coil Lo1, and the resonance capacitors Co3 and Co4 form a series resonance circuit that resonates at an intermediate frequency, and the intermediate frequency signal is taken out at the output end 20.

[0004]

By the way, in the conventional electronic tuning tuner circuit described above, the U / VIC 15 is used.
Output of the conversion transformer To1 and intermediate frequency resonance coil L
o1 and the resonance capacitors Co3 and Co4 are supplied to the intermediate frequency amplifier circuit in the subsequent stage, but this configuration is easily affected by the input impedance of the intermediate frequency amplifier circuit in the subsequent stage, so that the selectivity characteristic and the power gain are unsatisfactory. There is a problem that it becomes stable and intermodulation performance is deteriorated.
The cross-modulation performance depends on the specifications of the conversion transformer To1, but the conversion transformer To1 cannot obtain sufficient balance performance. Further, the selectivity characteristic, which is the characteristic of the series resonant circuit, changes due to the change in impedance.

Therefore, the present invention provides an electronic tuning tuner circuit which is not affected by the input impedance of the intermediate frequency amplifier circuit in the subsequent stage, and which can stably obtain the selectivity characteristic and the power gain and can obtain the high intermodulation performance. It is intended to be provided.

[0006]

The invention according to claim 1 is UH
An electronic tuning tuner circuit comprising a U / V integrated circuit which comprises a local oscillation circuit and a mixing circuit dedicated to F and VHF, respectively, and which balance-outputs an intermediate frequency signal obtained by converting an input signal; said U / V integrated circuit A first series circuit consisting of a resistor and a capacitor connected to one of the balanced output terminals of
A tuning circuit connected to the first series circuit for extracting the intermediate frequency signal; a buffer circuit for outputting the intermediate frequency signal extracted by the tuning circuit; the other of the balanced output terminals of the U / V integrated circuit A second series circuit composed of a resistor and a capacitor for grounding.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the circuit configuration of the latter stage of the U / V integrated circuit of the electronic tuning tuner circuit of the embodiment. In this figure, the same parts as those in FIG. 4 described above are designated by the same reference numerals. In this figure, U / V
The other output terminal O2 of the IC15 has a resistor R4 and a capacitor C.
It is grounded by a series circuit 30 composed of o2 and one output terminal O1 is connected to a parallel resonance circuit 32 composed of a capacitor Co5 and a coil Lo2, which is a single tuning circuit, via a series circuit 31 composed of a resistor R3 and a capacitor Co1. Has been done. The resistors R3 and R4 having the same resistance value of 200Ω or more are used, and the capacitor Co5 of the parallel resonance circuit 32 is used.
The coil Lo2 having a value with which the intermediate frequency is tuned is used. The intermediate frequency signal extracted by the parallel resonance circuit 32 is output from the output terminal 20 via the buffer circuit 33 including the transistor Qo2 whose emitter is grounded.
The voltage Vcc is applied to the collector of the transistor Qo2 of the buffer circuit 33 via the resistor R8.

Since the U / VIC 15 has a balanced output, it is necessary to balance the load and extract a balanced output signal with high impedance. However, by connecting the series circuits 30 and 31 to the balanced output terminal, the balanced load can be obtained. Becomes equivalent to U
The high-frequency currents inside the / VIC 15 are small and balanced, and they cancel each other out. As a result, modulation is hardly applied from one high-frequency current to the other high-frequency current, so that high intermodulation performance can be obtained. In addition, the buffer circuit 33
The load impedance can be made high by providing. In this case, the general load impedance required for the U / VIC 15 is 300Ω or more as shown in FIG. 2, but the conventional conversion transformer To1 cannot always satisfy this value, and sufficient balance characteristics are obtained. I couldn't do it. However, by providing this buffer circuit 33, the U / VIC1
The load impedance of No. 5 becomes sufficiently high, so that the influence of the input impedance of the intermediate frequency amplifier circuit of the next stage is reduced, and the selectivity characteristic and the power gain are stabilized.

In this way, the balanced output type U / VIC1 is used.
One of the balanced outputs of 5 is taken out by a series circuit 31 composed of a resistor R3 and a capacitor Co1 and supplied to a single tuning circuit 32, and an intermediate frequency signal tuned by the single tuning circuit 32 is output from an output terminal 20 via a buffer circuit 33. While outputting
The other balanced output of the U / VIC 15 is grounded by the series circuit 30 including the resistor R4 and the capacitor Co2. As a result, the high-frequency current inside the U / VIC 15 decreases and cancels each other, so that one high-frequency current hardly modulates the other high-frequency current, and high intermodulation performance can be obtained. Further, since the load impedance of the U / VIC 15 is sufficiently increased by providing the buffer circuit 33, the selectivity characteristic and the power gain are stabilized.

[0010]

According to the invention of claim 1, one of the balanced outputs of the U / V integrated circuit of the balanced output type is taken out by a series circuit composed of a resistor and a capacitor and supplied to a parallel resonant circuit, and the parallel resonant circuit is provided. While the intermediate frequency signal tuned by the circuit is output from the buffer circuit, the other of the balanced outputs of the U / V integrated circuit is grounded by the series circuit including the resistor and the capacitor, so that high intermodulation performance can be obtained and selectivity characteristics can be obtained. Also, an electronic tuning tuner with a stable power gain can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of a latter stage of a U / V integrated circuit of an electronic tuning tuner circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing the degree of intermodulation with respect to the load impedance of a U / V integrated circuit.

FIG. 3 is a block diagram showing a configuration of a conventional electronic tuning tuner circuit.

FIG. 4 is a diagram showing a circuit configuration of a subsequent stage of a U / V integrated circuit of a conventional electronic tuning tuner circuit.

[Explanation of symbols]

 15 U / V integrated circuit 30 series circuit (second series circuit) 31 series circuit (first series circuit) 32 tuning circuit 33 buffer circuit

Claims (1)

[Claims] 1. An electronic tuning tuner circuit comprising a U / V integrated circuit which comprises a local oscillation circuit and a mixing circuit dedicated to each of UHF and VHF, and balance-outputs an intermediate frequency signal obtained by converting an input signal; A first series circuit consisting of a resistor and a capacitor connected to one of the balanced outputs of the U / V integrated circuit; a tuning circuit connected to the first series circuit for extracting the intermediate frequency signal; A buffer circuit for outputting the intermediate frequency signal extracted by the tuning circuit; and a second series circuit composed of a resistor and a capacitor for grounding the other of the balanced output terminals of the U / V integrated circuit. Electronic tuning tuner circuit.