JPS63155807A - Mixer circuit - Google Patents

Abstract

PURPOSE:To eliminate the spurious disturbance, the mutual interference disturbance of local oscillation, etc., caused in a first mixer stage by inserting a trap corresponding to a second local oscillation frequency and changing this trap in accordance with a channel. CONSTITUTION:A second local oscillation signal is applied to one side of a resonance line 19 from a second local oscillator 10, and a first local oscillation signal is charged to the middle point between mixing diodes 20 and 21 from a first local oscillater 9, and the difference signal between them is taken out from the center of the resonance line and is led to a low-pass circuit 13 by a capacitor 22. A trap 23 corresponding to the second local oscillation frequency is inserted to prevent the second local oscillation signal from going to the first local oscillator. With respect to the trap 23, a parallel trap circuit consists of a resonance line 25 and capacities 26 and 27 and the trap frequency is changed as shown in a figure. Since the second local oscillation frequency is 3GHz, it is trapped by this circuit. Thus, the second local oscillation is suppressed to eliminate the spurious disturbance, the mutual interference disturbance of local oscillation, etc., caused in a first mixer stage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mixer circuit for a television tuner. It is possible to perform a PLL operation by mixing the signal and the second local oscillation frequency (this is used in the third mixer). However, no consideration was given to spurious interference and local mutual interference.

[Problem that the invention seeks to solve]

Spurious interference refers to interference that occurs at the tuner output due to the first intermediate frequency generated by the first local oscillation frequency, the fundamental wave of the input signal frequency, and the high frequency. Instead of the first station source, the second station source passes through the third mixer and becomes a new spurious interference.

An object of the present invention is to improve the above-mentioned spurious interference and local mutual interference.

[Means for solving problems]

The above purpose is achieved in the third mixer by l! 2 local oscillator frequency (
This can be achieved by inserting matching traps and changing these traps depending on the channel.

[Effect]

The trap suppresses the second station emanation and transmits the first station emanation via 'j41
Since the signal does not leak to the mixer section, spurious interference caused by the second station and local mutual interference are also eliminated. in this case,
The second local oscillator and the first local oscillator may be close to each other, and in this case, this trap will affect the first local oscillator, so in this case, set this trap frequency to be different from the first local oscillator frequency. I'll do it. In this case, the trap frequency changes for the second local oscillation, and the second local oscillation cannot be suppressed, but in this case, spurious interference is not a problem due to the relationship with the input interference frequency.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. The circuit in Figure 1 is a double super one type VHF -
It is a UHF all-channel tuner, in which the signal from the antenna 1 is amplified by a wideband amplifier 2, converted to a first IF frequency by a first frequency converter 3, and further transmitted via an 11F filter 4 to a second frequency converter 5. 2nd IF
J! 1 wave number (the Eirin TF frequency of a normal television receiver), and is further led to an output 81 via a filter 6 and an amplifier 7. 9 is a first oscillator for first frequency conversion, and 10 is a second oscillator for second frequency conversion.

The first oscillator 9 and the second oscillator 10 are combined by a synthesizer 11, frequency converted by a third mixer 12, and only the difference signal between the first local oscillator and the second local oscillator is selected by a low-pass filter 15. Furthermore, the branch unit 14. Program switch 152 Phase detector 16. The reference signal generator 17 and the Yohilow bass filter 18 are both circuits composed of P and L L fe. Here, FIG. 2 shows the composite word 11 and the fifth mixer 1.
FIG. 2 is an actual circuit configuration diagram of No. 2.

This figure shows a 1/2 person phase shift type mixer circuit, in which the second local oscillator 10 applies the second local oscillator signal to one side of the resonant line 19, and the mixing diode 20, 21 bow point-saving mechanism is applied. 1st
A local oscillator signal is injected from the first local oscillator 9, the difference signal between the two is taken out from the center of the resonance line, and the difference signal between the two is taken out from the center of the resonant line and connected to the capacitor 22.
1.24, which leads to the low-pass circuit 15, drops the mixer diode to ground in a direct current manner /! - It is a resonant line for the purpose.

Here, in order to prevent the second local oscillator signal from going to the first local oscillator (a drag 23 that matches the second local oscillator frequency is inserted), this trap is specifically shown in Figure 3. 25 is a resonant line, 26 is a tuning capacitor whose capacitance changes in the reception channel, and 27 is an i51 constant capacitor.The resonant line 25 and capacitors 1i and 26 and 27 form a parallel trap circuit, and the trap frequency is It changes as shown in Fig. 4. Here, since the second local oscillation frequency is 3Gfiz, it is dragged by this circuit.

It is particularly effective against sgeriatric interference, which is a problem when receiving UHF.

〔Effect of the invention〕

According to the present invention, since it is possible to suppress the second station oscillation, it is possible to eliminate spurious interference, local oscillation mutual interference, etc. generated in the first mixer stage.

[Brief explanation of the drawing]

FIG. 1 is a Pronk diagram of one embodiment of the present invention, FIGS. 2 and 3 are its actual circuit diagrams, and FIG. 4 is a diagram showing the effects of the present invention. 1... Antenna 2... Wideband amplifier 6...
・First frequency converter 5...Second frequency converter 6...Filter 7...Amplifier 14...Bunch unit/ Dimensions 1 Dimensions in the figure 2153 9 units, l, -''2 -3

Claims (1)

[Claims] 1. In the mixer circuit that mixes the first local oscillator and the second local oscillator, a trap circuit is provided to suppress the second local oscillator to the first local oscillator, and the trap circuit is configured to enter at a specific channel time. A mixer circuit featuring: