JPH02195705A - Semiconductor integrated circuit for television tuner - Google Patents

Abstract

PURPOSE:To obtain a stable output in a broad frequency band by connecting a resistor between the first and second transistors(TR) of a differential amplifier which converts and outputs a local oscillating output, and equalizing collector outputs. CONSTITUTION:The output of a local oscillating circuit D of a TV tuner is level-converted by a differential amplifying circuit F formed by TRs Tr5 and Tr6, which are decoupled at capacity C2, supplied to the base of TRs Tr1 to Tr4 of a double-balance type mixing circuit, which an RF input signal is applied to the emitter, and an intermediate frequency output is produced through an intermediate frequency amplifying circuit A, etc. The collectors of the Tr5 and Tr6 of the circuit F are connected by a resistor R3, and the collector outputs are equalized. Thus the balance of a circuit E is maintained and stable operation is continued starting from a time when the applied voltage level of the circuit D is low up to the time when it is high.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor integrated circuit for a television tuner.

Conventional technology Conventionally, television tuners (hereinafter referred to as tuners) absorb frequencies from 60 to 1ooOM)-Iz, so it is extremely difficult to integrate them into ICs, and each circuit block is constructed with discrete circuits. The mainstream was to do so. Even today, most tuners have circuit configurations using discrete transistors. On the other hand, performance requirements in the market are becoming increasingly strict, and countries around the world are placing particularly strong demands on ensuring high interference rejection capability and reducing unnecessary radiation from tuners. In addition, the progress of semiconductor ICs has been remarkable, and the processing technology for ultra-fine patterns has been progressing year by year.
With the advancement of CJ, it has become possible to achieve high performance, which could not be obtained with conventional discrete circuits, at low cost on an industrial basis.

The problem that the invention aims to solveHowever, there is a problem that must be addressed here. It is a local oscillator circuit required for wideband reception, which makes it difficult to maintain a constant output level over a wide frequency range.

As a result, stable output cannot be obtained on each channel in wideband reception.

Therefore, it is an object of the present invention to enable each channel to obtain a stable output even if the output level from the local oscillation circuit fluctuates.

In order to solve the problem and achieve the above object, the present invention provides a first local oscillation concave. The second transistor is connected to the base of the first transistor of the differential amplifier circuit, the base I of the second transistor is in a decoupling state, and the output of the differential amplifier circuit is The balanced output is taken out from the collector of the transistor and connected to the double-balanced mixed circuit [1]. Second
The collectors of the transistors are connected with a resistor.

Effect: With the above configuration, even if the output level from the local oscillation circuit fluctuates, the first oscillator that constitutes the differential amplifier circuit. Second
The collector voltages of the transistors can be made uniform, and as a result, stable mixing operation can be performed over a wide frequency range in the double-balanced mixing circuit, and the output can be stabilized.

Example FIG. 1 is a circuit diagram of a main part showing a complete example of the present invention.

It is supplied to the base of the transistor Tr7 of the differential amplifier circuit composed of the RF double signal transistor Tr'7'''a.The base of the transistor Tr8 is still grounded by the decoupling capacitor C2.The transistor T
r7' From the collector of Tr8, transistor Tr1
The RF multiplied signal supplied to the emitter of the double-balanced mixing circuit E composed of "r2"r3"r4 is injected from the base of the transistor darrl"r2"r3Tr4 and mixed with the 6 local oscillation components, resulting in a cross-type signal. Only the intermediate frequency component is guided to the load from the connected collector,
I/ductance L4. It is selected by an intermediate frequency bandpass filter constituted by a capacitor C1, and is guided to the next stage intermediate frequency amplification circuit. is the current determined by the current source.

On the other hand, the local oscillation component is injected into the base of the first transistor Tr6 of the differential amplifier circuit F via the local oscillator S circuit and the coupling capacitor C3.

The base of the second transistor Tr5 is grounded through a decoupling capacitor C2. The role of the differential amplifier circuit F composed of the first and second transistors Tr5 and Tr6 is to amplify the local oscillation component and to act as the transistors ``l''r2''r3 of the double-balanced mixing circuit E in the next stage.
It supplies the base voltage of r4 and converts the local oscillation component input as an unbalanced signal into a balanced signal mode.The local oscillation component injected into the base of the first transistor Tr60 is Transistor FR5”
From the collector of r6, the double-balanced mixing circuit E
injected into. If a local oscillation component is injected into the first transistor Tr6 with a large input, an operational imbalance will occur as seen from the emitter current generator 8 shown in FIG. This is because the base current of the first transistor Tr6 increases.

In other words, the total emitter current of the second transistor Tr5 and the first transistor Tr6 is determined by the current source, and as the emitter current I8 of the first transistor Tr6 increases, the emitter current of the second transistor Tr5 increases. , will decrease. And this is the first one from K. The collector avoidance pressure of the second transistor "r6'Tr5 becomes unbalanced, and the base voltage of the double-balanced mixed circuit E directly connected to each collector also decreases as shown in Fig. 3 (a).
) As a result, the balanced operation is disrupted and the conversion efficiency is reduced. In order to eliminate this slang, in one embodiment of the Ashiki invention, a resistor R5 is connected between the collectors of the second transistor Tr5 and the first transistor Tr6, and the collector voltage v1 of the first transistor Tr6 and the second transistor Tr5 are This equalizes the voltage v2 at the collector of the circuit, thereby ensuring stable operation from low to high levels of the voltage injected from the local oscillator circuit, as shown in Figure 3(b)r:J. .

Note that R1 and R2 are resistors, B is a power supply, and G is an intermediate frequency output terminal. Further, FIG. 4 shows the conversion gain with respect to the value of the resistor R3.

Effects of the Invention According to the present invention, even when it is difficult to obtain a stable oscillation force from a local oscillation circuit in a wide band, it is possible to obtain a stable output in a wide frequency range.

[Brief explanation of the drawing]

FIG. 1 is a main circuit diagram showing an embodiment of the present invention. Figure 2 is 1. The characteristic diagram showing the relationship between the emitter current of the second Tr6"r5 and the injection voltage from the local oscillation circuit, No. 31ffl 71L) shows the base voltage of the transistor forming the double-balanced mixed circuit without adding the resistor R5. Characteristic diagram showing the relationship between injection voltage and Figure 3(b)
4 is a characteristic diagram showing the relationship between the base voltage and the injection direct voltage of the transistor constituting the double-balanced mixed circuit with the resistor R3 added, and FIG. 4 is a characteristic diagram showing the relationship between the direct conversion gain of the resistor R3. . D...Local oscillation circuit, G...Double balanced mixed circuit,!・・・・・・Differential amplification circuit-”r6
'Tr5...1st! Transistor 2, R3... Resistor. Name of agent Patent attorney Shigetaka Awano and one other person Figure 3 (aL-Cb) Figure 2 1i4 Figure 56 767) JJo, 366mV

Claims (1)

[Claims] A local oscillation circuit is connected to the base of the first transistor of a differential amplifier circuit composed of first and second transistors, the base of the second transistor of the differential amplifier circuit is in a decoupled state, and the differential For a television tuner, the output of the amplifier circuit is taken out as a balanced output from the collectors of the first and second transistors and connected to a double-balanced mixing circuit, and the collectors of the first and second transistors are connected with a resistor. Semiconductor integrated circuit.