JPS5819006A - intermediate frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To improve the elimination characteristics of interference waves by connecting a intermediate frequency circuit to a connecting point between a detecting circuit connected to an interfrequency amplifying circuit in multistage cascade connection and a load resistor. CONSTITUTION:An intermediate frequency amplifying circuit is of a differential amplifier constitution of three-stage direct coupling consisting of transistors (TR) Q1-Q6, load resistors R2-R7, and constant current sources A1-A3. A constant current power supply source A4 is connected to a TRQ7, and an LPF consisting of capacitors C5 and C6 is connected to a terminal P6, and a detected output is picked up from a terminal 6. A parallel resonance circuit consisting of a coil L and a capacitor C4 and a coil L is connected to a terminal P4. An interference wave invaded to an output terminal P1 of a filter 2 and its succeeding stage is eliminated at this parallel resonance circuit and not outputted to the terminal 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intermediate frequency amplification circuit capable of adding a function to improve interference wave removal characteristics.

FIG. 1 shows the configuration of a conventional, common intermediate frequency amplification circuit and detection circuit. An intermediate frequency signal applied to an input terminal 1 passes through an intermediate frequency pass filter 2 and enters an intermediate frequency amplifier 3 connected in cascade in multiple stages. The intermediate frequency signal amplified by the intermediate frequency amplification section enters the detection circuit section 4, is detected, and is taken out from the output terminal 6. In this conventional circuit, interference waves other than the intermediate frequency are removed by input terminal 1. It was only necessary to use filter 2 connected to the . For this reason, under the strong electric field of broadcast radio waves, radio waves other than intermediate frequencies that directly enter the output terminal of the filter mentioned above may be detected by the detection section 4 and become an interference wave output. The object of the present invention is to provide an intermediate frequency amplification circuit that can add a function to enhance this interference wave removal characteristic by connecting a resonant circuit to a terminal.

I will explain.

FIG. 2 is a diagram showing a specific configuration of the intermediate frequency amplifier circuit of the present invention, in which the intermediate frequency amplifier circuit section is composed of a three-stage directly connected differential amplifier, and the detection circuit is composed of an emitter follower and a low-pass filter. Yes, the intermediate frequency amplification circuit section is
It has a three-stage directly connected differential amplifier configuration including transistors Q and Q9, load resistors R2 to R7, and constant current power supplies 1 to 'sk. The connection point between the load resistor R7 on one side of the final stage and the collector of the transistor Q6 is connected to the base of the emitter follower transistor Q7.

A constant current power supply A4 is connected to the emitter of the emitter follower transistor Q7, and a capacitor a5. A low-pass filter consisting of a resistor R1o is connected, and a capacitor C6 and a resistor R1
At the connection point with 0, there is a terminal 5 for taking out the detection output signal.
is attached. Resistors R1゜R8 and R7d are DC feedback resistors, and capacitors C, C2 are AC bypass capacitors.In the intermediate frequency amplifier circuit shown in Fig. 2, the load resistor R7 on one side of the final stage of the intermediate frequency amplifier is , the connection point between the collector of transistor Q6 and the pace of transistor Q7 is connected to terminal P4. A parallel resonant circuit consisting of a coil L and a capacitor C4 is connected to this terminal P4 via a DC blocking capacitor C6, and the other end of this parallel resonant circuit is connected to a power supply terminal P5 as an AC ground.

Note that the parallel resonant circuit has a resistance R for intermediate frequency signals.
It can be set so that it has a sufficiently high impedance compared to 7, and has a low impedance almost like a short circuit for other interference waves. Therefore, even if interference waves directly enter after output terminal P1 of filter 2,
The interference wave is removed in this parallel resonant circuit, and the inconvenience that the interference wave is detected by the detection circuit and appears as an interference wave output at the terminal 5 is reliably eliminated.

Furthermore, in the intermediate frequency amplification circuit of the present invention, nothing may be connected to the terminal P4, and the terminal P4 may be left in an open state. The DC operating state in this case is the same as when connected to a parallel resonant circuit. Furthermore, since the impedance of the parallel resonant circuit is sufficiently larger than the resistance for intermediate frequency signals, the characteristics other than the interference wave removal characteristics can be made almost unchanged even without this parallel resonant circuit. That is, in the intermediate frequency amplifier circuit of FIG. 2, if there is no particular need to improve the interference wave removal characteristics, it is sufficient to use the intermediate frequency amplifier circuit with the terminal P4 in an open state.

As is clear from the above explanation, the intermediate frequency amplifier circuit of the present invention can impart interference wave rejection characteristics or not by selecting whether or not to connect a resonant circuit to the connection point between the load resistor and the detection circuit. The circuit characteristics can be easily changed depending on the purpose, and the range of application can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional intermediate frequency amplifier, and FIG. 2 is a diagram showing a specific circuit configuration of an intermediate frequency amplifier according to an embodiment of the present invention. 1...Intermediate frequency input terminal, 2...Intermediate frequency pass filter, 3...Intermediate frequency amplifier, 4
...Detection circuit section, 5...Output terminal, Q
1~Q7...Transistor, R7...
Resistor, C5-C6... Capacitor, R4...
...Terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
figure

Claims (1)

[Claims] It has an intermediate frequency amplification circuit section composed of intermediate frequency amplifiers connected in cascade in multiple stages, a detection circuit section connected to the output load resistance of the circuit section, and an intermediate frequency amplifier circuit section at the connection point between the load resistance and the detection circuit. An intermediate frequency amplification circuit characterized by having an external terminal for connecting a frequency resonant circuit.