JPS6347375B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides low-pass filter characteristics to the AM detection circuit and eliminates the need for an external low-pass filter.
Regarding AM radio receivers.

Conventionally, in AM radio receivers, when the intermediate frequency amplifying section and the detection circuit were constructed using monolithic integrated circuits (ICs), the intermediate frequency amplifying section was constructed from a wideband amplifier, so local oscillation was applied to the intermediate frequency amplifying section. The disadvantage was that oscillation frequency signals, shortwave signals, strong input signals, etc. of the

Therefore, the intermediate frequency amplification section and detection circuit are
When configured with an IC, measures are taken to prevent signal components other than the intermediate frequency signal from entering the detection circuit by externally connecting an intermediate frequency transformer or capacitor filter to the external terminal (pin) provided in the intermediate frequency amplification section. has been applied.

However, such countermeasures increase the number of external terminals for the IC, and the formation of these terminals causes unnecessary radiation.Furthermore, it requires an intermediate frequency transformer or a capacitor filter, which increases the number of components. There were some shortcomings.

Therefore, an object of the present invention is to realize an AM radio receiver that blocks unnecessary signals other than AM signals and that has a simplified configuration by reducing the number of parts.

That is, the AM radio receiver of the present invention includes, for example, as shown in FIG. A differential pair of transistors (transistors 34 and 36) is provided for detection, and a capacitor 4 is provided between the bases of each transistor 34 and 36 and between each base and collector.
4, 46, and 48, and an AM detection circuit 8 provided with low-pass filter characteristics with a passband up to an intermediate frequency.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of an AM radio receiver of the present invention.

The intermediate frequency AM signal, which has been changed to an intermediate frequency by a frequency conversion circuit or the like, is input to the intermediate frequency amplification section 4 from input terminals 2a and 2b. Intermediate frequency amplification section 4
The emitters of the pair of transistors 12 and 14 are made common, and a constant current source 16 is connected between the emitters and a reference potential point (ground), and a resistor 18 is connected between the collectors of the transistors 12 and 14 and the power supply terminal 15. 20
A differential amplifier is installed. Therefore, the intermediate frequency AM signals applied to the input terminals 2a and 2b are differentially amplified by the intermediate frequency amplifying section 4.

Then, as the amplified output of the intermediate frequency amplification section 4,
The AM signal is taken out from the collector side of each transistor 12, 14 and applied to the AM detection circuit 8. The AM detection circuit 8 includes transistors 22, 24, resistors 26, 28, and a constant current source 3 at the input section.
0 and 32 are installed, and transistors 34 and 36 are installed as a transistor differential pair. That is, the emitters and collectors of the transistors 34 and 36 are connected in common, the emitter of the transistor 22 is connected to the base of the transistor 34 via the resistor 38, and the emitter of the transistor 24 is connected to the base of the transistor 36. are connected via a resistor 40. The collectors of the transistors 34 and 36 are connected to the power supply terminal 15 through a power supply line, and a constant current source 41 is installed on the emitter side of the transistors 34 and 36. Further, a capacitor 42 is connected between the bases of the transistors 22 and 24.
Capacitors 44, 46, 48 are connected between the bases of each transistor 34, 36 and between the base and collector.
are respectively installed, and the AM detection circuit 8 is provided with a low-pass filter characteristic whose passband is up to the intermediate frequency.

Transistors 22 and 24 from the intermediate frequency amplification section 4
The intermediate frequency AM signal applied to the base of is applied to the base of each transistor 34, 36 via transistors 22, 24 and resistors 38, 40,
AM detection is performed by the operation of transistors 34 and 36. In that case, the AM detection circuit 8 is provided with a low-pass filter characteristic whose passband is up to the intermediate frequency using the capacitors 42 to 48, so that the intermediate frequency AM It is possible to prevent signals other than signals from entering, and only AM signals are selectively detected. Then, the AM detection output is the transistor 3
Output terminal 10 provided on the emitter side of 4 and 36
taken from.

According to this configuration, the low-pass filter characteristics are imparted by the capacitors 42 to 48 installed inside the AM detection circuit 8, thereby preventing the intrusion of unnecessary signals other than the intermediate frequency AM signal. hand
The AM detection circuit 8 can detect only AM signals. In particular, the capacitors 42 to 48 have a PN junction capacitance of 5 pF to 5 pF within the monolithic integrated circuit.
10pF can be used and can be realized using normal manufacturing processes, so the manufacturing cost of the IC will not increase.

In the embodiment, the capacitors 42 to 48 are combined to form a secondary filter to determine necessary frequency band characteristics, and a pass band below the intermediate frequency is set as an effective band. , 46, 48 also provide an intermediate frequency
This provides low-pass filter characteristics for removing unnecessary signal components other than AM signals.

Therefore, there is no need to connect an intermediate frequency transformer or a capacitor filter to the outside, reducing the number of parts and eliminating the need for terminals to connect them, making it possible to simplify the configuration of the integrated circuit.
No radiation occurs due to external terminals. Even if the intermediate frequency amplifying section 4 is constituted by a wideband amplifier, the bandwidth of the intermediate frequency amplifying section 4 is equivalently narrowed by imparting low-pass filter characteristics using a capacitor to the AM detection circuit 8 side. Malfunctions due to broadband expansion can be prevented.

As explained above, according to this invention, AM
The capacitor installed in the detection circuit provides low-pass filter characteristics, making it possible to prevent the intrusion of unnecessary signals other than AM signals, such as local oscillation signals, shortwave signals, and strong input signals. ,
In addition to the low-pass filter that was conventionally connected externally, there is no longer a need for a terminal for external connection of the low-pass filter, there is no unnecessary radiation when the terminal is formed, and there is no need for components due to the omission of the external low-pass filter. The configuration can be simplified by reducing the number of points.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an AM radio receiver of the present invention. 4...Intermediate frequency amplification section, 8...AM detection circuit,
34, 36...Transistor (transistor differential pair), 44, 46, 48...Capacitor as a low-pass filter.

Claims (1)

[Claims] 1. An intermediate frequency amplifying section that amplifies an AM signal changed to an intermediate frequency, and a differential pair of transistors that detects the AM signal from this intermediate frequency amplifying section. An AM radio receiver consisting of an AM detection circuit with a capacitor installed between the base and collector and a low-pass filter characteristic with a passband up to the intermediate frequency.