JPH0590985A - Multi-path noise detection circuit - Google Patents

Abstract

PURPOSE:To accurately detect the production of muiti-path noise by providing an operational amplifier circuit amplifying an AC signal generated due to multi- path and a detection circuit detecting the level of an output signal of the operational amplifier circuit to the title detection circuit. CONSTITUTION:Since negative feedback is applied from an output terminal to the 2nd input terminal of an operational amplifier circuit 7 by means of resistors 20, 21 and a capacitor 22, the circuit acts like an AC amplifier whose AC gain is G and whose DC gain is the unity, and then the DC component of an output composite signal of an electric field detection circuit 6 is not amplified only the AC component is amplified. Then the level of an output signal of the operational amplifier circuit 7 is detected by a detection circuit 8. In this case, a bottom detection output signal is obtained from an emitter of a detection transistor (TR) 9 and the bottom detection output signal is fed to a separation control circuit 16 and an attenuation control circuit 17 via an output circuit 11. Thus, the deterioration in the stereo separation is reduced and the high frequency component of the stereo multiplex circuit 5 is attenuated to eliminate multi-path noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipath noise detection circuit for detecting noise generated according to multipath.

[0002]

2. Description of the Related Art Conventionally, various multipath noise detection circuits have been proposed and put to practical use. For example, Japanese Patent Publication Sho 63
JP-40379 discloses a multipath noise detection circuit including a detection circuit for detecting the level of a received signal and a level of a multipath signal, and an operational amplifier for obtaining a difference signal between the two signals. .. This detection circuit, the level of the received signal, that is, a signal indicating the electric field strength of the received signal,
The multipath signal, that is, the noise generated by the multipath is detected separately, and the difference between the two signals is detected to detect the occurrence of the multipath.

[0003]

However, the multipath noise detection circuit described in the above publication has a complicated structure and in particular uses a lot of capacitors.
Not suitable for (integrated circuit). Further, the multipath noise detection circuit described in the above publication has a problem that it is apt to malfunction. Furthermore, if a circuit having a high smoothing ability is used as a circuit for generating a signal indicating the electric field strength of the received signal, the AC component of the signal indicating the electric field strength will not be generated. Therefore, the circuit described in the above publication is used. There was a problem that I could not do it.

[0004]

The present invention has been made in view of the above points, and an operational amplifier circuit for amplifying an AC component of a signal indicating the electric field strength of a received signal obtained from an IF amplifier circuit, And a detection circuit for level-detecting the output signal of the operational amplifier circuit. A signal indicating the electric field strength of the received signal is applied to the first input terminal, and a high frequency AC component of the signal indicating the electric field strength of the received signal or a high frequency noise component in the detection output signal is applied to the second input terminal. And a detection circuit for level-detecting the output signal of the operation amplification circuit.

[0005]

According to the first embodiment of the present invention, first, the alternating-current component of the signal indicating the electric field strength of the received signal is amplified by the operational amplifier circuit. After that, the output signal of the operational amplifier circuit is level-detected by the detection circuit. According to the second embodiment, a signal indicating the electric field strength of the received signal is applied to the first input terminal of the operational amplifier circuit, and a signal indicating the electric field strength of the received signal is applied to the second input terminal. A high frequency AC component or a high frequency noise component in the detected output signal is applied and amplified by the operational amplifier circuit. After that, the output signal of the operational amplifier circuit is detected by the detection circuit, and a signal corresponding to the multipath noise is generated at the output end of the detection circuit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of the present invention.
(1) is a receiving antenna, (2) is a front end that amplifies the received signal and converts it to an IF signal, (3) is an IF amplifier circuit that amplifies the IF signal, and (4) is an output IF signal of the IF amplifier circuit. F
An FM detection circuit for M detection, (5) a stereo multiplex circuit for separating the output signal of the FM detection circuit into left and right stereo signals, and (6) for detecting the electric field strength of the received signal,
The electric field detection circuit connected to the IF amplification circuit (3), (7) is the first
An operational amplifier circuit in which the output signal of the electric field detection circuit (6) is applied to the input terminal and a negative feedback is applied from the output terminal to the second input terminal ( 8 ) is the detection transistor (9) and the capacitor (10). And a detection circuit for level-detecting the output signal of the operational amplifier circuit (7), ( 11 ) is composed of transistors (12) to (15),
Output circuit for extracting the detection output signal, (16) is the output circuit ( 11 )
Stereo multiplex circuit according to the output signal of (5)
Degree control circuit for controlling stereo degree of separation, and (17)
Is an attenuation degree control circuit for controlling the high frequency component attenuation degree of the stereo multiplex circuit (5) according to the output signal of the output circuit ( 11 ).

The reception signal received by the antenna (1) is amplified by the front end (2) and converted into an IF signal.
The IF signal is amplified by the IF amplification circuit (3), detected by the FM detection circuit (4), and then separated into left and right stereo signals by the stereo multiplex circuit (5). The separability control circuit (16) reduces the separability of the left and right stereo signals when the electric field strength of the received signal decreases, thereby improving the audibility. The attenuation control circuit (17) attenuates the high frequency component of the left and right stereo signals when the electric field strength of the received signal further decreases, thereby improving the audibility.

While the multipath is not generated, the output signal is not generated from the output circuit, and the isolation control circuit (16) and the attenuation control circuit (17) do not operate according to the multipath. Therefore, right and left stereo signals can be correctly obtained at the left and right output terminals (18) and (19), respectively. When noise is generated according to the multipath, the noise is generated at the output end of the electric field detection circuit (6). Therefore, the output signal of the electric field detection circuit (6) is a composite signal of a DC component according to the electric field strength and an AC component according to the multipath noise. The composite signal is applied to the first input terminal of the operational amplifier circuit (7) and amplified. The operational amplifier circuit (7), from the output terminal to the second input terminal,
Since negative feedback is performed by the resistors (20) and (21) and the capacitor (22), the AC amplifier has a predetermined value G and a DC gain of 1. Therefore, of the output composite signal of the electric field detection circuit (6), the direct current component is not amplified and only the alternating current component is amplified. The output signal of the operational amplifier circuit (7) is the detection circuit ( 8 ).
Level detected by. In that case, the output signal of the operational amplifier circuit (7) is applied to the base (9) of the PNP type detection transistor, and the capacitor (10) is connected to the emitter of the detection transistor (9). A bottom detection output signal is obtained at the emitter. Since the bottom detection output signal is applied to the separation control circuit (16) and the attenuation control circuit (17) via the output circuit ( 11 ), deterioration of stereo separation in the stereo multiplex circuit (5) and High-frequency components are attenuated, and multipath noise is removed.

FIG. 2 is a circuit diagram showing another embodiment of the multipath noise detection circuit according to the present invention. In FIG. 2, the output signal of the electric field detection circuit (6) of FIG. 1 is applied to the first input terminal of the operational amplifier circuit (7), and the high frequency AC of the signal indicating the electric field strength is applied to the second input terminal. A high frequency noise component in the component or the detection output signal is applied. The high frequency AC component is obtained by extracting the IF signal through a high pass filter. Further, the high frequency noise component is obtained by extracting the detection output signal through a high pass filter. With the configuration shown in FIG. 2, the signal applied to the second input terminal is amplified by using the signal applied to the first input terminal as a bias voltage.
A signal corresponding to the noise generated by the multipath is generated at the output terminal of (7). Then, since the signal generated at the output terminal is detected by the detection circuit ( 8 ), the output terminal (2
A signal indicating the occurrence of multipath is obtained in 3).

FIG. 3 is a circuit diagram showing still another embodiment of the multipath noise detection circuit according to the present invention. (24) is an input terminal to which a signal indicating the electric field strength of the received signal is applied, and (25) Is an AC amplifier circuit for amplifying the AC component of the signal indicating the electric field strength, (26) is an output signal of the AC amplifier circuit (25) is applied to the base, and the emitter is a capacitor (2) via a resistor (27).
The detection transistor connected to (8), the emitter and collector of (29) are connected to the emitter and collector of the detection transistor (26), and the base is connected to the input terminal for offset setting transistor, and (30) is It is an output transistor to which the detection output signal obtained at one end of the capacitor is applied to the base.

In the circuit of FIG. 3, the AC amplification operation of the AC amplification circuit (25) with respect to the input signal applied to the input terminal (24) is exactly the same as in the case of FIG. The difference from the circuit of FIG. 1 lies in the operation of the offset setting transistor (29). That is, since the input signal is applied as a bias to the base of the transistor (29), the transistor for offset setting is higher than the base voltage of the detection transistor (26) while the multipath is not occurring. The base voltage of (29) becomes lower, the detection transistor (26) is turned off, and the offset setting transistor (29) is turned on. Therefore, the detection transistor (26) does not react to a small noise or the like generated by a reason other than the multipath, and a malfunction can be prevented. The offset voltage is determined by the value of the resistor (31) and the current value flowing through it. When multipath occurs and the base voltage of the detection transistor (26) drops below the offset voltage, the detection transistor (26) turns on, the offset setting transistor (29) turns off, and the detection transistor (26) is shown in FIG. The detection operation of multipath noise is performed in the same manner as the case. The resistor (27) in FIG. 3 is arranged to increase the discharge time constant of the capacitor (28),
By setting the discharge time constant to an appropriate length, it is possible to prevent the generation of shock noise.

[0012]

As described above, according to the present invention, it is possible to provide a multipath noise detection circuit capable of accurately detecting multipath noise. In particular, since the circuit is configured by using the AC amplification circuit and the level detection circuit, it is possible to provide a multipath noise detection circuit that is suitable for integration into an IC with a simple configuration.

Furthermore, if an offset setting transistor is provided corresponding to the detection transistor as in the embodiment of the present invention, malfunction can be prevented and multipath noise can be detected more accurately.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing still another embodiment of the present invention.

[Explanation of symbols]

(6) Electric field detection circuit (7) Operational amplification circuit ( 8 ) Level detection circuit (9) Detection transistor (10) Capacitor (16) Separation control circuit (17) Attenuation control circuit (29) Offset transistor

Claims (5)

[Claims] 1. A detection circuit comprising: an operational amplifier circuit for amplifying an AC component of a signal indicating an electric field strength of a received signal obtained from an IF amplifier circuit; and a detection circuit for level-detecting an output signal of the operational amplifier circuit. A multipath noise detection circuit characterized in that a signal corresponding to multipath noise is generated at an output end of the circuit. 2. A signal indicating the electric field strength of the received signal is applied to the first input terminal, and a high frequency AC component of the signal indicating the electric field strength or a high frequency noise component in the detection output signal is applied to the second input terminal. And a detection circuit for level-detecting the output signal of the operation amplification circuit, and a signal according to multipath noise is generated at the output end of the detection circuit. Path noise detection circuit. 3. The detection circuit supplies a first transistor to which the output signal of the operational amplifier circuit is applied to the base, a capacitor connected to the emitter of the first transistor, and an emitter current of the first transistor. 3. A constant current source, a second transistor having an emitter and a collector commonly connected to the first transistor, and means for supplying an offset voltage to the base of the second transistor. Multipath noise detection circuit. 4. The multipath noise detection circuit according to claim 3, wherein a resistor is connected between the common emitter of the first and second transistors and one end of a capacitor. 5. The multi signal according to claim 1, wherein the output signal of the multi-path noise detection circuit is used to control the degree of separation or the high frequency component attenuation of the stereo multiplex circuit. Path noise detection circuit.