JPS5936045Y2 - Receiver pulse noise removal circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse noise removal circuit for a receiver, particularly an AM receiver.

FIG. 1 is a circuit diagram showing a pulse noise removal circuit of a conventional AM receiver (for example, the receiver section of a citizen's band CB) transceiver. Diode and bypass capacitor, 3 is automatic gain control (AGC) signal transmission line, D2
is an amplitude limiting diode for removing pulse noise from the detection output, and R1-R6 are bias resistors for applying the power supply voltage +VB0 and reverse AGC voltage as bias voltages to the diodes, respectively. A set voltage for removing natural noise, that is, a set voltage for limiting the amplitude of the detected output (hereinafter referred to as an amplitude limiting set voltage for the detected output) is determined.

C2 is an electrolytic capacitor, and 4 is an audio signal output terminal.

In the circuit shown in Fig. 1, the signal obtained by the tuning coil L of the intermediate frequency transformer 1 is negatively detected by the detection diode D1, the high frequency component is bypassed by the bypass capacitor C1, and only the audio signal component becomes the audio signal. It is transmitted to the output terminal 4 side.

By the way, the amplitude limiting diode D that performs switching operation
2 is set so that a forward current normally flows through bias resistors R1 to R6, and is in an ON state.

However, the output voltage after detection is negative, and when pulse noise enters and the detection output voltage decreases, the voltage on the anode side of diode D2 decreases, and the diode becomes OFF only during the period when pulse noise occurs. .

Therefore, the pulsed noise component is passed through the resistor R2 and the electrolytic capacitor C2 to ground.

However, in the case of a conventional noise removal circuit as shown in Fig. 1, the amplitude limit setting voltage vL of the detection output for removing pulse noise from the detection output is inputted as shown in Figure 2, A9. It is almost constant with respect to electric field strength.

Therefore, if the amplitude limit setting voltage of the detection output is low, when a large input signal is received, part of the audio signal will be removed, worsening the distortion rate, and the amplitude limit setting voltage of the detection output If this is high, there is a drawback that it becomes almost impossible to remove the pulse noise N when receiving a small human power signal, as shown in FIG. 2A.

In view of this, the present invention attempts to eliminate the above-mentioned drawbacks by changing the amplitude limit setting voltage of the detection output as the input signal level is amplified. An embodiment of the present invention will be described with reference to FIG.

In FIG. 3, the same numbers as in FIG. 1 are used for the same parts as in FIG. 1.

In the circuit shown in FIG. 3, a phase inversion transistor Q is provided between the output terminal (anode) of the detection diode D1 and the input terminal (anode) of the amplitude limiting diode D2.
The polarity of the automatic gain control voltage (e.g., reverse AGC voltage) obtained from the output side of the detection diode D1 is inverted by the transistor Q, and the amplitude of this voltage (e.g., forward AGC voltage) with the inverted polarity is passed through the resistor R7. A bias voltage is applied to the input terminal (anode) of the limiting diode D2.

In the circuit configured in this manner, the phase-inverted and amplified AGC voltage described above increases in accordance with the strength of the human electric field, so as the input signal level increases, it is applied to the anode of the amplitude limiting diode D2 in proportion to the increase in the input signal level. Since the forward bias voltage applied becomes higher, the internal impedance of the diode D2 decreases, and the amplitude limit setting voltage L' of the detection output for removing pulse noise becomes higher.

[Figure 4 entrance]. Therefore, when receiving a large input signal (during a strong electric field), there is no concern that part of the audio signal will be amplitude-limited and the distortion rate will deteriorate.

Conversely, if the input signal level decreases, the forward bias voltage applied to the anode of the amplitude-limiting diode D2 will decrease, so the internal impedance of the diode D2 will increase, and the amplitude-limiting setting voltage VL' of the detection output will decrease. It gets lower.

[Figure 4 A]. Therefore, even when receiving a small input signal (weak electric field), the effect of removing pulse noise can be sufficiently achieved.

Fig. 5 is a diagram showing the relationship between the input electric field strength and the amplitude limit setting voltage of the detection output, where curve A is when the conventional circuit shown in Fig. 1 is used, and curve B is when the inventive circuit shown in Fig. 3 is used. The characteristics of each case are shown.

As is clear from Figure 5, the amplitude limit setting voltage of the detection output is approximately constant with respect to the input electric field strength in the circuit of Figure 1, whereas in the circuit of Figure 3 it increases as the input limit strength increases. It turns out that things are changing.

As described above, according to the pulse noise removal circuit for a receiver according to the present invention, an amplification means for amplifying the AGC voltage obtained from the detection circuit is provided, and the output voltage of this amplification means is applied to the amplitude limiting diode. By reducing the internal impedance of the amplitude limiting diode as the human input signal increases, noise is removed when receiving small input signals and prevention of deterioration of distortion rate when receiving large input signals is achieved. There is no concern that part of the audio signal will be amplitude-limited and removed during signal reception and the distortion rate will worsen, and the effect of removing pulse noise is very good even when receiving a small input signal.

Furthermore, the degree of freedom in circuit design can be increased.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a pulse noise removal circuit of a conventional receiver, and Figure 2 (a) shows the input signal waveforms when the circuit in Figure 1 is used when a weak electric field is input and when a strong electric field is input. Figure 3 is a circuit diagram showing the pulse noise removal circuit of the receiver according to the present invention. A diagram showing the input signal waveform and the amplitude limit setting voltage of the detection output when a weak electric field is input and a strong electric field is input. Figure 5 shows the relationship between the input electric field strength and the amplitude limit setting voltage of the detection output in the conventional circuit and the inventive circuit. FIG. 2...Detection same figure, D2...Diode for amplitude limiting, Q...Transistor for phase inversion.

Claims (1)

[Scope of utility model registration request] In a receiver including an amplitude limiting diode for removing pulse noise from the detection output on the output side of the detection circuit, an amplification means for amplifying the AGC voltage obtained from the detection circuit is provided, and the amplification means is applied to the amplitude-limiting diode to reduce the internal impedance of the amplitude-limiting diode as the input signal increases. A receiver pulse noise removal circuit that prevents deterioration of distortion rate.