JPS628568Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is an AM receiver equipped with an automatic noise limiter circuit (hereinafter referred to as ANL circuit) for removing noise contained in the detection output.
This relates to the detection circuit of a CB transceiver.

The circuit shown in FIG. 1 has been known as a detection circuit for a CB transceiver equipped with an ANL circuit. _D1 is a detection diode, and D1 is an ANL circuit.

In the circuit shown in Figure 1, the intermediate frequency signal is negatively detected by the detection diode _D1 , the high frequency component is bypassed by the load capacitor _C1 , and only the audio signal component is sent to the audio signal output terminal (detection output terminal). transmitted to the side. By the way, the ANL circuit that performs switching
1 amplitude limiting diode is ANL SW ON
Normally, the bias resistor is set so that a forward current flows, and the switch is in the 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 the diode decreases, and the diode becomes OFF only during the period when pulse noise enters. . Therefore, the pulse noise component is
1 resistor and an electrolytic capacitor to ground. In this way the noise removal operation is achieved.

However, the circuit shown in FIG. 1 has the following drawbacks.

(a) If the DC current of the detection stage is I _DC , the DC resistance is R, the AC current is I _AC , and the AC resistance is |Z|, then the modulation degree m is m=I _AC・|Z|/I _DC・R. In general, R>|Z|, so when I _AC becomes larger than I _DC , the negative part of I _AC enters the cutoff point of the detection diode, causing distortion. Therefore, the highest distortion-free modulation degree in the detected output is determined by the ratio of the DC load to the AC load, assuming that the DC current and the AC current are equal.

However, in the case of Fig. 1, the DC load is approximately R ₂ +
Since R ³ = 160KΩ and the AC load is 10KΩ, the maximum distortion-free modulation degree is small, and distortion is likely to occur in the detected waveform when large input and high modulation (for example, 100% modulation) exceeds SG60dBμ.

(b) The degree of improvement in distortion during small input and high modulation is determined by the time constant of the load capacitance C ₁ of the detection diode D ₁ and the DC load, but when the input is small, the impedance of the detection diode D ₁ is large, so the time constant of the detection circuit [τ=C ₁・(R ₂ +
R ₃ )] is large, and when detecting a signal with a small input and high modulation degree (for example, 100% modulation, SG0dBμ or less), the lower the frequency, the less tracking becomes possible and the distortion rate worsens.

In view of this, the present invention is an AM system equipped with an ANL circuit.
In the detection circuit of the receiver, the detection distortion during large input high modulation and the detection distortion during small input high modulation are to be improved.One embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, the same reference numerals as in FIG. 1 are used for the same parts as in FIG. 1.

As is clear from FIG. 2, the circuit of the present invention is characterized in that a resistor _R4 is connected in parallel with a capacitor _C1 provided between the anode of the detection diode and the ground.

For example, if you choose a resistor R ₄ of 10KΩ, the DC load of the detection circuit will be approximately R ₄ = 10KΩ,
The AC load has a parallel circuit resistance value of resistors R ₁ and R ₄ , that is, R ₁ ·R ₄ /R ₁ +R ₄ =5KΩ.

Therefore, the difference between the DC load and the AC load of the detection circuit becomes small, and detection distortion at the time of large input and high modulation can be improved.

Furthermore, by providing the resistor R ₄ , the time constant of the detection circuit becomes smaller (τ'=C ₁ ·R ₄ ), so detection distortion during small input high modulation can also be improved.

As described above, the present invention enables detection distortion during large input high modulation and detection distortion during small input high modulation by simply adding one DC load in the detection circuit of an AM receiver equipped with an ANL circuit. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a detection circuit of a conventional AM receiver, and FIG. 2 is a circuit diagram showing a detection circuit of an AM receiver according to the present invention. 1 ...ANL circuit, D ₁ ...detection diode,
R ₄ ...Resistance.

Claims (1)

[Scope of utility model registration request] In the detection circuit of an AM receiver equipped with an automatic noise mitter circuit (ANL circuit), the DC load of the detection circuit is connected in parallel with the load capacitance of the detection diode and the AC load of the detection circuit is connected to the input side of the ANL circuit. A resistor having a resistance value equal to or lower than the resistance value of the load is provided, and the resistor reduces the difference between the DC load and the AC load of the detection circuit, and adjusts the time constant of the DC load and the load capacity of the detection circuit, A detection circuit for an AM receiver, characterized in that detection distortion is improved during large input high modulation and small input high modulation.