JPS61214806A - Am detecting circuit - Google Patents

Abstract

PURPOSE:To suppress the variation of amplitude and to improve the articulation of a detected and demodulated sound signal by inserting a PLL circuit between a pilot signal extracting circuit and a homodyne detecting circuit. CONSTITUTION:A pilot signal extracted from an SSB signal by a pilot signal extracting circuit 14 is amplified by an amplifier circuit 20 of a PLL circuit 19 and is given to a phase comparing circuit 22 as a reference frequency input signal. A signal from a VCO 21 whose frequency is approximately equal to that of the pilot signal is inputted to the comparing circuit 22. When phases of both signals are synchronized with each other, the signal from the VCO 21 is equal to the pilot signal and has a certain amplitude. This phase synchronized signal is inputted to the other input terminal 15b of a homodyne detecting circuit 10. As the result, the output is held down by K-number of times when the whole of the signal is increased by K-number of times because of the variance of amplitude. Thus, the articulation of the detected and demodulated sound signal is improved considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention is directed to a single sideband (S)
S B) In homodyne detection, which demodulates the modulated signal from the signal, even if there is amplitude fluctuation in the input signal due to fading in the propagation path, the change in the detection output is minimized to improve speech clarity. The present invention relates to an AM detection circuit.

"Prior Art" The SSB signal accompanied by a pilot carrier signal basically refers to a so-called Rinconvex signal as disclosed in Japanese Patent Publication No. 33-9159. This Rinconvex method separates the amplitude and frequency components of an audio signal, converts the amplitude component into frequency modulated (FM) frequency information, and transmits the frequency component as a constant amplitude. This is a method to obtain an audio signal by restoring the original amplitude component based on frequency information.

When this system is used for mobile communications, the radio waves arriving at the receiver change drastically due to electric field fluctuations due to Rayleigh fading in the propagation path. If the frequency component, which has a constant amplitude, changes due to fading, not only the FM information but also the magnitude of the audio signal will change due to fading. Furthermore, it is desirable that the amplitude be stable in order to correctly return FM information to amplitude information. Therefore, conventionally.

Amplitude fluctuations were suppressed using a fast-response automatic gain control (AGC) circuit. A specific conventional circuit is shown in FIG. In Fig. 2, an SSB signal in the VHF band, for example, which has arrived at the antenna (1) is amplified by the high frequency amplification circuit (3) of the receiving section (2), converted to an intermediate frequency by the mixing circuit (4), and then It is amplified by frequency amplification circuits (5)...(6). This output is normally fed back to the amplifier circuits (3), (5), . . . (6) via the AGC circuit (7) and is controlled to a constant gain. This gain-controlled signal is amplified by the amplifier circuit (9) of the homodyne detection section (8) and sent to one input terminal (15a) of the homodyne detection circuit (10).
input as is, an amplifier circuit (11), and a pilot signal extraction filter circuit (12).

A pilot signal extraction circuit (1) consisting of an amplifier circuit (13)
The pilot signal extracted through step 4) is input to the other input terminal (isb) of the homodyne detection circuit (10). This homodyne detection circuit (10) provides an output proportional to the product of two input signals.

Here, the arriving signal component is a pilot carrier signal fo,
Consisting of the SSB modulated wave signal fa modulated by audio, one input terminal (15b) of the homodyne detection circuit (10)
The signal applied to A 1 cosfo + B cos
fa, and the signal applied to the other input terminal (15b) is A.
2 CogfO, output ac (A 1 cosfo + B cosfa
) A2cosf.

cos(fa-fo)), which is output from the homodyne detection circuit (10). In this equation, if the DC component of the first term, the second term, and the third term are respectively removed by a DC cut capacitor and an LPF (low-pass filter circuit) (16), the final output is 2B - cos (fa fo) The following components are obtained.

Since fa-fo in this component is the original audio modulation signal, it can be amplified by the low frequency amplifier circuit (17) and the audio can be heard through the speaker (18).

"Problems to be Solved by the Invention" Now, when amplitude fluctuation is caused by fading due to the propagation path, the AGC circuit (7) operates to compensate for this fluctuation. However, due to operational delays and operating level ranges of the AGC circuit (7), amplitude fluctuations cannot be completely suppressed, and the remaining amplitude fluctuations are input to the homodyne detection section (8). In this case, if the signal 2B --cos(fa-fo) is multiplied by the amplitude fluctuation, the output fluctuation will increase by a factor of K2.

As a result, the sound changes to an unnatural volume, making it difficult to hear and reducing clarity.

``Means for Solving the Problems'' The present invention was made to solve the above-mentioned problems, and involves adding an AM signal accompanied by a pilot signal to one input terminal of a homodyne detection circuit.

A pilot signal extracted by a pilot signal extraction circuit is added to the other input terminal of the homodyne detection circuit, and a modulated signal is demodulated from these signals. A phase comparator compares the phases of the pilot signal inputted as a reference signal with the signal from the voltage controlled oscillation circuit between the other input terminal of the circuit, and the voltage controlled oscillation circuit when phase synchronization is obtained. A PLL circuit is inserted for inputting the output of the circuit to the homodyne detection circuit.

"Operation" The incoming SSB signal is converted into an intermediate frequency signal at the receiving section. On the one hand, this intermediate frequency signal is applied as is to one input terminal of the homodyne detection circuit.

On the other hand, the pilot signal extracted from the intermediate frequency signal by the pilot signal extraction circuit is used as the reference signal P
In addition to the LL circuit, this PLL circuit's voltage controlled oscillation circuit (
The phase of the signal from VCO) is compared with the phase comparator, and when phase synchronization is obtained, the output of vC0 is sent to the homodyne detection circuit,
to the other input terminal of the circuit. A modulated signal is demodulated from these input signals. Then, even if the overall signal doubles due to amplitude fluctuations, the output is suppressed to double, improving the clarity of the voice.

"Example" Hereinafter, one embodiment of the present invention will be described based on FIG.

The difference between the circuit of the present invention shown in FIG. 1 and the conventional circuit shown in FIG. between the input terminal (15b) of p
This is because an LL (Phase Locked Loop) circuit (19) is inserted. This PLL circuit (1
9) is an amplification circuit (20) that amplifies the pilot signal;
Extracted pilot signal and voltage controlled oscillator circuit (VCO)
) (21) Phase comparison circuit (22) that compares the phase with the signal of (21)
and a low-pass filter circuit (LPF) (23), and the output side of the VCO (21) is coupled to the other input terminal (15b) of the homodyne detection circuit (10).

Other parts are the same as those in FIG. 2, so the same reference numerals are given.

In the above configuration, the operation up to input to the PLL circuit (19) is the same as that of the conventional circuit shown in FIG.

The pilot signal extracted from the SSB signal by the pilot signal extraction circuit (14) is amplified by the amplifier circuit (20) of the PLL circuit (19), and this signal is input to the phase comparison circuit (22) as a reference frequency input signal. Ru. A signal having substantially the same frequency as the pilot signal is also input to the phase comparator circuit (22) from the VCO (21).

When the phase synchronization of both signals is obtained, V CO
The signal from (21) is equal to the pilot signal and has a constant amplitude. This phase-synchronized signal is input to the other input terminal (15b) of the homodyne detection circuit (10).

As a result, when the entire signal doubles due to amplitude variation, the output is.

Therefore, the output can be doubled.

"Effects of the Invention" As described above, the present invention uses a pilot signal extracted from a signal wave as a reference frequency input, synchronizes the phase of the oscillation signal of the vCO with this, and outputs the output of the vCO at this time as the other input of the homodyne detection circuit. Since it is applied to the terminal, even if the amplitude fluctuation of the input signal doubles due to fusing in the propagation path, the output fluctuation is suppressed to twice as much, and the clarity of the detected and demodulated audio signal is greatly improved. will be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an AM detection circuit according to the present invention, and FIG. 2 is a block diagram of a conventional circuit. (1)... Antenna, (2)... Receiving section, (3)...
...High frequency amplifier circuit, (4)...Mixing circuit, (5)
(6)...Intermediate frequency amplifier circuit, (7)...AGC circuit, (8)...Homodyne detection section. (9) (11) (13) (20)... Amplifier circuit, (10)... Homodyne detection circuit, (12)...
Filter circuit, (14)...Pilot signal extraction circuit, (15a)...One input terminal, (15b)...
The other input terminal, (16) (23)...LPF, (
17)...Low frequency amplifier circuit, (18)...Speaker, (19)...PLL circuit, (21)...VC
Ol(22)...Phase comparison circuit.

Claims (1)

[Claims] (1) Add an AM signal with a pilot signal to one input terminal of the homodyne detection circuit, add the pilot signal extracted by the pilot signal extraction circuit to the other input terminal of the homodyne detection circuit, and extract from these signals. In an AM detection circuit configured to demodulate a modulated signal, the pilot signal input as a reference signal and a signal from the voltage controlled oscillation circuit are provided between the pilot signal extraction circuit and the other input terminal of the homodyne detection circuit. and a PLL circuit for inputting the output of the voltage controlled oscillation circuit to the homodyne detection circuit when phase synchronization is obtained. .