JPH073957B2 - SSB receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention provides a high-quality SSB communication system using an amplitude limiter that extracts a real zero for eliminating amplitude fluctuations due to fading. The present invention relates to a device for obtaining a demodulated signal.

(Prior art) In the SSB communication method, since the amplitude information component exists in the modulated wave, it is necessary to use an AGC (automatic gain control circuit) on the receiving side in order to equalize the amplitude fluctuations that occur in the mobile propagation path. .
However, it is difficult to operate the AGC stably for high speed and deep fading, and improvement of transmission characteristics under fading is a major issue. In order to solve this, according to Japanese Patent Application No. 59-259354, Japanese Patent Application No. 60-82530, etc., the transmitting side performs SSB modulation with an information signal, then adds a carrier wave to this and transmits it, and the receiving side transmits the signal. After receiving the signal, the amplitude of the received signal is made constant by using the amplitude limiter that extracts the Real Zero, and then frequency detection is performed.
An SSB communication method was proposed.

(Problems to be Solved by the Invention) Although this method can remove the distortion added in the transmission line by using the amplitude limiter, since harmonic distortion occurs due to frequency detection, it is necessary to remove it. Therefore, Japanese Patent Application Sho 61
In -008111, a circuit for removing second-order distortion and third-order distortion of a detection output signal by using a Hilbert transformer is proposed. In this distortion elimination circuit, the delay amount of the Hilbert transformer was set to be sufficiently small. Therefore, for example, if the Hilbert transformer is composed of a high-order digital filter using digital signal processing, the delay amount becomes extremely large and the distortion is canceled out. There was a flaw that I could not do. Further, in the integrator, if there is an offset voltage at the input end due to the incompleteness of the operational amplifier that constitutes the integrator, this has the drawback that it is integrated and the DC drift of the output increases.

In order to solve the above-mentioned problems, the present invention provides an SSB receiving device that removes harmonic distortion and obtains high-quality transmission characteristics.

(Means for Solving the Problems) The feature of the present invention for achieving the above-mentioned object is to add a carrier wave to a signal SSB-modulated with an information signal to form a transmission signal on the transmission side, and on the reception side, In the SSB communication system that demodulates by frequency detection after adjusting the amplitude with an amplitude limiter that extracts the real zero after receiving the transmission signal, the integrator and the integrator that integrate the frequency-detected signal A DC drift elimination circuit that eliminates the generated DC fluctuation component, a high-pass filter that has a linear phase characteristic that eliminates out-of-band noise, and the amplitude of unnecessary signals such as click noise due to fading exceeds a certain level,
It has an amplitude limiter that limits its amplitude to a certain amplitude and operates linearly below a certain level, and a distortion removal circuit that removes harmonic distortion, and these are connected in cascade to restore the information signal. It is in the SSB receiver.

Further, the distortion removal circuit limits the amplitude when the Hilbert converter that converts the input signal to a Hilbert converter, a delay circuit that equalizes the delay amount of the Hilbert converter, and an amplitude limit when the output amplitude of the Hilbert converter exceeds a certain level. An amplitude limiter that operates linearly below a level is provided, and an amplitude limiter that operates linearly below a certain level is provided when the output amplitude of the delay circuit and the output amplitude of the Hilbert converter exceeds a certain level. A first multiplier for multiplying with the output of the amplitude limiter, which limits the amplitude when the output amplitude of the Hilbert converter exceeds a certain level, and outputs a linear operation when the output amplitude of the Hilbert transformer exceeds a certain level. A second multiplier that performs multiplication with the output of the first multiplier, a first amplifier that halves the output level of the second multiplier, a cuber that cubes the output of the delay circuit, three The vessel output level 1/6 multiplied second
The second amplifier, the delay circuit output, the first amplifier output, the adder circuit for adding the inverted output of the first multiplier and the inverted output of the second amplifier.

(Embodiment) FIG. 1 is an embodiment of the present invention, in which 1 is a demodulation signal input terminal, 2 is an integrator, 3 is a DC drift elimination circuit, and 4 is a high frequency band of a linear phase characteristic for eliminating out-of-band noise. Pass filter,
Reference numeral 5 is an amplitude limiter that limits the amplitude when the output level of the high-pass filter exceeds a certain value, and operates linearly below a certain value, 6 is a distortion removing circuit, and 7 is a demodulation signal output terminal.

The frequency-detected signal is input to the demodulation signal input terminal 1, and this signal is input to the integrator 2. The DC drift removing circuit 3 removes the DC fluctuation component superimposed on the output signal of the integrator 2.
And outputs the output of the DC drift removing circuit 3 to a high-pass filter 4 having a linear phase characteristic for removing noise outside the band, and when the output level of the high-pass filter exceeds a certain value. The amplitude is limited, and when the value is equal to or less than a certain value, it is input to a distortion removing circuit 6 that removes high frequency wave distortion through an amplitude limiter 5 that operates linearly, and a demodulation signal output terminal 7
Take out more.

The integrator 2 in FIG. 1 integrates the signal time-differentiated by the frequency detector and reproduces it as a signal having phase information. From the principle of frequency detection, the phase component is time-differentiated to extract a component proportional to the frequency change. Therefore, in order to obtain the phase information, it is necessary to obtain the phase component by integrating the frequency-detected signal.

This configuration is the same circuit configuration as that using a frequency detector and an integrator for phase demodulating a phase-modulated signal. At this time, the signal component is represented by the sum of the fundamental wave component and the second or higher harmonic components. The integrator made up of operational amplifiers has an offset voltage at the input of the operational amplifier.
This DC voltage is integrated and DC drift occurs in the integrator output. The DC drift changes the DC bias of the multiplier that constitutes the distortion removing circuit 6, and therefore adversely affects the harmonic distortion removing characteristics of the distortion removing circuit 6. The DC drift removing circuit 3 removes only the DC drift, and passes the fundamental wave component and second and higher harmonic components. Furthermore, the high pass filter 4
The noise outside the band and the DC drift that could not be removed by the DC drift removing circuit 3 are removed by passing the noise to the outside. Since DC drift adversely affects harmonic distortion removal characteristics, it is desirable to reduce DC drift as much as possible. As shown in FIG. 2, the DC drift elimination circuit 3 divides the output of the buffer amplifier circuit 9 into two parts, one of which is input to the subtraction circuit 11 and the other of which is input through the low-pass filter 10 so that fluctuation components are mutually generated. It is configured to offset. The integrator 2 extends the frequency characteristic to a reduction (1 Hz or less) so that the phase characteristic has a linear relationship with the frequency in order to remove harmonic components generated by the frequency detection as much as possible. Therefore, the DC drift removing circuit 3 alone cannot completely remove the DC drift. Therefore, the high pass filter 4
In addition, the DC drift is completely removed by using together with to remove the harmonic distortion. The high-pass filter 4 needs to have a linear phase characteristic in order for the distortion removing circuit 6 to remove higher-order and higher-order harmonic components.

When the receiver input level is below the threshold,
Since click noise occurs in the frequency detection output, the output signal of the high-pass filter 4 can be represented by the sum of the fundamental wave component, the second or higher harmonic components and the impulsive noise component. When this impulsive noise is input to the distortion removing circuit 6, it exceeds the dynamic range of the distortion removing circuit 6, so that the harmonic distortion removing characteristics deteriorate. Therefore, when the output level of the high-pass filter 4 exceeds a certain value, this level is limited to a certain value, and below that, the amplitude limiter 5 for extracting an output proportional to the input level is input to the distortion removing circuit 6. Will be needed. The DC drift removal circuit 3 removes DC drift, the high-pass filter 4 removes out-of-band noise, and the amplitude limiter 5 limits the level of impulsive noise to a constant value, thereby stabilizing the distortion removal circuit 6. Can be operated.

FIG. 2 is a block diagram of the DC drift elimination circuit 3 of the embodiment of FIG. 1 of the present invention, in which 8 is a DC drift elimination circuit input terminal, 9 is a buffer amplifier circuit, and 10 is a low frequency band through which only the DC fluctuation component passes. A pass filter, 11 is a subtracting circuit, and 12 is a DC drift removing circuit output terminal. The output signal of the integrator 2 of FIG. 1 having a DC fluctuation component is input to the DC drift elimination circuit input terminal 8, divided into two via the buffer amplification circuit 9, one of which is directly input to the subtraction circuit 11, and the other is reduced. Pass filter 10
And is input to the subtraction circuit 11. The output signal of the subtraction circuit 11 from which the DC fluctuation component is removed is the DC drift removal circuit output terminal.
Take out from 12.

FIG. 3 is a block diagram of the distortion removing circuit 6 according to the embodiment of FIG. 1 of the present invention. 13 is an input terminal of the distortion removing circuit, 14 is a Hilbert transformer, and 15 is a delay amount of the Hilbert transformer. Delay circuit, 16 is an amplitude limiter that limits the amplitude when the output of the Hilbert transformer exceeds a certain level, and operates linearly below a certain level, 17, 18 is a multiplier, 19 is a cuber, 20 and 21 are An amplifier, 22 is an adding circuit, and 23 is a distortion removing circuit output terminal.

Amplitude limiting is performed when the output level of the high-pass filter 4 having the linear phase characteristic of FIG. 1 exceeds a certain value, and the output signal of the amplitude limiting circuit 5 that operates linearly at a certain value or less is converted into the distortion of FIG. The signal is input to the elimination circuit input terminal 13, and the signal is divided into two and input to the Hilbert transformer 14 and the delay circuit 15 for equalizing the delay amount of the Hilbert transformer. The delay amount of the delay circuit 15 is set to be equal to the delay amount of the Hilbert transformer 14. The output of the Hilbert transformer 14 limits the amplitude when the output level of the Hilbert transformer 14 exceeds a certain value, and inputs it to the amplitude limiter 16 that operates linearly below a certain value, and divides the output into two. , Multiplier 17, and multiplier 18. Also, the output of the delay circuit 15 is divided into three, and the multiplier 17,
Input to the cuber 19 and the adder circuit 22. The output of the multiplier 17 that multiplies the output of the delay circuit 15 and the output of the amplitude limiter 16 is divided into two and input to the multiplier 18, and the adder circuit 22
Invert and enter. Output of multiplier 17 and the amplitude limiter
The output of the multiplier 18 that performs multiplication with the output of 16 is input to the adder circuit 22 via the amplifier 20 of gain 1/2. The output of the cuber 19 that cubes the output of the delay circuit 15 is inverted through an amplifier 21 with a gain of 1/6 and input to an adder circuit 22. The adder circuit 22 adds the output of the delay circuit 15, the output of the amplifier 20, the inverted output of the multiplier 17, and the inverted output of the amplifier 21. The output signal of the adder circuit 22 is taken out from the distortion elimination circuit output terminal 23.

The operation principle of the distortion removing circuit is described in Japanese Patent Application No. 61-008111.

(Effects of the Invention) As described above, by using the circuit of the present invention, the DC drift of the integrator output can be removed, and by removing the second-order distortion and the third-order distortion, a high-quality SSB demodulated signal can be obtained. There are advantages.

[Brief description of drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a DC drift elimination circuit, and FIG. 3 is a block diagram of a distortion elimination circuit. 1 ... Demodulation signal input terminal, 2 ... Integrator, 3 ... DC drift elimination circuit, 4 ... High-pass filter, 5 ... Amplitude limiter, 6 ... Distortion elimination circuit, 7 ... Demodulation signal output Terminal, 8 ... DC drift elimination circuit input terminal, 9 ... Buffer amplification circuit, 10 ... Low pass filter, 11 ... Subtraction circuit, 12 ... DC drift elimination circuit output terminal, 13 ... Distortion elimination circuit input Terminal, 14 …… Hilbert transformer, 15 …… Delay circuit, 16 …… Amplitude limiter, 17,18 …… Multiplier, 19 …… Square multiplier, 20,21 …… Amplifier, 22 …… Adding circuit, 23 …… Distortion elimination circuit output terminal.

Claims (2)

[Claims] 1. A transmitting side adds a carrier wave to an SSB-modulated signal with an information signal to form a transmitting signal, and a receiving side
In the SSB communication system in which after the transmission signal is received, the amplitude is limited by an amplitude limiter for extracting the real zero (Real Zero) and then demodulated by frequency detection, an integrator for integrating the frequency-detected signal and an integrator DC drift removal circuit to remove the DC fluctuation component generated in, high-pass filter having a linear phase characteristic to remove out-of-band noise, if the amplitude of unwanted signals such as click noise due to fading exceeds a certain level, The amplitude is limited to a constant amplitude, and has an amplitude limiter that operates linearly below a certain level, and a distortion removal circuit that removes harmonic distortion,
An SSB receiver characterized by restoring information signals by connecting these in cascade. 2. The DC drift elimination circuit includes a buffer amplifier circuit, a reduction pass filter connected to the output thereof, and a subtraction circuit having the output of the buffer amplifier circuit and the output of the low pass filter as inputs. The SSB receiving apparatus according to claim 1, further comprising: