JP2584023B2 - Quadrature two-phase modulator - Google Patents

Description

The modulator of the present invention generally transmits information as a means for modulating a color signal of a television signal or a color signal of a home VTR, for example. Alternatively, the present invention relates to a quadrature two-phase modulator widely used for recording.

2. Description of the Related Art FIG. 4 shows a basic configuration of a conventional quadrature two-phase modulator used as a color signal and signal processing in television signal transmission. Two modulated signals I and Q
Is a chrominance signal, which is a chrominance subcarrier SC and a signal whose phase is shifted by -90 ° by the -90 ° phase shifter 11.
The carrier is suppressed by 3 and amplitude modulation is performed, and their outputs are added by an adder 14 and taken out as a quadrature two-phase modulation output. By the way, recently, with the improvement of the miniaturization technology of semiconductor devices and the advance of digital circuit technology, digital circuits that have been conventionally realized by analog circuits are being replaced. FIG. 5 is a schematic circuit configuration block diagram of a digital circuit of the signal processing shown in FIG. 4 as it is. The modulated signals DI and DQ are digital data obtained by digitizing the color difference signals.

The waveform data generator 21 generates numerical data obtained by sampling a sine wave corresponding to a subcarrier at a constant period, and outputs waveform data having phases different from each other by 90 °. The multipliers 22 and 23 multiply the modulated data D1 and D2 by the waveform data, respectively, and perform the same function as the balanced modulator of FIG. The multiplied data is numerically added by an adder 24 and output as a quadrature two-phase modulated signal via a D / A modulator 25.

However, the configuration shown in FIG. 5 merely replaces the conventional analog circuit with a digital circuit as it is, and requires two multipliers. The scale becomes large, which is disadvantageous in terms of circuit configuration and integration.

Means for Solving the Problems According to the present invention, a first subcarrier (A), which is a sine wave having a first predetermined cycle, and a second subcarrier having the same cycle and the same waveform as the first subcarrier and having a 90 ° phase difference. Waveform data generating means (1) for generating digital data (a) of a subcarrier alternately sampled at a second predetermined period smaller than the first predetermined period, and two subcarriers (B). Modulated signal (I,
Multiplying means (2) for alternately inputting the digital data of Q) in synchronization with the second predetermined period and multiplying the digital data of the two modulated signals by the digital data (b) of the subcarrier; And a D / A converter (3) for digital-to-analog conversion of the output data of the multiplier, and a filter (4) for removing unnecessary components from the output signal of the D / A converter.

According to the configuration of the present invention, the multiplication process of the first subcarrier A and the modulated signal I and the multiplication process of the second subcarrier B and the modulated signal Q are performed by one multiplication unit 2 to perform the second multiplication process. Is performed every predetermined period (sampling period), and an output signal of quadrature two-phase modulation is obtained as an output obtained by D / A converting and filtering the output of the multiplying means 2. Then, two modulated signals required for multiplication can be processed on the same transmission line, and the circuit can be simplified.

Embodiment Next, an embodiment of a quadrature two-phase modulator according to the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of one embodiment of the present invention.

In FIG. 1, a waveform data generating means 1 includes a first sub-carrier which is a sine wave having a first predetermined period, and a second sub-carrier having the same period and the same waveform as the first sub-carrier and having a phase difference of 90 °. Are alternately sampled at a second predetermined period smaller than the first predetermined period to generate subcarrier digital data.

The multiplication means 2 has two modulated signals (I and Q in FIG. 2).
Are input alternately in synchronization with the second predetermined period, digital data of a subcarrier generated by the waveform data generating means 1 is input, and digital data of two modulated signals and digital of a subcarrier are input. This is to multiply by the data.

The D / A conversion means 3 performs digital-to-analog conversion of the data output from the multiplication means 2, and includes a filter 4
Removes unnecessary components from the D / A-converted signal.

Next, the operation of the apparatus of the embodiment shown in FIG. The waveform a in FIG. 2 is a representation of the digital data output from the waveform data generating means 1 in an analog manner. A rectangular wave indicated by a thick line indicates the sampled digital data of the output, and a thin line indicates the thin line. The two sine waves (A, B) having 90 ° phases different from each other indicate the waveform of the subcarrier before being sampled. The waveform b is a digital representation of the digital data of the modulated signal input to the multiplying means 2 in an analog manner. The modulated signals I and Q are alternately input at the same cycle as the sampling cycle of the waveform a in FIG. Is done. The waveform c is a waveform indicating the result of multiplying the modulated signal waveform b by the wavemeter a corresponding to the subcarrier. The waveform d after the D / A conversion is also in phase with c. A waveform e is a D / A conversion output waveform after the sampling cycle and its harmonic components have been removed by the filter 4. Thus, a quadrature two-phase modulation output e can be obtained.

FIG. 3 is a circuit configuration block diagram showing another embodiment of the present invention. For example, Pal (PAL: Phase Alternation Li
ne) television signal, the sub-carrier frequency of the chrominance signal is 4.43 MHz, and two color difference signals I (for example, BY) and Q
(For example, RY) are transmitted at the same time, but the subcarrier phase of this (RY) signal is switched every horizontal period. This can be realized by adding a waveform phase control means 6 for controlling one waveform phase of the waveform data generating means 1 with the horizontal synchronization signal _H shown in FIG. Other configurations are the same as those in FIG.

In a home VTR, for example, a VHS system VTR, for example, as shown in JP-B-56-9073, the NTSC system rotates a 90 ° phase for each horizontal period, and also for each track. A method (PS method) of changing the rotation direction is adopted.

Also in this case, the horizontal synchronizing signal and the rotation information (30 Hz) of the rotating drum are controlled by the waveform phase control means 6 shown in FIG.
Can be used to control the phase of the waveform data generating means 1.

In the above example, the waveform data generating means and the multiplying means are shown in a functional block diagram. However, it is needless to say that a software configuration using a microprocessor or the like is also possible.

As described above, according to the present invention, the multiplication process of the first subcarrier A and the modulated signal I and the multiplication process of the second subcarrier B and the modulated signal Q are the second process. Since the modulation is performed every predetermined period (sampling period), two modulated signals required for multiplication can be processed on the same transmission line. Moreover, since the signal processing is a digital method, there is no variation and no change with time. A stabilized quadrature two-phase modulator can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a circuit configuration of a quadrature two-phase modulator according to an embodiment of the present invention, FIG. 2 is a waveform diagram after each processing means for explaining the operation of the circuit shown in FIG. 1, and FIG. FIG. 4 is a circuit configuration block diagram of a conventional device, and FIG. 5 is a schematic circuit configuration block diagram when the conventional example is directly replaced with digital processing. . 1 ... waveform data generating means, 2 ... multiplying means, 3 ... D /
A conversion means, 4 ... filter, 5 ... waveform phase control means.

Claims (1)

(57) [Claims] 1. A first subcarrier which is a sine wave having a first predetermined period and a second subcarrier having the same period and the same waveform as that of the first subcarrier and having a phase difference of 90.degree. Waveform data generating means for generating digital data of a sub-carrier alternately sampled at a second predetermined period smaller than the predetermined period; and digital data of two modulated signals alternately synchronized with the second predetermined period. Multiplying means for multiplying the digital data of the two modulated signals and the digital data of the sub-carrier by inputting; D / A converting means for performing digital-to-analog conversion on output data of the multiplying means; A quadrature two-phase modulator comprising a filter for removing unnecessary components from an output signal of the conversion means.