JPS58146163A - Modulator - Google Patents

Abstract

PURPOSE:To reduce the amplitude error of a modulator with a simple constitution, by making the temperature characteristic of a data signal amplifier equal to that of a reference voltage generating circuit, and inputting a data signal through the amplifier and an output of a reference voltage generating circuit to each modulation input terminal of the modulator. CONSTITUTION:A binary data signal inputted to an input terminal 1 is amplified at an amplifier 2, passes through a low pass filter 3 and a buffer circuit 4 and this output is applied to an input terminal 10 of a biphase modulator 8. Further, a reference voltage generating circuit 5 has the same temperature characteristic as that of the amplifier 2, and the output is attenuated at an attenuator 2, passes through a buffer circuit 4' and is applied to an input terminal 9 of the modulator 8. Even if the output of the amplifier 2 and the buffer circuit 4 is fluctuated due to temperature change, since the output of the circuits 5 and 4' is changed equally, a voltage between input terminals 9 and 10 of the modulator is unchanged, and the temperature characteristics of the modulator 8 are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulation device used in a digital multilevel multiphase modulation system.

At present, a carrier wave digital transmission system using @: harmonic in polyphase P8 has already been put into practical use, but recently, in order to make effective use of frequency, not only the phase plane but also the amplitude plane has been changed at the same time. A multilevel polyphase modulation method is being considered, and 116QAM (Quadrat
ure Amplitude Modulation)
The method is known. This 16QAM system increases the amount of information, but on the other hand, the performance required of the circuit becomes stricter, and the 16QAM system also requires stricter performance from the modulation device that constitutes it, especially its characteristics against temperature fluctuations.

Conventionally, as a two-phase change 11 device, there is one shown in the block diagram of FIG. In the figure, 1 is the theta polarization input terminal, 2 is the amplifier, 3 is the low-pass filter, 4 is the buffer circuit, 7 is the carrier signal input terminal, 8 is the linear 〇-π modulator 9 and 10 are the modulation A data input terminal 11 of the device 8 indicates a modulated wave output terminal r.

As shown in the characteristic diagram of FIG. 2, the linear 0-π modulator 8 used here has a linear characteristic sound as shown by straight line A as a drive level vs. output level characteristic, and a linear characteristic sound as a drive level vs. output phase characteristic. Standard level ■T like curve B
It shall have a phase reversal characteristic in which the polarity is mutually reversed with respect to the center t. The 2filF data signal input to the input terminal 1 is amplified by the amplifier 2, the signal is band-limited by the low-pass filter 3, and the buffer circuit 4 converts the signal to a drive level aor'' as shown in FIG. o (at this time a01”
0 drive level difference? ) is added to the variable v8i8, the modulated wave output terminal 11 has an output level a1. −
It becomes a two-phase modulated signal with a1k. If a DC drift ΔV7 occurs in the amplifier 2 and buffer circuit 4 due to temperature fluctuations, the drive level difference V is
2 + '-32), at this time the output level a3+
-33, resulting in an output level error Δ■'. Therefore, the average level of the drive level aQ+-"O is T
appears to have moved by Δ■, and an amplitude error [occurs] in the two-phase modulated signal. The influence of this DC drift Δ■ becomes greater as the modulation becomes more multi-valued. For example, in a 16QAMf modulator, it is influenced in the following way.

FIG. 3 is a block diagram of a conventional 16QAM f-key fjlt. In the figure, 1.1' is a data signal input terminal, 8,
12 is a linear 〇-π modulator, 13 is a π/2 phase shifter, 14
Is it a synthesizer? show. A data signal is supplied to the data signal input terminal 1 on the CH1 side and the data signal input terminal 1' on the CH2 side, amplified by each amplifier 2, band-limited by each low-pass filter 3, and passed through each buffer circuit 4. 7]0 to the linear 0-πfv4 units 8 and 12, respectively.

- 10,000, the carrier wave signal input to the carrier wave input terminal 7 is modulated into a P signal by a linear 0-π modulator 8, and is also modulated by a linear 0-πf modulator 12 via an on-board phase shifter 13. The signal is modulated into a Q signal that is orthogonal to the P signal, and is supplied to the combiner 14, and orthogonally combined with the P and Q signal combination word 14.

Here, if the input data signals of CHI and CH2 are given to 41 and the four-value signal r drive level of ±a and ±b in FIG. 2 is used, then the data arrangement as shown in FIG. A 16-square QAM modulated signal as shown in the figure is obtained.However, if a DC drift ΔV7 occurs in the amplifier 2, buffer circuit 4, etc. due to temperature fluctuations, etc.
The drive level ±a (1 (level difference ■) in Figure 2 is PC
By shifting by the DC drift ΔV on the H side, the drive level becomes v'. Then, as the black point shifts to the white point in Figure 4, the output level becomes ±83 and the output level error Δ
(2), and therefore a phase error Δθ and an amplitude error ΔA2 occur. For example, if ±31 [±100 mV, Δθ
= 2° lΔA = 0, Δ■ to suppress within 2 dB
' must be kept within ±5mV. Also, PC
If the drive level of both H and QCH shifts by Δ■,
In the worst case, it is necessary to suppress the voltage to within about 2.5 mV.

As described above, the more the multi-level, multi-phase modulation method is used, the more DC drift in the drive level must be suppressed. Although it is very difficult to suppress the DC drift generated in the amplifier 2 and the buffer circuit 4, there is a modulation device that overcomes this and has good temperature characteristics. Figure 5 is a block diagram of a two-phase modulation system like this, and 2' in the figure is a differential amplifier that takes out two output chips with different polarities. show. 2 input to input terminal 1
The value data signals are made into mutually opposite phase signals by the differential amplifier 2'. This time difference increase @W2' is balanced by having opposite phases to each other so that the signal VtW width is adjusted so as not to cause DC drift ΔV7.

These data signals having mutually opposite phases are band-limited by the low-pass filter 3 and supplied to the fv4 unit 8 from the data signal input terminals 9 and 10 via the buffer circuit @4. When a carrier signal is applied from terminal 7, a two-phase modulated signal is output to modulated wave output terminal 11.

Since the converter 48 is driven by input signals balanced in this manner, DC drift occurring in the differential amplifier 2 and the buffer circuit 4 does not cause an amplitude error or a phase error r. Then, the drive level A is applied to the data signal input terminal 9 of the f adjuster 8. is applied, the drive level -a is applied to the other data signal input terminal 10 due to the reverse phase relationship. has been added.

Therefore, even if the DC drift Δ■ is applied to each input, the drive level of the terminal 9 is a0+Δ■, and the drive level of the terminal 10 is -a. -ΔV, so the average level 7 of the drive level aO* ao does not change. In this way, even if the DC offset Δ■ occurs and the drive level varies from ±ao to ±(ao+ΔV), no amplitude error occurs, so a modulation device with good temperature characteristics can be realized.

However, in such a V4 modulation device, the number of low-pass filters is two in a 2-phase V modulation system and four in a 16QAM modulation system, which is twice as low as in the cases of Figures 1 and 3. Area filter? It depends on what you need. In order to improve the convergence of the modulated wave spectrum, this low-pass filter needs to have a strict selection characteristic in order to improve the convergence of the modulated wave spectrum, in view of the effective use of the frequency band used in digital microsystems in recent years. It has become quite complex, and the number of times and scale has also increased. Therefore, using twice the low-pass filter exposure has the disadvantage of increasing cost and increasing the circuit scale.

SUMMARY OF THE INVENTION An object of the present invention is to provide a modulation device that eliminates the above-mentioned drawbacks, has good temperature characteristics, has a simple circuit, and has a small circuit scale.

The modulator of the present invention controls the output level of a predetermined carrier wave so that it is proportional to the voltage supplied between two input terminals, and adjusts the phase of the carrier wave around a predetermined reference voltage. A modulator that inverts each other's output, an amplifier that amplifies the input data signal,
The output signal of this 111 width amplifier is band-limited and supplied to one input terminal of the modulator, and the low-frequency P-wave generator has the same temperature characteristics as that of the Indo-I amplifier. A reference voltage circuit that outputs the same voltage R, and an attenuator that gives substantially the same attenuation to the output voltage of the reference voltage circuit as that of the low frequency door filter and supplies it to the other input terminal of the modulator. .

The present invention will be described in detail below with reference to FIG.

FIG. 6 is a block diagram of one embodiment of the present invention.

In the figure, the same numbers as in FIGS. 1 to 5 indicate the same configuration elements, 5 is a reference voltage generation circuit having a temperature characteristic r equivalent to that of the amplification 'g9!2, and 6 is a low-pass filter 3. These attenuators have the same amount of attenuation for the DC component. The binary data signal input to the input terminal 1 is amplified by the amplifier 2, and the data signal passes through the low-pass filter 3 and is applied to the buffer circuit @4.
is applied to the modulator 80 input terminal 10. - 10,000, the DC voltage generated by the reference voltage generation circuit 5, which has temperature characteristics equivalent to that of the amplifier 2, is attenuated by the attenuator 6, and then passes through the buffer circuit 4 and is applied to the input terminal 9 of the modulator 8. At this time, drive level a0. -a, (at this time, the drive level difference is 7V) becomes 2 [signal is applied to terminal 10, and drive level a is applied to terminal 9. .

When the carrier wave signal is input to the terminal 7 with the addition of the 7 average levels of -ao, the VJ 4 converter (mixer) 8 is driven,
The terminal 11 has an output level a1. A two-phase modulated signal with −31 k is obtained. Here, even if the drive level "Oe" applied to the terminal 10 varies by Δ■ due to temperature fluctuations etc., the reference voltage generation port W115, the attenuator 6 and the buffer circuit 4 Since the voltage Vd applied to the output terminal 9 also varies by ΔV, no amplitude error occurs in the two-phase modulation signal. This reference voltage generation port%
5, the same circuit as amplifier 2 is used, and the output voltage is
A can be used.

FIG. 7 is a block diagram of an implementation sequence applied to the 'k16QAM & adjustment device of the present invention. CH1ggl data signal input terminal 1. CH291] The data signal supplied from the data signal input terminal 1' is amplified by the amplifier 2, and then passed through the low-pass filter 3.
and a linear O-π phase adjuster 12 via a buffer circuit 4. - 10,000, the DC voltage generated by the reference voltage generation circuit 5, which has a temperature characteristic r equivalent to that of the amplifier 2, is attenuated by the attenuator 6, and is passed through the buffer circuit 4r to the V linear O-π phase modulators 8, 12. available. The carrier wave signal inputted to the carrier wave input terminal 7 is supplied to a linear 0-πf modulator 8 and a linear 0-π modulator 12 via a πh phase shifter 13r. The Q signal is orthogonally combined by the combiner 14.

These linear O-π-π devices 8.12 have the characteristic t shown in FIG.
Using the input data signals of CH1 and CH2, the output signal of the synthesizer 14 is 16QAM modulated as shown in the data arrangement diagram of FIG. I get a signal. Here, even if a DC drift ΔV-2 occurs in the amplifier 2 and the buffer circuit 4 due to temperature fluctuations, the reference voltage generation circuit 5, attenuator 6, and buffer circuit 4 will have the same DC drift ΔVi as p1.
is causing it. Really% b# “ILb4
The drive level of the plate is input, and the drive level is D.
Even if the C drift Δ■ changes, the reference voltage generation circuit 5,
It is generated by an attenuator 6 and a buffer circuit 4. -b, -a,
By moving the average level of 4[■TtΔ■ of a and b! '%The data arrangement of the 16QAM modulated signal does not change.

Here, there are separate reference voltage generation ports on CHI and CH2 sides @r
However, the voltage generated in one circuit is changed by 11 transformers8.1
A similar effect can be obtained even if it is added in common to 2.

As described above, the modulation device according to the present invention requires only intermediate low-pass filtering compared to the conventional modulation device, so that the circuit can be configured to be simple and small in scale while also having good temperature i characteristics.

Although the embodiments of the present invention have been described with respect to a two-phase variable iti device and a 16-value quadrature amplitude modulation device, the present invention can also be applied to other multilevel polyphase modulation devices.

[Brief explanation of drawings]

@Figure 1 is a block diagram of a conventional two-phase modulator, and Figure 2 is 1.
Figure 3 shows the characteristic diagram of @type 〇-π phase shifter 14.
6 [Block diagram of quadrature amplitude modulation device, Figure 4 is a data arrangement diagram of 16-value quadrature amplitude @f14 wave, Figure 5 is a block diagram of an improved conventional two-phase modulation device, and Figure 6 is a diagram of the improved conventional two-phase modulation device. FIG. 7 is a block diagram of a 16-cage quadrature amplitude modulation device of an embodiment according to the present invention. In the figure, 1.1'...data signal input terminal, 2
......Amplifier, 2'...Differential amplifier, 3
...Low-pass filter, 4...Buffer circuit, 5...Reference voltage generation circuit, 6...Attenuator, 7...・Carrier signal input terminal, 8.12・
...Linear type 〇-π phase modulator, 9.10...
...Modulator data signal input terminal, 11...Modulated wave output terminal, 13...Phase shifter, 14...
...It is a synthesizer. W.11 Raid

Claims (1)

[Claims] The output level kfl! of a given carrier is proportional to the voltage supplied between the two input terminals. A modulator that outputs a carrier wave whose phase is inverted with respect to a predetermined reference voltage r, and an input data signal ? an amplifier for amplification, a low-frequency ν wave amplifier that limits the band of the output signal of this amplifier and supplies it to one input terminal of the FG unit, and has a temperature characteristic similar to that of the amplifier and is substantially equal to the reference voltage. A modulation device including a reference voltage circuit that outputs the same voltage, and an attenuator that gives substantially the same attenuation to the output voltage of the reference voltage circuit as that of the low-frequency p-wave generator and supplies it to the other input terminal of the modulator. .