JPH02280540A - Modulation circuit - Google Patents

Abstract

PURPOSE:To form a modulation signal independently from 2 kinds of signals by providing an adding circuit to apply FM modulation to a carrier signal with a 2nd signal before the input to a PSK modulator and fixing the 2nd signal to a prescribed value when the carrier signal is subjected to PSK modulation and outputted by a 1st signal. CONSTITUTION:A 1st switch circuit 17 is closed to switch the movable contact of a 2nd switch circuit 22 to a fixed contact at the earth side and an analog voice signal AS is supplied to an input terminal 16. A carrier signal Asin((omega+delta)t) FM-modulated by an analog voice signal AS is generated from a voltage controlled oscillator 14 and fed to modulators 24, 25. In the case of transmitting a digital data DD, the 1st switch circuit 17 is opened to switch the movable contact of a 2nd switch circuit 22 to the fixed position at a high level logic '1' to supply the digital data DD to the input terminal 18. Since regular carrier signals Asinomegat and Acosomegat are supplied respectively to the modulators 24, 25, a QPSK modulation signal 27 whose center frequency is 140MHz is generated from a band pass filter 28.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a modulation circuit suitable for use in, for example, a satellite communication system.

[Summary of the invention]

The present invention provides a modulation circuit suitable for use in, for example, a satellite communication system, in which a P
LL circuit, a PSK modulator that PSK-modulates this carrier signal with a first signal and outputs it, and
and an additional circuit for FM modulating the carrier signal with the second signal before inputting it to the SK modulator, and when the carrier signal is PSK modulated with the first signal and outputted, the "!2 signal is When fixing the output signal of the PSK modulator to a predetermined value and outputting the FM modulated carrier signal using the second signal, fix the 11 signals to a predetermined value and extract the output signal of the PSK modulator. By extracting the output signal as it is, the PSK modulator can be used in common as an output circuit for the FM modulation signal and PSK modulation signal, making it possible to downsize the entire circuit and reduce costs. It is.

[Conventional technology]

As various business entities have come to own communication satellites, various devices for transmitting information using satellite communication systems are being developed.

Figure 5 shows a news gathering system 5NG (Satellite) using communication satellites as an example of a satellite communication system.
e News Gathering), and this fifth
In the figure, news video and audio signals collected by a vehicle-mounted station (1) are transmitted to a broadcasting center (3) via a transponder of a communication satellite (2).

In this case, in the Ku band, the frequency band of the uplink from the earth station to the communication satellite is, for example, 14 GHz to 14.4 GHz.
The downlink frequency band from the communication satellite to the earth station is, for example, 12.35 GHz to 12.75 GHz. In the uplink, as shown in Figure 6, a frequency band from 14 GHz to 40 MHz is assigned to each repeater for horizontally polarized signals, and the downlink corresponding to Figure 6B is shown in Figure 6C. 12. With a vertically polarized signal like this.
Frequency bands from 35 GHz to 40 MHz are allocated to each.

As mentioned above, since the center frequency interval of each repeater is 40 MHz, the bandwidth of each repeater is < 3 as shown in FIG. 6A.
The frequency is about 6 MHz. On the other hand, the basebands of news video signals and audio signals (FM modulated signals) collected by the in-vehicle station (1) are, for example, the military 6 frequency band (6) (cutoff frequency of about 4.2 MHz) and the frequency band, respectively. (7) (Center frequency 4.51)! It is set to about zz. Then, the baseband signal in Figure 6 is FM
It is modulated and transmitted to the communication satellite (2) on the uplink in the 14 GHz band as a signal on the main channel [8] (FIG. 6A) in the repeater bandwidth.

However, from the beginning, the main channel (8
) signal is likely to cause communication abnormalities, etc., therefore, the narrowband order wire circuit I! shown in FIG. 6A is used in advance. (9)
, (10) Intermediate, IE station (1) and C1 broadcast-tx:/ter (3) are designed to be able to exchange audio signals for meetings. Those order wire lines (9).

Among (10), for example, the order wire line (9) is allocated for transmitting FM audio signals from the center to the local, and the order wire line (lO) is allocated for transmitting FM audio signals from the local to the center. It is being The main channel (8) is used alternately to transmit information from the center to the locals and from the locals to the center. Furthermore, these order wire lines (9) and (10) can be thought of as being allocated to each broadcast station, and are used to check whether the main channel (8) is open or not. Sometimes used for.

[Problem to be solved by the invention]

As mentioned above, conventionally, the main channel (8) that transmits signals with a large amount of information and the order wire lines (9) and (10) that transmit signals with a small amount of information are used in parallel. It is necessary to prepare two types of independent modulators in the vehicle-mounted station (1), which increases the size of the modulators and increases the manufacturing cost. This is a major obstacle to further downsizing the vehicle-mounted station (1) and developing it into a portable mobile station, etc. in the future.

In view of the above, an object of the present invention is to propose a compact modulation circuit that can independently form modulation signals from two types of signals.

[Means to solve the problem]

The modulation circuit according to the present invention is a PLL (Phase Locked Loop) that generates a carrier signal (for example, Δsinωt) from a reference signal, as shown in FIG.
The circuits (12) to (15) and their carrier signals are
P S K (P
a PSK modulator (24) that modulates and outputs the carrier signal
An additional circuit (1
7), and its first signal PS
When outputting K modulation, the second signal is fixed to a predetermined value (for example, 0), the output signal of the PSK modulator (24) is taken out, and the second signal is used to convert the carrier wave signal to F.
When M-modulated and output, the first signal is fixed at a predetermined value (for example, high level rlJ or low level rO), and the output signal of the PSK modulator (24) is taken out as is. .

[Effect]

According to the present invention, by fixing the second signal to a predetermined value, a signal PSK modulated by the first signal is extracted, and by fixing the first signal to a predetermined value, the PSK modulated signal is extracted. A signal FM modulated by the second signal is extracted. Furthermore, since the PSK modulator (24) is also used as an output circuit, the modulation circuit as a whole can be made smaller.

〔Example〕

Hereinafter, an embodiment of the modulation circuit according to the present invention will be explained with reference to FIGS.
Let's explain with reference to FIG. In this example, the present invention is applied to a transmitter for a satellite communication system.

FIG. 1 shows the transmitter of this example, and in this FIG.
11) is a reference oscillator consisting of a highly stabilized crystal oscillator, and this reference oscillator (11) has a stability of 2.5 ppm.
A reference clock pulse with a frequency to of approximately 10 MHz is generated at approximately 10 MHz and is supplied to one input terminal of a phase error detector (PD) (12). This phase error detector (12)
The error signal generated by
) (13) The control signal obtained by filtering is supplied to a voltage controlled oscillator (V CO) (14), and this voltage controlled oscillator (14) changes the frequency f (angular frequency 2πf) in response to the control signal. ω) carrier wave signal As1
n a) Generate t and convert this carrier signal As1nω to N
A signal obtained by dividing the frequency by N in a frequency dividing circuit (15) is supplied to the other input terminal of the phase error detector (12).

These phase error detectors (12), low-pass filters (1
3), voltage controlled oscillator (14) and N frequency divider circuit (15)
From P L L (Phase Locked Loo)
p) The circuit is constructed.

Therefore, if the value of N is set to 14, the carrier wave signal As+nω which is the output signal of the voltage controlled oscillator (14)
The frequency f of t is f = N x fo = 140 (MHz).

In addition, (16) indicates an input terminal, and this input terminal (16)
) is supplied with an analog audio signal As from the outside.

This analog audio signal AS is the same as the audio signal transmitted on the order wire line (lO) in FIG. 6A. Then, the analog audio signal AS is supplied to the manual contact of the first switch circuit (17), and the output contact of this first switch circuit (17) is passed through the low-pass filter (13).
and the input terminal of the voltage controlled oscillator (14). In this case, the analog audio signal AS is band-limited to about 300 tlz to 3.4 kHz, and the cutoff frequency of the low-pass filter (13) is set to 300 tlz to 3.4 kHz.
Set to a value sufficiently smaller than Hz.

Therefore, when the first switch circuit (17) is closed and the analog audio signal AS is injected, the analog audio signal AS is blocked by the low-pass filter (13) and the loop characteristics do not change. (1
The carrier wave signal As1nωt, which is the output signal of step 4), is FM-modulated with the analog audio signal AS. Also, the first
When the switch circuit (17) is opened to reduce the inflow of the analog audio signal As to the PLL circuit to 0, the frequency of the carrier wave signal As1nωt is fixed to N f o.

18 indicates an input terminal, and digital data DD is supplied from the outside to this input terminal (18). This digital data DD includes, for example, video data obtained by digitizing a video signal for news, PCM data of an audio signal for news, and an audio signal for a meeting transmitted on the order wire circuit fi (10) to FIG. The PCM data is configured by time division multiplexing (TDM). Therefore, in this example, the audio signal transmitted on the conventional order wire line can be converted into the analog audio signal AS, and the audio signal transmitted on the order wire line can be converted into PCM data, and the PCM data can also be included in the digital data DD.

In this example, the digital data DD is qua
drature Phase-5hift Keyin
g) Transmit it as a modulated signal. This QPS
In the modulation, the digital data DD is first supplied to the conversion circuit (19).

That digital data DD too b+ b2bs b
n bs..., the modulation circuit (19) divides the digital data DD into 2-bit units, for example, into a data string. It is separated into I-series data consisting of bz b4 . . . and Q-series data consisting of data sequence b+ bs bs . These I series data and Q series data are respectively supplied to one input terminal of the AND gate (20) and one input terminal of the AND gate (21). A second switch circuit (2
2), and connects to the movable contact of this second switch circuit (2).
One fixed contact of 2) is grounded, and the other fixed contact of this second switch circuit (22) is connected to a power terminal (23) to which a DC voltage Vcc corresponding to high level "1" is supplied.
Connect to.

Therefore, by connecting the movable contact of the second switch circuit (22) to the fixed contact on the ground side, the respective output signals of these two switch circuits (20> and (21) are fixed at the low level "0". On the other hand, by connecting the movable contact of the second switch circuit (22) to the fixed contact on the high level "1" side, I series data and Q sequence data is output as is. However, the output signals of (20) and (21) are +1 when the data is high level "1", and -l when the data is low level "mouth".
shall be.

Furthermore, (24) and (25) are carrier suppressed double balanced types, respectively.
The modulator (24) includes a voltage controlled oscillator (
14) is supplied with the carrier wave signal As1n wt, which is the output signal of the modulator (25), and the carrier wave signal As1nωL
A carrier wave signal Acos6Ut is supplied by shifting the phase of the carrier wave signal Acos6Ut by 90° phase shifter 26).

In the modulator (24) the carrier signal ASIII
(A modulation product of IJt and the output signal of the AND gate (20) is generated, and this modulation product is supplied to one input terminal of the adder (27). Then, in the modulator (25), the carrier wave signal is and the output signal of the AND gate (21), and this modulation product is sent to the adder (27).
), and the output signal of the adder (27) is supplied to a bandpass filter (28) whose center frequency is Nfo, that is, 140 MHz, to remove harmonic components.

The movable contact of the second switch circuit (22) is set to high level "
The operation of QPS modulation will be explained with reference to FIG. 3 assuming that the fixed contact on the lj side is connected. First, the modulation product of the modulator (24) is As1n, depending on whether the series data is high level "1" or low level "0".
act or =A sinωL. - side, modulator (25
) is Acosω or −Acosa+t, respectively, corresponding to the Q sequence data having a high level “l” or a low level “mouth”. In this case, if the ■ series data and Q series data are represented by (I, Q), as is clear from FIG. 3, the output signal of the adder (27) is (1, Q).
1,1), it becomes a signal proportional to A31rl(ωt+45°), and when (1°Q) is (0,1), A31rl(ωt+45°) becomes a signal.
It becomes a signal proportional to cos(a+t+45°), and becomes (1
, Q) is <0.0>, -Asin(a+t+4
5'), and (1°Q) becomes (1,0>
When , the signal becomes proportional to -Acos(ωt +45°). Therefore, from the signal modulated to that QPS, I
It can be seen that in order to demodulate the sequence data and Q sequence data, it is sufficient to identify the phase change of the input carrier signal with a resolution of about 90°. And the modulator (24) and (
25) and an adder (27), a modulator is configured in the QPS.

Moreover, since the modulators (24) and (25) can be considered to phase-modulate the carrier signal to 06 and 180'' in 1-bit units, respectively, the modulators (24) and (25) can be considered to phase-modulate the carrier signal to 06'' and 180'', respectively, so that the modulators (24) and (25) can perform BPS (Binary) phase modulation, respectively. PS) can be considered as a modulator.Generally, using PSKRjl will result in low C/
Since information can be transmitted without error even with the N (carrier power/noise power) ratio, the power of the human signal can be reduced by about 8.5 dB compared to FM modulation, so it is particularly suitable for use in mobile stations, etc. .

In FIG. 1, the output signal of the bandpass filter (28) is supplied to a double-balanced modulator (29), and the reference clock pulse is applied to the modulator (29) by a PLL circuit (30).
A carrier wave signal with a frequency of I GHz multiplied by the modulator (29) is supplied to the modulator (31). A carrier wave signal with a frequency of 14 GHz obtained by multiplying the reference clock pulse by a PLL circuit (32) is supplied to this modulator (31).
The 146)lz band modulation product of 1) is supplied to the amplifier circuit (33). The output signal of this amplifier circuit (33) is transmitted to a communication satellite via a transmitting antenna (34). The uplink signal of the 14G)lz band is converted into a downlink signal of the 126)lz band by the communication satellite's core equipment, and is transmitted to the earth station in the pond.

To explain the operation of the example in Figure 1, first, in order to transmit an audio signal for a meeting, the first switch circuit (17) is closed and the movable contact of the second switch circuit (22) is fixed on the ground side. Switch to contact. Then, an analog audio signal AS corresponding to the audio for the meeting is supplied to the input terminal (16). In this case, the voltage controlled oscillator (14) outputs the analog audio signal AS'''QFM modulated carrier wave signal As
1n((ω+δ)1) is generated and this carrier signal is supplied to modulators (24) and (25). Since the AND gates (20) and (21) each output a signal of -1, as is clear from FIG. 3, the adder (27) outputs approximately -As+n((ω+δ) t +45
) is generated.

Therefore, the output signal of this adder (27) is an FM modulation signal (36) with a center frequency of 140M1 (z) shown in FIG. ).

Next, in order to transmit the digital data DD, the first switch circuit (17) is opened and the second switch circuit (22) is opened.
Switch the movable contact to the fixed contact on the high level "1" side. Then, the digital data DD is supplied to the input terminal (18). In this case, it is assumed that the baseband of this digital data DD is the signal (35) shown in FIG. 2C. This signal (35) includes the digital data of the news video signal, the PCM data of the news audio signal, and the PCM data of the audio signal for meetings, etc., which was conventionally transmitted on the order wire line (10) in FIG. 6A. Contains data.

Since the modulators (24) and (25) are each supplied with the regular carrier signal As+nω (and ACO8ωt), the bandpass filter (28) outputs the signal within the repeater bandwidth as shown in FIG. A QPSK modulated signal (37
) is generated. The modulation signal (37) is the 6th QPS
This is the signal corresponding to the main channel (8) to the figure.

Thus, according to this example, the first switch circuit (17)
By simply switching the second switch circuit (22), either a signal FM modulated by the analog audio signal AS or a signal modulated into QPS by the digital data DD can be output from the adder circuit (27). . In this case, any modulation signal is sent to the modulator (24), (25)
Since the signal is outputted from an output circuit consisting of an adder (27) and an adder (27), the output circuit can also be used, making it possible to miniaturize the entire modulation circuit and have the advantage of reducing manufacturing costs.

In particular, in this example, the FM modulation of the carrier wave signal As+n tIJt by the analog audio signal AS is performed by simply adding the analog audio signal AS to the output signal of the low-pass filter (13). 1
The switch circuit (17) is only required, and there is an advantage that the circuit scale can be further miniaturized.

Next, another example of the operation of the example shown in FIG. 1 will be described with reference to FIG. 4. In this example, when FM modulating the carrier signal As1n art with S to an analog audio signal, the center frequency is as shown by signal (38) in FIG. 4A.
-Δ) MHz, so as to substantially match the center frequency of the order wire line (10) shown in FIG. 6A. In FIG. 1, this is achieved, for example, by switching the frequency division number N of the N frequency divider circuit (15) to a small value. When a modulated signal is generated in QPS using the digital data DD, the number of divisions N of the N frequency divider circuit (15) is switched to 14, and the 41st! The QPS modulation signal (37) shown at IB will be the same as that shown in FIG. 2B. According to the example of FIG. 4, the frequency arrangement shown in FIG. 6A is almost reproduced, and there is an advantage that compatibility with the conventional system can be easily maintained.

Note that the above embodiment applies the present invention to a QPSK modulator, but instead of the QPSK modulator, for example, a BP
The present invention is also applicable to cases where a modulator is used for S.

As described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various configurations may be adopted without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, the carrier signal can be modulated by PSK and FM with the first signal and the second signal, respectively, and the PSK modulator is also used as an output circuit for these modulated signals, so the modulation circuit can be miniaturized. This has the advantage of reducing production costs.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of a modulation circuit according to the present invention, FIGS. 2 and 3 are diagrams each explaining the operation of the embodiment, and FIG. 4 is an explanation of other operations of the embodiment. a line diagram for
FIG. 5 is a configuration diagram showing an example of a satellite communication system, and FIG. 6 is a diagram showing a frequency arrangement of conventional satellite communication. (12) is a phase error detection circuit, (13) is a low-pass filter, (14) is a voltage controlled oscillator, (15) is an N frequency divider, (17) is a first switch circuit, and (22) is a second switch circuit. The switch circuits (24) and (25) are double-balanced modulators, respectively, and (27) is an adder. Fig. 5 f (GHz) Heasl Fig. 8 Distribution of frequency of conventional th star communication

Claims (1)

[Claims] A PLL circuit that generates a carrier signal from a reference signal, and a PSK that modulates the carrier signal with a first signal and outputs the PSK modulated signal.
K modulator and an additional circuit for FM modulating the carrier signal with a second signal before inputting it to the PSK modulator, PSK modulating the carrier signal with the first signal and outputting the resultant signal. When the second signal is fixed at a predetermined value and the output signal of the PSK modulator is extracted, when the carrier wave signal is FM modulated by the second signal and output, the first signal is fixed at a predetermined value. A modulation circuit characterized in that the output signal of the PSK modulator is taken out as it is by fixing the value to a fixed value.