JP2003179658A - Modulator unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an I/Q modulator unit capable of keeping an RF output signal level fixed at all times. <P>SOLUTION: An I/Q modulator unit 30 up-converts digitally modulated I signals and Q signals of a base band having a 90° phase difference to RF signals of a GHz band through a modulation circuit 2 and outputs them through a power amplifier 2. The level of the RF signals outputted from the power amplifier 2 is detected in a level detector 10 and a gain of a gain variable amplifier 4 provided between the modulation circuit 5 and the power amplifier 2 is controlled by the detected output. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator unit having a function of up-converting digitally modulated baseband signals such as I and Q signals having a 90 ° phase difference into RF signals of GHz band through a modulation circuit. It is about.

[0002]

2. Description of the Related Art In a system for receiving digital satellite broadcasts such as BS broadcasts, CS broadcasts, and digital broadcasts, it is common to use a telephone line as an upstream line. As an alternative to this, a two-way communication system using an I / Q modulator and satellite broadcasting is under study. As the circuit configuration on the upstream side in this system, a digitally-modulated baseband signal having a 90 ° phase difference is directly converted into a 2 GHz band through a modulation circuit having a built-in adder or is converted twice through an intermediate frequency. What is up-converted is considered.

FIG. 1 shows a direct conversion method for up-conversion. In the figure,
Broadband I and Q signals input from the input terminals 8 and 9 of the I / Q modulator unit 30 are amplified by a variable gain amplifier 4 through a modulation circuit 5 including a phase shifter and an adder, and then wideband. The band is limited by the band pass filter 3, amplified by the next power amplifier 2, and led to the RF output terminal 1. In the modulation circuit 5, the PLL circuit 7
Is mixed with the oscillation signal of the local oscillator 6, which oscillates at the same frequency as the RF output signal frequency controlled by Directly converted. Such a modulation circuit 5 is disclosed, for example, in JP-A-200
0-36846 and the like.

[0004]

As described above, 90 °
In a system for performing satellite communication by converting two baseband signals of an I signal and a Q signal having a phase difference of 1 into an RF signal, the level of the RF signal output from the RF output terminal 1 needs to be always kept constant. is there.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a modulator unit in which the RF output signal level is always kept constant.

[0006]

In order to achieve the above-mentioned object, in the present invention, a digitally modulated baseband signal such as an I / Q signal having a 90 ° phase difference is transmitted through a modulation circuit to a G signal.
In a modulator unit that up-converts into an RF signal in the Hz band and outputs it through a power amplifier, the level of the RF signal output from the power amplifier is detected by a level detector, and the detection output from the modulator circuit and the power amplifier. The gain of the variable gain amplifier provided between the two is controlled.

Further, a programmable attenuator may be provided between the modulation circuit and the power amplifier, and the degree of attenuation of the programmable attenuator may be externally set. In this case, the programmable attenuator receives the setting data via the serial data bus.
Before the level detector detects the level of the RF signal output from the power amplifier, an unnecessary signal may be removed through a bandpass filter. The bandpass filter is a variable bandpass filter whose frequency can be varied.

Further, according to the present invention, the digitally-modulated 9
In a modulator unit which up-converts a baseband signal such as an I / Q signal having a 0 ° phase difference into a GHz band RF signal through a modulation circuit and outputs the RF signal through a power amplifier, the RF output from the power amplifier The level of the signal is detected by the level detector, the detected output is converted into a digital signal by the A / D converter, and is taken into the CPU.
Controls the programmable attenuator to set the RF signal to a predetermined level. In this case, the A / D converter, the programmable attenuator, and the CPU
Are connected by a serial data bus. This CPU may be provided externally.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG.
The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the present embodiment (first embodiment), the output level of the power amplifier 2 is detected by the level detector 10, and the detected output is fed back to the variable gain amplifier 4 to control the gain of the variable gain amplifier 4. I have to. As a result, fluctuations in the level of the RF signal led to the output terminal 1 are suppressed, and a constant level is maintained at all times.

Next, in a second embodiment shown in FIG. 3, a programmable attenuator 12 is provided between the variable gain amplifier 4 and the wideband bandpass filter 3 in the first embodiment, and the programmable attenuator 12 is attenuated. Degree 11
It can be set arbitrarily by serial data given from the outside through. 20 is a unit 30
The i ² C bus (serial data bus) formed inside is shown. According to the second embodiment, since the programmable attenuator 12 is provided, a highly accurate AGC loop can be formed, and the attenuation degree can be controlled from the outside, so that the RF output level can be adjusted arbitrarily. be able to.

In the third embodiment shown in FIG. 4, an A / D converter 13 is provided in the structure of the second embodiment to provide a level detector 1.
The detection output of 0 is converted into a digital signal to control the programmable attenuator 12. In this case, A /
The D-converted level detection data is transmitted to the external CPU 21 via the terminal 11. The CPU 21 gives control data for setting the RF output signal to a predetermined level to the programmable attenuator 12 based on the level detection data. In this way, the RF output signal is constantly controlled so as to have a predetermined level determined by the CPU 21. In addition, CP
U21 may be provided inside the unit 30.

The fourth embodiment shown in FIG. 5 is a variable bandpass filter 1 having the same structure as the second embodiment (FIG. 3).
4 is provided, and the RF of the output terminal 1 is provided by this filter 14.
The signal is band-limited and then applied to the level detector 10. With this configuration, when the RF signal at the output terminal 1 has an unnecessary component such as spurious, the unnecessary component is removed by the filter 14, so that the level detector 10 can detect the correct level of the RF signal. As a result, the AGC becomes more accurate, and the reliability of leveling the RF output signal is improved.

In the fifth embodiment shown in FIG. 6, the low-pass filter 3 in the second embodiment (FIG. 3) is replaced with a variable low-pass filter 14. By setting the low-pass filter 14 so as to remove unnecessary components such as spurious contained in the RF signal, the level detector 1
The correct level of the RF signal can be detected with 0, and
C becomes accurate, and the reliability of leveling the RF output signal is improved. Moreover, in this embodiment, since unnecessary components such as spurious do not appear in the output terminal 1, there is an advantage that the unnecessary components are not radiated to the outside from the output terminal 1.

[0014]

As described above, according to the present invention, the level of the RF signal in the GHz band output from the demodulator unit can always be kept constant.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration of a conventional I / Q modulator unit.

FIG. 2 is a block circuit diagram showing a configuration of an I / Q modulator unit according to the first embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a configuration of an I / Q modulator unit according to a second embodiment of the present invention.

FIG. 4 is a block circuit diagram showing a configuration of an I / Q modulator unit according to a third embodiment of the present invention.

FIG. 5 is a block circuit diagram showing a configuration of an I / Q modulator unit according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing the configuration of an I / Q modulator unit according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 output terminal 2 power amplifier 3 bandpass filter Variable gain amplifier 5 Modulation circuit 6 Local oscillator 7 PLL circuit 8, 9 input terminals 10 level detector 11 terminals 12 programmable attenuator 13 A / D converter 14 Variable bandpass filter 21 CPU 30 I / Q demodulator unit

Claims (9)

[Claims] 1. A GH for transmitting a baseband signal through a modulation circuit.
In a modulator unit that up-converts into a z-band RF signal and outputs it through a power amplifier, the level of the RF signal output from the power amplifier is detected by a level detector, and the detection output thereof is used for the modulation circuit and the power amplifier. A modulator unit characterized in that the gain of a variable gain amplifier provided between the two is controlled. 2. The modulation according to claim 1, further comprising a programmable attenuator provided between the modulation circuit and the power amplifier, and an attenuation degree of the programmable attenuator can be set from the outside. Unit. 3. The modulator unit according to claim 2, wherein the programmable attenuator receives setting data through a serial data bus. 4. An undesired signal is removed through a bandpass filter before the level of the RF signal output from the power amplifier is detected by the level detector. The modulator unit according to any one of 1. 5. The modulator unit according to claim 4, wherein the bandpass filter is a variable bandpass filter whose frequency can be varied. 6. A baseband signal is supplied to a GH via a modulation circuit.
In a modulator unit that up-converts into a z-band RF signal and outputs it through a power amplifier, the level of the RF signal output from the power amplifier is detected by a level detector, and the detection output is detected by an A / D converter. A modulator unit, wherein the modulator unit controls the programmable attenuator so that the signal is converted into a digital signal and is taken into a CPU, and the CPU sets the RF signal to a predetermined level. 7. The modulator unit according to claim 6, wherein the A / D converter, the programmable attenuator and the CPU are connected by a serial data bus. 8. The modulator unit according to claim 6, wherein the CPU is provided outside. 9. The modulator unit according to claim 1, wherein the baseband signal is a digitally modulated I / Q signal having a 90 ° phase difference.