JP3361764B2 - Indirect modulation circuit and radio using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indirect modulation circuit used in a radio device or the like, and more particularly to an indirect modulation circuit in which a frequency of an image component is largely separated from a transmission frequency.

[0002]

2. Description of the Related Art It is known that an indirect modulation circuit is used in one chip so that an image component of a modulation circuit used in a radio device or the like can be removed by an on-chip high-pass filter. An example of a conventional indirect modulation circuit is the indirect modulation circuit disclosed in Japanese Patent Laid-Open No. 7-170301. As shown in FIG. 2, this circuit includes a baseband signal input terminal 41, a baseband signal input terminal 42, and an output terminal 43.
, Frequency generator 10, frequency divider 21 and frequency divider 22
, A modulator 23 that modulates with a baseband signal, a mixer 24 that frequency-converts to a transmission frequency, and a high frequency range that removes a frequency component that is 3/5 times the transmission frequency corresponding to an image component generated at the output of the mixer 24. And a pass filter circuit 25.

The frequency of the signal input from the frequency generator 10 of this circuit is (4/5) fo [Hz], the base band signal is α [Hz], and the output frequency of the frequency divider 21 is f21 [Hz]. ],
The output frequency of the frequency divider 22 is f22 [Hz], the output frequency of the modulator 23 is f23 [Hz], and the output frequency of the mixer 24 is f24 [Hz].
z], the output frequency of the high-pass filter circuit 25 is f25 [Hz]
If so, 2 divider 21, 2 divider 22, modulator 23, mixer
The output frequencies of 24 and the high pass filter circuit 25 are expressed as follows. However, fo is a transmission frequency. f21 = (2/5) fo [Hz] f22 = (1/5) fo [Hz] f23 = (1/5) fo + α [Hz] f24 = fo + α and (3/5) fo−α [Hz] f25 = fo + α

In this way, the frequency of the image component output from the mixer 24 is set to 3/5 times the transmission frequency, and the image component can be removed by the on-chip high-pass filter circuit 25.

[0005]

However, in the conventional configuration, the frequency component of 3/5 times the transmission frequency corresponding to the image component generated at the output of the mixer is 2 / of the transmission frequency as compared with the transmission frequency. Since only the frequency component of 5 times is separated, it is necessary to increase the amount of attenuation in order to remove it by the high-pass filter circuit and to keep the cutoff frequency constant against variations in resistors and capacitors. There is a problem that the circuit scale of the bandpass filter circuit becomes large.

It is an object of the present invention to solve the above-mentioned conventional problems and remove the image component generated at the output of the mixer by a high-pass filter circuit having a small circuit scale.

[0007]

In order to solve the above problems, in the present invention, an indirect modulation circuit is provided with a transmission frequency of 4 MHz.
A frequency generator that generates a local oscillation signal having a frequency of / 5 times, a first modulator that modulates the local oscillation signal divided by 2 with a baseband signal, and a local oscillation signal divided by 2 by 4 A second modulator that modulates with, a mixer that mixes the output of the first modulator and the output of the second modulator so that the frequency of the image component is ⅕ times the transmission frequency, and the image component A high pass filter circuit for removal is provided.

With this configuration, the frequency of the image component can be separated from the transmission frequency as much as possible, and the image component can be removed by the high-pass filter circuit having a small circuit scale.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a frequency generator which generates a local oscillation signal having a frequency of 4/5 times the transmission frequency, and a frequency division local oscillation signal divided by 2 into a baseband signal. And a second modulator that modulates a frequency-divided 2 local oscillation signal with a frequency-divided 4 local oscillation signal, and the frequency of the image component is ⅕ times the transmission frequency. An image generated at the mixer output, which is an indirect modulation circuit including a mixer for mixing the output of the first modulator and the output of the second modulator, and a high-pass filter circuit for removing the image component. It has the function of separating the frequency of the component from the transmission frequency as much as possible and removing the image component by a high-pass filter circuit having a small circuit scale.

According to a second aspect of the present invention, in the indirect modulation circuit according to the first aspect, a first frequency divider connected to the output of the frequency generator and the first frequency divider are provided. A second frequency divider connected to the output of the frequency divider,
Is connected to one end of the input of the first modulator and one end of the input of the second modulator, and the baseband signal input terminal is the other end of the input of the first modulator. The output of the second frequency divider is connected to the other end of the input of the second modulator, the output of the first modulator is connected to one end of the input of the mixer, The output of the second modulator is connected to the other end of the input of the mixer, and the output of the mixer is connected to the input of the high-pass filter circuit for removing an image component having a frequency of 1/5 times the transmission frequency. The output of the high-pass filter circuit is connected to the output terminal, and the high-pass filter circuit removes the frequency component of 1/5 times the transmission frequency generated at the output of the mixer. Have.

According to a third aspect of the present invention, in the indirect modulation circuit according to the second aspect, the high-pass filter circuit removes an image component having a frequency ⅕ times the transmission frequency. It is a high-pass filter circuit having a minimum necessary circuit scale, and has an action of removing an image component having a frequency ⅕ times the transmission frequency by a high-pass filter circuit having a small circuit scale.

According to a fourth aspect of the present invention, there is provided a semiconductor integrated circuit incorporating the indirect modulation circuit according to any one of the first to third aspects, wherein the indirect modulation circuit has a high-pass filter circuit having a small circuit scale. It has the effect of reducing the size of the integrated circuit.

According to a fifth aspect of the present invention, there is provided a radio device having the semiconductor integrated circuit according to the fourth aspect built therein, which has an effect of reducing the size and weight of the radio device by the small semiconductor integrated circuit.

FIG. 1 shows an embodiment of the present invention.
Will be described in detail with reference to.

(Embodiment) In the embodiment of the present invention, a modulated signal having a frequency of 2/5 times the transmission frequency and a signal having a frequency of 3/5 times the transmission frequency are mixed by a mixer to transmit the frequency. Is an indirect modulation circuit that generates a signal of (1) and removes an image component having a frequency of 1/5 times the transmission frequency by a high-pass filter circuit having a small circuit scale.

FIG. 1 is a block diagram of an indirect modulation circuit according to an embodiment of the present invention. In FIG. 1, the frequency generator 10
Is an oscillator that generates a local oscillation signal having a frequency of 4/5 times the transmission frequency. The frequency divider 11 divides the local oscillation signal by 2
It is a circuit for frequency division. The modulator 12 is a circuit that modulates a local oscillation signal whose frequency is divided by two with a baseband signal. The divide-by-two frequency divider 13 is a circuit that divides the local oscillation signal, which is divided by two, into two. The modulator 14 is a circuit that modulates a local oscillation signal whose frequency is divided by 2 with an output signal of the frequency divider 2. Mixer 15
It is a circuit that frequency-converts a modulated signal into a transmission frequency. The wide-pass filter circuit 16 is a circuit that removes a frequency component that is ⅕ times the transmission frequency corresponding to the image component generated at the output of the mixer 15.

The indirect modulation circuit of the embodiment of the present invention comprises a baseband signal input terminal 41 and a baseband signal input terminal 42, an output terminal 43, a frequency generator 10, and a frequency divider by two.
11 and 2 frequency divider 13, modulator 12 that modulates with a baseband signal, and modulator 14 that modulates with the output signal of frequency divider 2
And a mixer 15 for frequency conversion into a transmission frequency, and a mixer 15
High-pass filter circuit that removes the frequency component 1/5 times the transmission frequency corresponding to the image component generated in the output of the
16 and.

Compared to the conventional indirect modulation circuit shown in FIG. 2, this indirect modulation circuit has a baseband signal input terminal 41.
And a baseband signal input terminal 42, output terminal 43, frequency generator 10, 2 frequency divider 11 and 2 frequency divider 13, modulator 12,
Although the mixers 15 are the same, they are different in that the modulator 14 is newly connected and the circuit configuration of the high-pass filter circuit 16 is small, and the arrangement of other circuit elements is also different.

The operation of the indirect modulation circuit according to the embodiment of the present invention configured as described above will be described with reference to FIG.
The frequency of the signal input from the frequency generator 10 of this circuit is (4/5) fo [Hz], and the baseband signal is α [H
z]. The output frequency of the frequency divider 11 is f11 [Hz],
The output frequency of the frequency divider 13 is f13 [Hz]. Modulator 12
Is f12 [Hz], the output frequency of the modulator 14 is f14 [Hz], the output frequency of the mixer 15 is f15 [Hz], and the output frequency of the high-pass filter circuit 16 is f16 [Hz].
And

The output frequencies of the divide-by-2 frequency divider 11, the modulator 12, the divide-by-2 frequency divider 13, the modulator 14, the mixer 15 and the high-pass filter circuit 16 are expressed as follows. However, fo is a transmission frequency. f11 = (2/5) fo [Hz] f12 = (2/5) fo + α [Hz] f13 = (1/5) fo [Hz] f14 = (3/5) fo [Hz] f15 = fo + α and (1 / 5) fo-α [Hz] f16 = fo + α [Hz]

Thus, the image component is (1/5)
fo-α [Hz], which is far from the transmission frequency fo + α [Hz]. Removing image components that are separated by a frequency component that is 4/5 times the transmission frequency compared to the transmission frequency is
Since this can be easily done with a high-pass filter circuit having a small circuit scale, the scale of the high-pass filter circuit can be minimized.

By integrating this indirect modulation circuit with other circuits to form a bipolar semiconductor integrated circuit or the like, the integrated circuit can be downsized. Furthermore, by incorporating this semiconductor integrated circuit into a wireless device such as a mobile phone, it is possible to reduce the size and weight of the wireless device.

As described above, in the embodiment of the present invention,
The indirect modulation circuit mixes a modulation signal having a frequency of 2/5 times the transmission frequency and a signal having a frequency of 3/5 times the transmission frequency with a mixer to generate a signal of the transmission frequency, and Since the image component having a frequency of 5 times is removed by the high-pass filter circuit having a small circuit scale, the frequency of the image component is separated from the transmission frequency by a frequency component that is 4/5 times the transmission frequency. An image component can be removed by a high-pass filter circuit having a small circuit scale.

[0024]

As is apparent from the above description, in the present invention, the indirect modulation circuit includes a frequency generator that generates a local oscillation signal having a frequency of 4/5 times the transmission frequency and a local oscillation signal divided by two. With a baseband signal, a second modulator that modulates a local frequency-divided oscillation signal of 2 with a local frequency-divided oscillation signal of 4, and the frequency of the image component is 1/5 times the transmission frequency. As described above, the mixer that mixes the output of the first modulator and the output of the second modulator and the high-pass filter circuit that removes the image component are provided.
The effect that the image component generated in the output of the mixer can be removed as far as possible from the transmission frequency and the image component can be removed by the high-pass filter circuit having a small circuit scale is obtained.

Further, since the semiconductor integrated circuit incorporating this indirect modulation circuit is constructed, there is an effect that the integrated circuit can be downsized.

Further, since the radio device incorporating this integrated circuit is constructed, there is an effect that the radio device can be reduced in size and weight.

[Brief description of drawings]

FIG. 1 is a block diagram of an indirect modulation circuit according to an embodiment of the present invention,

FIG. 2 is a block diagram of a conventional indirect modulation circuit.

[Explanation of symbols]

10 frequency generator 11, 13, 21, 22 2 frequency divider 12, 14, 23 modulators 15, 24 mixer 16 High-pass filter circuit 25 High pass filter circuit 41, 42 Baseband signal input terminal 43 Output terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-11-168519 (JP, A) JP-A-4-355540 (JP, A) JP-A-7-283842 (JP, A) JP-A-7- 170301 (JP, A) JP 4-137845 (JP, A) JP 5-30146 (JP, A) JP 11-68863 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04L 27/00-27/38

Claims (5)

(57) [Claims] 1. A frequency generator that generates a local oscillation signal having a frequency that is 4/5 times the transmission frequency, a first modulator that modulates the frequency-divided local oscillation signal by a baseband signal, and 2
A second method for modulating a frequency-divided local oscillation signal with a frequency-divided 4 local oscillation signal
And the frequency of the image component is 1 / the transmission frequency
An indirect circuit comprising: a mixer that mixes the output of the first modulator and the output of the second modulator so as to be 5 times, and a high-pass filter circuit that removes the image component. Modulation circuit. 2. A first divide-by-2 divider connected to the output of the frequency generator, and a second divide-by-2 divider connected to the output of the first divide-by-2 divider, The output of the first frequency divider is connected to one end of the input of the first modulator and one end of the input of the second modulator, and the baseband signal input terminal is connected to the input of the first modulator. The other end is connected to the second
Output of the second modulator is connected to the other end of the input of the second modulator, the output of the first modulator is connected to one end of the input of the mixer, and the output of the second modulator Is connected to the other end of the input of the mixer, the output of the mixer is connected to the input of the high-pass filter circuit that removes an image component having a frequency of ⅕ times the transmission frequency, and the high-pass filter is connected. The indirect modulation circuit according to claim 1, wherein an output of the circuit is connected to an output terminal. 3. The high-pass filter circuit is a high-pass filter circuit having a minimum circuit scale necessary for removing an image component having a frequency ⅕ times the transmission frequency. The indirect modulation circuit according to claim 2. 4. A semiconductor integrated circuit having the indirect modulation circuit according to claim 1 built therein. 5. A wireless device having the semiconductor integrated circuit according to claim 4 built therein.