JP2919328B2 - Modulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PLL (Phase
The present invention relates to a modulation circuit for modulating a carrier signal from a lock loop type frequency synthesizer with a baseband signal, and more particularly to a modulation circuit suitable for a wireless device transmitting and receiving a digital modulation signal.

[0002]

2. Description of the Related Art FIG.
This will be described with reference to the block diagram of FIG. In this modulation circuit,
A PLL type frequency synthesizer 1 generates a variable frequency synthesized frequency signal g, and an I / Q signal generator 2 generates an I-phase baseband signal k and a Q-phase baseband signal 1 from a digital data signal s. Then, the quadrature modulator 3 sets the synthesized frequency signal g as a carrier signal, sets the I-phase baseband signal k and the Q-phase baseband signal 1 as modulation data, and quadrature-modulates the carrier signal with the modulation data to change the carrier frequency. Of the modulated signal p. The modulation circuit shown in FIG. 1 uses the synthesized frequency signal g having a good C / N ratio from the frequency synthesizer 1 as a carrier signal, so that a modulation signal p having good frequency stability and a good C / N ratio can be obtained. There is a feature. Hereinafter, this modulation circuit will be described in detail.

A voltage controlled oscillator (VCO) 15 of the frequency synthesizer 1 has a variable frequency Fe corresponding to a control voltage of a control signal d supplied from the phase comparator 13 via a low-pass filter (LPF) 14. A frequency signal e is generated, and the variable frequency signal e is supplied to the mixer 18. The fixed frequency signal oscillator (OSC) 19 has a fixed frequency F
A fixed frequency signal Fi having stable and low noise is generated, and the fixed frequency signal Fi is supplied to the mixer 18. The mixer 18 mixes the frequency of the variable frequency signal e and the fixed frequency signal i to generate a composite frequency signal f having a frequency Ff. The synthesized frequency signal f becomes the original output signal of the frequency synthesizer 1. The mixer 18 may be an up (UP) converter in which the frequency Ff of the composite frequency signal f is (Fe + Fi) or a down (DOWN) converter in which the frequency Ff is | Fe-Fi |. The composite frequency signal f is filtered by a band-pass filter 17 to remove unnecessary waves to become a composite frequency signal g. The composite frequency signal g is supplied to the variable frequency divider 16.

The variable frequency divider 16 divides the composite frequency signal g by a frequency division number N corresponding to the supplied variable frequency divided signal r to generate a frequency divided signal h having a frequency Ff / N. On the other hand, a reference signal generator (TCXO) 11 generates a reference signal a having a fixed frequency Fa. The TCXO 11 is, for example, a temperature-compensated crystal oscillator, has good frequency stability against temperature changes and the like, and has little noise such as phase noise. The reference signal a is supplied to the fixed frequency divider 12. The fixed frequency divider 12 divides the frequency of the reference signal a by a fixed number M to generate a frequency-divided signal b having a frequency Fa / M. The phase comparator 13 compares the phase of the frequency-divided signal h and the frequency-divided signal b to generate a control signal c corresponding to the phase difference. The control signal c is a signal before the control signal d is smoothed by the LPF 14.

Now, when the frequency Fa / M of the frequency-divided signal b and the frequency Ff / N of the frequency-divided signal h become equal and the phases of the frequency-divided signal b and the frequency-divided signal h become equal, the control signals c and d
Is stabilized at a predetermined value, and the VCO 15 outputs the composite frequency signal f having the desired frequency Ff. As described above, the synthesized frequency signal g output by the frequency synthesizer 1, that is, the frequency Ff of the synthesized frequency signal f changes according to the frequency division number N corresponding to the frequency-divided signal r.

The I / Q signal generator 2 outputs a data signal s
, An I-phase baseband signal k and a Q-phase baseband signal 1 are generated. The I-phase baseband signal k is supplied to a mixer 31 of the quadrature modulator 3 and the Q-phase baseband signal 1 is supplied to a mixer 33 of the same quadrature modulator 3. Mixer 3
1 also receives the synthesized frequency signal g from the frequency synthesizer 1, and the mixer 32 receives the carrier signal m obtained by shifting the synthesized frequency signal g by 90 ° by the phase shifter 32. The mixer 32 multiplies the I-phase baseband signal k by the composite frequency signal g, that is, amplitude-modulates the composite frequency signal g as a carrier signal with the I-phase baseband signal k to generate a modulation signal o.
The mixer 33 includes a Q-phase baseband signal 1 and a carrier signal m.
That is, the carrier signal m is amplitude-modulated with the Q-phase baseband signal 1 to generate a modulation signal n orthogonal to the modulation signal o. An adder 34 using a hybrid circuit or the like adds the modulation signal o and the modulation signal n to generate a quadrature-modulated, in this example, four-phase PSK-modulated, modulated signal p having a carrier frequency Ff.

[0007]

The above-mentioned modulation circuit according to the prior art has a good C / N ratio because the synthesized frequency signal from the PLL type frequency synthesizer is used for the carrier signal.
In addition, a modulated signal with good frequency stability can be obtained, but a modulated signal with a better C / N ratio has been demanded.

Further, in this modulation circuit, a carrier signal having the same high frequency as the modulation signal is modulated by the modulation data, so that there is a disadvantage that the power consumption of the PLL type frequency synthesizer is large.

Accordingly, a first object of the present invention is to provide a modulation circuit capable of obtaining a modulation signal having a good C / N ratio and frequency stability with low power consumption.

A second object of the present invention is to provide a modulation circuit which satisfies the above conditions and has a small circuit scale and therefore a low manufacturing cost.

[0011]

A modulation circuit according to the present invention comprises a voltage controlled oscillator for generating a variable frequency signal having a frequency corresponding to a supplied control signal, a fixed frequency signal oscillator for generating a fixed frequency signal, A first mixer circuit that mixes the frequency of the fixed frequency signal with the fixed frequency signal to generate a synthesized frequency signal, and divides the synthesized frequency signal by a division number corresponding to the supplied frequency-divided signal to generate a first frequency-divided signal; A variable frequency divider, a reference signal generator for generating a reference signal, a fixed frequency divider for dividing the reference signal to generate a second frequency-divided signal, and the first frequency-divided signal and a second frequency-divided signal. A PLL type frequency synthesizer having a phase comparator for generating the control signal by comparing a phase with a frequency signal, and a baseband signal using one of the variable frequency signal and the fixed frequency signal as a carrier signal. A modulator for generating a first modulated signal by modulating the second modulated signal and a second modulated signal by frequency-mixing another one of the variable frequency signal and the fixed frequency signal with the first modulated signal. And two mixer circuits.

The first of the modulation circuits is that the modulator converts an I / Q signal into a I-phase baseband signal and a Q-phase baseband signal; A configuration including a quadrature modulator that generates the first modulation signal that is a quadrature modulation signal in response to a Q-phase baseband signal and the carrier signal can be adopted.

[0013] The second of the modulation circuits may have a configuration in which the second mixer circuit is an up-converter.

A third aspect of the modulation circuit is that the modulator uses the variable frequency signal as a carrier signal, the second mixer circuit is a down converter, and the frequency of the variable frequency signal is the frequency of the fixed frequency signal. Can be adopted.

A fourth aspect of the modulation circuit is that the modulator uses the fixed frequency signal as a carrier signal, the second mixer circuit is a down converter, and the frequency of the fixed frequency signal is the same as the frequency of the variable frequency signal. A configuration higher than twice can be taken.

[0016]

Next, the present invention will be described with reference to the drawings.

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

This modulation circuit is a quadrature modulation circuit, and includes the same frequency synthesizer 1, I / Q signal generator 2, and quadrature modulator 3 as the modulation circuit of FIG. However, the mixer 31 and the phase shifter 32 of the quadrature modulator 3 use the OSC 19 of the same frequency synthesizer 1 instead of the synthesized frequency signal g.
Supplies a fixed frequency signal i. This modulation circuit further includes a mixer 4 and a band-pass filter (BPF) 5. The mixer 4 multiplies the variable frequency signal e from the VCO 15 and the modulation signal p from the adder 34 to generate a modulation signal q. The BPF 5 removes an unnecessary wave from the modulation signal q to generate a modulation signal t having a predetermined spectrum. The modulation signal t is transmitted from a wireless device including this modulation circuit.

FIG. 3 is a frequency diagram showing a frequency relationship of main signals in the first embodiment and a second embodiment to be described later. Hereinafter, the operation of the modulation circuit will be described in detail with reference to FIGS.

First, when the mixer 18 is an up-converter, the frequency Ff of the composite frequency signal f is Ff = Fe
+ Fi. At this time, the mixer 4 can have both an up converter and a down converter. The frequency Fq of the modulation signal q when the mixer 4 is an up-converter is
Fq = Fe + Fi = Ff, that is, the same as the frequency Ff of the composite frequency signal f. The frequency Fq when the mixer 4 is a downconverter is Fq = Fe-Fi. However,
The frequency Fi of the fixed frequency signal i, which is the carrier frequency signal of the quadrature modulation circuit 3, is the frequency Fq of the modulation signal q (= Fe-F
i) If the condition of being lower is included, the fixed frequency signal i
Is 1/2 of the frequency Fe of the variable frequency signal e.
Must be lower.

Next, when the mixer 18 is a down-converter, the frequency Ff of the composite frequency signal f is expressed as Ff = Fe
-Fi. Also at this time, the mixer 4 can take both configurations of an up converter and a down converter. Mixer 4
Is the frequency Fq of the modulation signal q when is an upconverter
Is Fq = Fe + Fi. The frequency Fq when the mixer 4 is a downconverter is Fq = Ff = Fe-Fi,
That is, it becomes the same as the frequency Ff of the composite frequency signal f. However, if the condition that the frequency Fi of the fixed frequency signal i that is the carrier frequency signal of the quadrature modulation circuit 3 is lower than the frequency Fq of the modulation signal q is included, the frequency Fi of the fixed frequency signal i
Must be lower than 1/2 of the frequency Fe of the variable frequency signal e.

Under the above frequency conditions, the frequency Fi of the carrier signal (fixed frequency signal i) of the quadrature modulation circuit 3
Are lower than the carrier frequency of the modulation signal q. Therefore, the quadrature modulator 3 of FIG. 1 can use a low-frequency carrier signal that can lower the C / N ratio, that is, reduce the nearby noise, as compared with the quadrature modulator 3 of FIG. Modulated signal q or modulated signal t with improved N ratio
Can be obtained.

The quadrature modulation circuit shown in FIG.
, A high-power carrier signal is directly obtained from the mixer, so that a carrier signal is obtained after passing through the mixer 18 as shown in FIG.
There is an advantage that power consumption for generating a carrier signal is small.

Further, the quadrature modulation circuit generates a modulated signal p
And two signals, a carrier signal and a frequency conversion signal, are required for generating q and q. Since these two signals can be easily obtained from the frequency synthesizer 1, there is no need to increase the circuit scale, and the manufacturing cost is reduced. Also has the advantage of being low.

Although the embodiment of FIG. 1 has a configuration of a quadrature modulation circuit, it is obvious that the quadrature modulator 3 may be changed to another modulator such as a two-phase PSK modulator or an amplitude modulator. is there.

FIG. 2 is a block diagram of a modulation circuit according to a second embodiment of the present invention.

This modulation circuit includes the same frequency synthesizer 1, I / Q signal generator 2, quadrature modulator 3, mixer 4, and BPF 5 as the modulation circuit of FIG. However, the variable frequency signal e is supplied from the VCO 15 to the mixer 31 and the phase shifter 32 of the quadrature modulator 3 instead of the fixed frequency signal i. The fixed frequency signal i is supplied to the mixer 4 instead of the variable frequency signal e. Hereinafter, the operation of the modulation circuit will be described in detail with reference to FIGS.

First, when the mixer 18 is an up-converter, the frequency Ff of the composite frequency signal f is Ff = Fi
+ Fe. At this time, the mixer 4 can have both an up converter and a down converter. The frequency Fq of the modulation signal q when the mixer 4 is an up-converter is
Fq = Fi + Fe = Ff, that is, the same as the frequency Ff of the composite frequency signal f. The frequency Fq when the mixer 4 is a down converter is Fq = Fi-Fe. However,
The frequency Fe of the variable frequency signal e that is the carrier frequency signal of the quadrature modulation circuit 3 is equal to the frequency Fq of the modulation signal q (= Fi−F
e) the lower frequency signal e
Is 1/2 of the frequency Fi of the fixed frequency signal i.
Must be lower.

Next, when the mixer 18 is a down-converter, the frequency Ff of the composite frequency signal f is Ff = Fi.
-Fe. Also at this time, the mixer 4 can take both configurations of an up converter and a down converter. Mixer 4
Is the frequency Fq of the modulation signal q when is an upconverter
Is Fq = Fi + Fe. The frequency Fq when the mixer 4 is a downconverter is Fq = Ff = Fi-Fe,
That is, it becomes the same as the frequency Ff of the composite frequency signal f. However, if the condition that the frequency Fe of the variable frequency signal e as the carrier frequency signal of the quadrature modulation circuit 3 is lower than the frequency Fq of the modulation signal q is included, the frequency Fe of the variable frequency signal e
Must be lower than 1/2 of the frequency Fi of the fixed frequency signal i.

In the modulation circuit of FIG. 2, the frequency Fe of the carrier signal (variable frequency signal e) of the quadrature modulator 3 is lower than the frequency of the modulation signal q or t to be output. Has features.

[0031]

As described above, according to the present invention, one of a variable frequency signal and a fixed frequency signal generated by a PLL type frequency synthesizer is modulated as a carrier signal by a baseband signal to generate a first modulated signal. And a second mixer circuit for frequency-mixing another one of the variable frequency signal and the fixed frequency signal with the first modulation signal to generate a second modulation signal. The circuit is small and the manufacturing cost is low.
There is an effect that a carrier signal having a low N ratio and a stable frequency can be generated with low power consumption, and a modulated signal with an improved C / N ratio can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a modulation circuit according to a second embodiment of the present invention.

FIG. 3 is a frequency diagram showing a frequency relationship of main signals in the first and second embodiments.

FIG. 4 is a block diagram of a conventional quadrature modulation circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 frequency synthesizer 11 reference signal generator (TCXO) 12 fixed frequency divider 13 phase comparator 14 low-pass filter (LPF) 15 voltage-controlled oscillator (VCO) 16 variable frequency divider 17 band-pass filter (BPF) ) 18 mixer 19 fixed frequency signal generator (OSC) 2 I / Q signal generator 3 quadrature modulator 31, 33 mixer 32 phase shifter 34 adder 4 mixer 5 band pass filter (BPF)

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04L 27/20

Claims (5)

(57) [Claims] 1. A voltage-controlled oscillator for generating a variable frequency signal having a frequency corresponding to a supplied control signal, a fixed frequency signal oscillator for generating a fixed frequency signal, and frequency-mixing and combining the variable frequency signal and the fixed frequency signal. A first mixer circuit for generating a frequency signal, a variable frequency divider for dividing the synthesized frequency signal by a division number corresponding to the supplied frequency-divided signal to produce a first frequency-divided signal, and a reference for producing a reference signal A signal generator, a fixed frequency divider for dividing the reference signal by a fixed frequency to generate a second frequency-divided signal, and comparing the phase of the first frequency-divided signal with the second frequency-divided signal to control the control signal A PLL type frequency synthesizer having a phase comparator that generates a first modulated signal by modulating one of the variable frequency signal and the fixed frequency signal with a baseband signal as a carrier signal. And a second mixer circuit for frequency-mixing another one of the variable frequency signal and the fixed frequency signal and the first modulation signal to generate a second modulation signal. circuit. 2. An I / Q converter for converting a data signal into an I-phase baseband signal and a Q-phase baseband signal.
A signal generation circuit; and a quadrature modulator that generates the first modulation signal that is a quadrature modulation signal in response to the I-phase baseband signal, the Q-phase baseband signal, and the carrier signal. The modulation circuit according to claim 1, wherein 3. The modulation circuit according to claim 1, wherein said second mixer circuit is an up-converter. 4. The modulator according to claim 1, wherein the variable frequency signal is a carrier signal, the second mixer circuit is a down converter, and the frequency of the variable frequency signal is more than twice the frequency of the fixed frequency signal. 2. The modulation circuit according to claim 1, wherein the modulation circuit is set to be higher. 5. The modulator according to claim 1, wherein the modulator uses the fixed frequency signal as a carrier signal, the second mixer circuit is a down converter, and the frequency of the fixed frequency signal is higher than twice the frequency of the variable frequency signal. 2. The modulation circuit according to claim 1, wherein the modulation circuit is set to be higher.