JPH09172465A - Modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a demodulating signal of a low C/N and to reduce a circuit scale and power consumption. SOLUTION: A frequency synthesizer 1 of PLL (phase lock loop) type generates a variable frequency signal (e) and a fixed frequency signal (i). An I/Q signal generator 2 generates an I base band signal (k) and a Q base band signal (1). A quadrature modulator 3 generates an orthogonal modulation signal (p) by setting the fixed frequency signal (i) to be a carrier signal and signals (K) AND (L) to be modulation data. A mixer 4 generates a quadrature modulation signal (q) by frequency-mixing the variable frequency signal (e) and the quadrature modulation signal (p). When both of a mixer 8 and the mixer 4 and up-converters, the frequency Ff of a synthetic frequency signal F and the frequency Fq of the modulation signal (q) are equal to each other. In addition the frequency Fi of the carrier signal (i) of the quadrature modulator 3 is lower than the carrier signal frequency Fq of the modulation signal (q).

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 that modulates a carrier wave signal from a lock loop type frequency synthesizer with a baseband signal, and particularly to a modulation circuit suitable for a wireless device that transmits and receives a digital modulation signal.

[0002]

2. Description of the Related Art A conventional modulation circuit of this type is shown in 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 composite 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 format data signal s. Then, the quadrature modulator 3 uses the composite frequency signal g as a carrier signal, 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. To produce a modulated signal p. Since the modulation circuit of FIG. 1 uses the composite frequency signal g having a good C / N ratio from the frequency synthesizer 1 as a carrier signal, a modulation signal p having a good frequency stability and a good C / N ratio can be obtained. There is a feature called. Hereinafter, this modulation circuit will be described in detail.

The voltage controlled oscillator (VCO) 15 of the frequency synthesizer 1 varies the frequency Fe corresponding to the control voltage of the control signal d supplied from the phase comparator 13 via the low pass filter (LPF) 14. A frequency signal e is generated and this variable frequency signal e is supplied to the mixer 18. Further, the fixed frequency signal oscillator (OSC) 19 has a fixed frequency F
A fixed frequency signal Fi having stable i and less noise is generated, and the fixed frequency signal Fi is supplied to the mixer 18. The mixer 18 frequency-mixes 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 bandpass filter 17 removes unnecessary waves from the combined frequency signal f to form a combined frequency signal g, which 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 division signal r to generate a frequency division signal h of a frequency Ff / N. On the other hand, the 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 with respect to temperature changes, etc., 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 fixedly divides the reference signal a by a frequency division number M to generate a frequency-divided signal b having a frequency Fa / M. The phase comparator 13 compares the phases 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 divided signal b and the frequency Ff / N of the divided signal h become equal and the phases of the divided signal b and the divided signal h become equal, the control signals c and d are obtained.
The voltage of is stable at a predetermined value, and the VCO 15 outputs the composite frequency signal f having the desired frequency Ff. As described above, the composite frequency signal g output from the frequency synthesizer 1, that is, the frequency Ff of the composite frequency signal f changes according to the frequency division number N corresponding to the frequency division signal r.

Further, the I / Q signal generator 2 outputs the data signal s
To generate an I-phase baseband signal k and a Q-phase baseband signal l. The I-phase baseband signal k is supplied to the mixer 31 of the quadrature modulator 3, and the Q-phase baseband signal 1 is supplied to the mixer 33 of the same quadrature modulator 3. Mixer 3
1 also receives the composite frequency signal g from the frequency synthesizer 1, and the mixer 32 receives the carrier signal m obtained by phase-shifting the composite 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, performs amplitude modulation with the I-phase baseband signal k as a carrier signal to generate a modulation signal o.
The mixer 33 has a Q-phase baseband signal 1 and a carrier signal m.
Are multiplied, that is, the carrier wave signal m is amplitude-modulated by the Q-phase baseband signal l 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 modulation signal p of the carrier frequency Ff.

[0007]

The above-mentioned conventional modulation circuit uses a composite frequency signal from a PLL type frequency synthesizer as a carrier signal, and therefore has a good C / N ratio.
Moreover, a modulated signal with good frequency stability can be obtained, but a modulated signal with a better C / N ratio is being demanded.

Further, in this modulation circuit, since the carrier signal of the same high frequency as the modulation signal is modulated by the above-mentioned modulation data, there is a drawback that the power consumption of the PLL type frequency synthesizer is large.

Therefore, 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 that produces a variable frequency signal having a frequency corresponding to a control signal supplied, a fixed frequency signal oscillator that produces a fixed frequency signal, and the variable frequency signal. A first mixer circuit that mixes the fixed frequency signal with the frequency to generate a combined frequency signal; divides the combined frequency signal by a frequency division number corresponding to the supplied divided signal to generate a first divided signal; A variable frequency divider that generates a reference signal, a reference signal generator that generates a reference signal, a fixed frequency divider that frequency-divides the reference signal to generate a second frequency-divided signal, and the first frequency-divided signal and the second frequency-divided signal. A PLL type frequency synthesizer having a phase comparator for phase-comparing with a frequency signal to generate the control 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, and a second modulator for generating a second modulated signal by frequency mixing another one of the variable frequency signal and the fixed frequency signal with the first modulated signal. 2 mixer circuits.

The first of the modulating circuits is an I / Q signal generating circuit for converting the data signal into an I-phase baseband signal and a Q-phase baseband signal by the modulator, the I-phase baseband signal and the I / Q signal generating circuit. A quadrature modulator that produces the first modulated signal, which is a quadrature modulated signal, in response to a Q-phase baseband signal and the carrier signal can be employed.

The second modulation circuit may be configured such that the second mixer circuit is an up converter.

In a third modulation circuit, 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. It is possible to adopt a configuration in which it is higher than twice.

In a fourth of the modulation circuits, 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 frequency of the variable frequency signal. It is possible to adopt a configuration in which the height is higher than twice.

[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 is provided with the same frequency synthesizer 1, I / Q signal generator 2 and quadrature modulator 3 as the modulation circuit of FIG. However, in the mixer 31 and the phase shifter 32 of the quadrature modulator 3, the OSC 19 of the same frequency synthesizer 1 is used instead of the composite frequency signal g.
From the fixed frequency signal i. The modulation circuit further includes a mixer 4 and a bandpass 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 unnecessary waves 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 described later. Hereinafter, the operation of the modulation circuit will be described in detail with reference to FIGS. 1 and 3.

First, when the mixer 18 is an up converter, the frequency Ff of the composite frequency signal f is Ff = Fe
It becomes + Fi. At this time, the mixer 4 can have both an up-converter configuration and a down-converter configuration. 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 down converter 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 (= Fe-F) of the modulation signal q.
i), the fixed frequency signal i
Frequency Fi is 1/2 of frequency Fe of 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 Ff = Fe
-Fi. Also at this time, the mixer 4 can have both an up-converter configuration and a down-converter configuration. Mixer 4
Is the frequency Fq of the modulation signal q when is an up converter
Is Fq = Fe + Fi. The frequency Fq when the mixer 4 is a down converter 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, which is the carrier frequency signal of the quadrature modulation circuit 3, is lower than the frequency Fq of the modulated signal q, the frequency Fi of the fixed frequency signal i is entered.
Must be lower than 1/2 of the frequency Fe of the variable frequency signal e.

Under the frequency conditions as described above, the frequency Fi of the carrier signal (fixed frequency signal i) of the quadrature modulation circuit 3 is
Is lower than the carrier frequency of the modulated 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, can reduce the nearby noise, compared to the quadrature modulator 3 of FIG. Modulation signal q or modulation signal t with improved N ratio
Can be obtained.

Further, the quadrature modulation circuit of FIG.
Since a high-power carrier signal is obtained directly from, compared to obtaining a carrier signal after passing through the mixer 18 as shown in FIG.
There is an advantage that the power consumption for generating the carrier wave signal is small.

Further, this quadrature modulation circuit has a modulation signal p
Two signals, a carrier signal and a frequency conversion signal, are required for generating q and q. However, 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 can be reduced. Is also 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 the 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. Further, the fixed frequency signal i is supplied to the mixer 4 instead of the variable frequency signal e. The operation of this modulation circuit will be described in detail below 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
It becomes + Fe. At this time, the mixer 4 can have both an up-converter configuration and a down-converter configuration. 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 which is the carrier frequency signal of the quadrature modulation circuit 3 is the frequency Fq (= Fi-F) of the modulation signal q.
e), the variable frequency signal e
Frequency Fe is 1/2 of frequency Fi of 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 have both an up-converter configuration and a down-converter configuration. Mixer 4
Is the frequency Fq of the modulation signal q when is an up converter
Is Fq = Fi + Fe. The frequency Fq when the mixer 4 is a down converter 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 which is the carrier frequency signal of the quadrature modulation circuit 3 is lower than the frequency Fq of the modulation signal q is entered, the frequency Fe of the variable frequency signal e is
Must be lower than 1/2 of the frequency Fi of the fixed frequency signal i.

In the modulation circuit of FIG. 2 as well, since 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, it is similar to the modulation circuit of FIG. It has characteristics.

[0031]

As described above, according to the present invention, one of a variable frequency signal and a fixed frequency signal generated by a PLL frequency synthesizer is used as a carrier signal to modulate a baseband signal to generate a first modulated signal. And a second mixer circuit that frequency-mixes another one of the variable frequency signal and the fixed frequency signal with the first modulated signal to generate a second modulated signal. 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 quadrature modulation circuit according to the related art.

[Explanation of symbols]

 1 Frequency Synthesizer 11 Reference Signal Generator (TCXO) 12 Fixed Divider 13 Phase Comparator 14 Low Pass Filter (LPF) 15 Voltage Controlled Oscillator (VCO) 16 Variable 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)

Claims (5)

[Claims] 1. A voltage-controlled oscillator that generates a variable frequency signal having a frequency corresponding to a supplied control signal, a fixed frequency signal oscillator that generates a fixed frequency signal, and frequency-mix and synthesize the variable frequency signal and the fixed frequency signal. A first mixer circuit for generating a frequency signal, a variable frequency divider for generating a first frequency-divided signal by dividing the composite frequency signal by a frequency division number corresponding to the frequency-divided signal supplied, and a reference for generating a reference signal A signal generator, a fixed frequency divider that fixedly divides the reference signal to generate a second divided signal, and the control signal that compares the phases of the first divided signal and the second divided signal And a modulator for generating a first modulated signal by modulating a baseband signal with one of the variable frequency signal and the fixed frequency signal as a carrier signal, A second mixer circuit that frequency mixes another one of the variable frequency signal and the fixed frequency signal with the first modulated signal to produce a second modulated signal. circuit. 2. The I / Q, wherein the modulator converts a data signal into an I-phase baseband signal and a Q-phase baseband signal.
A quadrature modulator for generating the first modulation signal which 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. 3. The modulation circuit according to claim 1, wherein the second mixer circuit is an up converter. 4. 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 less than twice the frequency of the fixed frequency signal. The modulation circuit according to claim 1, wherein the modulation circuit is made higher. 5. 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 greater than twice the frequency of the variable frequency signal. The modulation circuit according to claim 1, wherein the modulation circuit is made higher.