JP2001148721A - Fsk modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FSK modulator which makes it easy to adjust a frequency shift quantity and is reducible in electric power consumption and cost. SOLUTION: A base-band signal generating means consisting of a 90 deg. phase shifter 1, a 180 deg. phase shifter 2, and a switch 3 outputs two base-band signals BBI and BBQ (BBQP, BBPN) which become mutually orthogonal modulated signals and shifts the phase of one base-band signal BBQ by 180 deg. according to transmit data BB. An orthogonal modulating means consisting of an oscillator 4, a 90 deg. phase shifter 5, mixers 6 and 7, and an adder 8 modulates two local signals LOI and LOQ which become mutually orthogonal carriers with the two base-band signals BBI and BBQ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency shift keying (Frequen
The present invention relates to an ncy shift keying (hereinafter abbreviated as FSK) type modulator.

[0002]

2. Description of the Related Art A typical example of a conventional FSK modulator is shown in FIG.
Shown in In FIG. 5, LO is a local signal serving as a carrier, and its frequency is ω0. For simplicity, the local signal LO will be represented by LO = cosω0t. This local signal LO is output from the oscillator 20. The oscillator 21 outputs a signal of the frequency ω1, and the oscillator 22 outputs a signal of the frequency ω2. BB is transmission data serving as a modulation signal, and changes at a data rate of a period 2π / ωb. The switch 23 selects and outputs the output of the oscillator 21 when the transmission data BB is “0” (low level), and selects and outputs the output of the oscillator 22 when the transmission data BB is “1” (high level). . The signal output from the oscillator 21 or the oscillator 22 via the switch 23 and the local signal LO output from the oscillator 20 are multiplied by the mixer 24. Thereby, the frequency of the local signal LO is modulated according to the transmission data BB.

When the output of the mixer 24 is input to the BPF 25, the BPF 25 extracts only a signal in a predetermined frequency range. Then, the output signal of the BPF 25 is amplified by the power amplifier 26 and transmitted from the antenna 27 as a radio wave. Fig. 6 shows the frequency spectrum of this radio wave.
Shown in The radio wave includes two frequency components ω0 + ω1 and ω0 + ω2. Transmission data BB is "0"
In this case, the frequency component of ω0 + ω1 is output, and when the transmission data BB is “1”, the frequency component of ω0 + ω2 is output. As described above, in the FSK modulation, the transmission data BB can be transmitted by associating two frequencies with “0” or “1” of the transmission data BB.

FIG. 7 is a block diagram showing the configuration of another conventional FSK modulator. The same components as those in FIG. 5 are denoted by the same reference numerals. This FSK modulator uses a voltage variable capacitance diode (hereinafter, referred to as a varicap) 28. The switch 23 selects and outputs the voltage V1 when the transmission data BB is “0”, and sets the transmission data BB to “1”.
At this time, the voltage V2 is selected and output. Thus, the bias voltage to the varicap 28 is changed in accordance with the transmission data BB, and the oscillation frequency of the oscillation circuit OSC connected to the varicap 28 via the capacitor C is changed. As a result, similarly to the case of FIG. 5, when the transmission data BB is “0”, the signal of the frequency ω 1 is
4 and the signal of frequency ω2 is supplied to the mixer 24 when the transmission data BB is “1”. Thus, also in the FSK modulator of FIG. 7, the frequency spectrum of the radio wave is as shown in FIG. 6, and the two frequencies correspond to “0” or “1” of the transmission data BB.

Here, two frequencies ω0 + ω shown in FIG.
The difference between 1 and ω0 + ω2 is called a frequency shift. When half of this frequency shift is Δω, the FSK-modulated radio wave can be regarded as a signal shifted by a frequency ± Δω around the frequency ωc = ω0 + (ω1 + ω2) / 2. When this radio wave is received by an FSK receiver as shown in FIG. 8, a clock signal CLK0 having a period of 2π / Δω is extracted, whereby the transmission data BB can be directly demodulated as a digital signal. In FIG. 8, 30 is an antenna, 31 is a low noise amplifier, 32 is an oscillator that outputs a local signal LO, 33 is a 90-degree phase shifter that shifts the phase of the local signal LO by 90 degrees, and 34 is a device that converts the received signal and the local signal LO. A mixer for multiplication, 35 is a mixer for multiplying the received signal by the output signal of the 90-degree phase shifter 33, 36 and 37 are low-pass filters, 38 and 39 are limiter amplifiers, and 40 is a D flip-flop. The detailed operation of the FSK receiver shown in FIG.
Solid-State Circuits, vol. 30, No. 12, pp. 1399-1410, Dec
ember 1999 ".

[0006]

However, the conventional FSK modulator has the following problems. First,
The FSK modulator shown in FIG. 5 requires three oscillation frequencies and has a problem that it is difficult to reduce the power because the power consumption of the oscillators 20 to 22 is large. Further, since three oscillators of the oscillators 20 to 22 are required, the cost increases. Phase locked loop (PLL) instead of oscillator
Even if a circuit is used, power consumption and cost will increase. On the other hand, in the FSK modulator of FIG. 7, the number of oscillators is reduced by one compared to the case of FIG. 5, so that low power and low cost can be achieved, but adjustment of the frequency shift amount by the varicap 28 becomes complicated. There is a problem. Further, even if an attempt is made to reduce the power by lowering the voltage, if the power supply voltage decreases, the variable capacitance value of the varicap 28 decreases, the amount of frequency shift decreases, and the characteristics deteriorate. Therefore, there is a limit to the reduction in power consumption due to the reduction in voltage. Further, since it is difficult to manufacture a varicap having a large variable capacitance using an LSI technology such as a normal CMOS process, it is difficult to make the varicap monolithic. Therefore, there is a problem that it is not possible to reduce the size, power consumption, and cost by monolithic technology.

Further, none of the FSK modulators shown in FIGS. 5 and 7 has means for transmitting the data rate of the transmission data BB to the receiver. Therefore, the receiver side needs to independently have a reference clock signal having the same frequency as the data rate of the transmission side in order to demodulate the transmission data BB. For this reason, in order to change the transmission rate of the wireless signal, it is necessary to change the data rates of both the transmitter and the receiver. In consideration of the actual use situation, there is a problem that it is necessary to collect all the transceivers, and it is difficult to change the transmission rate. As described above, the conventional FSK modulator has a problem that power consumption is large because a plurality of oscillation frequencies are required, and the use of a varicap complicates the design and makes it difficult to reduce the voltage and make it monolithic. . Furthermore, since there is no means for transmitting the data rate of the transmission data to the receiver side, the receiver side must have a clock signal for transmission data demodulation independently, and it is difficult to change the transmission rate of the radio signal. There was a problem. SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-power FSK modulator in which the amount of frequency shift can be easily adjusted, low voltage and monolithic to solve the above problem, To provide an FSK modulator having means for transmitting to the FSK modulator.

[0008]

The FSK modulator according to the present invention includes a means for controlling the amount of frequency shift of a local signal serving as a carrier with the data rate of a baseband signal serving as a modulation signal. Further, the FSK modulator of the present invention outputs two baseband signals (BBI, BBQ), which are orthogonally modulated signals, and converts the phase of one of the two baseband signals (BBQ) into transmission data. Baseband signal generating means (1 to 3, 11 to 13) for changing the angle by 180 degrees according to the following equation, and quadrature modulating means for modulating two local signals (LOI, LOQ) which are orthogonal to each other with two baseband signals (4-8)
It is provided with. Further, as one configuration example of the FSK modulator of the present invention, the baseband signal generation means outputs a baseband signal having a frequency corresponding to the data rate of the transmission data. It is controlled by the rate. Further, as an example of the configuration of the FSK modulator of the present invention, the baseband signal generation means converts the baseband signal into a square wave.
Further, one configuration example of the FSK modulator of the present invention is realized by using LSI manufacturing technology.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of the FSK modulator according to the first embodiment of the present invention. The FSK modulator of FIG.
90 degree phase shifter 1, 180 degree phase shifter 2, switch 3
Oscillator 4, 90-degree phase shifter 5, mixers 6, 7,
It has an adder 8, a power amplifier 9, and an antenna 10. In this FSK modulator, a 90-degree phase shifter 1,
The 180-degree phase shifter 2 and the switch 3 constitute baseband signal generation means, and the oscillator 4, the 90-degree phase shifter 5, the mixers 6, 7, and the adder 8 constitute quadrature modulation means.

In this embodiment, a local signal LO having a frequency of ω0 and two signals BBI and BBQ as baseband signals having a frequency of ωb and a phase shifted from each other by 90 degrees (hereinafter referred to as orthogonal) are used. For simplicity,
The local signal LO is represented by LO = cosω0t, the baseband signal BBI is represented by BBI = cosωbt, and the baseband signal BBQ (BBQP) is BBQ = sinωb
It is represented by t. Here, a sine wave and a cosine wave are used to facilitate the description of the relationship between the frequency and the phase of each signal, but the waveform is not limited and may be a square wave, a triangular wave, or the like.

Hereinafter, the operation of the FSK modulator shown in FIG. 1 will be briefly described. The 90-degree phase shifter 1 shifts the phase of the baseband signal BBI = cosωbt by 90 degrees, and makes the baseband signal BB orthogonal to the baseband signal BBI.
Generate QP = sin ωbt. The 180-degree phase shifter 2
Baseband signal BBQP = −sin baseband signal BBQN = 180 sin in phase shifted from sinωbt
ωbt is generated. Note that an inverter may be used instead of the 180-degree phase shifter 2.

BB is transmission data, which changes at the data rate of the frequency ωb. The switch 3 transmits the transmission data BB
, One of the baseband signals BBQP and BBQN is selected and output. That is, switch 3
Selects and outputs the baseband signal BBQP when the transmission data BB is “0” (low level).
When B is "1" (high level), the baseband signal BB
Select and output QN. Thus, the phase of baseband signal BBQ changes by 180 degrees according to transmission data BB.

On the other hand, the oscillator 4 outputs the local signal LO = c
osω0t is output. Then, the 90-degree phase shifter 5 shifts the phase of the local signal LO by 90 degrees, and
Local signal LOQ orthogonal to O = sin ω0t
Generate Here, the local signal LO input to the mixer 6 is described as LOI in correspondence with the local signal LOQ input to the mixer 7.

Next, a mixer 6 multiplies the local signal LOI and the baseband signal BBI by a signal cosω.
bt × cosω0t is output. On the other hand, the mixer 7 includes a local signal LOQ and a baseband signal BBQP or BB
Signal sinωbt × sinω0t multiplied by QN
Alternatively, -sin ωbt × sin ω0t is output.

In this manner, frequency multiplexing is performed by the mixers 6 and 7, and the local signals LOI and LOP which are orthogonal to each other.
Are the baseband signals BBI and BBQ orthogonal to each other.
(BBQP, BBQN). Adder 8
Is a signal cos (ω0 + ωb) t or cos (ω0) obtained by adding the output signal of the mixer 6 and the output signal of the mixer 7.
-Ωb) Output t. Then, the output signal of the adder 8 is amplified by the power amplifier 9 and transmitted from the antenna 10 as a radio wave. Note that a current adding method by driving the same node without using the adder 8 may be used.

FIG. 2 shows the frequency spectrum of this radio wave.
Shown in The radio wave is an FSK signal shifted by ± ωb around the frequency ω0. Specifically, by associating the baseband signal BBQ with “0” or “1” of the transmission data BB, two frequencies ω0−ωb and ω0 + ωb
Can be respectively associated with “0” and “1” of the transmission data BB. Thereby, the transmission data BB can be transmitted.

As described above, according to the present invention, the oscillator is connected to the oscillator 4 for the local signal LO and the baseband signal BB.
Since the number of oscillators for I (not shown) can be reduced to a total of two, power consumption and cost can be reduced. Further, since no varicap is used, it is possible to realize a monolithic or low voltage using LSI technology such as a CMOS process, thereby realizing low power and low cost.

According to the present invention, when quadrature modulation is performed by the quadrature modulation means, the baseband signals BBI, BB
The frequency of Q (BBQP, BBQN) is set to a frequency ωb that matches the data rate of the transmission data BB, and the phase of the baseband signal BBQ is set to 180 according to the transmission data BB.
The local signal LO (LOI,
LOQ) can be easily controlled by the data rate of the transmission data BB (data rate of the baseband signal).

As described above, since the frequency shift amount of the local signal LO corresponds to the data rate, the FS of the present invention is
When the FSK signal transmitted from the K modulator is demodulated by the receiver shown in FIG. 8, a clock signal having the same frequency ωb as the data rate can be extracted. Therefore, it is not necessary for the receiver to have a clock signal for demodulating transmission data independently, and the transmission rate of the FSK signal can be easily changed only on the transmission side.

[Embodiment 2] FIG. 3 is a block diagram showing a configuration of an FSK modulator according to a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. It is. In the present embodiment, the baseband signal generating means is a D flip-flop (hereinafter abbreviated as DFF) 11, 12,
It is composed of an inverter 13 and a switch 3, and has a baseband signal of a square wave.

The input terminals D of the DFFs 11 and 12 receive a pulse-like baseband signal BBI having a frequency ωb. The clock input terminal CK of the DFF 11 has ω
b, a clock signal CLK having a frequency twice as high
An inverter 13 is connected to a clock input terminal CK of the FF 12.
, The inverted clock signal CLK is input.

The DFF 11 fetches and outputs the baseband signal BBI in synchronization with the clock signal CLK,
F12 takes in and outputs the baseband signal BBI in synchronization with the clock signal CLK. This gives D
The output terminal Q of the FF 11 outputs a baseband signal BBI as shown in FIG.
4B output a baseband signal BBQP as shown in FIG.
A baseband signal BBQN as shown in (c) is output.

The operation after the switch 3 is exactly the same as in the first embodiment. As described above, even when a square wave as shown in FIG. 4 is given as a baseband signal, radio waves with two frequencies ω0−ωb and ω0 + ωb as shown in FIG. 2 are obtained, and the same as in the first embodiment. The effect of is obtained.

[0024]

According to the present invention, the means for controlling the amount of frequency shift of a local signal serving as a carrier by the data rate of a baseband signal serving as a modulation signal is provided, so that the amount of frequency shift can be adjusted at the data rate. Can be easily controlled. Also, since the amount of frequency shift corresponds to the data rate, the FS transmitted from the FSK modulator of the present invention is
When the K signal is demodulated by the receiver, a clock signal having the same frequency as the data rate can be extracted. Therefore, it is not necessary to have a clock signal for demodulating transmission data on the receiver side, and the radio signal (FSK signal) Can be easily changed only on the transmission side.

A baseband signal generating means for outputting two baseband signals which are modulated signals orthogonal to each other and changing the phase of one of the two baseband signals by 180 degrees according to transmission data; And a quadrature modulating means for modulating two local signals, which are orthogonal to each other, with two baseband signals, whereby the number of oscillators can be reduced to two, a local signal oscillator and a baseband signal oscillator. Therefore, power consumption and cost can be reduced. Further, since no varicap is used, it is possible to realize a monolithic or low voltage using LSI technology such as a CMOS process, thereby realizing low power and low cost. Therefore,
If the FSK modulator of the present invention is applied to a low power wireless device or a weak radio wave wireless device, it is possible to significantly reduce power and cost by the above effects.

When performing quadrature modulation by the quadrature modulation means, the frequency of the two baseband signals is set to a frequency that matches the data rate of the transmission data, and the phase of one baseband signal is set to 180 in accordance with the transmission data. By changing the degree, the frequency shift amount of the local signal can be easily controlled by the data rate of the transmission data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an FSK modulator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum of a radio wave output from the FSK modulator of FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of an FSK modulator according to a second embodiment of the present invention.

FIG. 4 is a signal waveform diagram of a baseband signal according to a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a conventional FSK modulator.

6 is a diagram showing a frequency spectrum of an output radio wave of the FSK modulator of FIG. 5;

FIG. 7 is a block diagram showing a configuration of another conventional FSK modulator.

FIG. 8 is a block diagram illustrating a configuration of an FSK receiver.

[Explanation of symbols]

1 90 degree phase shifter, 2 180 degree phase shifter, 3 switch, 4 oscillator, 5 90 degree phase shifter, 6, 7 mixer
8 adder, 9 power amplifier, 10 antenna, 1
1, 12 ... D flip-flop, 13 ... inverter.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoshi Shigematsu 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation 5K004 AA04 EE09

Claims (5)

[Claims] 1. An FSK modulator comprising means for controlling the amount of frequency shift of a local signal serving as a carrier with a data rate of a baseband signal serving as a modulation signal. 2. A baseband signal generating means for outputting two baseband signals, which become modulated signals orthogonal to each other, and changing the phase of one of the two baseband signals by 180 degrees according to transmission data. And a quadrature modulator for modulating two local signals that are orthogonal to each other with the two baseband signals. 3. The FSK modulator according to claim 2, wherein said baseband signal generating means outputs said baseband signal having a frequency corresponding to the data rate of said transmission data, FSK characterized in that the shift amount is controlled by the data rate.
Modulator. 4. The FSK modulator according to claim 1, wherein the baseband signal generating means converts the baseband signal into a square wave. 5. The FSK modulator according to claim 1, wherein the FSK modulator is realized by using an LSI manufacturing technique.
K modulator.