Signal generator

Abstract

To attenuate harmonic wave.SOLUTION: A signal generator includes: a signal generation circuit 104 for generating a first signal at a first frequency; a multiplication circuit 101 for generating a multiplication signal at a multiplication frequency of multiplied first frequency; a phase synchronization circuit 108 for generating a second signal at a second frequency based on an external reference signal, the phase synchronization circuit 108 generating the second signal by synchronizing the phase of the external reference signal with the phase of a divided signal of the second signal; a mixer 111 for generating an output signal with an output frequency which is the sum of the multiplication frequency and the second frequency; and a filter 103 for passing a frequency component in a predetermined band including an output frequency, within frequency components included in the output signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a signal generation device.

Background Art

[0002] There is known a signal generation device that outputs a signal having a set target frequency (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the signal generation device described in Patent Document 1, the generated signal may contain harmonics. When the signal contains harmonics, the harmonics may cause spurious signals. For this reason, in the signal generation device, it is conceivable to attenuate the harmonics with a filter. When the detuning frequency at which the frequency of the harmonics detunes from the target frequency is relatively large, it is relatively easy to attenuate the harmonics with a filter. On the other hand, when this detuning frequency is relatively small, it may not be possible to attenuate the harmonics with a filter.

[0005] The present invention has been made in view of the above problems, and an object thereof is to attenuate harmonics contained in an oscillation signal generated by a signal generation device.

Means for Solving the Problems

[0006] The signal generation device according to the first aspect of the present invention includes a signal generation circuit that generates a first signal having a first frequency, a filter that passes frequency components in a predetermined band including the first frequency among the frequency components included in the first signal, a frequency doubling circuit that generates a frequency doubled signal having a frequency doubled from the first frequency, and a phase synchronization circuit that generates a second signal having a second frequency based on an external reference signal, the phase synchronization circuit generating the second signal by synchronizing the phase of the external reference signal and the phase of a signal obtained by dividing the second signal, and a mixer that generates an output signal having an output frequency that is the sum of the frequency doubled frequency and the second frequency.

[0007] The filter may attenuate frequency components not included in the predetermined band among the frequency components included in the first signal. The frequency of the harmonic of the first frequency may not be included in the predetermined band of the filter.

[0008] The second frequency may be a frequency that is the difference between the frequency doubled frequency and the target frequency of the output frequency. The filter may be a surface acoustic wave filter. [Advantages of the Invention]

[0009] According to the present invention, there is an effect that harmonics included in the oscillation signal generated by the signal generation device can be attenuated. [Brief Description of the Drawings]

[0010]

Figure 1

Figure 2

[0011] [Configuration of Signal Generation Device] FIG. 1 shows the configuration of the signal generation device 100 of the present embodiment. The signal generation device 100 includes a multiplication circuit 101, a filter 103, a signal generation circuit 104, a filter 105, a multiplication circuit 106, a filter 107, a phase synchronization circuit 108, a VCO (Voltage-controlled oscillator) 109, a frequency divider 110, a mixer 111, a filter 112, and an amplifier 113.

[0012] The multiplication circuit 101 generates a signal obtained by multiplying the clock frequency of an external reference signal input via the input terminal 102 from an external device (not shown) or the like. The filter 103 is, for example, a band-pass filter. The filter 103 passes the frequency components of the signal input from the multiplication circuit 101 in a predetermined first band and attenuates the frequency components not included in the first band. The first band is determined, for example, by the specifications of the filter 103.

[0013] The signal generation circuit 104 is, for example, a DDS (Direct Digital Synthesizer). The signal generation circuit 104 generates a first signal having a first frequency. For example, the signal generation circuit 104 generates the first signal by converting the clock frequency of the external reference signal input from the multiplication circuit 101 to the first frequency. In the signal generation circuit 104, the first frequency of the generated first signal can be externally set by the user or the circuit designer.

[0014] FIG. 2 shows an example of the harmonics of the first signal generated by the signal generation circuit 104. The horizontal axis in FIG. 2 indicates the frequency. The vertical axis in FIG. 2 indicates the signal level. The broken line in FIG. 2 indicates the clock frequency of the external reference signal. The fundamental wave is the frequency component of the first frequency (f C ) included in the first signal. "Second harmonic" and "third harmonic" in FIG. 2 are the harmonics of the frequency twice (2f C ) and three times (3f C ) the first frequency, respectively.

[0015] "Second harmonic folding" in FIG. 2 is the clock frequency (f CLK) the frequency (f CLK - 2f C ) is a harmonic of. The "third - harmonic fold - back" on the left in Fig. 2 is the frequency obtained by subtracting the clock frequency from three times the first frequency (3f C - f CLK ) is a harmonic of. The "third - harmonic fold - back" in the center of Fig. 2 is the frequency obtained by subtracting three times the first frequency from twice the clock frequency (2f CLK - 3f C ) is a harmonic of. The frequencies of such folded - back harmonics tend to be close to the first frequency of the fundamental wave.

[0016] Filter 105 is, for example, a SAW (Surface Acoustic Wave) filter. Filter 105 passes the frequency components of the first signal generated by signal generation circuit 104 within a predetermined second band (corresponding to the predetermined band). The second band includes the first frequency of the first signal generated by signal generation circuit 104. Filter 105 attenuates the frequency components of the first signal generated by signal generation circuit 104 that are not included in the second band. The second band is, for example, a band determined by the frequency characteristics of filter 105.

[0017] Multiplication circuit 106 generates a multiplied signal with a multiplied frequency that multiplies the first frequency of the first signal generated by signal generation circuit 104. Filter 107 passes the frequency components of the multiplied signal input from multiplication circuit 106 within a predetermined third band and attenuates the frequency components not included in the third band. The third band is, for example, a band determined by the frequency characteristics of filter 107.

[0018] The phase-locked loop 108, VCO 109, and frequency divider 110 are a PLL (Phase-Locked Loop) that generates a second signal of a second frequency based on an external reference signal. The phase-locked loop 108 inputs a DC control signal for controlling the frequency of the signal generated by the VCO 109 to the VCO 109 based on the result of comparing the phase of the external reference signal with the phase of the divided signal obtained by dividing the second signal. The VCO 109 generates a second signal of a second frequency corresponding to the voltage of the DC control signal input from the phase-locked loop 108. The frequency divider 110 generates a divided signal obtained by dividing the second signal generated by the VCO 109. The frequency divider 110 feeds back the generated divided signal to the phase-locked loop 108.

[0019] Here, the phase-locked loop 108 changes the second frequency of the second signal generated by the VCO 109 by feedback control that changes the voltage of the DC control signal input to the VCO 109 based on the phase difference between the external reference signal and the fed-back divided signal. The phase-locked loop 108 synchronizes the phase of the external reference signal with the phase of the fed-back divided signal by this feedback control, and causes the VCO 109 to generate a second signal in this state. The VCO 109 inputs the generated second signal to the mixer 111.

[0020] The mixer 111 is an element that mixes the multiplied signal generated by the multiplier circuit 106 and the second signal input from the VCO 109. The mixer 111 generates an output signal having an output frequency that is the sum of the multiplication frequency of the multiplied signal and the second frequency of the second signal. The mixer 111 inputs the generated output signal to the filter 112.

[0021] The filter 112 is, for example, a band-pass filter. Among the frequency components of the output signal input from the mixer 111, it passes the frequency components of a predetermined fourth band and attenuates the frequency components not included in the fourth band. The fourth band is determined, for example, by the frequency characteristics of the filter 112. The amplifier 113 amplifies the output signal that has passed through the filter 112. The amplifier 113 outputs the amplified output signal to another device (not shown) that is the destination of the signal via the output terminal 114.

[0022] [Frequency setting method] The first frequency of the first signal generated by the signal generation device 100 can be set from the outside, for example. In the signal generation device 100, for the purpose of reducing spurs caused by the harmonics of the first signal generated by the signal generation circuit 104, the circuit designer sets the first frequency generated by the signal generation circuit 104 so that harmonics occur in the frequency band attenuated by the filter 105. In the example of FIG. 2, in the signal generation circuit 104, the first frequency is set so that the frequency of the harmonics of the first signal is not included in any of the second bands (double-headed arrows in FIG. 2) that can pass through the filter 105. The harmonics not included in the second band are harmonics below a predetermined target order, for example, harmonics below several hundred orders.

[0023] The output frequency of the output signal output by the mixer 111 changes according to the value of the first frequency. On the other hand, the target frequency of the output frequency is often predetermined according to the specifications of the device to which the signal is supplied. Therefore, in the signal generation device 100, the second frequency of the second signal may be set so that the changed output frequency matches the target frequency. The signal generation device 100 may adjust the second frequency so that the frequency of the difference between the multiplication frequency and the target frequency of the output frequency matches the second frequency of the second signal. For example, the signal generation device 100 sets a PLL circuit (for example, the free-running frequency of the VCO 109) composed of the phase-locked loop circuit 108, the VCO 109, and the frequency divider 110 so that the frequency of the difference between the multiplication frequency and the target frequency of the output frequency becomes the second frequency.

[0024] As an example, assume that the output frequency of the output signal is 3180 MHz, the first frequency is 530 MHz, the first band of the filter 105 ranges from 528 MHz to 532 MHz, the multiplication factor by the multiplication circuit 106 is 6 times, and the target order of the harmonics not included in the second band is 100 or less. At this time, the output frequency of the output signal output by the amplifier 113 is 3180 MHz.

[0025] Among the harmonics below the target order of the first signal, the harmonic having the frequency closest to the first frequency is the folded spur of the 73rd harmonic, which is 531.7 MHz. Since the frequency of this folded spur of the 73rd harmonic is within the first band of the filter 105, it passes through the filter 105. Therefore, there is a possibility that this harmonic is included in the output signal output by the amplifier 113.

[0026] On the other hand, when the first frequency is 530.5 MHz, the folded spur of the 73rd harmonic becomes 532.5 MHz, and the folded spur of the 73rd harmonic is not included in the first band. In this way, since the 73rd harmonic is attenuated by the filter 105, the output signal output by the amplifier 113 does not include the 73rd harmonic.

[0027] However, due to the change in the first frequency, the output frequency changes to 3183 MHz and does not match the target frequency. Therefore, the multiplication factor of the multiplier circuit 106 is changed so that the PLL circuit composed of the phase-locked loop circuit 108, the VCO 109, and the frequency divider 110 outputs a second signal of 1588.5 MHz as the second frequency. In this way, the output frequency of the output signal output by the amplifier 113 is set to the target frequency of 3180 MHz, and harmonics below a predetermined order can be sufficiently attenuated.

[0028] [Effect of the signal generation device 100 of the present embodiment] In this way, in the signal generation device 100, since the first frequency of the first signal is set so that the harmonic of the first signal can be attenuated by the filter 105, spurs caused by the harmonic of the first signal can be suppressed. At this time, by setting an appropriate frequency as the second frequency generated by the phase-locked loop circuit 108, the output frequency of the output signal generated by the mixer 111 can be made to match a predetermined target frequency.

[0029] As described above, the present invention has been explained using embodiments. However, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist. For example, all or part of the device can be configured by functionally or physically dispersing and integrating it in any unit. Also, new embodiments resulting from any combination of a plurality of embodiments are included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination have the effects of the original embodiments combined.

Explanation of Reference Numerals

[0030] 100 Signal generation device 101 Multiplier circuit 102 Input terminal 103 Filter 104 Signal generation circuit 105 Filter 106 Multiplier circuit 107 Filter 108 Phase synchronization circuit 109 VCO 110 Divider 111 Mixer 112 Filter 113 Amplifier 114 Output terminal

Claims

1. A signal generation circuit that generates a first signal of a first frequency; A filter that passes frequency components in a predetermined band including the first frequency among the frequency components included in the first signal; A frequency doubling circuit that generates a frequency doubled signal of a frequency doubled from the first frequency; A phase locked loop circuit that generates a second signal of a second frequency based on an external reference signal, the phase locked loop circuit generating the second signal by synchronizing the phase of the external reference signal and the phase of a signal obtained by dividing the second signal; A mixer that generates an output signal of an output frequency that is the sum of the frequency doubled frequency and the second frequency; A signal generation device comprising the above.

2. The filter attenuates frequency components not included in the predetermined band among the frequency components included in the first signal. The signal generation device according to Claim 1.

3. The frequency of the harmonic of the first frequency is not included in the predetermined band of the filter. The signal generation device according to Claim 1 or 2.

4. The second frequency is the frequency of the difference between the frequency doubled frequency and the target frequency of the output frequency. The signal generation device according to Claim 1 or 2.

5. The filter is a surface acoustic wave filter. The signal generation device according to Claim 1 or 2.

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