JP2011147005A - Frequency sweep circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency sweep circuit capable of performing high-speed frequency shift in a simple configuration. <P>SOLUTION: The frequency sweep circuit for modulating a frequency includes: a single frequency oscillator 10 for oscillating a single frequency; and a variable phase unit 20 for modulating the single frequency by inputting a temporally varying operation signal and varying a phase rotation amount in accordance with the operation signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a frequency sweep circuit that modulates a reference frequency according to an operation signal.

  FM-CW radar is a type of radar that measures the distance to an object, and is used for measuring weather fluctuations, measuring obstacles, and the like. The FW-CW radar can obtain a frequency proportional to the distance to the target by emitting a transmission wave frequency-modulated with a sawtooth wave and combining the reception wave scattered by the target with a part of the transmission wave. Yes (see Non-Patent Document 1). Therefore, in order to realize the FM-CW radar, a frequency sweep circuit capable of generating a frequency modulation signal of a sawtooth wave is required.

  The technique most often used as a frequency sweep circuit is a technique using a VCO (Voltage Controlled Oscillator). A VCO is an oscillator that can control the frequency of oscillation by an applied voltage. By appropriately changing the applied voltage, it is possible to emit a signal whose frequency changes to a sawtooth wave. In the VCO, the oscillation frequency becomes variable by changing the resonance condition of the resonance circuit according to the voltage. However, since the resonance frequency is likely to change depending on conditions such as temperature, a PLL (Phase locked loop) is often used in combination.

  FIG. 4 shows a frequency oscillator using a PLL. The PLL is a technique for comparing the high-accuracy reference signal oscillated from the crystal resonator with the output signal of the VCO with a phase comparator and applying feedback to increase the accuracy of the VCO oscillation frequency.

  A frequency sweep circuit using a PLL is described in Patent Document 1, for example.

The Institute of Electronics, Information and Communication Engineers “Antenna Engineering Handbook”, Ohmsha

JP-A-2005-150856

  In a VCO using a PLL, it takes a long time to change the frequency in order to make a comparison with the oscillation signal of the crystal resonator. As a result, there is a problem that the frequency sweep time becomes long. When the frequency sweep time becomes longer, the maximum measurement distance of the FM-CW radar increases unnecessarily, and the use efficiency of the frequency sweep width deteriorates. An example of this problem is given below.

  Consider the case where the required maximum measurement distance is 1.5 km and the maximum frequency transition width is 100 MHz. In this case, if the repetition time of frequency sweep is 10 microseconds, the combined frequency of the received wave when the distance to the target is 0 to 1.5 km is 0 to 100 MHz, and distance measurement using the entire frequency transition width is possible It is. However, due to the frequency sweep time limitation by the VCO, if 1 ms is used as the frequency sweep repetition time, the composite frequency of the received wave when the distance to the target is 0 to 1.5 km is 0 to 1 MHz, and the frequency transition width is The frequency range of 1 MHz to 100 MHz corresponding to 99% is not used.

  In order to improve the frequency sweep speed, a method that does not use a PLL is conceivable. However, in this case, since the frequency shift due to temperature or the like is large, there is a possibility that a signal is transmitted outside the frequency band permitted to be used.

  To deal with such a problem, Patent Document 1 proposes a frequency sweep oscillation circuit that enables high-speed and high-accuracy frequency modulation by using a memory circuit in addition to the PLL. However, in the configuration of Patent Document 1, in addition to the PLL configuration, a memory circuit, a CPU, and the like are required, and there is a problem that the circuit scale and manufacturing cost increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a frequency sweep circuit capable of high-speed frequency transition with a simple configuration.

  In order to achieve the above object, a first aspect of the present invention is a frequency sweep circuit that modulates a frequency, and inputs a single frequency oscillator that oscillates a single frequency, and an operation signal that changes with time, and The gist is to have a variable phase shifter that modulates the single frequency by changing the amount of phase rotation in accordance with the operation signal.

  Further, according to a second aspect of the present invention, in the first aspect of the present invention, the input operation signal is a voltage represented by a predetermined linear function with respect to time, and the variable phase shifter is the input The gist is to modulate the single frequency with a phase rotation amount changed according to a predetermined quadratic function.

  According to the present invention, it is possible to provide a frequency sweep circuit capable of high-speed frequency transition with a simple configuration.

It is a block diagram of the frequency sweep circuit which concerns on the 1st Embodiment of this invention. It is a block diagram which shows an example of a variable phase shifter. It is a block diagram of the frequency sweep circuit which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of a frequency oscillation circuit using a PLL.

[First Embodiment]
FIG. 1 is a diagram showing a frequency sweep circuit according to the first embodiment of the present invention.

  The frequency sweep circuit of the present embodiment includes a single frequency oscillator 10 and a variable phase shifter 20 that changes an internal effective electrical length by an operation signal from the outside. It is characterized in that a single frequency input from the single frequency oscillator 10 is modulated by changing the amount of phase rotation when passing through the variable phase shifter 20.

  The operation signal input to the variable phase shifter 20 is an operation signal that changes with time, and is an operation signal that is appropriate for performing frequency modulation desired by a device to which the frequency sweep circuit is applied. For example, when the frequency sweep circuit is applied to an FM-CW radar, an appropriate operation signal that periodically changes in time is input in order to perform sawtooth frequency modulation with a predetermined frequency sweep width required by the FM-CW radar. To do.

  The operation principle of this embodiment will be described below.

Assuming that the phase of the signal of the frequency f0 generated from the single frequency oscillator 10 is 2πf0t at the time of input to the variable phase shifter 20 and θ (t) at the time of output, their relationship can be described by the following equation 1. .

Here, G is the amount of phase rotation generated by the variable phase shifter 20 and is a constant when the electrical length of the variable phase shifter 20 does not change. Further, when the angular frequency ω1 at the output of the variable phase shifter 20 is obtained by taking the time differentiation of both sides of Equation 1, the following Equation 2 is obtained.

  In this way, the frequency can be changed by changing the electrical length of the variable phase shifter 20 by the operation signal changing with time and changing the phase rotation amount, that is, changing the phase rotation amount G with time.

  In the frequency sweep circuit of the present embodiment, the single frequency oscillator 10 can be used as a generation source of f0 which is the fundamental frequency. Therefore, in the present embodiment, the VCO and its control circuit are not required, and the frequency sweep circuit can be manufactured at low cost. That is, in this embodiment, a frequency sweep circuit capable of frequency transition with a simple configuration can be provided.

  In addition, since the frequency transition period according to the present embodiment depends on the change rate of the phase rotation amount G, for example, when the variable phase shifter 20 using a semiconductor circuit capable of high-speed operation is used, high-speed frequency modulation is possible. is there. As the variable phase shifter 20, for example, by designing a transmission line in which the length of a waveguide such as a waveguide and a coaxial line is physically changed, or a transmission line provided with a variable ground capacitance, and changing the capacity, For example, there is a method for changing the effective electrical length. However, the present invention is not limited to these, and any variable phase shifter that can pass a signal having a frequency to be swept and can change a desired phase range may be used.

  Note that the frequency modulation signal output from the frequency sweep circuit of the present embodiment can be applied to, for example, modulation of a transmission wave of FM-CW radar or spectroscopy.

[Second Embodiment]
FIG. 2 is a diagram showing a frequency sweep circuit according to the second embodiment of the present invention.

This embodiment is different from the first embodiment in that the variable phase shifter 20A that can describe the phase rotation amount Δθ with a quadratic function of the following expression 3 with respect to the input control voltage is different from the FM-CW radar. And so on.

  Here, α and β are predetermined coefficients and constants when the phase rotation amount Δθ is described as a quadratic function of the applied voltage V. These α and β can be arbitrarily set by the designer.

  In the first embodiment, an appropriate operation signal needs to be input to the variable phase shifter 20 in order to perform sawtooth frequency modulation desired by the FM-CW radar. For example, when a voltage is used as the operation signal, it is necessary to produce a signal generator that generates an operation signal (voltage) having a complicated time change.

  In the present embodiment, by using the variable phase shifter 20A that changes the phase rotation amount in accordance with Equation 3 with respect to the input voltage, it is possible to perform sawtooth wave-like frequency modulation even with a simple time-varying operation signal (voltage). Become. The operation of this embodiment will be described below.

The control voltage applied to the variable phase shifter 20A of the present invention is represented by the following formula 4.

Here, γ and η are predetermined coefficients and constants when the voltage V is described as a linear function of time, and can be arbitrarily set by the designer. Substituting Equation 3 and Equation 4 into Equation 2 yields Equation 5 below.

That is, the frequency f (t) output from the variable phase shifter 20A is expressed by the following Expression 6, and can be described by a predetermined linear function with respect to time.

  That is, by using the configuration of the present embodiment and applying a voltage expressed by a predetermined linear function with respect to time, the frequency output from the variable phase shifter 20A can also be changed by a linear function. For example, a voltage source that generates a sawtooth wave may be used as the voltage source of the voltage used in the present embodiment, and the power source circuit using a variable resistor can be easily realized.

  FIG. 3 is a configuration diagram showing an example of the variable phase shifter 20A of the present embodiment. The illustrated variable phase shifter 20A includes a phase shifter composed of at least one transmission line 22 and at least one field effect transistor (FET) 23, and a voltage circuit 21 for applying a control voltage to the phase shifter. Have The phase shifter adjusts the amount of phase rotation by changing the gate-drain capacitance, which is a parasitic capacitance of the field effect transistor 23, and the gate-source capacitance depending on the voltage applied to the gate of the field effect transistor 23. It is possible.

  Since the variable amount of the phase can be adjusted by the number of field effect transistors 23 connected in the variable phase shifter 20A, the designer can arbitrarily design it. Further, by using the field effect transistor 23 capable of high-speed operation, the amount of phase rotation can be changed with sufficient responsiveness to a sudden change in control voltage.

  In the present embodiment described above, similarly to the first embodiment, the single frequency oscillator 10 can be used as the generation source of f0, which is the fundamental frequency. Therefore, the VCO and its control circuit are not required, The frequency sweep circuit can be manufactured at low cost. That is, in the present embodiment, it is possible to provide a frequency sweep circuit capable of high-speed frequency transition with a simple configuration.

  Further, the frequency modulation signal output from the frequency sweep circuit according to the present embodiment can be applied to, for example, modulation of FM-CW radar transmission waves or spectroscopy, as in the first embodiment.

  In the present embodiment, the variable phase shifter 20A is such that the amount of phase rotation changes according to a quadratic function of voltage, but it does not have to be a strict quadratic function, and may be approximated. Further, it can be implemented by approximation of a quadratic function that is limited to a predetermined voltage range.

  The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the gist.

DESCRIPTION OF SYMBOLS 10 Single frequency oscillator 20 Variable phase shifter 20A Variable phase shifter 21 Voltage circuit 22 Transmission line 23 Field effect transistor (FET)

Claims (2)

A frequency sweep circuit for modulating the frequency,
A single frequency oscillator that oscillates a single frequency; and
A frequency sweeping circuit comprising: a variable phase shifter that modulates the single frequency by inputting an operation signal that changes with time and changing a phase rotation amount according to the operation signal. The frequency sweep circuit of claim 1,
The input operation signal is a voltage represented by a predetermined linear function with respect to time,
The frequency sweeping circuit, wherein the variable phase shifter modulates the single frequency with a phase rotation amount changed according to a predetermined quadratic function with respect to the input voltage.

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