Frequency Conversion Circuit

Abstract

To provide a frequency conversion circuit capable of suppressing spurious.SOLUTION: A frequency conversion circuit comprises a first mixer, a first oscillator connected to the first mixer, a switch connected to an output side of the first mixer, first and second band pass filters connected in parallel to the switch, a second mixer connected to the first and second band pass filters, a second oscillator connected to the second mixer, and a controller. Correspondingly to an input wave of the first mixer, an output wave having a fixed frequency is outputted from the second mixer. The controller controls the switch in such a manner that output of the first mixer is inputted to the first or second band pass filter, and controls the first oscillator in such a manner that a local signal inputted from the first oscillator to the first mixer in a specific oscillation frequency of the first oscillator has a frequency subtracting the double of the fixed frequency from the specific oscillation frequency.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiment relates to a frequency conversion circuit. [Background technology]

[0002] The frequency conversion circuit used for wideband microwave reception includes a mixer that changes the local frequency over a wide range, which can result in unwanted spurious signals generated by the mixer being included in the output frequency band of the frequency conversion circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-120822 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiment provides a frequency conversion circuit that can suppress spurious signals. [Means for solving the problem]

[0005] A frequency conversion circuit according to an embodiment includes a first mixer, a first oscillator having a variable frequency connected to the first mixer, a switch connected to an output side of the first mixer, a first band-pass filter connected to the switch, a second band-pass filter connected to the switch in parallel with the first band-pass filter, a second mixer connected to the output sides of the first band-pass filter and the second band-pass filter, a second oscillator connected to the second mixer, and a controller that controls the first oscillator and the switch. The frequency conversion circuit outputs an output wave from the second mixer that corresponds to an input wave of the first mixer and has a constant frequency, wherein the pass band of the first band-pass filter has a center frequency equal to the sum of the oscillation frequency of the second oscillator and the constant frequency, and the pass band of the second band-pass filter has a center frequency equal to the sum of the oscillation frequency of the second oscillator and the constant frequency. The aforementioned The first mixer has a center frequency obtained by subtracting the constant frequency from an oscillation frequency, and the controller sweeps the oscillation frequency of the first oscillator, and the output of the first mixer is input to the first band-pass filter. Selecting between an A mode and a B mode in which the output of the first mixer is input to the second band-pass filter The switch Switching Control the In the A mode, the frequency of the input from the first mixer to the first band-pass filter is the oscillation frequency of the first oscillator minus the frequency of the input wave, and in the B mode, the frequency of the input from the first oscillator to the second band-pass filter is the oscillation frequency of the first oscillator minus the frequency of the input wave and twice the constant frequency, and the controller switches from the A mode to the B mode if the output wave contains a spurious during the sweep process in the A mode, and from the B mode to the A mode if the output wave contains a spurious during the sweep process in the B mode. The switch Switching Control. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a block diagram showing a frequency conversion circuit according to an embodiment; [Figure 2] FIG. 2 is another block diagram showing a frequency conversion circuit according to an embodiment. [Figure 3] FIG. 10 is a block diagram showing a frequency conversion circuit according to a modified example of the embodiment. [Figure 4] 10 is a graph showing characteristics of a frequency conversion circuit according to a modified example of the embodiment. [Figure 5] 10 is a graph showing another characteristic of the frequency conversion circuit according to the modified example of the embodiment. [Figure 6] 10 is a graph showing output characteristics of a frequency conversion circuit according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. Identical parts in the drawings are assigned the same numbers, and detailed descriptions thereof will be omitted as appropriate, and different parts will be described. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc., are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing.

[0008] 1 is a block diagram showing a frequency conversion circuit 1 according to an embodiment. The frequency conversion circuit 1 is configured to convert a wideband microwave into an output wave having a constant frequency and input it to a digital signal processing circuit (not shown) via, for example, an A / D conversion circuit.

[0009] As shown in FIG. 1, the frequency conversion circuit 1 includes a first oscillator 10, a first mixer 20, a switch 30A, a switch 30B, a controller 40, a first bandpass filter 50A, a second bandpass filter 50B, a second mixer 60, and a second oscillator 70.

[0010] The first oscillator 10 is connected to the first mixer 20 and supplies a first local signal. The first oscillator 10 is a variable oscillator that can sweep the oscillation frequency. The switch 30A is connected to the output side of the first mixer 20. The controller 40 controls the oscillation frequency of the first oscillator 10 and controls the switching of the switch 30A.

[0011] The first band-pass filter 50A and the second band-pass filter 50B are connected in parallel to the switches 30A and 30B. The output of the first mixer 20 is input to either the first band-pass filter 50A or the second band-pass filter 50B via the switch 30A. The outputs of the first band-pass filter 50A and the second band-pass filter 50B are input to the second mixer 60 via the switch 30B. The controller 40 simultaneously controls the switches 30A and 30B to input the output of the first band-pass filter 50A or the second band-pass filter 50B selected by the switch 30A to the second mixer 60.

[0012] The second mixer 60 is connected to the output sides of the first band-pass filter 50A and the second band-pass filter 50B via the switch 30B. The second oscillator 70 is connected to the second mixer 60 and supplies a second local signal. The oscillation frequency of the second oscillator 70 is fixed.

[0013] The frequency conversion circuit 1 outputs a signal corresponding to the input wave of the first mixer 20 from the second mixer 60. The frequency conversion circuit 1 converts the output of the second mixer 60 into a signal having a constant frequency f OUT The device is configured to have:

[0014] The controller 40 sweeps the oscillation frequency of the first oscillator 10 and switches the switches 30A and 30B. The controller 40 operates the first oscillator 10 in, for example, two modes, mode A (without frequency shift) and mode B (with frequency shift). In mode A, the first oscillator 10 is controlled to oscillate within a predetermined frequency range. In mode B, the first oscillator 10 is controlled to oscillate within a predetermined frequency range from the oscillation frequency in mode A to the frequency f of the output wave. OUT It is controlled to oscillate at a frequency twice that of the reference frequency.

[0015] The frequency of the first local signal input from the first oscillator 10 to the first mixer 20 (hereinafter referred to as the first local frequency f LI) is swept within the frequency range of A mode. The controller 40 controls the oscillator 10 to operate in B mode at a specific frequency within that range. The switch 30A is controlled to input the output of the first mixer 20 to the first band-pass filter 50A while the first oscillator 10 is operating in A mode. The switch 30A is also controlled to input the output of the first mixer 20 to the second band-pass filter 50B at a specific frequency.

[0016] The first mixer 20 mixes the first local frequency f LI to the input wave frequency f IN The frequency (f LI -f IN ) is input to a first bandpass filter 50A.

[0017] In addition, the first mixer 20 generates a first local frequency f LI to the input wave frequency f IN and the frequency of the output wave, f OUT The frequency (f LI -f IN -2×f OUT ) is input to a second bandpass filter 50B via a switch 30A.

[0018] The pass band of the first band-pass filter 50A is the frequency of the second local signal output from the second oscillator 70 to the second mixer 60 (hereinafter referred to as the second local frequency f LO ) and the frequency of the output wave f OUT The passband of the second bandpass filter 50B has a center frequency equal to the sum of the second local frequency f LO to frequency f OUT The center frequency is subtracted from the center frequency.

[0019] For example, the frequency band of the input wave is minf IN ≦f IN ≦maxf IN Then, the first band-pass filter 50A has a filter frequency of f LI-maxf IN From f LI -minf IN The frequency f of the output of the first mixer 20, which varies in frequency from LO +f OUT The second band-pass filter 50B outputs a signal having f LI -maxf IN -2×f OUT From f LI -minf IN -2×f OUT The frequency f of the output of the first mixer 20, which varies in frequency from LO -f OUT The signal output has the following characteristics:

[0020] The controller 40 sweeps the oscillation frequency of the first oscillator 10, for example, within the frequency range shown in the following equation (1).

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[0021] The second mixer 60 mixes the frequency (f LO +f OUT ) to the second local frequency f LO Frequency f minus OUT The second mixer 60 outputs a signal having a second local frequency f LO to the frequency (f LO -f OUT ) minus the frequency f OUT In this way, the first band-pass filter 50A and the second band-pass filter 50B output a signal having a constant frequency f OUT A signal having the following formula is output:

[0022] The controller 40 sweeps the oscillation frequency of the first oscillator 10 within the frequency range shown in equation (1), thereby causing the second mixer 60 to output an output wave corresponding to changes in signal strength within the frequency band of the input wave.

[0023] 2 is another block diagram showing the frequency conversion circuit 1 according to the embodiment. FIG. 2 shows a specific example of the frequency conversion circuit 1.

[0024] In this example, the input wave to the first mixer 20 has a frequency band of 2 to 10 GHz. The first oscillator 10 operates in an A mode with an oscillation frequency of 23 to 31 GHz and in a B mode with an oscillation frequency of 21 to 29 GHz.

[0025] The center frequency of the pass band of the first band pass filter 50A is 21 GHz. The center frequency of the pass band of the second band pass filter 50B is 19 GHz. The second local frequency f LO The frequency f of the output of the second mixer 60 is 20 GHz. OUT is 1 GHz. The frequency conversion circuit 1 converts a change in signal strength in the microwave band of, for example, 2 to 10 GHz into a signal with a frequency of 1 GHz and outputs it.

[0026] 3 is a block diagram showing a frequency conversion circuit 2 according to a modified example of the embodiment. In the frequency conversion circuit 2, a multiplier 90 is provided between the first mixer 20 and the first oscillator 80.

[0027] The first oscillator 80 is a variable oscillator. The multiplier 90 multiplies the frequency f of the first local signal output from the first oscillator 80. OB For example, double the first local frequency f LI and input to the first mixer 20.

[0028] The first oscillator 80 has an A mode that sweeps in the frequency range of 11.5 to 15.5 GHz and a B mode that operates in the frequency range of 10.5 to 14.5 GHz. The controller 40 controls the frequency f OUT The first oscillator 80 is controlled to oscillate at a frequency obtained by subtracting the frequency of the first oscillator 80 from the frequency of the second oscillator 80 .

[0029] In this example, the first local frequency f LIis input to the first mixer 20. In the frequency conversion circuit 2, the multiplier 90 is inserted immediately before the first mixer 20 so that the first oscillator 80 does not operate at a high frequency.

[0030] 4(a) and 4(b) are graphs showing the characteristics of the frequency conversion circuit 2 according to a modified example of the embodiment. 4(a) and 4(b) show the characteristics when the switch 30A is controlled so that the output of the first mixer 20 is input to the first band-pass filter 50A.

[0031] For example, when a first local signal is input to the first mixer 20, its leakage and its harmonic components are also mixed, and so-called spurious signals are output from the first mixer 20. Furthermore, when a 2x multiplier 90 is used, harmonic components of the first harmonic wave, the third harmonic wave, and higher are also mixed by the first mixer 20 and output.

[0032] Figure 4(a) is a graph showing the characteristics in B mode, as shown in Table 1. The horizontal axis is the frequency f of the input wave. IN The vertical axis is the frequency of the output wave f OUT The symbols A, B, C, and D in the figure represent the spurious signals SP_A, SP_B, SP_C, and SP_D that appear. [Table 1] where frequency f OUT is expressed by the following equation (2): f OB is the oscillation frequency of the first oscillator 80.

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[0033] Each of the spurious signals SP_A, SP_B, SP_C, and SP_D is expressed by the formula (3).

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[0034] As shown in Figure 4(a), each spurious appears across the output frequency band. The frequency at which the spurious appears is the frequency f IN Depends on.

[0035] Figure 4(b) shows the frequency of the input wave f IN The horizontal axis shows the frequency of the input wave f IN Here, the frequency of the output wave is f OUT is 1 GHz. As shown in Figure 4(b), f IN Eight spurious signals appear in the frequency band from 2 to 10 GHz.

[0036] 5(a) and 5(b) are graphs showing other characteristics of the frequency conversion circuit 2 according to the modified example of the embodiment. 5(a) and 5(b) show the characteristics when the switch 30A is controlled so that the output of the first mixer 20 is input to the second band-pass filter 50B.

[0037] Figure 5(a) is a graph showing the characteristics in A mode, as shown in Table 2. The horizontal axis is the frequency f of the input wave. IN The vertical axis is the frequency of the output wave f OUT In the figure, the symbols A, B, C, and D represent spurious signals SP_A, SP_B, SP_C, and SP_D, respectively. [Table 2]

[0038] As shown in Figure 5(a), each spurious appears across the output frequency band. As in Figure 4(a), the spurious appears at the frequency f IN Depends on.

[0039] Figure 5(b) shows the frequency of the input wave f IN The horizontal axis is the frequency of the input wave f IN Here, the frequency of the output wave is f OUT is 1GHz.

[0040] In this example, the input wave frequency f IN Eight spurious signals appear in the frequency band of 2 to 10 GHz. The frequency f of the input wave where spurious signals appear is IN 4(b). That is, the frequency f at which spurious components appear when the output of the first mixer 20 is input to the first band-pass filter 50A is IN is the frequency f at which spurious signals appear when the output of the first mixer 20 is input to the second band-pass filter 50B. IN is different.

[0041] 6 is a graph showing the output characteristics of the frequency conversion circuit 2 according to the modified embodiment. The horizontal axis represents the frequency f IN The vertical axis represents the presence or absence of spurious signals. Here, the frequency of the output wave f OUT is 1GHz.

[0042] In the frequency conversion circuit 2, the controller 40 (see FIG. 3) controls the switch 30A so that the output of the first mixer 20 is input to the first band-pass filter 50A, and the first oscillator 80 operates in the A mode. That is, the oscillation frequency f OB is swept from 11.5GHz to 15.5GHz.

[0043] The controller 40 controls the oscillation frequency f of the first oscillator 80. OB While sweeping, 2×f OB -f LO -f OUT The value of and the spurious frequency f shown in Figure 4(b) IN When the specific frequencies match, the operation of the first oscillator 80 is switched to mode B, and the switch 30A is controlled so that the output of the first mixer 20 is input to the second band-pass filter 50B.

[0044] Next, the controller 40 calculates 2×f OB -f LO -f OUT The value of is the frequency f without spurious shown in Figure 4(b).IN When the first mixer 20 outputs the first signal, the first oscillator 80 switches to mode A, and the switch 30A is controlled so that the output of the first mixer 20 is input to the first band-pass filter 50A.

[0045] In this way, by controlling the first oscillator 80 and the switches 30A and 30B, it is possible to change the frequency of the spurious components contained in the output wave. For example, the A mode or the B mode is selected so that the spurious components are not mixed into the output frequency band as much as possible. This allows the frequency f of the input wave to be adjusted. IN The number of spurious signals appearing in the frequency band of 2 to 10 GHz can be reduced to, for example, 5 (see FIG. 6).

[0046] In the frequency conversion circuits 1 and 2 according to the embodiments, the first oscillators 10 and 80 are operated in A mode and B mode, and the output of the first mixer 20 is input to the first band-pass filter 50A or the second band-pass filter 50B according to the respective modes, thereby suppressing spurious signals contained in the output wave.

[0047] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0048] 1, 2... frequency conversion circuit, 10, 80... first oscillator, 20... first mixer, 30A, 30B... switch, 40... controller, 50A... first band-pass filter, 50B... second band-pass filter, 60... second mixer, 70... second oscillator, 90... multiplier

Claims

1. a first mixer; a first oscillator having a variable frequency connected to the first mixer; a switch connected to the output side of the first mixer; a first bandpass filter connected to the switch; a second bandpass filter connected in parallel with the first bandpass filter to the switch; a second mixer connected to the output sides of the first bandpass filter and the second bandpass filter; a second oscillator connected to the second mixer; a controller that controls the first oscillator and the switch; Equipped with a frequency conversion circuit that outputs an output wave having a constant frequency from the second mixer, the output wave corresponding to an input wave of the first mixer, the passband of the first bandpass filter has a center frequency equal to the sum of the oscillation frequency of the second oscillator and the constant frequency; a pass band of the second band pass filter has a center frequency obtained by subtracting the constant frequency from the oscillation frequency of the second oscillator; the controller sweeps an oscillation frequency of the first oscillator and controls switching of the switch to select an A mode in which an output of the first mixer is input to the first band-pass filter and a B mode in which the output of the first mixer is input to the second band-pass filter; In the A mode, the frequency of the input from the first mixer to the first band-pass filter is a frequency obtained by subtracting the frequency of the input wave from the oscillation frequency of the first oscillator, In the B mode, the frequency of the input from the first oscillator to the second band-pass filter is a frequency obtained by subtracting the frequency of the input wave and twice the constant frequency from the oscillation frequency of the first oscillator, The controller controls switching of the switch from the A mode to the B mode when the output wave contains a spurious component during the sweep process in the A mode, and from the B mode to the A mode when the output wave contains a spurious component during the sweep process in the B mode.

2. the input wave has a band between a first frequency and a second frequency higher than the first frequency; 2. The frequency conversion circuit according to claim 1, wherein the first oscillator is swept between a lower limit frequency obtained by adding the first frequency to the sum of the oscillation frequency of the second oscillator and the constant frequency, and an upper limit frequency obtained by adding the second frequency to the sum of the oscillation frequency of the second oscillator and the constant frequency.

3. 3. The frequency conversion circuit according to claim 1, wherein the first mixer is configured to input an output having a frequency obtained by subtracting the frequency of the input wave from the frequency of the local signal input from the first oscillator to the first band-pass filter or the second band-pass filter via the switch.

4. 4. The frequency conversion circuit according to claim 1, wherein the output wave of the constant frequency having a frequency obtained by subtracting the oscillation frequency of the second oscillator from the frequency of the output of the first band-pass filter or the second band-pass filter is output from the second mixer.

5. 5. The frequency conversion circuit according to claim 1, further comprising a multiplier provided between the first oscillator and the first mixer.

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