JP2003158402A - Variable attenuator and variable attenuation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable attenuator which adjusts the output amplitude of the sine-wave signal generated by a sine-wave generating circuit and is characterized in that the constitution is simple and inexpensive and the attenuation quality can visually be grasped. SOLUTION: The variable attenuator comprises a demultiplexing means which demultiplexes and outputs an AC input signal vi to two or more transmission lines, a phase adjusting means L which adjusts the phase of at least one of the branched and filtered outputs, and a multiplexing means which multiplexes all the demultiplexed outputs including the phase-adjusted demultiplexed output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable attenuator that attenuates an AC signal such as a sine wave signal to an arbitrary value.

[0002]

2. Description of the Related Art As a variable attenuator of this kind of AC signal, a diode is used to utilize the bias dependence of the forward resistance of the diode, and a FET is used to depend on the gate voltage dependence of the channel cross-sectional area. Those that utilize are known. An example of the former is described in Japanese Utility Model Laid-Open No. 05-009029. In the publication, as shown in FIG. 7, "PIN diode 1 is connected in series in a signal line composed of signal input terminal 3 and signal output terminal 6 via capacitors 2 and 5.
And a forward current is passed through the PIN diode through first and second resistors 4 and 5 connected to the cathode and anode of the PIN diode, respectively, and the forward current is changed to change the signal. In a signal attenuator that changes the amount of attenuation of a variable capacitance diode (varactor diode) connected in reverse bias between the signal line and a ground conductor.
12 and the forward current of the PIN diode,
A signal attenuator provided with voltage control means for changing the reverse bias voltage of the variable capacitance diode "
Is disclosed.

An example of the latter is shown in FIG. FIG. 2 shows that a FET composed of a source (S), a drain (D) and a gate (G) is connected between a sine wave input and a sine wave output, and a control voltage is applied to the gate from the bias circuit. The amount of attenuation between the input and the output is changed by the gate voltage dependence of the channel cross-sectional area.

FIG. 3 is a diagram for explaining the control of the attenuation amount (resistance value) of the FET. The source (S), the drain (D), the gate (G), the channel and the depletion layer constituting the FET. Shows the relationship. By controlling the potential of the gate (G) by the bias circuit, the depletion layer region immediately below the gate electrode is controlled. When the depletion layer region spreads, the channel region is limited and the resistance between the source (S) and the drain (D) increases.

[0005]

However, the conventional signal attenuator has the following problems. -Harmonic components are generated in the process of signal attenuation, and harmonic components are included in the output waveform. -A bias power supply for varying the amount of attenuation is required. -Since it is composed of active elements such as diodes and FTE, it is easily affected by parasitic reactance. -I / O impedance and frequency are easily degraded. -To accurately grasp the relationship between the amount of attenuation and the amount of control, the model and actual measurement of the active element must be used, which is complicated and has a large variation.

An object (object) of the present invention is to adjust the output amplitude of a sine wave signal generated from a sine wave generating circuit used as a signal source of a frequency characteristic measuring instrument such as a network analyzer, which has a simple structure and is inexpensive. Another object of the present invention is to provide a variable attenuator having a feature that the amount of attenuation can be visually grasped.

[0007]

In order to solve the above problems, the demultiplexing means for demultiplexing and outputting an AC input signal to two or more transmission lines, and the phase of at least one demultiplexing output of the demultiplexing output are adjusted. A variable attenuator is constituted by the phase adjusting means for performing the above-mentioned phase adjustment and the combining means for combining all the demultiplexed outputs including the phase adjusted demultiplexed outputs. (Claim 1)

The phase adjusting means uses a line stretcher. (Claim 2) By adjusting the phase of the signal demultiplexed by the line stretcher, it is possible to obtain a variable attenuator having a simple structure without using an active element and requiring no bias power supply. Further, it is particularly suitable when the AC input signal is a sine wave or a cosine wave. (Claim 3) In addition, as the line stretcher, a plurality of line stretchers having different ratings can be selectively provided in one transmission path. (Claim 4)

Further, the line stretcher can visually recognize the attenuation amount by displaying a scale of the attenuation amount corresponding to the input AC frequency according to the movable length thereof. (Claim 5) Further, by providing the variable attenuator according to any one of claims 1 to 5 in the sine wave signal generation circuit, the amplitude of the output sine wave signal can be arbitrarily changed. (Claim 6)

Demultiplexing and outputting an AC input signal to two or more transmission lines; adjusting the phase of at least one demultiplexing output of the demultiplexing outputs; and including all of the phase-adjusted demultiplexing outputs. The amplitude of the AC input signal is arbitrarily changed in the step of combining the demultiplexed outputs of. (Claim 7)

The phase adjustment is performed by a line stretcher. (Claim 8) Further, the present invention is applied to a case where a sine wave or a cosine wave is used as the AC input signal. (Claim 9) In adjusting the phase, a plurality of line stretchers having different ratings are selectively used according to the frequency of the input AC. (Claim 10)

[0012]

1 is a block diagram of a variable attenuator of the present invention.
Will be explained. FIG. 1 is a diagram for explaining the principle of the variable attenuator of the present invention, in which a sine wave input signal (Vi) is demultiplexed (in this case, demultiplexed) and input to a transmission line 1 and a transmission line 2. To do. Sine wave signal (V1) flowing through transmission line 1
The sine wave signal flowing through is (V2). A line stretcher is connected to one transmission line 2 to combine the outputs of the transmission line 1 and the transmission line 2 to obtain a sine wave output signal whose amplitude is attenuated (variable).

Here, the line stretcher is a device capable of adjusting the amount of phase shift of the input signal in a state where the impedance is kept constant by expanding and contracting the movable portion inserted inside the coaxial tube. .

Next, the principle of varying (attenuating) the amplitude of the sine wave input signal by the phase shift will be described. In FIG. 1, when the sine wave input signal is Vi (t), Vi (t) = Sinωt (1) where ω is the angular frequency. Further, the signal branched to the transmission line 1 is V1 (t), and the signal branched to the transmission line 2 is V2 (t). V1 (t) = V2 (t) = 1/2 Sinωt (2) If the phase shift amount by the line stretcher is Φ, the sine wave output signal Vo (t) after combining is Vo (t ) = 1 / 2Sin ωt + 1 / 2Sin (ωt + Φ) ・ ・ ・ ・ ・ (3) ＝ (CosΦ / 2) × Sin (ωt ＋ Φ / 2) ・ ・ ・ ・ ・ (4) Therefore, the attenuation A is expressed in decibels. , A = −20 × log ₁₀ [CosΦ / 2] [dB] (5)

The waveform of FIG. 4 represents the change in the amplitude of the sine wave output signal when the phase shift amount Φ by the line stretcher is 0, 45, 90, 135 [deg]. In addition,
The frequency of the sine wave input signal in this case is 10 GHz.
As shown in FIG. 4, it can be understood that the amplitude of the sine wave output signal decreases as the phase shift amount Φ by the line stretcher increases to 0, 45, 90, 135 [deg].

FIG. 5 is a graph showing the relationship between the phase shift amount Φ [deg] and the attenuation amount [dB] by the line stretcher, and the attenuation amount according to the change of the phase shift amount Φ [deg]. The change in [dB] is shown as shown. Even in this case, the frequency of the sine wave input signal is 10 GH.
z.

In FIG. 1, by adding a scale indicating the amount of attenuation according to the movable length of the movable portion of the line stretcher, the amount of attenuation of the sine wave input signal can be directly calculated from the movable length (scale) of the line stretcher. It becomes possible to grasp visually. Since the attenuation amount of the sine wave input signal according to the movable length of the line stretcher changes according to the frequency of the sine wave input signal, it is necessary to provide a scale for each frequency.

Next, an example in which the movable length (scale) of the line stretcher changes according to the frequency of the input sine wave signal will be described with reference to the tables and graphs shown in FIGS. 6 (a), 6 (b) and 6 (c). Explain. In Figure 6, the frequency of the sine wave input signal is 10GHz, 1GHz
And 0.1 GHz. The movable distance of the line stretcher required to change the attenuation of the sine wave input signal from 1 to 15 (dB) at each frequency (m
m) is shown.

Although the line stretcher is connected only to the transmission line 2 in FIG. 1, it is also possible to connect it to the transmission line 1. Further, in FIG. 1, the sine wave input signal is split into two, but it is also possible to split the output into three or more split waves and combine the outputs. Furthermore, in the figure, the line stretcher is used for the phase shift of the sine wave input signal, but it can be replaced with another phase shift device as long as it has a function of shifting the phase. It is also possible to provide a plurality of line stretchers having different characteristics and switch to an arbitrary one.

[0020]

According to the invention described in claim 1, the demultiplexing means for demultiplexing and outputting the AC input signal to two or more transmission lines, and the phase adjustment for adjusting the phase of at least one demultiplexed output of the demultiplexed output. By forming a variable attenuator by means and a multiplexing means for multiplexing all the demultiplexed outputs including the phase-adjusted demultiplexed output, the drawbacks of the conventional attenuator using a diode or FET are solved. The new variable attenuator is obtained.

Further, in the invention described in claim 2, the phase adjusting means is a variable attenuator having a simple structure without using an active element by using a line stretcher and requiring no bias power supply. Obtainable. According to the invention described in claim 3, a variable attenuator particularly suitable for the case where the AC input signal is a sine wave or a cosine wave can be obtained. Further, in the invention according to claim 4, as the line stretcher, a plurality of line stretchers having different ratings are provided so as to be selectable in one transmission path. Therefore, an optimum line according to the frequency of the AC input signal is provided. Stretchers can be used.

Further, in the invention according to claim 5, the attenuation amount is visually displayed on the line stretcher by displaying the attenuation amount scale corresponding to the input AC frequency corresponding to the movable length thereof. It will be possible to grasp. Further, in the invention described in claim 6, since the variable attenuator according to any one of claims 1 to 5 is provided in the sine wave signal generation circuit, the amplitude of the output sine wave signal can be arbitrarily changed. .

According to a seventh aspect of the invention, a step of demultiplexing the AC input signal to two or more transmission lines, a step of adjusting the phase of at least one demultiplexing output of the demultiplexing outputs, and the phase With the step of combining all the demultiplexed outputs including the adjusted demultiplexed output, without using active elements,
The amplitude of the AC input signal can be changed arbitrarily.

According to the eighth aspect of the invention, since the phase is adjusted by the line stretcher, an output in which the generation of harmonic components is suppressed can be obtained. In addition, claim 9
The invention described in (4) is suitable for the one using a sine wave or a cosine wave as the AC input signal. Further, in the invention according to claim 10, in the phase adjustment, a plurality of line stretchers having different ratings are selectively used according to the frequency of the input alternating current, so that the optimum line depending on the frequency of the alternating current input signal. Stretchers can be used.

As described above, when the line stretcher is used, the following effects can be obtained.・ Because it is composed of only passive elements without using diodes or FETs, there is no need for a bias power supply. -Because it is composed of only passive elements, it is possible to suppress the generation of harmonic components. -Adjustment and setting of the amount of attenuation is performed by changing the movable length of the line stretcher, so that the amount of attenuation can be visually ascertained by marking the movable portion of the line stretcher. A variable attenuator with a simple and inexpensive structure can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of a variable attenuator of the present invention.

FIG. 2 is a diagram showing a configuration of a variable attenuator using an FET.

FIG. 3 is a diagram for explaining the operating principle of a FET.

FIG. 4 is a waveform diagram showing a change in amplitude of a sine wave output signal according to a phase shift amount.

FIG. 5 is a graph showing the relationship between the amount of phase shift and the amount of attenuation.

FIG. 6 is a diagram for explaining that the relationship between the attenuation amount and the movable length of the line stretcher changes according to the frequency.

FIG. 7 is a diagram showing a configuration of a variable attenuator using diodes.

[Explanation of symbols]

Vi Sine wave input signal V1 First demultiplexed signal V2 Second split signal Vo Sine wave output signal L line stretcher M scale

Claims (10)

[Claims] 1. A demultiplexing unit that demultiplexes and outputs an AC input signal to two or more transmission lines, a phase adjusting unit that adjusts the phase of at least one demultiplexing output of the demultiplexing output, and the phase-adjusted component. A variable attenuator comprising: a combining unit that combines all the demultiplexed outputs including the wave output. 2. The variable attenuator according to claim 1, wherein the phase adjusting unit is a line stretcher. 3. The variable attenuator according to claim 1, wherein the AC input signal is a sine wave or a cosine wave. 4. The variable attenuation according to claim 1, wherein a plurality of line stretchers having different ratings are provided as selectable on one transmission line as the line stretcher. vessel. 5. The line stretcher according to claim 2, wherein an attenuation amount corresponding to an input AC frequency is displayed on a scale corresponding to the movable length of the line stretcher. Variable attenuator described. 6. A sine wave signal generation circuit comprising the variable attenuator according to any one of claims 1 to 5. 7. A step of demultiplexing an AC input signal to two or more transmission lines, a step of adjusting a phase of at least one demultiplexing output of the demultiplexing outputs, and a step of demultiplexing the phase-adjusted demultiplexing outputs. And a step of combining all the demultiplexed outputs including the variable attenuation method. 8. The variable attenuation method according to claim 7, wherein the phase adjustment is performed by a line stretcher. 9. The variable attenuator according to claim 7, wherein a sine wave or a cosine wave is used as the AC input signal. 10. The variable attenuation method according to claim 7, wherein a plurality of line stretchers having different ratings are selectively used according to the frequency of the input AC during the phase adjustment.