JP2008271451A - Variable attenuation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable attenuation apparatus which reduces the effect of noise or the like even with a great attenuation amount and suppresses deterioration in the waveform of an input signal over wide bands. <P>SOLUTION: This variable attenuation apparatus, that attenuates an electric signal inputted to an input terminal and outputs the attenuated electric signal from an output terminal. is characteristically provided with: a preceeding stage attenuator for attenuating the electric signal from the input terminal by dividing its potential through a resistor; a trailing stage attenuator which attenuates the electric signal from the preceeding stage attenuator by dividing its potential through the resistor and outputs the attenuated electric signal to the output terminal; a signal line that is provided in parallel with the trailing stage attenuator and grounded via the resistor; and a changeover switch which transmits output from the preceeding stage attenuator either to the trailing stage attenuator or to the signal line. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is used, for example, in an input unit of a measuring instrument such as an oscilloscope or a wattmeter, or an output unit of a signal generator such as a function generator, and attenuates and outputs an electric signal input to an input terminal of the apparatus. More particularly, the present invention relates to a variable attenuating device that reduces the influence of noise and the like and suppresses the deterioration of the waveform of an input signal over a wide band even when the amount of attenuation is large.

  A variable attenuator is provided in the input unit of the measuring instrument, the output unit of the signal generator, and the like in order to set the signal from the measuring object and the signal to the measuring object to an appropriate signal level (see, for example, Patent Document 1).

  5 and 6 are diagrams showing a configuration example of a conventional variable attenuating device, in which the input impedance viewed from the input side of the variable attenuating device is 1 [MΩ]. Moreover, the same code | symbol is attached | subjected to the same thing.

  FIG. 5 shows an example of an apparatus in which the attenuation amount of an input signal can be varied between 1/1 and 1/100 with one attenuator having an attenuation ratio of 1/100. FIG. 6 shows an example of an apparatus in which two stages of attenuators with an attenuation ratio of 1/10 are arranged in series and the attenuation can be varied to 1/1, 1/10, and 1/100.

  In FIG. 5, an input terminal Pi is an input terminal of the present apparatus, an output terminal Po is an output terminal of the present apparatus, and an input signal (electric signal) input to the input terminal Pi is converted into a desired attenuation amount (1/1). ˜ 1/100) and output from the output terminal Po.

  The signal line L1 and the signal line L2 are provided in parallel between the input terminal Pi and the output terminal Po. The signal line L1 has no attenuator (attenuation ratio 1/1), and the attenuator 1 (attenuation ratio 1/100) is provided on the signal line L2.

  The changeover switch includes an input side switch SW1a and an output side switch SW1b, and the switches SW1a and SW1b are switched in conjunction with each other. That is, the selector switches SW1a and SW1b selectively select the signal line L1 or the signal line L2, and transmit the electrical signal from the input terminal Pi to the output terminal Po via the selected signal lines L1 and L2.

  The resistor (resistance value 1 [MΩ]) R0 is provided between the output terminal of the output side switch SW1b and the output terminal Po, one end is electrically connected to the output terminal Po, and the other end is grounded.

  In the attenuator 1, a resistor R1a and a resistor R1b constitute a voltage dividing circuit, and a contact point between the resistors R1a and R1b becomes an output of the attenuator 1. The resistance values of the resistors R1a and R1b are, for example, 990 [kΩ] and 10.1 [kΩ].

The operation of such an apparatus will be described.
When the attenuation is 1/1, the changeover switches SW1a and SW1b switch the connection, select the signal line L1, and connect the signal line L1 to the terminals Pi and Po. As a result, the electrical signal from the input terminal Pi is transmitted to the output terminal Po with the attenuation of 1/1 via the selected signal line L1.

  When the attenuation is set to 1/100, the change-over switches SW1a and SW1b select the signal line L2 having the attenuator 1 by switching the connection, and connect the signal line L2 to the terminals Pi and Po. As a result, the signal from the input terminal Pi is input to the attenuator 1 on the signal line L2 via the switch SW1a. Then, the attenuator 1 attenuates the signal level to 1/100 and outputs it to the output terminal Pi via the switch SW1b.

  Subsequently, in FIG. 6, between the input terminal Pi and the output terminal Po, the switch SW2a, the signal lines L3 and L4 provided in parallel, the switch SW2b, the switch SW3a, and the signal lines provided in parallel from the input terminal Pi side. L5 and L6, a switch SW3b, and a resistor R0 are provided.

  The signal lines L3 and L5 have no attenuator and have an attenuation ratio of 1/1. The signal line L4 is provided with an attenuator 2, the signal line L6 is provided with an attenuator 3, and both the attenuators 2 and 3 have an attenuation ratio of 1/10.

  The attenuator 2 is a voltage dividing circuit using resistors, and includes resistors R2a and R2b. The attenuator 3 is also a voltage dividing circuit using resistors, and includes resistors R3a and R3b.

  The change-over switches SW2a and SW2b are switched in conjunction to selectively select the signal line L3 or the signal line L4, and switch the electrical signal from the input terminal Pi through the selected signal lines L3 and L4 to the subsequent stage. Output to the switch circuit SW3a.

  The change-over switches SW3a and SW3b are switched in conjunction to selectively select the signal line L5 or the signal line L6, and the electric signal from the change-over switch SW2b is output to the output terminal Po via the selected signal lines L5 and L6. Output to.

The operation of such an apparatus will be described.
When the attenuation amount is 1/1, the changeover switches SW2a and SW2b switch the connection and select the signal line L3, and the changeover switches SW3a and SW3b switch the connection and select the signal line L5. As a result, the input terminal Pi, the signal lines L3 and L5, and the output terminal Po are electrically connected, and the electrical signal from the input terminal Pi is transmitted to the output terminal Po with an attenuation of 1/1.

  When the attenuation is 1/10, the changeover switches SW2a and SW2b change the connection to select the signal line L4 (path with the attenuator), and the changeover switches SW3a and SW3b change the connection to change the signal line L5 ( Select a path without an attenuator. As a result, the input terminal Pi, the signal lines L4 and L5, and the output terminal Po are electrically connected. The signal level of the electrical signal from the input terminal Pi is attenuated to 1/10 by the attenuator 2 and transmitted to the output terminal Po.

  When the attenuation is set to 1/100, the changeover switches SW2a and SW2b switch the connection and select the signal line L4, and the changeover switches SW3a and SW3b switch the connection and select the signal line L6. Thereby, the input terminal Pi, the signal lines L4 and L6, and the output terminal Po are electrically connected. Then, the signal level of the electric signal from the input terminal Pi is attenuated by 1/10 by the attenuators 2 and 3 respectively, attenuated to 1/100 of the input signal as a whole, and transmitted to the output terminal Po.

JP 2001-345659 A

  In this way, the path of the signal line with the attenuator and the path of the signal line without the attenuator are provided, and by selecting these paths, the input signal is attenuated and output by a desired attenuation amount.

  In general, the variable attenuator is required to attenuate the input signal while maintaining the waveform quality without degrading the shape of the waveform of the input signal in any frequency band. Also, the input impedance needs to be constant so as not to affect the circuits and devices connected to the variable attenuation device.

  However, in the case of the apparatus shown in FIG. 5 (attenuated to 1/100 with the one-stage attenuator 1), the voltage dividing ratio of the attenuator 1 (resistance value of the resistor R1a >> resistance value of the resistor R1b) is large. Therefore, due to the parasitic capacitance of the resistor R1a, in a high frequency region exceeding several tens [MHz], a phenomenon such as overshoot occurs in the signal of the output terminal Po, the waveform is distorted, and the waveform quality is deteriorated. There was a problem.

  Even if a variable capacitor is provided in parallel with the resistor R1b in order to compensate for the effect of the parasitic capacitance of the resistor R1a, the resistance ratio (about 100 times) of the resistors R1a and R1b is large. There is a problem that it is necessary to adjust the compensation capacitor with a sensitivity of about 100 times, and it is practically difficult to remove the influence of the parasitic capacitance.

  On the other hand, in the case of the apparatus shown in FIG. 6 (attenuators 2 and 3 having an attenuation ratio of 1/10 are connected in two stages in series), the voltage dividing ratio at the attenuators 2 and 3 is small, so the characteristics are good up to the high frequency region.

  However, since it is necessary to set the input impedance to 1 [MΩ] regardless of the amount of attenuation, the resistance values of the resistors R2b and R3b connected in parallel with the resistor R0 are inevitably increased. As a result, the output impedance viewed from the output side (output terminal Po) is increased (in FIG. 6, about 100 [kΩ]). In particular, when the attenuation is 1/100, the thermal noise due to the resistor R3b increases. There was a problem that noise increased. In addition, there is a problem that it is easily affected by external noise from the outside.

  Accordingly, an object of the present invention is to realize a variable attenuation device that reduces the influence of noise and the like even with a large attenuation amount and suppresses the deterioration of the waveform of an input signal over a wide band.

The invention described in claim 1
In the variable attenuation device that attenuates the electrical signal input to the input terminal and outputs it from the output terminal,
A first-stage attenuator that divides and attenuates the electrical signal from the input terminal by a resistor;
An electrical signal from the first-stage attenuator is divided by a resistor to attenuate and output to the output terminal, and a subsequent-stage attenuator.
A signal line that is provided in parallel to the attenuator at the subsequent stage and is grounded via a resistor,
One of the latter-stage attenuator and the signal line is provided with a changeover switch for transmitting the output from the first-stage attenuator.
The invention according to claim 2
In the variable attenuation device that attenuates the electrical signal input to the input terminal and outputs it from the output terminal,
A first signal line;
A second signal line provided in parallel with the first signal line and having a plurality of attenuators that divide and attenuate the electrical signal by a resistor;
A first changeover switch that selects one of the first signal line or the second signal line and transmits an electric signal from the input terminal to the output terminal via the selected signal line;
The second signal line is
A first-stage attenuator that divides and attenuates the electrical signal from the input terminal by a resistor;
An electrical signal from the first-stage attenuator is divided by a resistor to attenuate and output to the output terminal, and a subsequent-stage attenuator.
A signal line that is provided in parallel to the attenuator at the subsequent stage and is grounded via a resistor,
One of the latter-stage attenuator and the signal line is provided with a second changeover switch for transmitting an output from the first-stage attenuator.
The invention according to claim 3 is the invention according to claim 2,
A voltage dividing resistor is provided between the input terminal and the first changeover switch.
The invention according to claim 4 is the invention according to any one of claims 1 to 3,
The input impedance is constant regardless of the amount of attenuation.

  Two stages of attenuators that divide the voltage by resistors and attenuate the electrical signal are arranged, and the signal line for through (attenuation ratio 1/1) to the attenuators in the subsequent stage is grounded through the resistors. The resistance value of the resistor can be reduced. As a result, the output impedance can be reduced even with a large amount of attenuation (when attenuated by both the first-stage and subsequent-stage attenuators), and the input signal is attenuated by the two-stage attenuator, so the voltage dividing ratio of each attenuator is reduced. The waveform quality of the signal does not deteriorate even in the high frequency range. Therefore, even if the amount of attenuation is large, the influence of noise and the like can be reduced, and deterioration of the waveform of the input signal can be suppressed over a wide band.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
1 to 3 are block diagrams showing a first embodiment of the present invention, showing an example in which the input impedance viewed from the input side of the variable attenuator is 1 [MΩ]. Here, FIG. 1 is an example of a configuration in which the attenuation amount of the output signal with respect to the input signal is 1/1, FIG. 2 is 1/10 attenuation amount, and FIG. 3 is 1/100 attenuation amount.

  1 to 3, an input terminal Pi is an input terminal of the present apparatus, an output terminal Po is an output terminal of the present apparatus, and an input signal (electric signal) input to the input terminal Pi is converted into a desired attenuation amount ( Attenuated by 1/1 to 1/100) and output from the output terminal Po. The signal from the output terminal Po is input to a subsequent high input impedance buffer circuit (not shown).

  The signal line L7 without an attenuator is provided between the terminals Pi and Po, has an attenuation ratio of 1/1, and is a through path.

  The signal line L8 is provided in parallel with the signal line L7, and has a total of two attenuators 4 and 5 that divide the voltage with resistors.

  The signal line L7 corresponds to the first signal line in the claims, and the signal line L8 corresponds to the second signal line.

  The first change-over switches SW5a (input side) and SW5b (output side) are switched in conjunction to selectively select the signal line L7 or the signal line L8, and pass through the selected signal lines L7 and L8. An electric signal from the input terminal Pi is transmitted to the output terminal Po.

  More specifically, the input end of the switch SW5a on the input side is connected to the input terminal Pi, one output end is connected to one end of the signal line L7, and the other output end is connected to one end of the signal line L8. One input end of the output-side switch SW5b is connected to the other end of the signal line L7, the other input end is connected to the other end of the signal line L8, and an output end is connected to the output terminal Po.

  The signal line L8 includes a first-stage attenuator 4, a subsequent-stage attenuator 5 provided on the signal line L9, a signal line L10 without an attenuator, a second changeover switch SW6a (input side), and SW6b (output side). The signal level (voltage amplitude) of the input signal from the changeover switch SW5a is attenuated to 1/10 or 1/100 and transmitted to the switch SW5b. Here, the first stage means that the signal is input earlier than the latter stage, closer to the input terminal Pi.

  The first-stage attenuator 4 is a voltage dividing circuit that divides a signal by the resistance ratio of the resistor R4a and the resistor R4b, and the contact point of the resistors R4a and R4b becomes the output of the attenuator 4. The resistance values of the resistors R4a and R4b are, for example, 990 [kΩ] and 222 [kΩ]. The attenuator 4 divides and attenuates the signal input from one end of the signal line L8 according to the resistance ratio of the resistors R4a and R4b, and transmits the attenuated signal to the switch SW6a. The resistor R4a is provided on the signal line L8, and the resistor R4b is provided between the signal line L8 and the ground.

  The attenuator 5 in the subsequent stage is a voltage dividing circuit that divides the signal by the resistance ratio of the resistor R5a and the resistor R5b, and the contact point of the resistors R5a and R5b becomes the output of the attenuator 5. The resistance values of the resistors R5a and R5b are 200 [kΩ] and 22.7 [kΩ], for example. The attenuator 5 is provided between the changeover switches SW6a and SW6b, divides and attenuates the signal from the switch SW6a according to the resistance ratio of the resistors R5a and R5b, and transmits the attenuated signal to the switch SW6b. The resistor R5a is provided on the signal line L9, and the resistor R5b is provided between the signal line L9 and the ground.

  The signal line L10 has an attenuation ratio of 1/1, is provided in parallel with the signal line L9, and is grounded through the resistor R6. The resistance value of the resistor R6 is 222 [kΩ].

  The second change-over switches SW6a and SW6b are switched in conjunction with each other to selectively select the signal line L9 or the signal line L10, and from the input-side change-over switch SW5a via the selected signal lines L9 and L10. The electrical signal is transmitted to the output side switch SW5b.

  More specifically, the input end of the switch SW6a is connected to the output side of the attenuator 5, one output end is connected to one end of the signal line L9 (input side of the attenuator 5), and the other output end is connected to the signal line. Connected to one end of L10. One input end of the switch SW6b is connected to the other end of the signal line L9 (the output side of the attenuator 5), the other input end is connected to the other end of the signal line L10, and the output end is the other end of the changeover switch SW5b. Connected to the input end.

The resistor R0 is provided between the output terminal Po and the ground, and the resistance value is 1 [MΩ].
The resistance value of each resistor may be any value, regardless of the connection of the first change-over switches SW5a and SW5b and the second change-over switches SW6a and SW6b, that is, attenuation amounts 1/1 and 1/10. Regardless of 1/100, a resistance value that makes the input impedance constant at 1 [MΩ] may be combined.

The operation of such an apparatus will be described.
When the attenuation amount (the amplitude of the output signal with respect to the amplitude of the input signal) is 1/1 (see FIG. 1), the change-over switches SW5a and SW5b switch the connection and select the signal line L7. At this time, the connection of the changeover switches SW6a and 6b may be in any state. Thereby, the input terminal Pi, the signal line L7, and the output terminal Po are electrically connected, and the electric signal from the input terminal Pi is transmitted to the output terminal Po with an attenuation of 1/1. Of course, the input impedance is 1 [MΩ].

  When the attenuation is 1/10 (see FIG. 2), the change-over switches SW5a and SW5b switch the connection and select the signal line L8, and the change-over switches SW6a and SW6b switch the connection and select the signal line L10. . As a result, the input terminal Pi, the signal lines L8 and L10, and the output terminal Po are electrically connected. The signal level of the electrical signal from the input terminal Pi is attenuated to 1/10 by the attenuator 4 and transmitted to the output terminal Po.

  At this time, the input impedance is a combined resistance of the resistors R0, R4a, R4b, and R6, and is about 1 [MΩ]. That is, the resistance value of the resistor R4b of the first-stage attenuator 4 can be increased by providing the resistor R6 on the through signal line L10 for the latter-stage attenuator 5 as compared with FIG. The output impedance viewed from the output side (output terminal Po) is about 111 [kΩ], which is almost the same as in FIG. 6, and the noise characteristics are not deteriorated.

  When the attenuation is 1/100 (see FIG. 3), the change-over switches SW5a and SW5b switch the connection and select the signal line L8, and the change-over switches SW6a and SW6b switch the connection and select the signal line L9. . As a result, the input terminal Pi, the signal lines L8 and L9, and the output terminal Po are electrically connected. Then, the signal level of the electric signal from the input terminal Pi is attenuated to 1/10 by the first-stage attenuator 4, further attenuated to 1/10 by the subsequent-stage attenuator 5, and as a whole, 1 / The signal is attenuated to 100 and transmitted to the output terminal Po.

  At this time, the input impedance is a combined resistance of the resistors R0, R4a, R4b, R5a, and R5b, and is about 1 [MΩ]. The output impedance viewed from the output side (output terminal Po) is also a combined resistance of the resistors R0, R4a, R4b, R5a, and R5b, but the resistance R5b between the signal line L9 of the 1/100 path and the ground is dominant. It is about 20 [kΩ]. That is, since the resistance value of the resistor R4b of the first-stage attenuator 4 can be increased (because there is a resistor R6 of the through signal line L10), the resistance value of the subsequent-stage resistor R5b is decreased ((the resistance of the resistor R0). Value >> resistance value of resistor R5b)).

  In this way, the path without the attenuator (signal line L7) is parallel to the entire path with the attenuator (signal line L8). Then, by arranging two stages of attenuators 4 and 5 having an attenuation ratio of 1/10 on a path with an attenuator (signal line L8), a through path (attenuation amount of the entire apparatus) for the attenuator 5 at the subsequent stage is arranged. Even if the resistor R6 is provided on the signal line L10) used for 1/10, the input impedance can be kept at 1 [MΩ]. Further, unlike FIG. 6, since the resistor R6 is provided in the through path (signal line L10), the resistance of the resistor R5b of the attenuator 5 used with an attenuation of 1/100 while maintaining the input impedance of 1 [MΩ]. The value can be reduced. As a result, the output impedance can be reduced even with a large attenuation (1/100 in FIG. 1), and the input signal is attenuated by the two-stage attenuators 4 and 5. It is possible to reduce the signal degradation even in a high frequency region. Therefore, even if the amount of attenuation is large, the influence of noise and the like can be reduced, and deterioration of the waveform of the input signal can be suppressed over a wide band.

[Second Embodiment]
FIG. 4 is a block diagram showing a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. FIG. 4 shows an example in which a desired attenuation ratio is used instead of the attenuation of 1/1, 1/10, and 1/100.

  In FIG. 4, a resistor R7 is newly provided on the signal line of the input terminal Pi and the input side switch SW5a. Here, by selecting a resistance ratio between the resistance R7 and the resistance R0, it is possible to obtain a desired attenuation amount instead of the attenuation amount 1/1.

  In FIG. 4, a constant partial pressure is obtained by the partial pressure of the resistor R0 (800 [kΩ]) and the resistor R7 (200 [kΩ]), and the smallest attenuation is 8/10. The other resistors are, for example, a resistor R4a = 720 [kΩ], a resistor R4b = 178 [kΩ], a resistor R5a = 131 [kΩ], and a resistor R5b = 14.8 [1] so that the input impedance is 1 [MΩ]. kΩ] and resistance R6 = 178 [kΩ].

  The operation of such a device is almost the same as that of the device shown in FIG. 1, but 1/1 in the device shown in FIG. 1, depending on the resistance ratio between the resistor R7 before the switch SW5a and the resistor after the switch SW5a. Attenuation amounts for input signals that were 1/10 and 1/100 are 8/10, 8/100, and 8/1000.

The present invention is not limited to this, and may be as shown below.
(1) In the apparatus shown in FIG. 1, the configuration in which the input signal is attenuated by three types of 1/1, 1/10, and 1/100 is shown. However, when the path 1/1 that does not attenuate the signal is unnecessary, that is, In the case of two types of attenuation of 1/10 and 1/100, the signal line L7 and the first change-over switches SW5a and SW5b are not necessary. The same applies to FIG.

(2) In the apparatus shown in FIG. 1, an example of input impedance 1 [MΩ] at an attenuation of 1/1 is shown. However, the resistance values of the other resistors R4a, R4b, R5a, R5b, and R6 are the attenuation values. The combined resistance value (input impedance) at 1/10 and 1/100 only needs to be about 1 [MΩ], and any resistance value may be combined. Further, the input impedance does not have to be particularly 1 [MΩ], and may be any value.

(3) In the apparatus shown in FIG. 1 and FIG. 2, the configuration in which two attenuators, the first-stage attenuator 4 and the second-stage attenuator 5 are provided on the signal line L8, but a plurality of attenuators are provided. Good. For example, in the case of three, a signal line having an attenuator and a through signal line (grounded through a resistor) are provided in parallel between the attenuator 5 at the subsequent stage and the second changeover switch SW6b. It is advisable to use a change-over switch for connection.

It is the block diagram which showed the 1st Example (attenuation amount 1/1) of this invention. It is the block diagram which showed the Example in the case of attenuation amount 1/10 with the apparatus shown in FIG. It is the block diagram which showed the Example in the case of attenuation amount 1/100 with the apparatus shown in FIG. It is the block diagram which showed the 2nd Example of this invention. It is the figure which showed the structure of the conventional variable attenuation apparatus. It is the figure which showed the other structure of the conventional variable attenuation apparatus.

Explanation of symbols

4 First-stage attenuator 5 Second-stage attenuator Pi input terminal Po output terminal L7 to L10 Signal lines R0, R4a, R4b, R5a, R5b, R6, R7 Resistors SW5a, SW5b, SW6a, SW6b Changeover switch

Claims (4)

In the variable attenuation device that attenuates the electrical signal input to the input terminal and outputs it from the output terminal,
A first-stage attenuator that divides and attenuates the electrical signal from the input terminal by a resistor;
The subsequent-stage attenuator that divides and attenuates the electrical signal from the first-stage attenuator with a resistor and outputs it to the output terminal;
A signal line that is provided in parallel to the attenuator at the subsequent stage and is grounded via a resistor;
A variable attenuating device, wherein a switching switch for transmitting an output from the first attenuator is provided on one of the attenuator at the rear stage or the signal line. In the variable attenuation device that attenuates the electrical signal input to the input terminal and outputs it from the output terminal,
A first signal line;
A second signal line provided in parallel with the first signal line and having a plurality of attenuators that divide and attenuate the electrical signal by a resistor;
A first changeover switch that selects one of the first signal line or the second signal line and transmits an electric signal from the input terminal to the output terminal via the selected signal line;
The second signal line is
A first-stage attenuator that divides and attenuates the electrical signal from the input terminal by a resistor;
The subsequent-stage attenuator that divides and attenuates the electrical signal from the first-stage attenuator with a resistor and outputs it to the output terminal;
A signal line that is provided in parallel to the attenuator at the subsequent stage and is grounded via a resistor;
A variable attenuating apparatus comprising: a second changeover switch for transmitting an output from the first-stage attenuator to one of the latter-stage attenuator or the signal line.   The variable attenuator according to claim 2, wherein a voltage dividing resistor is provided between the input terminal and the first changeover switch.   4. The variable attenuation device according to claim 1, wherein the input impedance is constant regardless of the attenuation.

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