JPH0540456Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a trigger signal switching circuit for an oscilloscope, and particularly to an AC coupled trigger signal switching circuit.

(Prior art) In the case of a two-phenomenon oscilloscope, there are four types of trigger signal selection modes: single trigger signal A, B mode, alternate mode, and addition mode when the trigger signals are A and B. It is possible to select one.

Conventional trigger signal switching circuits, for example,
It is constructed as shown in FIGS. The trigger signal switching circuit shown in FIG. 2 uses a switching circuit including a transistor 1 and a diode 2 to select a trigger signal A applied to an input terminal a by a selection signal C applied to a selection signal input terminal c. , similarly transistor 3 and diode 4
A switching circuit consisting of input terminal b
Select the trigger signal B applied to the signal input terminal d
The signal system is selected and switched by the selection signal D applied to the terminal, and an output is obtained at the common connection point F (hereinafter referred to as output point F) between the collector of transistor 1 and the collector of transistor 3, and the output is output via the coupling capacitor 5. A trigger signal was obtained at the output terminal OUT. In addition,
7 and 8 are transistors that amplify the trigger signals A and B, respectively.

Furthermore _, in the conventional example shown in FIG. 3, in addition to the circuit shown in _FIG . It is set as.

(Problem to be solved by the invention) In the conventional example shown in FIG. 2 above, in a mode other than the addition mode, transistor 1 or 3
When either one of them is turned on, the output of transistor 7 or 8 is selected. However, in the addition mode, diodes 2 and 4 are controlled to be off, transistors 1 and 3 are both turned on, and the outputs of transistors 7 and 8 are added and output. Therefore, in the addition mode, the DC level at the output point F is twice that in other modes, and in order to operate normally, the dynamic range at the output point F must be large, and the transistor 1 When viewed from 3 and 3, there was a problem in that the dynamic range required twice as many transistors.

In addition, in order to solve this problem, as _shown in _FIG .
_is further provided in the circuit shown in FIG.
Select V ₂ and connect it to the output point F via the resistor 10.
The bias current increased in the addition mode shown in FIG. 2 is compensated for. However, in this case, a power supply, a changeover switch, a resistor, and accompanying wiring are required, making the circuit complex and expensive.

The purpose of the present invention is to solve the above problems and provide a trigger signal switching circuit for an oscilloscope that does not require a large dynamic range and does not require the addition of the above-mentioned changeover switch. shall be.

(Means for solving the problems) In order to solve the above problems, the present invention is constructed as follows.

In a trigger signal switching circuit for an oscilloscope, which has a common output point and is composed of a plurality of switching transistors whose switching is controlled by a selection signal, the plurality of switching transistors have a common output point and a switching transistor which leads a selected input trigger signal to the output point. 1
A second switching transistor group guides a non-selected input trigger signal to the output point via a low-pass filter.

(Function) Since the present invention is configured as described above, the selected input trigger signal is outputted via the first switching transistor, and the non-selected input trigger signal is outputted via the second switching transistor via the low-pass filter. supplied to the point. Therefore, there is no fluctuation in the DC level at the output point, and the AC component of the selection trigger signal appears at the output point.

For example, to explain the case of a two-phenomenon oscilloscope, in A mode, trigger signal A is passed through the first switching transistor, and trigger signal B is passed through the second switching transistor and low-pass filter. Output to the output point. Therefore, at the output point, the DC level of trigger signal B is added to trigger signal A, and the AC component of trigger signal B is blocked by the low-pass filter. In the case of B mode, the trigger signal B is outputted to the output point via the first switching transistor, and the trigger signal A is outputted to the output point via the second switching transistor and the low-pass filter. Therefore, at the output point, the DC level of trigger signal A is added to trigger signal B, and the AC component of trigger signal A is blocked by the low-pass filter. Furthermore, in the case of the alternate mode, the above A and B modes are repeated.

Then, in the addition mode, the trigger signals A and B are guided to the output point via the first switching transistor, and at the output point, the DC level of the trigger signal A and the DC level of the trigger signal are added, and the trigger signal is AC component of signal A and trigger signal B
The output is obtained by adding the AC component of

Therefore, the change in the DC level at the output point is constant regardless of the selected mode, and the AC component at the output point has a value corresponding to the selected mode.

(Example of idea) The present invention will be explained below with reference to examples.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, the same components as those of the conventional example shown in FIGS. 2 and 3 are denoted by the same reference numerals.

In this embodiment, instead of the diode 2, a transistor 12 which is differentially connected to the transistor 1 is used.
is provided, and a selection signal C is applied to the base of the transistor 12. Further, a transistor 13 differentially connected to the transistor 3 is provided in place of the diode 4, and a selection signal D is applied to the base of the transistor 13.

The collector of the transistor 12 and the collector of the transistor 13 are commonly connected, and this common connection point is connected to the output point F via the low-pass filter 17. The low-pass filter 17 consists of resistors 14 and 15 connected in series between the output point F and the collector of the transistor 12, and a capacitor 16 connected between the common connection point H of the resistors 14 and 15 and the ground. ing. The cutoff frequency determined by the time constant of the low-pass filter 17 is set lower than the frequency of the trigger signal required in the circuit after the output terminal OUT. That is, low pass filter 1
The time constant of 7 is set smaller than the time constant of a high pass filter consisting of capacitor 5 and a circuit connected to the subsequent stage.

In one embodiment of the present invention configured as described above, the DC levels of trigger signals A and B are set to the same level.

Now, in the case of A mode in which trigger signal A is selected, selection signal C is set to a low potential, and selection signal D is set to high potential. Therefore, transistors 1 and 13 are controlled to be on, and transistors 3 and 12 are controlled to be off. As a result, trigger signal A is amplified by transistor 7 and its collector current flows through transistor 1, and trigger signal B is amplified by transistor 8 and its collector current flows through transistor 13. Further, the AC component in the amplified output of the trigger signal B flowing through the transistor 13 is blocked by the low-pass filter 17.

Furthermore, in the case of the B mode in which the trigger signal B is selected, the selection signal C is set to a high potential and the selection signal D is set to a low potential. Therefore, transistors 3 and 12 are controlled to be in an on state, and transistors 1 and 13 are controlled to be in an off state. As a result, as in the case above, trigger signal B is amplified by transistor 8 and its collector current flows through transistor 3, and trigger signal A is amplified by transistor 7 and its collector current flows through transistor 12. .
Furthermore, the AC component in the amplified output of the trigger signal A flowing through the transistor 12 is filtered through the low-pass filter 1.
Blocked by 7. In the case of the alternate mode, the above A and B modes are alternately repeated.

In addition mode, selection signals C and D are both set to low potential. Therefore, transistors 1 and 3 are turned on, transistors 12 and 1 are turned on, and transistors 12 and 1 are turned on.
3 is controlled to be in the off state. As a result, trigger signals A and B are amplified by transistors 7 and 8, respectively, and their collector currents flow through transistors 1 and 3, respectively.

As is clear from the above description, the DC signal supplied to the output point F is the same regardless of the mode in which the trigger signal is switched. Therefore, there is no need to increase the dynamic range at the output point F, and there is no need to correct the bias current using other switching means as in the conventional example shown in FIG.

Furthermore, since the cutoff frequency of the low-pass filter 17 is set below the frequency required in the downstream circuit of the output terminal OUT, the AC component is blocked by the low-pass filter 17, and the AC component transmitted to the output point F is It will be the same as the selected mode. In other words, when in A mode, trigger signal B
The AC component of the trigger signal A is blocked by the low-pass filter 17 in the B mode, and the AC component in the trigger signals B and A is blocked by the low-pass filter 17 in synchronization with the switching of the trigger signals A and B in the alternate mode. It does not appear at the output point F. Further, in the addition mode, the sum of the AC components of the trigger signals A and B is output to the output point F.

(Effects of the invention) As explained above, according to the invention, the dynamic range of the output point can be greatly increased by providing a low-pass filter that guides non-selected trigger signals to the output point in the trigger signal switching circuit of the oscilloscope. There is no need to ensure this, there are fewer design constraints, and there is less variation in performance due to bias changes.

Furthermore, compared to the case of bias correction, there is no need for a changeover switch, resistor, power supply, or wiring to connect these, and there is no performance deterioration due to these.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIGS. 2 and 3 are circuit diagrams showing the configuration of a conventional example. 1, 3, 7, 8, 12 and 13...transistor, 5...coupling capacitor, 14 and 15...
...Resistor, 16...Capacitor, 17...Low pass filter, F...Output point.

Claims (1)

[Scope of utility model registration request] In a trigger signal switching circuit for an oscilloscope, which has a common output point and is composed of a plurality of switching transistors whose switching is controlled by a selection signal, the plurality of switching transistors have a common output point and a switching transistor which leads a selected input trigger signal to the output point. 1
1. A trigger signal switching circuit for an oscilloscope, comprising a switching transistor group and a second switching transistor group that guides a non-selected input trigger signal to the output point via a low-pass filter.