JPH0130328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sweep signal generator useful for oscilloscopes and the like, and an object of the present invention is to make the voltage value of a sweep signal constant at a sweep start point.

FIG. 1 is a circuit diagram of a conventional sweep signal generator of the type that shares a timing capacitor and a hold-off capacitor. 1 in the figure is an input gate circuit, and the input signal e _i is applied via the capacitor C ₁ .
turns on and off the switching transistor _Q1 . 4 is a constant current source, and constant current source 4 supplies current to transistor Q ₁ or capacitor C _2.
Supply Io. 2 is an impedance converter that converts the impedance of capacitor C ₂ seen from output terminal 5 to a low impedance, making it easier to transmit the sweep signal to the next stage. Reference numeral 3 denotes an input gate control circuit consisting of a switching circuit that operates when the level of the sweep signal reaches a predetermined value, and inverts the input gate circuit 1 to temporarily stop the operation of the input gate circuit 1 due to the input signal e _i .

Q ₂ is a transistor that constitutes a hold-off circuit, and at the end of the sweep, capacitor C ₂
The input gate control circuit 3 is controlled to cut off the input signal e _i while the charges accumulated in the input signal e i are discharged to the level of the sweep start point.

Next, this operation will be explained. a in Figure 2 is the first
In the figure, e _i , b is e _p , c is the base voltage of the transistor Q ₂ , and d is the collector voltage waveform of the transistor Q ₂ . When the collector level of transistor _Q1 is at the voltage level of the sweep start point, Fig. 2a
As shown in , when the first input trigger pulse is applied, the input gate circuit 1 is inverted, the transistor Q ₁ becomes non-conductive, the capacitor C ₂ begins to be charged, and the sweep is started. Shown in Figure 2c.
T ₂ and T ₄ indicate the time points at which the sweep is started.

Here, at the end of the sweep, the transistor
_Q1 becomes conductive and discharges the charge stored in capacitor _C2 . At this time, transistor _Q2 becomes non-conducting, that is, in a hold-off state,
The input gate control circuit 3 is supplied with _the voltage shown in FIG.
Keep Q ₁ conductive. The base potential of the transistor _Q2 changes in the negative direction as shown in FIG. 2c, and as the capacitor _C2 continues to discharge through the resistor _R4 , the voltage gradually returns to the positive direction. If _{the base voltage of the transistor Q 2 during the inversion operation is V 1 as shown in FIG} . Figure 2 d
Supply the voltage shown in
The input gate circuit 1 is set to a trigger pulse waiting bias value through _R1 . The input gate circuit 1 enters a trigger pulse waiting state, but the base potential of the transistor _Q2 rises until it reaches the base current determined by the resistor _R4 .

Further, the collector level of the transistor Q ₁ reaches the voltage level at the sweep start point and maintains this state until the next input trigger pulse is applied to the input gate circuit 1 .

Now, considering the times T ₁ and T ₃ when the base potential of the transistor Q ₂ becomes V ₁ , T ₁ is near when the input gate circuit 1 enters the standby state, and the first trigger pulse is applied to the input gate circuit 1. , and the sweep begins. At this time, transistor Q ₁ becomes non-conductive, and current Io from constant current source 4 flows through the capacitor.
It is added to C ₂ and weighed by the base current of transistor Q ₂ . However, since the base potential V ₁ of the transistor Q ₂ has just been reached, the capacitor C ₂ is not completely discharged. Therefore, the level of the sweep signal at the start point of the sweep varies by a voltage width e ₁ as shown in FIG. 2b.

At time T ₃ , the trigger pulse is connected to the capacitor.
Since C ₂ is added after the discharge is completed and the sweep starts,
The amount of variation in the base voltage of transistor Q ₂ due to current Io is minute. The voltage width e ₂ indicates the fluctuation value in that case.

As shown in Figure 3, the sweep start point changes depending on the timing of the trigger pulse applied after the hold is released.
A double waveform is observed on the surface.

Also, by adjusting the resistor _R4 , the voltage shown in Figure 2c
If V ₁ is set to the base current in the linear region of transistor Q ₂ , it takes time to discharge capacitor C ₂ , which not only lengthens the blanking period but also makes it unstable with respect to temperature.

The present invention eliminates these drawbacks and provides a sweep signal generator that reduces fluctuations in voltage value at the start point of the sweep and generates a stable sweep signal.

A sweep signal generator which is an embodiment of the present invention will be described below with reference to FIGS. 4 and 5. FIG. 4 is a circuit diagram of a sweep signal generator according to an embodiment of the present invention, and FIG. 5 is a timing chart of input and output of amplifier _u1 . Here, _U1 is an amplifier consisting of a transistor or other active element, and the other components are constructed in the same manner as in FIG. 1, so the same reference numerals as in FIG. 1 indicate the same parts and a description thereof will be omitted. The operation of the sweep signal generator shown in FIG. 4 will be explained below. This circuit converts the sweep signal synchronized with the input trigger pulse e _i to the output voltage e _p
This is a circuit that generates power at the terminal. When the first input trigger pulse in which the square wave signal shown in _FIG . Supply voltage. Transistor _Q1 changes from a conductive state to a non-conductive state, and a ramp signal is generated at the collector according to a time constant determined by constant current source 4 and capacitor _C2 .

This slope signal is output by the impedance converter 2 to the output terminal 5 as a sweep signal. When the output voltage e _p reaches V ₂ in Fig. 2b, the input gate control circuit 3 operates through the resistors R ₂ and R ₃ and the diode CR ₂ , inverting the input gate circuit 1 through the resistor R ₁ and making the transistor Q ₁ conductive. state. Figure 5b
T ₆ indicates this point. When transistor Q ₁ becomes conductive, the charge charged in capacitor C ₂ passes through resistors R _f and R ₈ and is gradually discharged. Therefore, from the input voltage V ₃ of amplifier U ₁ shown in FIG.
At T ₆ , it changes in the negative direction and is gradually charged in the positive direction. During this time, the output voltage of the amplifier _U1 is at a level higher than _V4 as shown in FIG. 5b, and controls the input gate control circuit 3 and the input gate circuit 1, keeping the transistor _Q1 conductive. When the input voltage of amplifier U ₁ reaches V ₃ −e ₄ in Fig. 5a,
That is, when reaching T ₇ in FIG. 5b, the output voltage of the amplifier U ₁ changes to a level lower than V ₄ , causing the input gate control circuit 3 to perform an inversion operation, and transmitting the input gate circuit 1 through the resistor R ₁ to the next trigger pulse. Set bias to standby state. From T ₇ in Figure 5b to T 5 in Figure _5a
The period up to this point indicates the above state and is called the hold-off period. When the next trigger pulse is applied to the input gate circuit 1 at T5 in FIG. _5a , the transistor _Q1 becomes non-conductive and the above operation is repeated.
From the above explanation of the operation, time _T5 in FIG. 5a indicates the sweep start point. R _f is the feedback resistance. Feedback resistance R _f ,
The currents I _f and I ₁ determined by the variable resistor R ₈ are sufficiently large compared to the current Io. Figure 5b shows the output voltage of amplifier _U1 , and time _T6 in the figure is the sweep end point, time
T ₇ is the holdoff end point. Voltage V ₄ indicates the voltage value necessary to invert the input gate control circuit 3, voltage V ₅ indicates the voltage value after the hold-off ends, and voltage V ₆ indicates the voltage value during the sweep period. Next, this operation will be explained.

The feedback resistor R _f and the variable resistor R ₈ are set so that the output voltage of the amplifier U ₁ does not exceed the voltage V ₄ after time T ₇ in a linear region. At this time, the input impedance of the amplifier _U1 exhibits a very small value due to the virtual ground state.

From this, the first input trigger pulse is applied to the input gate circuit 1 and the sweep is started. amplifier
Since the current Io is applied to the input of U ₁ , the voltage width becomes e ₃ as shown in FIG. 5a. The output voltage value is the current Io
Therefore, −IoR changes by _f .

At the end of the sweep, the transistor Q ₁ becomes conductive, and the charge stored in the capacitor C ₂ is discharged through the feedback resistor R _f and the variable resistor R ₈ . Here, the feedback resistor R _f and the variable resistor R ₈ are determined by the following equation with respect to the discharge time constant Tc of the capacitor C ₂ .

Tc=R _f R ₈ /R _f +R ₈ C ₂ Therefore, the discharge period of the capacitor C ₂ can be set to an optimum value by the feedback resistor R _f and the variable resistor R ₈ .

At the end of the hold-off, the inversion level of the amplifier _U1 becomes the voltage _V3 shown in FIG. 5a. This is because the operating point of amplifier _U1 is set in the linear operating region after the end of holdoff. amplifier
When the output voltage of U ₁ exceeds V ₄ when U 1 is inverted, the input gate circuit 1 enters a state of waiting for an input gate pulse. If the sweep is started at this time,
The sweep signal voltage level is represented by a voltage width _e4 as shown in FIG. 5a, and the relationship with the voltage width _e3 is as follows.

e ₄ - e ₃ = V ₄ - V ₅ /A ... (1) (A: Amplification degree of amplifier U ₁ ) In the above equation (1), if the amplification degree A of amplifier U ₁ is sufficiently large, e ₄ ≒ e ₃ and the sweep signal voltage value when the sweep is started immediately after the hold-off ends,
Since the sweep signal voltage values are equal when the sweep is started after the inverting operation of amplifier U ₁ is finished,
The phenomenon of double triggering as shown in FIG. 3 does not appear.

Furthermore, with this configuration, the discharge time of the capacitor _C2 can also be set arbitrarily. Furthermore, it is possible to suppress the change in the sweep signal voltage value at the sweep start point even when the current Io changes due to a change in the sweep speed.

As described above, according to the present invention, changes in the voltage value at the sweep start point of the sweep signal can be reduced, and a stable sweep signal can be generated.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional sweep signal generator, Figure 2 is a circuit diagram of a conventional sweep signal generator.
Figure 3 is a waveform diagram showing the waveforms observed on the cathode ray tube of an oscilloscope equipped with the same device. Figure 4 is a circuit diagram of a sweep signal generator that is an embodiment of the present invention. 5 are timing charts of input and output waveforms of each part. DESCRIPTION OF SYMBOLS 1... Input gate circuit, 2... Impedance converter, 3... Input gate control circuit, 4... Constant current source, 5... Output terminal, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ ,
R ₆ , R ₇ ... Resistor, R ₈ ... Variable resistor, R _f ... Feedback resistor, C ₁ , C ₂ ... Capacitor, Q ₁ ... Switching transistor, Q ₂ ... Transistor,
CR ₁ , CR ₂ ... diode, U ₁ ... amplifier.

Claims (1)

[Claims] 1 an input gate circuit into which a trigger signal is input;
a switching circuit that is turned on and off by the output of the input gate circuit; a constant current source connected to the switching circuit; an input gate control circuit that controls the input gate circuit; A feedback amplifier for controlling an input gate control circuit; and an integrating capacitor having one end connected to the output side of the switching circuit and the other end connected to the input side of the feedback amplifier, and an integrating capacitor connected to the input terminal of the feedback amplifier. A sweep signal generator that applies a negative voltage through a resistor.