JPS5934048Y2 - Sawtooth wave generation circuit - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to improving the scanning circuit of a scanning electron microscope.

FIG. 1 is a block diagram showing a general scanning microscope. In the figure, an electron beam 2 generated from an electron gun 1 is focused by focusing lenses 3 and 4, and is irradiated onto a sample 5.

This electron beam 2 is deflected by a deflection coil 7 operated by a scanning circuit 6.
A certain area of the sample 5 is scanned by.

The signal generated from the sample 5 by electron beam irradiation is transmitted to the detector 8.
The signal is detected by the amplifier 9, amplified by the amplifier 9, and introduced into the cathode ray tube 10.

Further, the electric signals sent to the deflection coil and the cathode ray tube deflection coil in this case are synchronized, so that a scanned image of the sample whose brightness is modulated by the detection signal is displayed on the screen of the cathode ray tube 10.

In this case, to obtain high resolution, the scanning speed should be slowed down,
Furthermore, in order to dynamically observe a sample, it is necessary to change the scanning speed according to various objectives, such as increasing the scanning speed.

This switching is performed by changing the frequency of the signal output from the scanning circuit 6.

Generally, the commercial frequency (50Hz) from a power transformer or other
Periodic noise (or 60Hz) has a large effect on the receiver, and becomes more noticeable when the receiver is slow. Therefore, when using at a low frequency, that is, a frequency below the commercial frequency (50Hz or 60Hz), it is necessary to synchronize with the power supply frequency. I need to take it.

On the other hand, when the scanning speed becomes very high, for example when using a television frequency, the power source synchronization cannot be performed and it is therefore necessary to switch to asynchronous mode.

In conventional devices, such switching was performed mechanically, for example, by a switch, in conjunction with the scanning speed switching operation, but it is necessary to constantly switch between power synchronous and power asynchronous depending on the purpose of observing the sample. Since the switch is used more frequently, the switch is more likely to fail, reducing the reliability of the scanning circuit.

The present invention is intended to solve the above-mentioned drawbacks, and aims to automatically switch between power supply synchronization and power supply asynchronous mode by electrical means in accordance with the change in electron beam scanning speed.

FIG. 2 is a block diagram showing an embodiment of the present invention,
In the figure, 11 is a commercial frequency (50Hz or 60Hz) power supply, and the AC voltage (current) generated by the power supply 11 is
The pulse waveform shaper 12 generates a period T as shown in FIG. 3a.
After being waveform-shaped into a clock pulse signal, the signal is applied to the set input section of the flip-flop circuit (control circuit) 13.

When a start signal is generated at the output of the flip-flop circuit 13, a scanning waveform generator 14 consisting of a Miller integrator or a D-A converter generates a scanning signal having a constant slope as shown in FIG. 3C. However, the inclination can be arbitrarily varied depending on the purpose of observing the sample, and the scanning speed of the electron beam scanning over the sample is controlled by adjusting the inclination.

A portion of the output of the scanning waveform generator 14 is supplied to the deflection coil 7 and the deflection coil of the plan tube 10, and a portion thereof is introduced to the amplitude detector 15.

The amplitude detector detects the amplitude of the sawtooth wave generated from the generator 14 at a certain level value, and introduces this as a trigger pulse to the monostable multivibrator 16.

The monostable multivibrator generates a trigger pulse with a pulse width T1 as shown in FIG. 3d, which is applied to the reset input R of the flip-flop circuit 13.

When a start signal is generated at the output of the flip-flop circuit 13, the reference time generating circuit 17 consisting of a monostable multivibrator etc. is activated to generate a pulse of a constant time width as shown in FIG. -Apply to the set input section S of the flop circuit.

The width T2 of this pulse is the period T of the clock pulse mentioned above.
It is set to a constant time that is shorter than , but longer than the period of the sawtooth wave in the case of power supply asynchronization.

Incidentally, assuming that the output signal of the flip-flop circuit 13 is as shown in Figure 3, the falling edge of the pulse (1 in the figure)
The part when the pulse changes from O to 0) is used as a start signal for the scanning waveform generator 14 and the reference time generation circuit 17, and the rising part of the pulse (when it changes from O to 1 in the figure) is used as the start signal for the scanning waveform generator 14. It is used as a reset signal.

When scanning a sample with an electron beam at a frequency lower than the commercial frequency of the power source and observing the signals generated by the scanning using a cathode ray tube, the signal change rate of the scanning waveform generator 14 is set to a desired value.

In this state, first, the scanning waveform generating circuit 14 generates a signal based on the power supply synchronization clock pulse (A1 in FIG. 3a), and at the same time, the reference time generator 17 also generates a pulse ( Figure 3 a) is generated.

At this time, the output of the flip-flop circuit 13 is in the 0 signal state, so even if the O signal pulse is applied from the reference time generator 17 to the set power S of the flip-flop circuit 13, the output remains the O signal. No change (3rd
Figure b).

This also applies when the clock pulse indicated by A2 in FIG. 3a is applied, and the flip-flop circuit 1
The output of No. 3 holds the O signal while the scanning waveform generating circuit 14 is generating the scanning signal.

Next, when the output of the scanning signal generation circuit 14 reaches a certain set level and a trigger pulse from the monostable multivibrator 16 is applied to the reset power R of the flip-flop circuit 13, the output becomes an O signal. This change acts as a reset signal for the scanning waveform generator 14, returning it to the state before the scanning wave was generated.

In this state, when the O signal is applied to the set input S of the flip-flop circuit 13, that is, when the clock pulse A1 is applied, a 0 signal is generated at the output of the flip-flop circuit 13 again and the process starts. It is used as a signal to repeat the above operations.

On the other hand, in order to rapidly scan the sample with an electron beam and observe the signals generated by the scanning on a cathode ray tube screen, the signal change rate of the scanning waveform generator 14 is set to a desired fast value.

In this state, the first clock pulse C shown in FIG.
5, when the output of the flip-flop circuit 13 changes from 1 to O as shown in FIG.
operates, and the reference time generating circuit 17 receives a time width T2.
The O signal pulse is generated.

Next, when the output of the scanning waveform generator 14 shown in FIG. 4 reaches the set level, a trigger pulse P1 shown in FIG.
is applied to

At this time, the set human power S is still held at the O signal by the output of the reference time generation circuit 17, so the output of the flip-flop circuit 13 is a signal with a waveform that is an inversion of the trigger pulse P1 as shown in FIG. is generated, a reset signal and a start signal are generated at time intervals equal to the trigger pulse width, and the above-described h operation is repeated.

As a result, the start signal is applied to the reference time generating circuit 17 at a cycle shorter than its output pulse width T2, and once the output signal changes to the O signal, as shown in FIG. 4e, The signal is always maintained at -8, that is, in this state, the frequency of the sawtooth wave of the generator 17 is not synchronized with the power supply frequency, and is asynchronous with the power supply.

If the device described above is used in the scanning circuit of a scanning electron microscope, it will automatically switch between power synchronous and power asynchronous depending on the change in electron beam scanning speed, eliminating the problem of conventional scanning circuit failures and improving scanning speed. Increased circuit reliability, etc.
The effect is great.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the entire scanning electron microscope, Fig. 2 is a block diagram showing one embodiment of the present invention, Fig. 3,
FIG. 4 is an explanatory diagram of the operation of FIG. 2. In Fig. 2, 11 is a commercial frequency power supply, 12 is a pulse waveform shaper, 13 is a flip-flop circuit, 14 is a scanning waveform generator, 15 is an amplitude detector, 16 is a monostable multivibrator, and 117 is a reference time. It is a generator.

Claims (1)

[Scope of utility model registration request] A scanning waveform generator that generates a scanning waveform with an arbitrary slope, and a time width T when the amount of change in the output signal of the generator reaches a certain value.
a trigger pulse generator that generates a pulse of 1, a clock pulse generator that generates a pulse with a period T synchronized with the cycle of the commercial power supply, and a scanning waveform of a pulse having a time width T2 that is longer than T1 and shorter than T. A reference time generation circuit that generates a reference time based on the start time of the generator, the trigger pulse, a clock pulse, and a pulse having a time width T2 are supplied, and the falling edge of the trigger pulse (rising 1
At the same time, the scanning waveform generation resets the circuit in synchronization with T2, and the trigger pulse is generated at T2.
Determine if it is later than that, and if it is later, start the scanning waveform generator based on the first clock pulse after each reset, and if not, trigger the scanning waveform generator. 1. A sawtooth generation circuit characterized by comprising a control circuit for starting in synchronization with the rising (falling) of a pulse.