JPS5928314B2 - Deflection circuits in scanning electron microscopes, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a deflection circuit suitable for use in scanning electron microscopes, X-ray microanalyzers, and the like.

In a scanning electron microscope, a narrowly focused electron beam is scanned two-dimensionally over a sample using a deflection coil, and information on reflected electrons, secondary electrons, etc. generated from the sample is collected from the electrons on the sample. A sample image is obtained by introducing it into a display device synchronized with line scanning.

As for the deflection circuit that drives the deflection coil, it is necessary to vary the scanning cycle over a wide range from about 0.1 seconds for observation to several hundred seconds for photography, so it is similar to a single cycle commercial television. For example, a so-called current drive type circuit as shown in FIG. 1 is used instead of a pulse drive type circuit. In the figure, 1 is a complementary circuit for power amplification consisting of transistors Q, Q2, 2 is a deflection coil connected to the output of the complementary circuit 1, and 3 is a drive circuit for driving the complementary circuit and also for driving the deflection coil 2. This is an error amplifier to which a detection signal from a detection resistor 4 that detects a flowing current is fed back.
FIG. 2a shows the input and output voltage waveforms of the complementary circuit in the deflection circuit, and FIG. 2b shows the current waveforms flowing through the deflection coil 2. As can be seen from the current waveform, the retrace period tl requires a voltage larger than the scanning period 2, and the circuit power supply voltages V1 and -V2 are used accordingly. On the other hand, recently, even scanning electron microscopes are required to perform high-speed scanning comparable to that of commercial televisions, and for this reason, shortening the retrace period requires the output voltage of the amplifier 3 to be as high as several hundreds of volts. The power supply voltage V1 must be increased accordingly.

However, it is extremely difficult to obtain an amplifier with such a large amplitude output and good frequency characteristics. Also transistor Q
1, a high voltage V1 which is not originally necessary is applied during the scanning period, which consumes extra power, making the design difficult from a thermal standpoint. The present invention has been made in view of this point, and it solves the above-mentioned drawbacks by providing means for detecting the retrace period and applying a high voltage to the deflection coil only during the retrace period based on a signal from the detection means. The purpose is to provide a deflection circuit that can be removed. The present invention will be explained in detail below using the drawings. FIG. 3 shows the configuration of an embodiment of the present invention. In addition to the conventional example shown in FIG. 1, there is also a changeover switch 5 that can apply a voltage V3 lower than V1 to the collector of the transistor Q1, a changeover switch 6 that can apply a voltage V1 to the input part of the complementary circuit 1, and an amplification switch 5. The output from the device 3 is connected to a predetermined constant voltage V4 (
A level detection circuit 7 is newly provided which detects the retrace period t1 by comparing it with the retrace period t1 (see FIG. is arranged so that it is tilted toward the normally open contact A side. Note that 8 is a protection diode for preventing V1 from affecting the amplifier 3. Here, the voltage 3 is the second
As shown in Figure a, V is slightly higher than the voltage required for the scanning period.
Since it is set much lower than 1, the scanning period T2
In this case, the correct scanning current is supplied to the deflection coil 2.

During retrace period t1, switches 5 and 6 are turned to the contact A side, and V is applied to the input of complementary circuit 1, so transistor Q1 becomes conductive, and V remains applied to deflection coil 2. be done. Therefore, during that period, a rapidly rising return current flows through the deflection coil 2. As described above, according to the present invention, the level detector 7 detects the blanking period, and only during that period, the collector voltage of the transistor Q is increased and Q1 is made conductive, so that the output voltage of the amplifier 3 is low. The voltage V3 is sufficient, and since no high voltage is applied to the transistor Q1 during the scanning period, power consumption is greatly reduced.

Furthermore, with scanning electron microscopes, etc., when observing with the naked eye, the scanning speed is comparable to that of commercial television;
The scanning speed can be changed over a wide range up to very low speed scanning of about 0.00 seconds, and the retrace period also changes in the range of several microseconds to several milliseconds.

In particular, since the retrace period is long during photographing, the voltage applied to the deflection coil during this period may also be low, and is lower than V4. Therefore, during photographing, the level detection circuit 7 does not operate, and the power supply voltage is not switched. Therefore, not only does noise not occur when switching the power supply voltage, but feedback is constantly working and it is possible to supply a scanning current with good linearity to the deflection coil, which eliminates deterioration in image quality due to noise and allows scanning with good linearity. The current allows clear, distortion-free scanning electron microscope images to be taken. FIG. 4 shows the configuration of a second embodiment of the present invention. In this embodiment, a low voltage V3 is always supplied to the collector of the transistor Ql via a diode 9, and a high voltage V3 is also supplied to the base during the retrace period. V1
is applied via switch 10.

With this configuration, the switch 10 is set to 0F during the scanning period.
F, so a scanning current with low voltages V3 and -V2 flows through the deflection coil 2, and during the retrace period, the switch 10 becomes 0N and high voltage 1 is applied to the base of the transistor Q1, so the deflection coil 2 has a low voltage V3 and -V2. - The high voltage V1 is applied via the emitter junction.

Therefore, during that period, a rapidly rising return current flows through the deflection coil 2. In this embodiment as well, a low voltage 3 is sufficient as the power source for the amplifier 3, and the power consumption of the transistor Q1 can also be kept low.

As the switch in the above-described embodiment, a semiconductor switch or the like having a high operating speed is suitable.

As detailed above, according to the present invention, a means for detecting the blanking period is provided based on the scanning signal, and only during the blanking period, the high voltage V1 is applied to the collector or base of the transistor Q1, and the transistor is made conductive. By supplying the high voltage to the deflection coil through the transistor, the power supply voltage of the amplifier 3 can be lowered, and the power consumption of the transistor Q1 can be kept low. Furthermore, in the present invention, since the retrace period is determined by comparing the scanning signal with a constant level V4, the power supply voltage is not switched during low-speed scanning such as during shooting when the voltage during the retrace period is low, resulting in sharp images. This also has the great effect of making it possible to take a picture of the subject.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional deflection circuit, FIG. 2 is a diagram showing the waveforms of the voltage applied to the deflection coil and the flowing current,
FIGS. 3 and 4 are diagrams showing the configuration of an embodiment of the present invention. 1: complementary circuit, 2: deflection coil, 3: error amplifier, 4: detection resistor, 5, 6: switch, 7 relevel detector, 8: diode.

Claims (1)

[Claims] 1 Level determination for detecting blanking period by comparing the scanning signal with a predetermined level in a deflection circuit equipped with a transistor for supplying current to a deflection coil and an amplifier for supplying a scanning signal to the transistor and a switching means for applying a voltage V_1 higher than the other period to the collector or base of the transistor only during the retrace period and controlled by the level discriminating means, and applying the voltage to the deflection coil through the transistor. A deflection circuit for a scanning electron microscope, etc., characterized in that the deflection circuit is configured to apply a voltage to the scanning electron microscope.