JPS63316915A - Sawtooth wave generation device - Google Patents

Abstract

PURPOSE:To set the resolution of a sawtooth wave arbitrarily at need, by providing a selector between a counter and a D/A converter DAC, and connecting the output of the counter to the number of bits of the digital input of the DAC responding to the setting of the resolution of the sawtooth wave equally in its function by operating the selector by a controller. CONSTITUTION:To set the resolution of the sawtooth wave, the low-order two bits of the counter 7 are connected to the 12th bit and 11th bit of the digital input so that all of the number of output bits of the counters 7-10 can be set equally to the number of bits of the digital input functionally by operating the selector 5 by the controller 1. In such a way, the elector 31 selects the output terminal of the counter 30 so as to set digital sweeping speed constant corresponding to the setting of the resolution by the controller 1. Therefore, when appropriate digital sweeping speed is selected, it is possible to set the resolution automatically responding to the sweeping speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sawtooth wave generator for sweeping energy beams in laser scanning microscopes, scanning electron microscopes, and the like.

[Conventional technology]

Conventionally, in scanning electron microscopes and the like, a sawtooth wave for beam deflection for scanning a beam on a sample surface has an analog waveform as shown in FIG. 4(a). Therefore,
Sample images were sometimes distorted due to poor analog waveform linearity. For this reason, recently, in order to reduce image distortion, digital scanning in which a beam is scanned with a stepped sawtooth wave as shown in FIG. 4(b) has been increasingly used.

Further, when observing a sample image or taking a photograph, the scanning speed of the beam is selected as appropriate, and the sweeping speed of the sawtooth wave is also set corresponding to the scanning speed.

An example of a conventional digital scanning configuration is shown in FIG.

In Figure 3, 1) is a controller that sets the digital sweep speed of the sawtooth wave, 2 is a clock generator that generates a lock as shown in Figure 5, and 3 is a controller that switches the frequency division ratio operated by controller 1). A frequency divider divides the clock of the clock generator 2 and outputs clocks having different clock rates. 4 is an n-bit counter that counts clock pulses from frequency divider 3, and 6 is an n-bit D.
When the DAC 6, which is a /A converter (hereinafter referred to as DAC), receives the count value of clock pulses as a digital value from the counter 4, the DAC 6 converts the value in proportion to the digital input value as shown in Fig. 4 (b).
) Outputs a step-like sawtooth wave as shown in ().

In addition, the digital sweep speed of the sawtooth wave is determined by the counter 4.
It is determined by the clock rate of the clock input to the For example, if the clock frequency division rate of the frequency divider 3 is set to 1/N of the value before the setting change using the controller 1) in response to the digital sweep speed of the sawtooth wave, the digital sweep speed of the sawtooth wave will become 1/N of the value before the setting change. Become N.

(Problem to be solved by the invention) In the conventional technology as described above, in order to increase the resolution, the sweep speed must be reduced, so the beam is digitally scanned with a high-speed, high-resolution sawtooth wave. Although it is desired to do so, it is often not possible to satisfy both at the same time. Therefore, in equipment that requires high-speed sweep, resolution is sacrificed, and the sawtooth wave is not suitable for the required sweep. The resolution was fixed at a relatively low level so that the highest speeds could be achieved.

Therefore, in equipment that requires such high-speed sweeping, even when the beam is digitally scanned at low speed when photographing an image, it is different from when the beam is digitally scanned at high speed to observe the image. Since the resolution of the waves is the same, there was a problem that sufficient resolution could not be obtained and a clear image could not be obtained.

Therefore, an object of the present invention is to be able to arbitrarily set the resolution of a sawtooth wave for digitally scanning a beam as required.

[Means for solving problems]

For the above purpose, the present invention provides a selector 5 between the counter 4 and the DAC 6 in the conventional digital scanning configuration example shown in FIG. The number of bits of the output of DAC 4 and the digital input of DAC 6 are connected functionally equally in accordance with the setting of the sawtooth wave resolution.

[Operation] In the present invention, the number of bits of the DAC 6 that sets the resolution of the sawtooth wave can be selected using the selector 5. Therefore, when performing digital scanning at high speed, low resolution with a small number of bits can be used. Sweep the beam with a sawtooth wave,
For slow digital scanning, the number of bits can be increased to increase the sawtooth resolution and sweep the beam.

〔Example〕

An example of the configuration of the present invention is shown in FIG.

In FIG. 1, 1 is a controller and 5 is a selector. The controller 1 sets the clock frequency division ratio of the frequency divider 3, and also operates the selector 5 so that the number of output bits of the counter 4 and the number of bits of the digital input of the DAC 6 correspond to the setting of the sawtooth wave resolution. so that they are functionally equally connected.

FIG. 2 shows an embodiment of the present invention that embodies FIG. 1, and the sawtooth wave can be set to resolutions of 10 bits, 1) bits, and 12 bits. The resolution of the sawtooth wave is determined by the number of bits of the DAC 6, and is the value (ILsB) obtained by dividing the analog full scale value of the DAC 6 by 2' (n is the number of focuses).

This embodiment will be explained using FIG. 2.

In Figure 2, 7.8.9.10 is 2 of the 4-bit output.
In the decimal counter, counter 7 is on the lower bit side, counter 1 is on the lower bit side.
0 is the upper bit side. The lower 2 bits of counter 7 are connected to selector 5 (upper 2 bits are not used)
. The DAC 6 has a resolution of 12 bits, and of the 2 bits output from the selector 5, the lower 1 bit is connected to the digital input 12 bits (LSB) of the DAC 6, and the higher 1 bit is connected to the 1) bit. Similarly below,
The lowest bit of counter 8 to the highest 1 bit of the lower 2 bits (upper 2 pins are not used) of counter 10 are connected in order to the 10 bits to 1 bit (MSB) of the digital input of DAC 6. .

To set the resolution of the sawtooth wave, controller l
By operating the selector 5, set the lower two bits of the carantuff and the 12 bits of the digital input of the DAC 6 so that the total number of output points of the counter 7, 8, 9, 10 and the number of bits of the digital input of the DAC 6 are functionally equal. , 1) Connect the bits. The specific operation of the selector 5 is as follows.

(1) When 1 resolution is 10 bits, output 2 of selector 5
Both bits output "L" level signals to the 12 digital input bits of the DAC 6, bit 1), and input an enable signal to the counter 8.

(2) When 0 resolution is 1) bit, selector 5 is DAC
Outputs an "L" level signal to the 12 pins of digital input 6, outputs the signal of the lower 1 bit of the lower 2 bits of the counter 7 to the 1) bit, and outputs the lower 1 bit of the lower 2 bits of the counter 7 to the 1) bit. When the signal becomes "H" level, it outputs an enable signal to the counter 8.

(3) When 1 resolution is 12 focus, selector 5 is DΔC
The signal of the lower 1 bit of the lower 2 pins of the counter 7 is output to the 12 bits of the digital input of the counter 6, and the signal of the higher 1 bit of the lower 2 bits of the counter 7 is output to the 1) bit. Then, the lower two bits of Carantuff are both “
When the signal reaches the "H" level, it outputs an enable signal to the counter 8.

At the same time as setting the resolution of the sawtooth wave, the controller also controls the frequency divider 3 so that the clock at the clock rate corresponding to the resolution is input to the counter 7.8.9.10 so that the digital sweep speed does not change. Set the clock division rate. That is, the frequency divider 3 is composed of a counter 30 and a selector 31, as shown in FIG. For example, the 0 frequency division ratios are, from top to bottom, l, □2. 4.8 To be more specific, when the frequency division ratio is selected to be - and the resolution is set to 10 and the resolution is set to 10 (state (1) above), the digital When a command is given to controller 1 so that the sweep speed is doubled, that is, the frequency division ratio becomes -, the selector 31 operates to select the terminal of the counter 30 with a frequency division ratio of 1. In this case, the resolution is 0th order, which does not change, and the resolution is 2
When a command is given to the controller to double the resolution, the selector 5 sets the resolution to 1) bit (state (2) above). Select a frequency division ratio of 1 and control the digital sweep speed so that there is no change.

As mentioned above, the resolution setting (
Since the selector 31 selects the output terminal of the counter 30 so that the digital sweep speed is constant according to the command to the selector 5, the digital sweep speed is constant and the resolution is the sawtooth wave shown in FIG. 4(b). Staircase step 1
When DAC6 is 12 bits (analog full scale value) / 4096.1) bits (analog full scale value) / 2048.10 When in focus (analog full scale value) / 1024 (to become direct)

In the above example, the frequency division ratio is automatically reset so that the sweep speed does not change according to the setting of the sawtooth wave resolution. However, when changing the digital sweep speed, the resolution remains the same. there were. However, if the digital sweep rate is selected accordingly, it is also possible to automatically set the resolution in response to the sweep rate. In this case, the resolution may be changed in conjunction with the setting of the digital sweep speed.For example, when the digital sweep speed becomes slow, a command is given to the selector 5 to improve the resolution.

In addition, in the above explanation, the digital sweep speed is also changed in conjunction with the resolution setting, or the resolution is also changed in accordance with the digital sweep speed setting, but the resolution setting and the digital sweep speed setting It is also possible to have an independent relationship without having an interlocking relationship with.

〔Effect of the invention〕

As described above, according to the present invention, the resolution of the sawtooth wave can be set arbitrarily, so that the beam can be scanned under optimal conditions.

Furthermore, when writing an image signal to a frame memory or the like, the resolution of the sawtooth wave can be set in accordance with the number of pixels to be written. For example, if the resolution of the sawtooth wave is fixed at 10 bits, the image signal is
When writing to a partial area of 512 x 512 pixels of a 024 pixel frame memory, the image signal captured by the l line 1024 pixels is written every other pixel, or the data of 2 pixels is averaged and written as 1 pixel. However, if the resolution of the sawtooth wave is changed from 10 focus to 9 bits corresponding to 512 pixels per line, the image signal can be directly written to the corresponding pixel, so the above image signal processing becomes unnecessary.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is a detailed block diagram of FIG. 1, FIG. 3 is a block diagram of a conventional digital scanning sawtooth wave generator, and FIG.
a) is a waveform diagram showing an analog sawtooth wave; Fig. 4(b)
) is a waveform diagram showing a digital sawtooth wave, FIG. 5 is a waveform diagram showing a clock signal of clock generator L2, and FIG.
The figure is a block diagram showing a detailed example of a frequency divider. [Explanation of symbols of main parts]

Claims (2)

[Claims] (1) The output clock of the frequency divider that inputs the clock from the clock generator is input to the counter, the count value of the counter is converted into a sawtooth wave by the D/A converter, and the controller What is claimed is: 1. A sawtooth wave generation device capable of changing the frequency division ratio of the sawtooth wave, characterized in that the sawtooth wave generation device is provided with resolution setting means for changing the resolution of the sawtooth wave. (2) The sawtooth wave generation device according to claim (1), characterized in that the resolution of the sawtooth wave is automatically set in accordance with the frequency division ratio of the frequency divider.