A wideband current-mode variable gain-control circuit

Author(s):  
B. Harvey
2004 ◽  
Vol 38 (2/3) ◽  
pp. 161-174 ◽  
Author(s):  
Arun Ravindran ◽  
Eva Vidal ◽  
Seoung-Jae Yoo ◽  
Kishore Ramarao ◽  
Mohammed Ismail

Author(s):  
N.S. Allen ◽  
R.D. Allen

Various methods of video-enhanced microscopy combine TV cameras with light microscopes creating images with improved resolution, contrast and visibility of fine detail, which can be recorded rapidly and relatively inexpensively. The AVEC (Allen Video-enhanced Contrast) method avoids polarizing rectifiers, since the microscope is operated at retardations of λ/9- λ/4, where no anomaly is seen in the Airy diffraction pattern. The iris diaphram is opened fully to match the numerical aperture of the condenser to that of the objective. Under these conditions, no image can be realized either by eye or photographically. Yet the image becomes visible using the Hamamatsu C-1000-01 binary camera, if the camera control unit is equipped with variable gain control and an offset knob (which sets a clamp voltage of a D.C. restoration circuit). The theoretical basis for these improvements has been described.


2010 ◽  
Vol 32 (11) ◽  
pp. 2772-2775
Author(s):  
Fei-hua Chen ◽  
Xin-zhong Duo ◽  
Xiao-wei Sun

2013 ◽  
Vol 709 ◽  
pp. 408-412
Author(s):  
Yan Ling Zhao ◽  
Rong Xing Liu

Abstract. A mid-frequency magnetron sputtering (MFMS) power supply based on TL494 and MCU was introduced. A Buck Chopper and full bridge inverter were applied to the main circuit. The PWM controller TL494 was used in the Buck voltage-regulation control circuit to realize closed loop control. The drive signal of the IGBT in full bridge inverter was based on precise digital pulse width modulator (DPWM) signal produced by the MCU M30290. The DPWM can be set by potentiometer so the power supply can output the square wave with adjustable frequency and duty cycle. The power supply was operated in constant current mode. For micro or strong arcing of the target, different safeguards were adopted by the control circuit. At last, the system test and experimental results show that the stability, reliability and tuning range of the MFMS power supply can meet the requirements of the magnetron sputtering coating.


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