CRT Design in VHDL

Hardware Design with VHDL

Design Example: VGA

ECE 443

VGA (Video Graphics Array)
Here we consider an 8 color 640-480 pixel resolution interface for the CRT
Vertical deflection coil
Horizontal deflection coil
Electron gun mono hsync vsync Horizontal osc and amp
Vertical
osc and amp

Phosphor coated screen

Electron beam

The electron gun generates a focused electron beam that strikes the phosphor screen
The intensity of the electron beam and the brightness of the dot are determine by the voltage level of the external video input signal (mono signal)
The mono signal is an analog signal whose voltage level is between 0 and 0.7 V
The horizontal and vertical deflection coils produce magnetic fields guide the electron beam to points on the screen
ECE UNM

1

(10/6/10)

Hardware Design with VHDL

Design Example: VGA

ECE 443

VGA (Video Graphics Array)
The electron beam scans the screen systematically in a fixed pattern
Screen

The horz and vert. osc. and amps gen. sawtooth wfms to control the deflection coils pixel(0,0) ’0’ and ’1’ periods of hsync signal correspond to rising and falling ramp of sawtooth wfm left border (48) h_video_on hsync right border (16)
ECE UNM

655
0

640

2

639

751

799 retrace(96) (10/6/10)

Hardware Design with VHDL

Design Example: VGA

ECE 443

VGA (Video Graphics Array)
A color CRT is similar except that it has three electron beams, that are projected to the red, green and blue phosphor dots on the screen
The three dots are combined to form a pixel
The three voltage levels determine the intensity of each and therefore the color.
The VGA port has five active signals, hsync, vsync, and three video signals for the red, green and blue beams
They are connected to a 15-pin D-subminiature connector
The video signals are analog signals -- the video controller uses a D-to-A converter to convert the digital output to the appropriate analog level
If video is