Noise And Calibration; Measurement Window; Noise Measurement - Analog Devices ADV7850 Hardware Manual

9.11

NOISE AND CALIBRATION

The ADV7850 provides hardware for a noise and calibration measurements. The two measurements share some hardware control
(window). However, they are different in the way they examine the input data. The measurements are executed during a time window.
The window can be positioned anywhere within a line of video and the length can be selected to be 16, 32, 64, or 128 LLC clock cycles.
Notes:
• Both measurements are performed on the channel A.
• Both measurements work on a video line basis and are performed during the active video.
•
The tap-off point for both measurements is right after the gain multiplier. Clamping and AGC/manual gain will affect the
numbers reported back.

Measurement Window

9.11.1
The window for the noise and calibration measurements is set via meas_ws[11:0] and meas_wl[1:0].
meas_ws[11:0], Addr 44 (CP), Address 0x81[3:0]; Address 0x82[7:0]
This control is used to set the start value of the measurement window use for noise and calibration. The unit is a pixel clock cycle. Refer
to noise[7:0] and calib[10:0]. A value of 0 positions the start of the window at the trailing edge of the incoming HSync.
Function
meas_ws[11:0]
0x000
0x004 
meas_wl[1:0], Addr 44 (CP), Address 0x81[7:6]
This control is used to set the width of the window length used for noise calibration measurements. The unit is a pixel clock cycle. Refer
to noise[7:0] and calib[10:0].
Function
meas_wl[1:0]
00
01
10
11 

Noise Measurement

9.11.2
For the noise or peak data measurement, the data during the window is monitored for the maximum and the minimum value. After the
window is closed, the difference between the two is presented. If programmed during a quiet time of the input video, the value presented
can be related back to the level of noise within the video signal. The noise level is presented as an unsigned number. Levels greater than
255 are saturated to 255.
noise[7:0], Addr 44 (CP), Address 0xE2[7:0] (Read Only)
This readback displays the noise value measured on the luma channel (i.e. channel A). It provides an unsigned value representing the
difference between the maximum and minimum value measured during the window configured by meas_ws[11:0] and meas_wl[1:0].
Function
noise[7:0]
xxxxxxxx
Rev. A May 2012
Description
Start value (in LLC clock cycles) of measurement window
Default
Description
Window length of 128 LLC clock cycles
Window length of 64 LLC clock cycles
Window length of 32 LLC clock cycles
Window length of 16 LLC clock cycles
Description
Readback value
298
ADV7850